draft-ietf-sigtran-sctp-11.txt   draft-ietf-sigtran-sctp-12.txt 
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Nortel Networks Nortel Networks
I. Rytina I. Rytina
Ericsson Ericsson
M. Kalla M. Kalla
Telcordia Telcordia
L. Zhang L. Zhang
UCLA UCLA
V. Paxson V. Paxson
ACIRI ACIRI
expires in six months July 3,2000 expires in six months July 10,2000
Stream Control Transmission Protocol Stream Control Transmission Protocol
<draft-ietf-sigtran-sctp-11.txt> <draft-ietf-sigtran-sctp-12.txt>
Status of This Memo Status of This Memo
This document is an Internet-Draft and is in full conformance with all This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of [RFC2026]. Internet-Drafts are working provisions of Section 10 of [RFC2026]. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Internet draft Stream Control Transmission Protocol July 2000
Abstract Abstract
This document describes the Stream Control Transmission Protocol This document describes the Stream Control Transmission Protocol
(SCTP). SCTP is designed to transport PSTN signaling messages over (SCTP). SCTP is designed to transport PSTN signaling messages over
IP networks, but is capable of broader applications. IP networks, but is capable of broader applications.
SCTP is a reliable transport protocol operating on top of a SCTP is a reliable transport protocol operating on top of a
connectionless packet network such as IP. It offers the following connectionless packet network such as IP. It offers the following
services to its users: services to its users:
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-- optional bundling of multiple user messages into a single SCTP -- optional bundling of multiple user messages into a single SCTP
packet, and packet, and
-- network-level fault tolerance through supporting of multi-homing -- network-level fault tolerance through supporting of multi-homing
at either or both ends of an association. at either or both ends of an association.
The design of SCTP includes appropriate congestion avoidance behavior The design of SCTP includes appropriate congestion avoidance behavior
and resistance to flooding and masquerade attacks. and resistance to flooding and masquerade attacks.
TABLE OF CONTENTS TABLE OF CONTENTS
1. Introduction.................................................. 4 1. Introduction.................................................. 5
1.1 Motivation.................................................. 5 1.1 Motivation.................................................. 5
1.2 Architectural View of SCTP.................................. 5 1.2 Architectural View of SCTP.................................. 5
1.3 Functional View of SCTP..................................... 6 1.3 Functional View of SCTP..................................... 6
1.3.1 Association Startup and Takedown........................ 7 1.3.1 Association Startup and Takedown........................ 7
1.3.2 Sequenced Delivery within Streams....................... 8 1.3.2 Sequenced Delivery within Streams....................... 7
1.3.3 User Data Fragmentation................................. 8 1.3.3 User Data Fragmentation................................. 8
1.3.4 Acknowledgement and Congestion Avoidance................ 8 1.3.4 Acknowledgement and Congestion Avoidance................ 8
1.3.5 Chunk Bundling ......................................... 8 1.3.5 Chunk Bundling ......................................... 8
1.3.6 Packet Validation....................................... 8 1.3.6 Packet Validation....................................... 8
1.3.7 Path Management......................................... 9 1.3.7 Path Management......................................... 9
1.4 Key Terms................................................... 9 1.4 Key Terms................................................... 9
1.5 Abbreviations............................................... 12 1.5 Abbreviations............................................... 12
1.6 Serial Number Arithmetic.................................... 12 1.6 Serial Number Arithmetic.................................... 13
2. Conventions.................................................... 13 2. Conventions.................................................... 13
3. SCTP packet Format............................................ 13 3. SCTP packet Format............................................ 13
3.1 SCTP Common Header Field Descriptions....................... 14 3.1 SCTP Common Header Field Descriptions....................... 14
3.2 Chunk Field Descriptions.................................... 15 3.2 Chunk Field Descriptions.................................... 15
3.2.1 Optional/Variable-length Parameter Format............... 17 3.2.1 Optional/Variable-length Parameter Format............... 17
3.3 SCTP Chunk Definitions...................................... 18 3.3 SCTP Chunk Definitions...................................... 18
3.3.1 Payload Data (DATA)..................................... 18 3.3.1 Payload Data (DATA)..................................... 18
3.3.2 Initiation (INIT)....................................... 20 3.3.2 Initiation (INIT)....................................... 20
3.3.2.1 Optional or Variable Length Parameters.............. 22 3.3.2.1 Optional or Variable Length Parameters.............. 23
3.3.3 Initiation Acknowledgement (INIT ACK)................... 25 3.3.3 Initiation Acknowledgement (INIT ACK)................... 25
3.3.3.1 Optional or Variable Length Parameters.............. 28 3.3.3.1 Optional or Variable Length Parameters.............. 28
Internet draft Stream Control Transmission Protocol July 2000
3.3.4 Selective Acknowledgement (SACK)........................ 28 3.3.4 Selective Acknowledgement (SACK)........................ 28
3.3.5 Heartbeat Request (HEARTBEAT)........................... 31 3.3.5 Heartbeat Request (HEARTBEAT)........................... 31
3.3.6 Heartbeat Acknowledgement (HEARTBEAT ACK)............... 32 3.3.6 Heartbeat Acknowledgement (HEARTBEAT ACK)............... 32
3.3.7 Abort Association (ABORT)............................... 33 3.3.7 Abort Association (ABORT)............................... 33
3.3.8 Shutdown Association (SHUTDOWN)......................... 33 3.3.8 Shutdown Association (SHUTDOWN)......................... 34
3.3.9 Shutdown Acknowledgement (SHUTDOWN ACK)................. 34 3.3.9 Shutdown Acknowledgement (SHUTDOWN ACK)................. 34
3.3.10 Operation Error (ERROR)................................ 34 3.3.10 Operation Error (ERROR)................................ 35
3.3.10.1 Invalid Stream Identifier.......................... 36 3.3.10.1 Invalid Stream Identifier.......................... 36
3.3.10.2 Missing Mandatory Parameter........................ 36 3.3.10.2 Missing Mandatory Parameter........................ 36
3.3.10.3 Stale Cookie Error................................. 37 3.3.10.3 Stale Cookie Error................................. 37
3.3.10.4 Out of Resource.................................... 37 3.3.10.4 Out of Resource.................................... 37
3.3.10.5 Unresolvable Address............................... 37 3.3.10.5 Unresolvable Address............................... 37
3.3.10.6 Unrecognized Chunk Type............................ 38 3.3.10.6 Unrecognized Chunk Type............................ 38
3.3.10.7 Invalid Mandatory Parameter........................ 38 3.3.10.7 Invalid Mandatory Parameter........................ 38
3.3.10.8 Unrecognized Parameters............................ 38 3.3.10.8 Unrecognized Parameters............................ 38
3.3.10.9 No User Data....................................... 39 3.3.10.9 No User Data....................................... 39
3.3.10.10 Cookie Received While Shutting Down............... 39 3.3.10.10 Cookie Received While Shutting Down............... 39
3.3.11 Cookie Echo (COOKIE ECHO).............................. 39 3.3.11 Cookie Echo (COOKIE ECHO).............................. 40
3.3.12 Cookie Acknowledgement (COOKIE ACK).................... 40 3.3.12 Cookie Acknowledgement (COOKIE ACK).................... 40
3.3.13 Shutdown Complete (SHUTDOWN COMPLETE).................. 40 3.3.13 Shutdown Complete (SHUTDOWN COMPLETE).................. 41
4. SCTP Association State Diagram................................. 41 4. SCTP Association State Diagram................................. 41
5. Association Initialization..................................... 44 5. Association Initialization..................................... 44
5.1 Normal Establishment of an Association...................... 44 5.1 Normal Establishment of an Association...................... 44
5.1.1 Handle Stream Parameters................................ 46 5.1.1 Handle Stream Parameters................................ 46
5.1.2 Handle Address Parameters............................... 46 5.1.2 Handle Address Parameters............................... 46
5.1.3 Generating State Cookie................................. 48 5.1.3 Generating State Cookie................................. 48
5.1.4 State Cookie Processing................................. 48 5.1.4 State Cookie Processing................................. 49
5.1.5 State Cookie Authentication............................. 49 5.1.5 State Cookie Authentication............................. 49
5.1.6 An Example of Normal Association Establishment.......... 50 5.1.6 An Example of Normal Association Establishment.......... 50
5.2 Handle Duplicate or unexpected INIT, INIT ACK, COOKIE ECHO, 5.2 Handle Duplicate or unexpected INIT, INIT ACK, COOKIE ECHO,
and COOKIE ACK.............................................. 51 and COOKIE ACK.............................................. 51
5.2.1 Handle Duplicate INIT in COOKIE-WAIT 5.2.1 Handle Duplicate INIT in COOKIE-WAIT
or COOKIE-ECHOED States................................. 52 or COOKIE-ECHOED States................................. 52
5.2.2 Unexpected INIT in States Other than CLOSED, 5.2.2 Unexpected INIT in States Other than CLOSED,
COOKIE-ECHOED and COOKIE-WAIT........................... 52 COOKIE-ECHOED and COOKIE-WAIT........................... 52
5.2.3 Unexpected INIT ACK..................................... 52 5.2.3 Unexpected INIT ACK..................................... 52
5.2.4 Handle a COOKIE ECHO when a TCB exists.................. 52 5.2.4 Handle a COOKIE ECHO when a TCB exists.................. 52
5.2.5 Handle Duplicate COOKIE ACK............................. 54 5.2.4.1 An Example of a Association Restart................. 55
5.2.6 Handle Stale COOKIE Error............................... 55 5.2.5 Handle Duplicate COOKIE ACK............................. 56
5.3 Other Initialization Issues................................. 55 5.2.6 Handle Stale COOKIE Error............................... 56
5.3.1 Selection of Tag Value.................................. 55 5.3 Other Initialization Issues................................. 56
6. User Data Transfer............................................. 56 5.3.1 Selection of Tag Value.................................. 56
6.1 Transmission of DATA Chunks................................. 57 6. User Data Transfer............................................. 57
6.2 Acknowledgement on Reception of DATA Chunks................. 58 6.1 Transmission of DATA Chunks................................. 58
6.2.1 Tracking Peer's Receive Buffer Space.................... 61 6.2 Acknowledgement on Reception of DATA Chunks................. 59
6.3 Management Retransmission Timer............................. 62 6.2.1 Tracking Peer's Receive Buffer Space.................... 62
6.3.1 RTO Calculation......................................... 62 6.3 Management Retransmission Timer............................. 63
6.3.2 Retransmission Timer Rules.............................. 63 6.3.1 RTO Calculation......................................... 63
6.3.3 Handle T3-rtx Expiration................................ 64 6.3.2 Retransmission Timer Rules.............................. 65
6.4 Multi-homed SCTP Endpoints.................................. 65 6.3.3 Handle T3-rtx Expiration................................ 65
6.4.1 Failover from Inactive Destination Address.............. 66 6.4 Multi-homed SCTP Endpoints.................................. 67
6.5 Stream Identifier and Stream Sequence Number................ 67 6.4.1 Failover from Inactive Destination Address.............. 67
6.6 Ordered and Unordered Delivery.............................. 67 6.5 Stream Identifier and Stream Sequence Number................ 68
6.7 Report Gaps in Received DATA TSNs........................... 68 6.6 Ordered and Unordered Delivery.............................. 68
6.8 Adler-32 Checksum Calculation............................... 69
6.9 Fragmentation............................................... 69 Internet draft Stream Control Transmission Protocol July 2000
6.10 Bundling .................................................. 70
7. Congestion Control .......................................... 71 6.7 Report Gaps in Received DATA TSNs........................... 69
7.1 SCTP Differences from TCP Congestion Control................ 71 6.8 Adler-32 Checksum Calculation............................... 70
7.2 SCTP Slow-Start and Congestion Avoidance.................... 72 6.9 Fragmentation............................................... 70
7.2.1 Slow-Start.............................................. 73 6.10 Bundling .................................................. 71
7.2.2 Congestion Avoidance.................................... 74 7. Congestion Control .......................................... 72
7.2.3 Congestion Control...................................... 75 7.1 SCTP Differences from TCP Congestion Control................ 73
7.2.4 Fast Retransmit on Gap Reports.......................... 75 7.2 SCTP Slow-Start and Congestion Avoidance.................... 74
7.3 Path MTU Discovery.......................................... 76 7.2.1 Slow-Start.............................................. 74
8. Fault Management.............................................. 77 7.2.2 Congestion Avoidance.................................... 75
8.1 Endpoint Failure Detection.................................. 77 7.2.3 Congestion Control...................................... 76
8.2 Path Failure Detection...................................... 77 7.2.4 Fast Retransmit on Gap Reports.......................... 76
8.3 Path Heartbeat.............................................. 78 7.3 Path MTU Discovery.......................................... 77
8.4 Handle "Out of the blue" Packets............................ 80 8. Fault Management.............................................. 78
8.5 Verification Tag............................................ 81 8.1 Endpoint Failure Detection.................................. 78
8.5.1 Exceptions in Verification Tag Rules.................... 81 8.2 Path Failure Detection...................................... 78
9. Termination of Association..................................... 82 8.3 Path Heartbeat.............................................. 79
9.1 Abort of an Association..................................... 82 8.4 Handle "Out of the blue" Packets............................ 81
9.2 Shutdown of an Association.................................. 83 8.5 Verification Tag............................................ 82
10. Interface with Upper Layer.................................... 85 8.5.1 Exceptions in Verification Tag Rules.................... 82
10.1 ULP-to-SCTP................................................ 85 9. Termination of Association..................................... 83
10.2 SCTP-to-ULP................................................ 94 9.1 Abort of an Association..................................... 83
11. Security Considerations....................................... 96 9.2 Shutdown of an Association.................................. 84
11.1 Security Objectives........................................ 96 10. Interface with Upper Layer.................................... 86
11.2 SCTP Responses To Potential Threats........................ 97 10.1 ULP-to-SCTP................................................ 86
11.2.1 Countering Insider Attacks............................. 97 10.2 SCTP-to-ULP................................................ 95
11.2.2 Protecting against Data Corruption in the Network...... 97 11. Security Considerations....................................... 98
11.2.3 Protecting Confidentiality............................. 97 11.1 Security Objectives........................................ 98
11.2.4 Protecting against Blind Denial of Service Attacks..... 98 11.2 SCTP Responses To Potential Threats........................ 98
11.2.4.1 Flooding........................................... 98 11.2.1 Countering Insider Attacks............................. 98
11.2.4.2 Masquerade......................................... 99 11.2.2 Protecting against Data Corruption in the Network...... 98
11.2.4.3 Improper Monopolization of Services................100 11.2.3 Protecting Confidentiality............................. 99
11.3 Protection against Fraud and Repudiation...................100 11.2.4 Protecting against Blind Denial of Service Attacks..... 99
12. Recommended Transmission Control Block (TCB) Parameters.......101 11.2.4.1 Flooding........................................... 99
12.1 Parameters necessary for the SCTP instance.................101 11.2.4.2 Blind Masquerade...................................100
12.2 Parameters necessary per association (i.e. the TCB)........101 11.2.4.3 Improper Monopolization of Services................101
12.3 Per Transport Address Data.................................102 11.3 Protection against Fraud and Repudiation...................101
12.4 General Parameters Needed..................................104 12. Recommended Transmission Control Block (TCB) Parameters.......102
13. IANA Consideration............................................104 12.1 Parameters necessary for the SCTP instance.................102
13.1 IETF-defined Chunk Extension...............................104 12.2 Parameters necessary per association (i.e. the TCB)........103
13.2 IETF-defined Additional Error Causes.......................104 12.3 Per Transport Address Data.................................104
13.3 Payload Protocol Identifiers...............................105 12.4 General Parameters Needed..................................105
14. Suggested SCTP Protocol Parameter Values......................105 13. IANA Consideration............................................105
15. Acknowledgements..............................................106 13.1 IETF-defined Chunk Extension...............................105
16. Authors' Addresses............................................106 13.2 IETF-defined Additional Error Causes.......................106
17. References....................................................107 13.3 Payload Protocol Identifiers...............................106
18. Bibliography..................................................108 14. Suggested SCTP Protocol Parameter Values......................107
Appendix A .......................................................109 15. Acknowledgements..............................................107
Appendix B .......................................................110 16. Authors' Addresses............................................107
17. References....................................................109
18. Bibliography..................................................110
Appendix A .......................................................110
Appendix B .......................................................111
Internet draft Stream Control Transmission Protocol July 2000
1. Introduction 1. Introduction
This section explains the reasoning behind the development of the This section explains the reasoning behind the development of the
Stream Control Transmission Protocol (SCTP), the services it offers, Stream Control Transmission Protocol (SCTP), the services it offers,
and the basic concepts needed to understand the detailed description and the basic concepts needed to understand the detailed description
of the protocol. of the protocol.
1.1 Motivation 1.1 Motivation
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as IP. The remainder of this document assumes SCTP runs on top of IP. as IP. The remainder of this document assumes SCTP runs on top of IP.
The basic service offered by SCTP is the reliable transfer of The basic service offered by SCTP is the reliable transfer of
user messages between peer SCTP users. It performs this service user messages between peer SCTP users. It performs this service
within the context of an association between two SCTP endpoints. within the context of an association between two SCTP endpoints.
Section 10 of this document sketches the API which should exist at the Section 10 of this document sketches the API which should exist at the
boundary between the SCTP and the SCTP user layers. boundary between the SCTP and the SCTP user layers.
SCTP is connection-oriented in nature, but the SCTP association is a SCTP is connection-oriented in nature, but the SCTP association is a
broader concept than the TCP connection. SCTP provides the means for broader concept than the TCP connection. SCTP provides the means for
Internet draft Stream Control Transmission Protocol July 2000
each SCTP endpoint (Section 1.4) to provide the other endpoint (during each SCTP endpoint (Section 1.4) to provide the other endpoint (during
association startup) with a list of transport addresses (i.e., multiple association startup) with a list of transport addresses (i.e., multiple
IP addresses in combination with an SCTP port) through which that IP addresses in combination with an SCTP port) through which that
endpoint can be reached and from which it will originate SCTP packets. endpoint can be reached and from which it will originate SCTP packets.
The association spans transfers over all of the possible The association spans transfers over all of the possible
source/destination combinations which may be generated from each source/destination combinations which may be generated from each
endpoint's lists. endpoint's lists.
_____________ _____________ _____________ _____________
| SCTP User | | SCTP User | | SCTP User | | SCTP User |
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..| | ____________________________ ..| | ____________________________
| | | Acknowledgement | | | | Acknowledgement |
| | | and | | | | and |
| | | Congestion Avoidance | | | | Congestion Avoidance |
..| | |____________________________| ..| | |____________________________|
| | | |
| | ____________________________ | | ____________________________
| | | Chunk Bundling | | | | Chunk Bundling |
| | |____________________________| | | |____________________________|
| | | |
Internet draft Stream Control Transmission Protocol July 2000
| | ________________________________ | | ________________________________
| | | Packet Validation | | | | Packet Validation |
| | |________________________________| | | |________________________________|
| | | |
| | ________________________________ | | ________________________________
| | | Path Management | | | | Path Management |
|______________ |________________________________| |______________ |________________________________|
Figure 2: Functional View of the SCTP Transport Service Figure 2: Functional View of the SCTP Transport Service
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The SCTP user can specify at association startup time the number of The SCTP user can specify at association startup time the number of
streams to be supported by the association. This number is negotiated streams to be supported by the association. This number is negotiated
with the remote end (see Section 5.1.1). User messages are associated with the remote end (see Section 5.1.1). User messages are associated
with stream numbers (SEND, RECEIVE primitives, Section 10). Internally, with stream numbers (SEND, RECEIVE primitives, Section 10). Internally,
SCTP assigns a stream sequence number to each message passed to it by SCTP assigns a stream sequence number to each message passed to it by
the SCTP user. On the receiving side, SCTP ensures that messages are the SCTP user. On the receiving side, SCTP ensures that messages are
delivered to the SCTP user in sequence within a given stream. However, delivered to the SCTP user in sequence within a given stream. However,
while one stream may be blocked waiting for the next in-sequence user while one stream may be blocked waiting for the next in-sequence user
message, delivery from other streams may proceed. message, delivery from other streams may proceed.
Internet draft Stream Control Transmission Protocol July 2000
SCTP provides a mechanism for bypassing the sequenced delivery SCTP provides a mechanism for bypassing the sequenced delivery
service. User messages sent using this mechanism are delivered to the service. User messages sent using this mechanism are delivered to the
SCTP user as soon as they are received. SCTP user as soon as they are received.
1.3.3 User Data Fragmentation 1.3.3 User Data Fragmentation
When needed, SCTP fragments user messages to ensure that the SCTP When needed, SCTP fragments user messages to ensure that the SCTP
packet passed to the lower layer conforms to the path MTU. On receipt, packet passed to the lower layer conforms to the path MTU. On receipt,
fragments are reassembled into complete messages before being passed to fragments are reassembled into complete messages before being passed to
the SCTP user. the SCTP user.
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congestion or retransmission. congestion or retransmission.
1.3.6 Packet Validation 1.3.6 Packet Validation
A mandatory Verification Tag field and a 32 bit checksum field (see A mandatory Verification Tag field and a 32 bit checksum field (see
Appendix B for a description of the Adler-32 checksum) are included in Appendix B for a description of the Adler-32 checksum) are included in
the SCTP common header. The Verification Tag value is chosen by each the SCTP common header. The Verification Tag value is chosen by each
end of the association during association startup. Packets received end of the association during association startup. Packets received
without the expected Verification Tag value are discarded, as a without the expected Verification Tag value are discarded, as a
Internet draft Stream Control Transmission Protocol July 2000
protection against blind masquerade attacks and against stale SCTP protection against blind masquerade attacks and against stale SCTP
packets from a previous association. The Adler-32 checksum should be packets from a previous association. The Adler-32 checksum should be
set by the sender of each SCTP packet to provide additional protection set by the sender of each SCTP packet to provide additional protection
against data corruption in the network. The receiver of an SCTP packet against data corruption in the network. The receiver of an SCTP packet
with an invalid Adler-32 checksum silently discards the packet. with an invalid Adler-32 checksum silently discards the packet.
1.3.7 Path Management 1.3.7 Path Management
The sending SCTP user is able to manipulate the set of transport The sending SCTP user is able to manipulate the set of transport
addresses used as destinations for SCTP packets through the addresses used as destinations for SCTP packets through the
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user message may be carried in the same SCTP packet. Each user user message may be carried in the same SCTP packet. Each user
message occupies its own DATA chunk. message occupies its own DATA chunk.
o Chunk: A unit of information within an SCTP packet, consisting of o Chunk: A unit of information within an SCTP packet, consisting of
a chunk header and chunk-specific content. a chunk header and chunk-specific content.
o Congestion Window (cwnd): An SCTP variable that limits the data, in o Congestion Window (cwnd): An SCTP variable that limits the data, in
number of bytes, a sender can send to a particular destination number of bytes, a sender can send to a particular destination
transport address before receiving an acknowledgement. transport address before receiving an acknowledgement.
Internet draft Stream Control Transmission Protocol July 2000
o Cumulative TSN Ack Point: The TSN of the last DATA chunk o Cumulative TSN Ack Point: The TSN of the last DATA chunk
acknowledged via the Cumulative TSN Ack field of a SACK. acknowledged via the Cumulative TSN Ack field of a SACK.
o Idle destination address: An address that has not had user messages o Idle destination address: An address that has not had user messages
sent to it within some length of time, normally the HEARTBEAT sent to it within some length of time, normally the HEARTBEAT
interval or greater. interval or greater.
o Inactive destination transport address: An address which is o Inactive destination transport address: An address which is
considered inactive due to errors and unavailable to transport user considered inactive due to errors and unavailable to transport user
messages. messages.
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control the return path taken by reply chunks and on which control the return path taken by reply chunks and on which
interface the packet is transmitted when the data sender interface the packet is transmitted when the data sender
is multi-homed. is multi-homed.
o Receiver Window (rwnd): An SCTP variable a data sender uses to store o Receiver Window (rwnd): An SCTP variable a data sender uses to store
the most recently calculated receiver window of its peer, in number the most recently calculated receiver window of its peer, in number
of bytes. This gives the sender an indication of the space available of bytes. This gives the sender an indication of the space available
in the receiver's inbound buffer. in the receiver's inbound buffer.
o SCTP association: A protocol relationship between SCTP endpoints, o SCTP association: A protocol relationship between SCTP endpoints,
Internet draft Stream Control Transmission Protocol July 2000
composed of the two SCTP endpoints and protocol state information composed of the two SCTP endpoints and protocol state information
including Verification Tags and the currently active set of including Verification Tags and the currently active set of
Transmission Sequence Numbers (TSNs), etc. An association can be Transmission Sequence Numbers (TSNs), etc. An association can be
uniquely identified by the transport addresses used by the endpoints uniquely identified by the transport addresses used by the endpoints
in the association. Two SCTP endpoints MUST NOT have more than one in the association. Two SCTP endpoints MUST NOT have more than one
SCTP association between them at any given time. SCTP association between them at any given time.
o SCTP endpoint: The logical sender/receiver of SCTP packets. On a o SCTP endpoint: The logical sender/receiver of SCTP packets. On a
multi-homed host, an SCTP endpoint is represented to its peers as a multi-homed host, an SCTP endpoint is represented to its peers as a
combination of a set of eligible destination transport addresses to combination of a set of eligible destination transport addresses to
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Note: The relationship between stream numbers in opposite Note: The relationship between stream numbers in opposite
directions is strictly a matter of how the applications use directions is strictly a matter of how the applications use
them. It is the responsibility of the SCTP user to create and them. It is the responsibility of the SCTP user to create and
manage these correlations if they are so desired. manage these correlations if they are so desired.
o Stream Sequence Number: A 16-bit sequence number used internally by o Stream Sequence Number: A 16-bit sequence number used internally by
SCTP to assure sequenced delivery of the user messages within a SCTP to assure sequenced delivery of the user messages within a
given stream. One stream sequence number is attached to each user given stream. One stream sequence number is attached to each user
message. message.
o Tie-Tags: Verification Tags from a previous association. These
Tags are used within a State Cookie so that the newly restarting
association can be linked to the original association within
the endpoint that did NOT restart.
o Transmission Control Block (TCB): An internal data structure o Transmission Control Block (TCB): An internal data structure
created by an SCTP endpoint for each of its existing SCTP created by an SCTP endpoint for each of its existing SCTP
Internet draft Stream Control Transmission Protocol July 2000
associations to other SCTP endpoints. TCB contains all the status associations to other SCTP endpoints. TCB contains all the status
and operational information for the endpoint to maintain and manage and operational information for the endpoint to maintain and manage
the corresponding association. the corresponding association.
o Transmission Sequence Number (TSN): A 32-bit sequence number used o Transmission Sequence Number (TSN): A 32-bit sequence number used
internally by SCTP. One TSN is attached to each chunk containing internally by SCTP. One TSN is attached to each chunk containing
user data to permit the receiving SCTP endpoint to acknowledge its user data to permit the receiving SCTP endpoint to acknowledge its
receipt and detect duplicate deliveries. receipt and detect duplicate deliveries.
o Transport address: A Transport Address is traditionally defined by o Transport address: A Transport Address is traditionally defined by
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o Unordered Message: Unordered messages are "unordered" with respect o Unordered Message: Unordered messages are "unordered" with respect
to any other message, this includes both other unordered messages to any other message, this includes both other unordered messages
as well as other ordered messages. Unordered message might be as well as other ordered messages. Unordered message might be
delivered prior to or later than ordered messages sent on the delivered prior to or later than ordered messages sent on the
same stream. same stream.
o User message: The unit of data delivery across the interface o User message: The unit of data delivery across the interface
between SCTP and its user. between SCTP and its user.
o Verification Tag: A 32 bit unsigned integer that is randomly
generated. The Verification Tag provides a key that allows
a receiver to verify that the SCTP packet belongs to the
current association and is NOT an old or stale packet from
a previous association.
1.5. Abbreviations 1.5. Abbreviations
MAC - Message Authentication Code [RFC2104] MAC - Message Authentication Code [RFC2104]
RTO - Retransmission Time-out RTO - Retransmission Time-out
RTT - Round-trip Time RTT - Round-trip Time
RTTVAR - Round-trip Time Variation RTTVAR - Round-trip Time Variation
SCTP - Stream Control Transmission Protocol SCTP - Stream Control Transmission Protocol
SRTT - Smoothed RTT SRTT - Smoothed RTT
TCB - Transmission Control Block TCB - Transmission Control Block
TLV - Type-Length-Value Coding Format TLV - Type-Length-Value Coding Format
Internet draft Stream Control Transmission Protocol July 2000
TSN - Transmission Sequence Number TSN - Transmission Sequence Number
ULP - Upper-layer Protocol ULP - Upper-layer Protocol
1.6 Serial Number Arithmetic 1.6 Serial Number Arithmetic
It is essential to remember that the actual Transmission Sequence It is essential to remember that the actual Transmission Sequence
Number space is finite, though very large. This space ranges from 0 to Number space is finite, though very large. This space ranges from 0 to
2**32 - 1. Since the space is finite, all arithmetic dealing with 2**32 - 1. Since the space is finite, all arithmetic dealing with
Transmission Sequence Numbers must be performed modulo 2**32. This Transmission Sequence Numbers must be performed modulo 2**32. This
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An SCTP packet is composed of a common header and chunks. A chunk An SCTP packet is composed of a common header and chunks. A chunk
contains either control information or user data. contains either control information or user data.
The SCTP packet format is shown below: The SCTP packet format is shown below:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Header | | Common Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Internet draft Stream Control Transmission Protocol July 2000
| Chunk #1 | | Chunk #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk #n | | Chunk #n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Multiple chunks can be bundled into one SCTP packet up to Multiple chunks can be bundled into one SCTP packet up to
the MTU size, except for the INIT, INIT ACK, and SHUTDOWN COMPLETE the MTU size, except for the INIT, INIT ACK, and SHUTDOWN COMPLETE
chunks. These chunks MUST NOT be bundled with any other chunk in a chunks. These chunks MUST NOT be bundled with any other chunk in a
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receiving host will use this port number to de-multiplex the receiving host will use this port number to de-multiplex the
SCTP packet to the correct receiving endpoint/application. SCTP packet to the correct receiving endpoint/application.
Verification Tag: 32 bits (unsigned integer) Verification Tag: 32 bits (unsigned integer)
The receiver of this packet uses the Verification Tag to validate The receiver of this packet uses the Verification Tag to validate
the sender of this SCTP packet. On transmit, the value of this the sender of this SCTP packet. On transmit, the value of this
Verification Tag MUST be set to the value of the Initiate Tag Verification Tag MUST be set to the value of the Initiate Tag
received from the peer endpoint during the association received from the peer endpoint during the association
initialization, with the following exceptions: initialization, with the following exceptions:
Internet draft Stream Control Transmission Protocol July 2000
- A packet containing an INIT chunk MUST have a zero - A packet containing an INIT chunk MUST have a zero
Verification Tag. Verification Tag.
- A packet containing a SHUTDOWN-COMPLETE chunk with the T-bit - A packet containing a SHUTDOWN-COMPLETE chunk with the T-bit
set MUST have the Verification Tag copied from the packet set MUST have the Verification Tag copied from the packet
with the SHUTDOWN-ACK chunk. with the SHUTDOWN-ACK chunk.
- A packet containing an ABORT chunk may have the verification - A packet containing an ABORT chunk may have the verification
tag copied from the packet which caused the ABORT to be sent. tag copied from the packet which caused the ABORT to be sent.
For details see Section 8.4 and 8.5. For details see Section 8.4 and 8.5.
An INIT chunk MUST be the only chunk in the SCTP packet carrying it. An INIT chunk MUST be the only chunk in the SCTP packet carrying it.
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ID Value Chunk Type ID Value Chunk Type
----- ---------- ----- ----------
0 - Payload Data (DATA) 0 - Payload Data (DATA)
1 - Initiation (INIT) 1 - Initiation (INIT)
2 - Initiation Acknowledgement (INIT ACK) 2 - Initiation Acknowledgement (INIT ACK)
3 - Selective Acknowledgement (SACK) 3 - Selective Acknowledgement (SACK)
4 - Heartbeat Request (HEARTBEAT) 4 - Heartbeat Request (HEARTBEAT)
5 - Heartbeat Acknowledgement (HEARTBEAT ACK) 5 - Heartbeat Acknowledgement (HEARTBEAT ACK)
6 - Abort (ABORT) 6 - Abort (ABORT)
7 - Shutdown (SHUTDOWN) 7 - Shutdown (SHUTDOWN)
Internet draft Stream Control Transmission Protocol July 2000
8 - Shutdown Acknowledgement (SHUTDOWN ACK) 8 - Shutdown Acknowledgement (SHUTDOWN ACK)
9 - Operation Error (ERROR) 9 - Operation Error (ERROR)
10 - State Cookie (COOKIE ECHO) 10 - State Cookie (COOKIE ECHO)
11 - Cookie Acknowledgement (COOKIE ACK) 11 - Cookie Acknowledgement (COOKIE ACK)
12 - Reserved for Explicit Congestion Notification Echo (ECNE) 12 - Reserved for Explicit Congestion Notification Echo (ECNE)
13 - Reserved for Congestion Window Reduced (CWR) 13 - Reserved for Congestion Window Reduced (CWR)
14 - Shutdown Complete (SHUTDOWN COMPLETE) 14 - Shutdown Complete (SHUTDOWN COMPLETE)
15 to 62 - reserved by IETF 15 to 62 - reserved by IETF
63 - IETF-defined Chunk Extensions 63 - IETF-defined Chunk Extensions
64 to 126 - reserved by IETF 64 to 126 - reserved by IETF
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Chunk Length: 16 bits (unsigned integer) Chunk Length: 16 bits (unsigned integer)
This value represents the size of the chunk in bytes including the This value represents the size of the chunk in bytes including the
Chunk Type, Chunk Flags, Chunk Length, and Chunk Value fields. Chunk Type, Chunk Flags, Chunk Length, and Chunk Value fields.
Therefore, if the Chunk Value field is zero-length, the Length Therefore, if the Chunk Value field is zero-length, the Length
field will be set to 4. The Chunk Length field does not count field will be set to 4. The Chunk Length field does not count
any padding. any padding.
Chunk Value: variable length Chunk Value: variable length
Internet draft Stream Control Transmission Protocol July 2000
The Chunk Value field contains the actual information to be The Chunk Value field contains the actual information to be
transferred in the chunk. The usage and format of this field is transferred in the chunk. The usage and format of this field is
dependent on the Chunk Type. dependent on the Chunk Type.
The total length of a chunk (including Type, Length and Value fields) The total length of a chunk (including Type, Length and Value fields)
MUST be a multiple of 4 bytes. If the length of the chunk is not a MUST be a multiple of 4 bytes. If the length of the chunk is not a
multiple of 4 bytes, the sender MUST pad the chunk with all zero bytes multiple of 4 bytes, the sender MUST pad the chunk with all zero bytes
and this padding is NOT included in the chunk length field. The sender and this padding is NOT included in the chunk length field. The sender
should never pad with more than 3 bytes. The receiver MUST ignore the should never pad with more than 3 bytes. The receiver MUST ignore the
padding bytes. padding bytes.
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including the Parameter Type, Parameter Length, and Parameter including the Parameter Type, Parameter Length, and Parameter
Value fields. Thus, a parameter with a zero-length Parameter Value fields. Thus, a parameter with a zero-length Parameter
Value field would have a Length field of 4. The Parameter Length Value field would have a Length field of 4. The Parameter Length
does not include any padding bytes. does not include any padding bytes.
Chunk Parameter Value: variable-length. Chunk Parameter Value: variable-length.
The Parameter Value field contains the actual information to be The Parameter Value field contains the actual information to be
transferred in the parameter. transferred in the parameter.
Internet draft Stream Control Transmission Protocol July 2000
The total length of a parameter (including Type, Parameter Length and The total length of a parameter (including Type, Parameter Length and
Value fields) MUST be a multiple of 4 bytes. If the length of the Value fields) MUST be a multiple of 4 bytes. If the length of the
parameter is not a multiple of 4 bytes, the sender pads the Parameter parameter is not a multiple of 4 bytes, the sender pads the Parameter
at the end (i.e., after the Parameter Value field) with all zero at the end (i.e., after the Parameter Value field) with all zero
bytes. The length of the padding is NOT included in the parameter bytes. The length of the padding is NOT included in the parameter
length field. A sender should NEVER pad with more than 3 bytes. The length field. A sender should NEVER pad with more than 3 bytes. The
receiver MUST ignore the padding bytes. receiver MUST ignore the padding bytes.
The Parameter Types are encoded such that the highest-order two bits The Parameter Types are encoded such that the highest-order two bits
specify the action that must be taken if the processing specify the action that must be taken if the processing
endpoint does not recognize the Parameter Type. endpoint does not recognize the Parameter Type.
00 - Stop processing this SCTP packet and discard it, do NOT process any 00 - Stop processing this SCTP packet and discard it, do NOT process any
further chunks within it. further chunks within it.
01 - Stop processing this SCTP packet and discard it, do NOT process any 01 - Stop processing this SCTP packet and discard it, do NOT process any
further chunks within it, and report the unrecognized parameter in further chunks within it, and report the unrecognized parameter in
an 'Unrecognized Parameter Type' (in either a Operational Error or an 'Unrecognized Parameter Type' (in either a Operational Error or
in the INIT ACK). in the INIT ACK).
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TSN | | TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Identifier S | Stream Sequence Number n | | Stream Identifier S | Stream Sequence Number n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Protocol Identifier | | Payload Protocol Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \ \ \
/ User Data (seq n of Stream S) / / User Data (seq n of Stream S) /
\ \ \ \
Internet draft Stream Control Transmission Protocol July 2000
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved: 5 bits Reserved: 5 bits
Should be set to all '0's and ignored by the receiver. Should be set to all '0's and ignored by the receiver.
U bit: 1 bit U bit: 1 bit
The (U)nordered bit, if set to '1', indicates that this is an The (U)nordered bit, if set to '1', indicates that this is an
unordered DATA chunk, and there is no Stream Sequence Number assigned unordered DATA chunk, and there is no Stream Sequence Number assigned
to this DATA chunk. Therefore, the receiver MUST ignore the Stream to this DATA chunk. Therefore, the receiver MUST ignore the Stream
Sequence Number field. Sequence Number field.
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============================================================ ============================================================
When a user message is fragmented into multiple chunks, the TSNs are When a user message is fragmented into multiple chunks, the TSNs are
used by the receiver to reassemble the message. This means that the used by the receiver to reassemble the message. This means that the
TSNs for each fragment of a fragmented user message MUST be strictly TSNs for each fragment of a fragmented user message MUST be strictly
sequential. sequential.
Length: 16 bits (unsigned integer) Length: 16 bits (unsigned integer)
This field indicates the length of the DATA chunk in bytes from the This field indicates the length of the DATA chunk in bytes from the
Internet draft Stream Control Transmission Protocol July 2000
beginning of the type field to the end of the user data field beginning of the type field to the end of the user data field
excluding any padding. A DATA chunk with no user data field will excluding any padding. A DATA chunk with no user data field will
have Length set to 16 (indicating 16 bytes). have Length set to 16 (indicating 16 bytes).
TSN : 32 bits (unsigned integer) TSN : 32 bits (unsigned integer)
This value represents the TSN for this DATA chunk. The valid range This value represents the TSN for this DATA chunk. The valid range
of TSN is from 0 to 4294967295 (2**32 - 1). TSN wraps back to 0 of TSN is from 0 to 4294967295 (2**32 - 1). TSN wraps back to 0
after reaching 4294967295. after reaching 4294967295.
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3.3.2 Initiation (INIT) (1) 3.3.2 Initiation (INIT) (1)
This chunk is used to initiate a SCTP association between two This chunk is used to initiate a SCTP association between two
endpoints. The format of the INIT chunk is shown below: endpoints. The format of the INIT chunk is shown below:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 | Chunk Flags | Chunk Length | | Type = 1 | Chunk Flags | Chunk Length |
Internet draft Stream Control Transmission Protocol July 2000
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initiate Tag | | Initiate Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertised Receiver Window Credit (a_rwnd) | | Advertised Receiver Window Credit (a_rwnd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Outbound Streams | Number of Inbound Streams | | Number of Outbound Streams | Number of Inbound Streams |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial TSN | | Initial TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \ \ \
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address types with the Host Name address in the INIT. The receiver address types with the Host Name address in the INIT. The receiver
of INIT MUST ignore any other address types if the Host Name address of INIT MUST ignore any other address types if the Host Name address
parameter is present in the received INIT chunk. parameter is present in the received INIT chunk.
Note 4: This parameter, when present, specifies all the address types Note 4: This parameter, when present, specifies all the address types
the sending endpoint can support. The absence of this parameter the sending endpoint can support. The absence of this parameter
indicates that the sending endpoint can support any address type. indicates that the sending endpoint can support any address type.
The Chunk Flags field in INIT is reserved and all bits in it should be The Chunk Flags field in INIT is reserved and all bits in it should be
set to 0 by the sender and ignored by the receiver. The sequence of set to 0 by the sender and ignored by the receiver. The sequence of
Internet draft Stream Control Transmission Protocol July 2000
parameters within an INIT can be processed in any order. parameters within an INIT can be processed in any order.
Initiate Tag: 32 bits (unsigned integer) Initiate Tag: 32 bits (unsigned integer)
The receiver of the INIT (the responding end) records the value of The receiver of the INIT (the responding end) records the value of
the Initiate Tag parameter. This value MUST be placed into the the Initiate Tag parameter. This value MUST be placed into the
Verification Tag field of every SCTP packet that the receiver of the Verification Tag field of every SCTP packet that the receiver of the
INIT transmits within this association. INIT transmits within this association.
The Initiate Tag is allowed to have any value except 0. See The Initiate Tag is allowed to have any value except 0. See
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Note: A receiver of an INIT with the MIS value of 0 SHOULD abort Note: A receiver of an INIT with the MIS value of 0 SHOULD abort
the association. the association.
Initial TSN (I-TSN) : 32 bits (unsigned integer) Initial TSN (I-TSN) : 32 bits (unsigned integer)
Defines the initial TSN that the sender will use. The valid range is Defines the initial TSN that the sender will use. The valid range is
from 0 to 4294967295. This field MAY be set to the value of the from 0 to 4294967295. This field MAY be set to the value of the
Initiate Tag field. Initiate Tag field.
Internet draft Stream Control Transmission Protocol July 2000
3.3.2.1 Optional/Variable Length Parameters in INIT 3.3.2.1 Optional/Variable Length Parameters in INIT
The following parameters follow the Type-Length-Value format as The following parameters follow the Type-Length-Value format as
defined in Section 3.2.1. Any Type-Length-Value fields MUST come defined in Section 3.2.1. Any Type-Length-Value fields MUST come
after the fixed-length fields defined in the previous section. after the fixed-length fields defined in the previous section.
IPv4 Address Parameter (5) IPv4 Address Parameter (5)
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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Combined with the Source Port Number in the SCTP common header, the Combined with the Source Port Number in the SCTP common header, the
value passed in an IPv4 or IPv6 Address parameter indicates a value passed in an IPv4 or IPv6 Address parameter indicates a
transport address the sender of the INIT will support for the transport address the sender of the INIT will support for the
association being initiated. That is, during the lifetime of this association being initiated. That is, during the lifetime of this
association, this IP address can appear in the source address field association, this IP address can appear in the source address field
of an IP datagram sent from the sender of the INIT, and can be used of an IP datagram sent from the sender of the INIT, and can be used
as a destination address of an IP datagram sent from the receiver of as a destination address of an IP datagram sent from the receiver of
the INIT. the INIT.
More than one IP Address parameter can be included in an INIT More than one IP Address parameter can be included in an INIT
Internet draft Stream Control Transmission Protocol July 2000
chunk when the INIT sender is multi-homed. Moreover, a multi-homed chunk when the INIT sender is multi-homed. Moreover, a multi-homed
endpoint may have access to different types of network, thus more endpoint may have access to different types of network, thus more
than one address type can be present in one INIT chunk, i.e., IPv4 than one address type can be present in one INIT chunk, i.e., IPv4
and IPv6 addresses are allowed in the same INIT chunk. and IPv6 addresses are allowed in the same INIT chunk.
If the INIT contains at least one IP Address parameter, then the If the INIT contains at least one IP Address parameter, then the
source address of the IP datagram containing the INIT chunk and any source address of the IP datagram containing the INIT chunk and any
additional address(es) provided within the INIT can be used as additional address(es) provided within the INIT can be used as
destinations by the endpoint receiving the INIT. If the INIT does destinations by the endpoint receiving the INIT. If the INIT does
not contain any IP Address parameters, the endpoint receiving the not contain any IP Address parameters, the endpoint receiving the
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Host Name Address (11) Host Name Address (11)
The sender of INIT uses this parameter to pass its Host Name (in The sender of INIT uses this parameter to pass its Host Name (in
place of its IP addresses) to its peer. The peer is responsible for place of its IP addresses) to its peer. The peer is responsible for
resolving the name. Using this parameter might make it more likely resolving the name. Using this parameter might make it more likely
for the association to work across a NAT box. for the association to work across a NAT box.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Internet draft Stream Control Transmission Protocol July 2000
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 11 | Length | | Type = 11 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Host Name / / Host Name /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Host Name: variable length Host Name: variable length
This field contains a host name in "host name syntax" per RFC1123 This field contains a host name in "host name syntax" per RFC1123
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The format of the INIT ACK chunk is shown below: The format of the INIT ACK chunk is shown below:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Chunk Flags | Chunk Length | | Type = 2 | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initiate Tag | | Initiate Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Internet draft Stream Control Transmission Protocol July 2000
| Advertised Receiver Window Credit | | Advertised Receiver Window Credit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Outbound Streams | Number of Inbound Streams | | Number of Outbound Streams | Number of Inbound Streams |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial TSN | | Initial TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \ \ \
/ Optional/Variable-Length Parameters / / Optional/Variable-Length Parameters /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Note: A receiver of an INIT ACK with the OS value set to 0 SHOULD destroy Note: A receiver of an INIT ACK with the OS value set to 0 SHOULD destroy
the association discarding its TCB. the association discarding its TCB.
Number of Inbound Streams (MIS) : 16 bits (unsigned integer) Number of Inbound Streams (MIS) : 16 bits (unsigned integer)
Defines the maximum number of streams the sender of this INIT ACK Defines the maximum number of streams the sender of this INIT ACK
chunk allows the peer end to create in this association. The value 0 chunk allows the peer end to create in this association. The value 0
MUST NOT be used. MUST NOT be used.
Note: There is no negotiation of the actual number of streams but Note: There is no negotiation of the actual number of streams but
Internet draft Stream Control Transmission Protocol July 2000
instead the two endpoints will use the min(requested, instead the two endpoints will use the min(requested,
offered). See Section 5.1.1 for details. offered). See Section 5.1.1 for details.
Note: A receiver of an INIT ACK with the MIS value set to 0 SHOULD destroy Note: A receiver of an INIT ACK with the MIS value set to 0 SHOULD destroy
the association discarding its TCB. the association discarding its TCB.
Initial TSN (I-TSN) : 32 bits (unsigned integer) Initial TSN (I-TSN) : 32 bits (unsigned integer)
Defines the initial TSN that the INIT-ACK sender will use. The valid Defines the initial TSN that the INIT-ACK sender will use. The valid
range is from 0 to 4294967295. This field MAY be set to the value range is from 0 to 4294967295. This field MAY be set to the value
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the variable size of the state cookie AND the variable address the variable size of the state cookie AND the variable address
list. For example if a responder to the INIT has 1000 IPv4 list. For example if a responder to the INIT has 1000 IPv4
addresses it wishes to send, it would need at least 8,000 bytes addresses it wishes to send, it would need at least 8,000 bytes
to encode this in the INIT ACK. to encode this in the INIT ACK.
In combination with the Source Port carried in the SCTP common header, In combination with the Source Port carried in the SCTP common header,
each IP Address parameter in the INIT ACK indicates to the receiver of each IP Address parameter in the INIT ACK indicates to the receiver of
the INIT ACK a valid transport address supported by the sender of the the INIT ACK a valid transport address supported by the sender of the
INIT ACK for the lifetime of the association being initiated. INIT ACK for the lifetime of the association being initiated.
Internet draft Stream Control Transmission Protocol July 2000
If the INIT ACK contains at least one IP Address parameter, then the If the INIT ACK contains at least one IP Address parameter, then the
source address of the IP datagram containing the INIT ACK and any source address of the IP datagram containing the INIT ACK and any
additional address(es) provided within the INIT ACK may be used as additional address(es) provided within the INIT ACK may be used as
destinations by the receiver of the INIT-ACK. If the INIT ACK does not destinations by the receiver of the INIT-ACK. If the INIT ACK does not
contain any IP Address parameters, the receiver of the INIT-ACK MUST contain any IP Address parameters, the receiver of the INIT-ACK MUST
use the source address associated with the received IP datagram as its use the source address associated with the received IP datagram as its
sole destination address for the association. sole destination address for the association.
The State Cookie and Unrecognized Parameters use the Type-Length- The State Cookie and Unrecognized Parameters use the Type-Length-
Value format as defined in Section 3.2.1 and are described below. The Value format as defined in Section 3.2.1 and are described below. The
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The SACK MUST contain the Cumulative TSN Ack and Advertised Receiver The SACK MUST contain the Cumulative TSN Ack and Advertised Receiver
Window Credit (a_rwnd) parameters. Window Credit (a_rwnd) parameters.
By definition, the value of the Cumulative TSN Ack parameter is the By definition, the value of the Cumulative TSN Ack parameter is the
last TSN received before a break in the sequence of received TSNs last TSN received before a break in the sequence of received TSNs
occurs; the next TSN value following this one has not yet been received occurs; the next TSN value following this one has not yet been received
at the endpoint sending the SACK. This parameter therefore acknowledges at the endpoint sending the SACK. This parameter therefore acknowledges
receipt of all TSNs less than or equal to its value. receipt of all TSNs less than or equal to its value.
Internet draft Stream Control Transmission Protocol July 2000
The handling of a_rwnd by the receiver of the SACK is discussed in The handling of a_rwnd by the receiver of the SACK is discussed in
detail in Section 6.2.1. detail in Section 6.2.1.
The SACK also contains zero or more Gap Ack Blocks. Each The SACK also contains zero or more Gap Ack Blocks. Each
Gap Ack Block acknowledges a subsequence of TSNs received following Gap Ack Block acknowledges a subsequence of TSNs received following
a break in the sequence of received TSNs. By definition, all TSNs a break in the sequence of received TSNs. By definition, all TSNs
acknowledged by Gap Ack Blocks are greater than the value of the acknowledged by Gap Ack Blocks are greater than the value of the
Cumulative TSN Ack. Cumulative TSN Ack.
0 1 2 3 0 1 2 3
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This parameter contains the TSN of the last DATA chunk received in This parameter contains the TSN of the last DATA chunk received in
sequence before a gap. sequence before a gap.
Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned integer) Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned integer)
This field indicates the updated receive buffer space in bytes of This field indicates the updated receive buffer space in bytes of
the sender of this SACK, see Section 6.2.1 for details. the sender of this SACK, see Section 6.2.1 for details.
Number of Gap Ack Blocks: 16 bits (unsigned integer) Number of Gap Ack Blocks: 16 bits (unsigned integer)
Internet draft Stream Control Transmission Protocol July 2000
Indicates the number of Gap Ack Blocks included in this SACK. Indicates the number of Gap Ack Blocks included in this SACK.
Number of Duplicate TSNs: 16 bit Number of Duplicate TSNs: 16 bit
This field contains the number of duplicate TSNs the endpoint This field contains the number of duplicate TSNs the endpoint
has received. Each duplicate TSN is listed following the Gap Ack has received. Each duplicate TSN is listed following the Gap Ack
Block list. Block list.
Gap Ack Blocks: Gap Ack Blocks:
skipping to change at page 30, line 50 skipping to change at page 31, line 5
| TSN=12 | | TSN=12 |
---------- ----------
| TSN=11 | | TSN=11 |
---------- ----------
| TSN=10 | | TSN=10 |
---------- ----------
then, the parameter part of the SACK MUST be constructed as then, the parameter part of the SACK MUST be constructed as
follows (assuming the new a_rwnd is set to 4660 by the sender): follows (assuming the new a_rwnd is set to 4660 by the sender):
Internet draft Stream Control Transmission Protocol July 2000
+--------------------------------+ +--------------------------------+
| Cumulative TSN Ack = 12 | | Cumulative TSN Ack = 12 |
+--------------------------------+ +--------------------------------+
| a_rwnd = 4660 | | a_rwnd = 4660 |
+----------------+---------------+ +----------------+---------------+
| num of block=2 | num of dup=0 | | num of block=2 | num of dup=0 |
+----------------+---------------+ +----------------+---------------+
|block #1 strt=2 |block #1 end=3 | |block #1 strt=2 |block #1 end=3 |
+----------------+---------------+ +----------------+---------------+
|block #2 strt=5 |block #2 end=5 | |block #2 strt=5 |block #2 end=5 |
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Chunk Flags: 8 bits Chunk Flags: 8 bits
Set to zero on transmit and ignored on receipt. Set to zero on transmit and ignored on receipt.
Heartbeat Length: 16 bits (unsigned integer) Heartbeat Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header Set to the size of the chunk in bytes, including the chunk header
and the Heartbeat Information field. and the Heartbeat Information field.
Internet draft Stream Control Transmission Protocol July 2000
Heartbeat Information: variable length Heartbeat Information: variable length
Defined as a variable-length parameter using the format described in Defined as a variable-length parameter using the format described in
Section 3.2.1, i.e.: Section 3.2.1, i.e.:
Variable Parameters Status Type Value Variable Parameters Status Type Value
------------------------------------------------------------- -------------------------------------------------------------
Heartbeat Info Mandatory 1 Heartbeat Info Mandatory 1
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Heartbeat Info Type=1 | HB Info Length | | Heartbeat Info Type=1 | HB Info Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Sender-specific Heartbeat Info / / Sender-specific Heartbeat Info /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Sender-specific Heartbeat Info field should normally include The Sender-specific Heartbeat Info field should normally include
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Chunk Flags: 8 bits Chunk Flags: 8 bits
Set to zero on transmit and ignored on receipt. Set to zero on transmit and ignored on receipt.
Heartbeat Ack Length: 16 bits (unsigned integer) Heartbeat Ack Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header Set to the size of the chunk in bytes, including the chunk header
and the Heartbeat Information field. and the Heartbeat Information field.
Internet draft Stream Control Transmission Protocol July 2000
Heartbeat Information: variable length Heartbeat Information: variable length
This field MUST contain the Heartbeat Information parameter of This field MUST contain the Heartbeat Information parameter of
the Heartbeat Request to which this Heartbeat Acknowledgement is the Heartbeat Request to which this Heartbeat Acknowledgement is
responding. responding.
Variable Parameters Status Type Value Variable Parameters Status Type Value
------------------------------------------------------------- -------------------------------------------------------------
Heartbeat Info Mandatory 1 Heartbeat Info Mandatory 1
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the sender did NOT have a TCB it should set this bit to 1. the sender did NOT have a TCB it should set this bit to 1.
Note: Special rules apply to this chunk for verification, please Note: Special rules apply to this chunk for verification, please
see Section 8.5.1 for details. see Section 8.5.1 for details.
Length: 16 bits (unsigned integer) Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header Set to the size of the chunk in bytes, including the chunk header
and all the Error Cause fields present. and all the Error Cause fields present.
Internet draft Stream Control Transmission Protocol July 2000
See Section 3.3.10 for Error Cause definitions. See Section 3.3.10 for Error Cause definitions.
3.3.8 Shutdown Association (SHUTDOWN) (7): 3.3.8 Shutdown Association (SHUTDOWN) (7):
An endpoint in an association MUST use this chunk to initiate a An endpoint in an association MUST use this chunk to initiate a
graceful close of the association with its peer. This chunk has graceful close of the association with its peer. This chunk has
the following format. the following format.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 8 |Chunk Flags | Length = 4 | | Type = 8 |Chunk Flags | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits Chunk Flags: 8 bits
Set to zero on transmit and ignored on receipt. Set to zero on transmit and ignored on receipt.
Internet draft Stream Control Transmission Protocol July 2000
3.3.10 Operation Error (ERROR) (9): 3.3.10 Operation Error (ERROR) (9):
An endpoint sends this chunk to its peer endpoint to notify it of An endpoint sends this chunk to its peer endpoint to notify it of
certain error conditions. It contains one or more error causes. An certain error conditions. It contains one or more error causes. An
Operation Error is not considered fatal in and of itself, but may be Operation Error is not considered fatal in and of itself, but may be
used with an ABORT chunk to report a fatal condition. It has the used with an ABORT chunk to report a fatal condition. It has the
following parameters: following parameters:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
skipping to change at page 35, line 48 skipping to change at page 36, line 4
Cause Code Cause Code
Value Cause Code Value Cause Code
--------- ---------------- --------- ----------------
1 Invalid Stream Identifier 1 Invalid Stream Identifier
2 Missing Mandatory Parameter 2 Missing Mandatory Parameter
3 Stale Cookie Error 3 Stale Cookie Error
4 Out of Resource 4 Out of Resource
5 Unresolvable Address 5 Unresolvable Address
6 Unrecognized Chunk Type 6 Unrecognized Chunk Type
7 Invalid Mandatory Parameter 7 Invalid Mandatory Parameter
Internet draft Stream Control Transmission Protocol July 2000
8 Unrecognized Parameters 8 Unrecognized Parameters
9 No User Data 9 No User Data
10 Cookie Received While Shutting Down 10 Cookie Received While Shutting Down
Cause Length: 16 bits (unsigned integer) Cause Length: 16 bits (unsigned integer)
Set to the size of the parameter in bytes, including the Cause Code, Set to the size of the parameter in bytes, including the Cause Code,
Cause Length, and Cause-Specific Information fields Cause Length, and Cause-Specific Information fields
Cause-specific Information: variable length Cause-specific Information: variable length
skipping to change at page 36, line 47 skipping to change at page 37, line 4
--------------- ---------------
Missing Mandatory Parameter: Indicates that one or more Missing Mandatory Parameter: Indicates that one or more
mandatory TLV parameters are missing in a received INIT or INIT ACK. mandatory TLV parameters are missing in a received INIT or INIT ACK.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=2 | Cause Length=8+N*2 | | Cause Code=2 | Cause Length=8+N*2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of missing params=N | | Number of missing params=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Missing Param Type #1 | Missing Param Type #2 | | Missing Param Type #1 | Missing Param Type #2 |
Internet draft Stream Control Transmission Protocol July 2000
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Missing Param Type #N-1 | Missing Param Type #N | | Missing Param Type #N-1 | Missing Param Type #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Number of Missing params: 32 bits (unsigned integer) Number of Missing params: 32 bits (unsigned integer)
This field contains the number of parameters contained in the This field contains the number of parameters contained in the
Cause-specific Information field. Cause-specific Information field.
Missing Param Type: 16 bits (unsigned integer) Missing Param Type: 16 bits (unsigned integer)
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=4 | Cause Length=4 | | Cause Code=4 | Cause Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.3.10.5 Unresolvable Address (5) 3.3.10.5 Unresolvable Address (5)
Cause of error Cause of error
--------------- ---------------
Unresolvable Address: Indicates that the sender is not able to Unresolvable Address: Indicates that the sender is not able to
resolve the specified address parameter (e.g., type of address is resolve the specified address parameter (e.g., type of address is
Internet draft Stream Control Transmission Protocol July 2000
not supported by the sender). This is usually sent in combination not supported by the sender). This is usually sent in combination
with or within an ABORT. with or within an ABORT.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=5 | Cause Length | | Cause Code=5 | Cause Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Unresolvable Address / / Unresolvable Address /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Unresolvable Address: variable length Unresolvable Address: variable length
The unresolvable address field contains the complete Type, Length The unresolvable address field contains the complete Type, Length
and Value of the address parameter (or Host Name parameter) that and Value of the address parameter (or Host Name parameter) that
contains the unresolvable address or host name. contains the unresolvable address or host name.
3.3.10.6 Unrecognized Chunk Type (6) 3.3.10.6 Unrecognized Chunk Type (6)
Cause of error Cause of error
--------------- ---------------
Unrecognized Chunk Type: This error cause is returned to the Unrecognized Chunk Type: This error cause is returned to the
skipping to change at page 38, line 46 skipping to change at page 39, line 4
parameters is set to a invalid value. parameters is set to a invalid value.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=7 | Cause Length=4 | | Cause Code=7 | Cause Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.3.10.8 Unrecognized Parameters (8) 3.3.10.8 Unrecognized Parameters (8)
Cause of error Cause of error
--------------- ---------------
Internet draft Stream Control Transmission Protocol July 2000
Unrecognized Parameters: This error cause is returned to the Unrecognized Parameters: This error cause is returned to the
originator of the INIT ACK chunk if the receiver does not originator of the INIT ACK chunk if the receiver does not
recognize one or more Optional TLV parameters in the INIT ACK chunk. recognize one or more Optional TLV parameters in the INIT ACK chunk.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=8 | Cause Length | | Cause Code=8 | Cause Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Unrecognized Parameters / / Unrecognized Parameters /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 39, line 46 skipping to change at page 40, line 5
--------------- ---------------
Cookie Received While Shutting Down: A COOKIE ECHO was received Cookie Received While Shutting Down: A COOKIE ECHO was received
While the endpoint was in SHUTDOWN-ACK-SENT state. This error is While the endpoint was in SHUTDOWN-ACK-SENT state. This error is
usually returned in an ERROR chunk bundled with the retransmitted usually returned in an ERROR chunk bundled with the retransmitted
SHUTDOWN ACK. SHUTDOWN ACK.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=10 | Cause Length=4 | | Cause Code=10 | Cause Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Internet draft Stream Control Transmission Protocol July 2000
3.3.11 Cookie Echo (COOKIE ECHO) (10): 3.3.11 Cookie Echo (COOKIE ECHO) (10):
This chunk is used only during the initialization of an association. This chunk is used only during the initialization of an association.
It is sent by the initiator of an association to its peer to complete It is sent by the initiator of an association to its peer to complete
the initialization process. This chunk MUST precede any DATA chunk the initialization process. This chunk MUST precede any DATA chunk
sent within the association, but MAY be bundled with one or more DATA sent within the association, but MAY be bundled with one or more DATA
chunks in the same packet. chunks in the same packet.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
skipping to change at page 40, line 44 skipping to change at page 41, line 5
same SCTP packet. same SCTP packet.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 11 |Chunk Flags | Length = 4 | | Type = 11 |Chunk Flags | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits Chunk Flags: 8 bits
Internet draft Stream Control Transmission Protocol July 2000
Set to zero on transmit and ignored on receipt. Set to zero on transmit and ignored on receipt.
3.3.13 Shutdown Complete (SHUTDOWN COMPLETE) (14): 3.3.13 Shutdown Complete (SHUTDOWN COMPLETE) (14):
This chunk MUST be used to acknowledge the receipt of the SHUTDOWN ACK This chunk MUST be used to acknowledge the receipt of the SHUTDOWN ACK
chunk at the completion of the shutdown process, see Section 9.2 for chunk at the completion of the shutdown process, see Section 9.2 for
details. details.
The SHUTDOWN COMPLETE chunk has no parameters. The SHUTDOWN COMPLETE chunk has no parameters.
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The state diagram in the figures below illustrates state changes, The state diagram in the figures below illustrates state changes,
together with the causing events and resulting actions. Note that some together with the causing events and resulting actions. Note that some
of the error conditions are not shown in the state diagram. Full of the error conditions are not shown in the state diagram. Full
description of all special cases should be found in the text. description of all special cases should be found in the text.
Note: Chunk names are given in all capital letters, while parameter Note: Chunk names are given in all capital letters, while parameter
names have the first letter capitalized, e.g., COOKIE ECHO chunk type names have the first letter capitalized, e.g., COOKIE ECHO chunk type
vs. State Cookie parameter. If more than one event/message can occur vs. State Cookie parameter. If more than one event/message can occur
which causes a state transition it is labeled (A), (B) etc. which causes a state transition it is labeled (A), (B) etc.
Internet draft Stream Control Transmission Protocol July 2000
----- -------- (frm any state) ----- -------- (frm any state)
/ \ / rcv ABORT [ABORT] / \ / rcv ABORT [ABORT]
rcv INIT | | | ---------- or ---------- rcv INIT | | | ---------- or ----------
--------------- | v v delete TCB snd ABORT --------------- | v v delete TCB snd ABORT
generate Cookie \ +---------+ delete TCB generate Cookie \ +---------+ delete TCB
snd INIT ACK ---| CLOSED | snd INIT ACK ---| CLOSED |
+---------+ +---------+
/ \ [ASSOCIATE] / \ [ASSOCIATE]
/ \ --------------- / \ ---------------
| | create TCB | | create TCB
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check outstanding | | check outstanding | |
DATA chunks | | DATA chunks | |
v | v |
+---------+ | +---------+ |
|SHUTDOWN-| | rcv SHUTDOWN/check |SHUTDOWN-| | rcv SHUTDOWN/check
|PENDING | | outstanding DATA |PENDING | | outstanding DATA
+---------+ | chunks +---------+ | chunks
| |------------------ | |------------------
No more outstanding | | No more outstanding | |
---------------------| | ---------------------| |
Internet draft Stream Control Transmission Protocol July 2000
snd SHUTDOWN | | snd SHUTDOWN | |
strt shutdown timer | | strt shutdown timer | |
v v v v
+---------+ +-----------+ +---------+ +-----------+
(4) |SHUTDOWN-| | SHUTDOWN- | (5,6) (4) |SHUTDOWN-| | SHUTDOWN- | (5,6)
|SENT | | RECEIVED | |SENT | | RECEIVED |
+---------+ +-----------+ +---------+ +-----------+
| \ | | \ |
(A) rcv SHUTDOWN ACK | \ | (A) rcv SHUTDOWN ACK | \ |
----------------------| \ | ----------------------| \ |
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Notes: Notes:
(1) If the State Cookie in the received COOKIE ECHO is invalid (i.e., (1) If the State Cookie in the received COOKIE ECHO is invalid (i.e.,
failed to pass the integrity check), the receiver MUST silently failed to pass the integrity check), the receiver MUST silently
discard the packet. Or, if the received State Cookie is expired discard the packet. Or, if the received State Cookie is expired
(see Section 5.1.5), the receiver MUST send back an ERROR chunk. (see Section 5.1.5), the receiver MUST send back an ERROR chunk.
In either case, the receiver stays in the CLOSED state. In either case, the receiver stays in the CLOSED state.
(2) If the T1-init timer expires, the endpoint MUST retransmit INIT (2) If the T1-init timer expires, the endpoint MUST retransmit INIT
and re-start the T1-init timer without changing state. This MUST be and re-start the T1-init timer without changing state. This MUST be
repeated up to 'Max.Init.Retransmits' times. After that, the repeated up to 'Max.Init.Retransmits' times. After that, the
Internet draft Stream Control Transmission Protocol July 2000
endpoint MUST abort the initialization process and report the endpoint MUST abort the initialization process and report the
error to SCTP user. error to SCTP user.
(3) If the T1-cookie timer expires, the endpoint MUST retransmit (3) If the T1-cookie timer expires, the endpoint MUST retransmit
COOKIE ECHO and re-start the T1-cookie timer without changing COOKIE ECHO and re-start the T1-cookie timer without changing
state. This MUST be repeated up to 'Max.Init.Retransmits' state. This MUST be repeated up to 'Max.Init.Retransmits'
times. After that, the endpoint MUST abort the initialization times. After that, the endpoint MUST abort the initialization
process and report the error to SCTP user. process and report the error to SCTP user.
(4) In SHUTDOWN-SENT state the endpoint MUST acknowledge any received (4) In SHUTDOWN-SENT state the endpoint MUST acknowledge any received
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5.1 Normal Establishment of an Association 5.1 Normal Establishment of an Association
The initialization process consists of the following steps (assuming The initialization process consists of the following steps (assuming
that SCTP endpoint "A" tries to set up an association with SCTP that SCTP endpoint "A" tries to set up an association with SCTP
endpoint "Z" and "Z" accepts the new association): endpoint "Z" and "Z" accepts the new association):
A) "A" first sends an INIT chunk to "Z". In the INIT, "A" must A) "A" first sends an INIT chunk to "Z". In the INIT, "A" must
provide its Verification Tag (Tag_A) in the Initiate Tag field. provide its Verification Tag (Tag_A) in the Initiate Tag field.
Tag_A SHOULD be a random number in the range of 1 to 4294967295 Tag_A SHOULD be a random number in the range of 1 to 4294967295
Internet draft Stream Control Transmission Protocol July 2000
(see 5.3.1 for Tag value selection). After sending the INIT, "A" (see 5.3.1 for Tag value selection). After sending the INIT, "A"
starts the T1-init timer and enters the COOKIE-WAIT state. starts the T1-init timer and enters the COOKIE-WAIT state.
B) "Z" shall respond immediately with an INIT ACK chunk. The B) "Z" shall respond immediately with an INIT ACK chunk. The
destination IP address of the INIT ACK MUST be set to the source destination IP address of the INIT ACK MUST be set to the source
IP address of the INIT to which this INIT ACK is responding. In IP address of the INIT to which this INIT ACK is responding. In
the response, besides filling in other parameters, "Z" must set the the response, besides filling in other parameters, "Z" must set the
Verification Tag field to Tag_A, and also provide its own Verification Tag field to Tag_A, and also provide its own
Verification Tag (Tag_Z) in the Initiate Tag field. Verification Tag (Tag_Z) in the Initiate Tag field.
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They MUST be the only chunks present in the SCTP packets that carry They MUST be the only chunks present in the SCTP packets that carry
them. them.
An endpoint MUST send the INIT ACK to the IP address from which it An endpoint MUST send the INIT ACK to the IP address from which it
received the INIT. received the INIT.
Note: T1-init timer and T1-cookie timer shall follow the same rules Note: T1-init timer and T1-cookie timer shall follow the same rules
given in Section 6.3. given in Section 6.3.
Internet draft Stream Control Transmission Protocol July 2000
If an endpoint receives an INIT, INIT ACK, or COOKIE ECHO chunk but If an endpoint receives an INIT, INIT ACK, or COOKIE ECHO chunk but
decides not to establish the new association due to missing mandatory decides not to establish the new association due to missing mandatory
parameters in the received INIT or INIT ACK, invalid parameter values, parameters in the received INIT or INIT ACK, invalid parameter values,
or lack of local resources, it MUST respond with an ABORT chunk. It or lack of local resources, it MUST respond with an ABORT chunk. It
SHOULD also specify the cause of abort, such as the type of the SHOULD also specify the cause of abort, such as the type of the
missing mandatory parameters, etc., by including the error cause missing mandatory parameters, etc., by including the error cause
parameters with the ABORT chunk. The Verification Tag field in the parameters with the ABORT chunk. The Verification Tag field in the
common header of the outbound SCTP packet containing the ABORT chunk common header of the outbound SCTP packet containing the ABORT chunk
MUST be set to the Initiate Tag value of the peer. MUST be set to the Initiate Tag value of the peer.
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following rules to discover and collect the destination transport following rules to discover and collect the destination transport
address(es) of its peer. address(es) of its peer.
A) If there are no address parameters present in the received INIT A) If there are no address parameters present in the received INIT
or INIT ACK chunk, the endpoint shall take the source IP address or INIT ACK chunk, the endpoint shall take the source IP address
from which the chunk arrives and record it, in combination with from which the chunk arrives and record it, in combination with
the SCTP source port number, as the only destination transport the SCTP source port number, as the only destination transport
address for this peer. address for this peer.
B) If there is a Host Name parameter present in the received INIT or B) If there is a Host Name parameter present in the received INIT or
Internet draft Stream Control Transmission Protocol July 2000
INIT ACK chunk, the endpoint shall resolve that host name to a INIT ACK chunk, the endpoint shall resolve that host name to a
list of IP address(es) and derive the transport address(es) of this list of IP address(es) and derive the transport address(es) of this
peer by combining the resolved IP address(es) with the SCTP source peer by combining the resolved IP address(es) with the SCTP source
port. port.
The endpoint MUST ignore any other IP address parameters if The endpoint MUST ignore any other IP address parameters if
they are also present in the received INIT or INIT ACK chunk. they are also present in the received INIT or INIT ACK chunk.
The time at which the receiver of an INIT resolves the host The time at which the receiver of an INIT resolves the host
name has potential security implications to SCTP. If the receiver of name has potential security implications to SCTP. If the receiver of
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The receiver should use only these transport addresses as The receiver should use only these transport addresses as
destination transport addresses when sending subsequent packets destination transport addresses when sending subsequent packets
to its peer. to its peer.
IMPLEMENTATION NOTE: In some cases (e.g., when the implementation IMPLEMENTATION NOTE: In some cases (e.g., when the implementation
doesn't control the source IP address that is used for transmitting), doesn't control the source IP address that is used for transmitting),
an endpoint might need to include in its INIT or INIT ACK all possible an endpoint might need to include in its INIT or INIT ACK all possible
IP addresses from which packets to the peer could be transmitted. IP addresses from which packets to the peer could be transmitted.
After all transport addresses are derived from the INIT or INIT ACK After all transport addresses are derived from the INIT or INIT ACK
Internet draft Stream Control Transmission Protocol July 2000
chunk using the above rules, the endpoint shall select one of the chunk using the above rules, the endpoint shall select one of the
transport addresses as the initial primary path. transport addresses as the initial primary path.
Note: The INIT-ACK MUST be sent to the source address of the INIT. Note: The INIT-ACK MUST be sent to the source address of the INIT.
The sender of INIT may include a 'Supported Address Types' The sender of INIT may include a 'Supported Address Types'
parameter in the INIT to indicate what types of address are parameter in the INIT to indicate what types of address are
acceptable. When this parameter is present, the receiver of INIT acceptable. When this parameter is present, the receiver of INIT
(initiatee) MUST either use one of the address types indicated in the (initiatee) MUST either use one of the address types indicated in the
Supported Address Types parameter when responding to the INIT, or Supported Address Types parameter when responding to the INIT, or
skipping to change at page 48, line 48 skipping to change at page 49, line 4
and the resultant MAC. and the resultant MAC.
After sending the INIT ACK with the State Cookie parameter, the sender After sending the INIT ACK with the State Cookie parameter, the sender
SHOULD delete the TCB and any other local resource related to the new SHOULD delete the TCB and any other local resource related to the new
association, so as to prevent resource attacks. association, so as to prevent resource attacks.
The hashing method used to generate the MAC is strictly a The hashing method used to generate the MAC is strictly a
private matter for the receiver of the INIT chunk. The use of a MAC private matter for the receiver of the INIT chunk. The use of a MAC
is mandatory to prevent denial of service attacks. The secret key is mandatory to prevent denial of service attacks. The secret key
SHOULD be random ([RFC1750] provides some information on randomness SHOULD be random ([RFC1750] provides some information on randomness
Internet draft Stream Control Transmission Protocol July 2000
guidelines); it SHOULD be changed reasonably frequently, and the guidelines); it SHOULD be changed reasonably frequently, and the
timestamp in the State Cookie MAY be used to determine which key should timestamp in the State Cookie MAY be used to determine which key should
be used to verify the MAC. be used to verify the MAC.
An implementation SHOULD make the cookie as small as possible to An implementation SHOULD make the cookie as small as possible to
insure interoperability. insure interoperability.
5.1.4 State Cookie Processing 5.1.4 State Cookie Processing
When an endpoint receives an INIT ACK chunk with a State Cookie When an endpoint receives an INIT ACK chunk with a State Cookie
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4) If the State Cookie is valid, create an association to the sender of 4) If the State Cookie is valid, create an association to the sender of
the COOKIE ECHO chunk with the information in the TCB data carried the COOKIE ECHO chunk with the information in the TCB data carried
in the COOKIE ECHO, and enter the ESTABLISHED state, in the COOKIE ECHO, and enter the ESTABLISHED state,
5) Send a COOKIE ACK chunk to the peer acknowledging reception of 5) Send a COOKIE ACK chunk to the peer acknowledging reception of
the COOKIE ECHO. The COOKIE ACK MAY be bundled with an outbound the COOKIE ECHO. The COOKIE ACK MAY be bundled with an outbound
DATA chunk or SACK chunk; however, the COOKIE ACK MUST be the first DATA chunk or SACK chunk; however, the COOKIE ACK MUST be the first
chunk in the SCTP packet. chunk in the SCTP packet.
6) Immediately acknowledge any DATA chunk bundled with the COOKIE ECHO 6) Immediately acknowledge any DATA chunk bundled with the COOKIE ECHO
Internet draft Stream Control Transmission Protocol July 2000
with a SACK (subsequent DATA chunk acknowledgement should follow the with a SACK (subsequent DATA chunk acknowledgement should follow the
rules defined in Section 6.2). As mentioned in step 5), if the SACK rules defined in Section 6.2). As mentioned in step 5), if the SACK
is bundled with the COOKIE ACK, the COOKIE ACK MUST appear first in is bundled with the COOKIE ACK, the COOKIE ACK MUST appear first in
the SCTP packet. the SCTP packet.
If a COOKIE ECHO is received from an endpoint with which the If a COOKIE ECHO is received from an endpoint with which the
receiver of the COOKIE ECHO has an existing association, the procedures receiver of the COOKIE ECHO has an existing association, the procedures
in Section 5.2 should be followed. in Section 5.2 should be followed.
5.1.6 An Example of Normal Association Establishment 5.1.6 An Example of Normal Association Establishment
skipping to change at page 50, line 49 skipping to change at page 51, line 4
(Cancel T3-rtx timer) <------/ (Cancel T3-rtx timer) <------/
... ...
... ...
{app sends 2 messages;strm 0} {app sends 2 messages;strm 0}
/---- DATA /---- DATA
/ [TSN=init TSN_Z / [TSN=init TSN_Z
<--/ Strm=0,Seq=1 & user data 1] <--/ Strm=0,Seq=1 & user data 1]
SACK [TSN Ack=init TSN_Z, /---- DATA SACK [TSN Ack=init TSN_Z, /---- DATA
Block=0] --------\ / [TSN=init TSN_Z +1, Block=0] --------\ / [TSN=init TSN_Z +1,
Internet draft Stream Control Transmission Protocol July 2000
\/ Strm=0,Seq=2 & user data 2] \/ Strm=0,Seq=2 & user data 2]
<------/\ <------/\
\ \
\------> \------>
Figure 4: INITiation Example Figure 4: INITiation Example
If the T1-init timer expires at "A" after the INIT or COOKIE ECHO If the T1-init timer expires at "A" after the INIT or COOKIE ECHO
chunks are sent, the same INIT or COOKIE ECHO chunk with the same chunks are sent, the same INIT or COOKIE ECHO chunk with the same
Initiate Tag (i.e., Tag_A) or State Cookie shall be retransmitted and Initiate Tag (i.e., Tag_A) or State Cookie shall be retransmitted and
the timer restarted. This shall be repeated Max.Init.Retransmits times the timer restarted. This shall be repeated Max.Init.Retransmits times
before "A" considers "Z" unreachable and reports the failure to its before "A" considers "Z" unreachable and reports the failure to its
upper layer (and thus the association enters the CLOSED state). When upper layer (and thus the association enters the CLOSED state). When
retransmitting the INIT, the endpoint MUST follow the rules retransmitting the INIT, the endpoint MUST follow the rules
defined in 6.3 to determine the proper timer value. defined in 6.3 to determine the proper timer value.
5.2 Handle Duplicate or Unexpected INIT, INIT ACK, COOKIE ECHO, and 5.2 Handle Duplicate or Unexpected INIT, INIT ACK, COOKIE ECHO, and
COOKIE ACK COOKIE ACK
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D) The chunk is a false packet generated by an attacker, or D) The chunk is a false packet generated by an attacker, or
E) The peer never received the COOKIE ACK and is retransmitting its E) The peer never received the COOKIE ACK and is retransmitting its
COOKIE ECHO. COOKIE ECHO.
The rules in the following sections shall be applied in order to The rules in the following sections shall be applied in order to
identify and correctly handle these cases. identify and correctly handle these cases.
5.2.1 INIT received in COOKIE-WAIT or COOKIE-ECHOED State (Item B) 5.2.1 INIT received in COOKIE-WAIT or COOKIE-ECHOED State (Item B)
Internet draft Stream Control Transmission Protocol July 2000
This usually indicates an initialization collision, i.e., each This usually indicates an initialization collision, i.e., each
endpoint is attempting, at about the same time, to establish an endpoint is attempting, at about the same time, to establish an
association with the other endpoint. association with the other endpoint.
Upon receipt of an INIT in the COOKIE-WAIT or COOKIE-ECHOED state, an Upon receipt of an INIT in the COOKIE-WAIT or COOKIE-ECHOED state, an
endpoint MUST respond with an INIT ACK using the same parameters it endpoint MUST respond with an INIT ACK using the same parameters it
sent in its original INIT chunk (including its Verification Tag, sent in its original INIT chunk (including its Verification Tag,
unchanged). These original parameters are combined with those from the unchanged). These original parameters are combined with those from the
newly received INIT chunk. The endpoint shall also generate a State newly received INIT chunk. The endpoint shall also generate a State
Cookie with the INIT ACK. The endpoint uses the parameters sent in its Cookie with the INIT ACK. The endpoint uses the parameters sent in its
INIT to calculate the State Cookie. INIT to calculate the State Cookie.
After that, the endpoint MUST NOT change its state, the T1-init After that, the endpoint MUST NOT change its state, the T1-init
timer shall be left running and the corresponding TCB MUST NOT be timer shall be left running and the corresponding TCB MUST NOT be
destroyed. The normal procedures for handling State Cookies when destroyed. The normal procedures for handling State Cookies when
a TCB exists will resolve the duplicate INITs to a single association. a TCB exists will resolve the duplicate INITs to a single association.
For an endpoint that is in the COOKIE-ECHOED state it MUST populate For an endpoint that is in the COOKIE-ECHOED state it MUST populate
its Tie-Tags with the Tag information of itself and its peer (see its Tie-Tags with the Tag information of itself and its peer (see
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5.2.3 Unexpected INIT ACK 5.2.3 Unexpected INIT ACK
If an INIT ACK is received by an endpoint in any state If an INIT ACK is received by an endpoint in any state
other than the COOKIE-WAIT state, the endpoint should discard other than the COOKIE-WAIT state, the endpoint should discard
the INIT ACK chunk. An unexpected INIT ACK usually indicates the the INIT ACK chunk. An unexpected INIT ACK usually indicates the
processing of an old or duplicated INIT chunk. processing of an old or duplicated INIT chunk.
5.2.4 Handle a COOKIE ECHO when a TCB exists 5.2.4 Handle a COOKIE ECHO when a TCB exists
Internet draft Stream Control Transmission Protocol July 2000
When a COOKIE ECHO chunk is received by an endpoint in any state for an When a COOKIE ECHO chunk is received by an endpoint in any state for an
existing association (i.e., not in the CLOSED state) the following existing association (i.e., not in the CLOSED state) the following
rules shall be applied: rules shall be applied:
1) Compute a MAC as described in Step 1 of Section 5.1.5, 1) Compute a MAC as described in Step 1 of Section 5.1.5,
2) Authenticate the State Cookie as described in Step 2 of Section 2) Authenticate the State Cookie as described in Step 2 of Section
5.1.5 (this is case C or D above). 5.1.5 (this is case C or D above).
3) Compare the timestamp in the State Cookie to the current time. If 3) Compare the timestamp in the State Cookie to the current time. If
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| M | A | A | A | (B) | | M | A | A | A | (B) |
+------------+------------+---------------+--------------+-------------+ +------------+------------+---------------+--------------+-------------+
| X | M | 0 | 0 | (C) | | X | M | 0 | 0 | (C) |
+------------+------------+---------------+--------------+-------------+ +------------+------------+---------------+--------------+-------------+
| M | M | A | A | (D) | | M | M | A | A | (D) |
+======================================================================+ +======================================================================+
| Table 2: Handling of a Cookie when a TCB exists | | Table 2: Handling of a Cookie when a TCB exists |
+======================================================================+ +======================================================================+
Legend: Legend:
Internet draft Stream Control Transmission Protocol July 2000
X - Tag does not match the existing TCB X - Tag does not match the existing TCB
M - Tag matches the existing TCB. M - Tag matches the existing TCB.
0 - No Tie-Tag in Cookie. 0 - No Tie-Tag in Cookie (unknown).
A - All cases match, no-match or unknown i.e. 0. A - All cases match, no-match or unknown.
Note: For any case not shown in Table 2, the cookie should be Note: For any case not shown in Table 2, the cookie should be
silently discarded. silently discarded.
Action Action
(A)In this case, the peer may have restarted. When the endpoint (A)In this case, the peer may have restarted. When the endpoint
recognizes this potential 'restart', the existing session is recognizes this potential 'restart', the existing session is
treated the same as if it received an ABORT followed by a new treated the same as if it received an ABORT followed by a new
Cookie Echo with the following exceptions: Cookie Echo with the following exceptions:
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a INIT and received a INIT-ACK and finally sent a a INIT and received a INIT-ACK and finally sent a
Cookie with the peers same tag but a new tag of Cookie with the peers same tag but a new tag of
its own. The cookie should be silently discarded. its own. The cookie should be silently discarded.
The endpoint should NOT change states and should The endpoint should NOT change states and should
leave any timers running. leave any timers running.
(D)When both local and remote tags match the endpoint should (D)When both local and remote tags match the endpoint should
always enter the Established state. It should stop any init always enter the Established state. It should stop any init
or cookie timers that may running and send a Cookie Ack. or cookie timers that may running and send a Cookie Ack.
Internet draft Stream Control Transmission Protocol July 2000
Note: The "peer's Verification Tag" is the tag received in the Note: The "peer's Verification Tag" is the tag received in the
Initiate Tag field of the INIT or INIT ACK chunk. Initiate Tag field of the INIT or INIT ACK chunk.
5.2.4.1 An Example of a Association Restart
In the following example, "A" initiates the association after a restart
has occured. Endpoint "Z" had no knowledge of the restart until the
exchange (i.e. Heartbeats had not yet detected the failure of "A").
(assuming no bundling or fragmentation occurs):
Endpoint A Endpoint Z
<-------------- Association is established---------------------->
Tag=Tag_A Tag=Tag_Z
<--------------------------------------------------------------->
{A crashes and restarts}
{app sets up a association with Z}
(build TCB)
INIT [I-Tag=Tag_A'
& other info] --------\
(Start T1-init timer) \
(Enter COOKIE-WAIT state) \---> (find a existing TCB
compose temp TCB and Cookie_Z
with Tie-Tags to previous
association)
/--- INIT ACK [Veri Tag=Tag_A',
/ I-Tag=Tag_Z',
(Cancel T1-init timer) <------/ Cookie_Z[TieTags=Tag_A,Tag_Z
& other info]
(destroy temp TCB,leave original in place)
COOKIE ECHO [Veri=Tag_Z',
Cookie_Z
Tie=Tag_A,
Tag_Z]----------\
(Start T1-init timer) \
(Enter COOKIE-ECHOED state) \---> (Find existing association,
Tie-Tags match old tags,
Tags do not match i.e.
case X X M M above,
Announce Restart to ULP
and reset association).
/---- COOKIE-ACK
/
(Cancel T1-init timer, <-----/
Enter ESTABLISHED state)
...
{app sends 1st user data; strm 0}
DATA [TSN=initial TSN_A
Strm=0,Seq=1 & user data]--\
(Start T3-rtx timer) \
\->
/----- SACK [TSN Ack=init TSN_A,Block=0]
(Cancel T3-rtx timer) <------/
Figure 5: A Restart Example
Internet draft Stream Control Transmission Protocol July 2000
5.2.5 Handle Duplicate COOKIE-ACK. 5.2.5 Handle Duplicate COOKIE-ACK.
At any state other than COOKIE-ECHOED, an endpoint should silently At any state other than COOKIE-ECHOED, an endpoint should silently
discard a received COOKIE ACK chunk. discard a received COOKIE ACK chunk.
5.2.6 Handle Stale COOKIE Error 5.2.6 Handle Stale COOKIE Error
Receipt of an Operational ERROR chunk with a "Stale Cookie" error Receipt of an Operational ERROR chunk with a "Stale Cookie" error
cause indicates one of a number of possible events: cause indicates one of a number of possible events:
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previous COOKIE ECHO / ERROR exchange, and should add no more previous COOKIE ECHO / ERROR exchange, and should add no more
than 1 second beyond the measured RTT, due to long State Cookie than 1 second beyond the measured RTT, due to long State Cookie
lifetimes making the endpoint more subject to a replay attack. lifetimes making the endpoint more subject to a replay attack.
5.3 Other Initialization Issues 5.3 Other Initialization Issues
5.3.1 Selection of Tag Value 5.3.1 Selection of Tag Value
Initiate Tag values should be selected from the range of 1 to Initiate Tag values should be selected from the range of 1 to
2**32 - 1. It is very important that the Initiate Tag value be 2**32 - 1. It is very important that the Initiate Tag value be
Internet draft Stream Control Transmission Protocol July 2000
randomized to help protect against "man in the middle" and "sequence randomized to help protect against "man in the middle" and "sequence
number" attacks. The methods described in [RFC1750] can be used for number" attacks. The methods described in [RFC1750] can be used for
the Initiate Tag randomization. Careful selection of Initiate Tags is the Initiate Tag randomization. Careful selection of Initiate Tags is
also necessary to prevent old duplicate packets from previous also necessary to prevent old duplicate packets from previous
associations being mistakenly processed as belonging to the current associations being mistakenly processed as belonging to the current
association. association.
Moreover, the Verification Tag value used by either endpoint in a given Moreover, the Verification Tag value used by either endpoint in a given
association MUST NOT change during the lifetime of an association MUST NOT change during the lifetime of an
association. A new Verification Tag value MUST be used each association. A new Verification Tag value MUST be used each
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In this section the term "data sender" refers to the endpoint that In this section the term "data sender" refers to the endpoint that
transmits a DATA chunk and the term "data receiver" refers to the transmits a DATA chunk and the term "data receiver" refers to the
endpoint that receives a DATA chunk. A data receiver will transmit endpoint that receives a DATA chunk. A data receiver will transmit
SACK chunks. SACK chunks.
+--------------------------+ +--------------------------+
| User Messages | | User Messages |
+--------------------------+ +--------------------------+
SCTP user ^ | SCTP user ^ |
==================|==|======================================= ==================|==|=======================================
Internet draft Stream Control Transmission Protocol July 2000
| v (1) | v (1)
+------------------+ +--------------------+ +------------------+ +--------------------+
| SCTP DATA Chunks | |SCTP Control Chunks | | SCTP DATA Chunks | |SCTP Control Chunks |
+------------------+ +--------------------+ +------------------+ +--------------------+
^ | ^ | ^ | ^ |
| v (2) | v (2) | v (2) | v (2)
+--------------------------+ +--------------------------+
| SCTP packets | | SCTP packets |
+--------------------------+ +--------------------------+
SCTP ^ | SCTP ^ |
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normally reassemble the fragmented message from DATA chunks normally reassemble the fragmented message from DATA chunks
before delivery to the user (see Section 6.9 for details). before delivery to the user (see Section 6.9 for details).
(2) Multiple DATA and control chunks may be bundled by the (2) Multiple DATA and control chunks may be bundled by the
sender into a single SCTP packet for transmission, as long as sender into a single SCTP packet for transmission, as long as
the final size of the packet does not exceed the current path the final size of the packet does not exceed the current path
MTU. The receiver will unbundle the packet back into MTU. The receiver will unbundle the packet back into
the original chunks. Control chunks MUST come before the original chunks. Control chunks MUST come before
DATA chunks in the packet. DATA chunks in the packet.
Figure 5: Illustration of User Data Transfer Figure 6: Illustration of User Data Transfer
The fragmentation and bundling mechanisms, as detailed in Sections 6.9 The fragmentation and bundling mechanisms, as detailed in Sections 6.9
and 6.10, are OPTIONAL to implement by the data sender, but they MUST and 6.10, are OPTIONAL to implement by the data sender, but they MUST
be implemented by the data receiver, i.e., an endpoint MUST be implemented by the data receiver, i.e., an endpoint MUST
properly receive and process bundled or fragmented data. properly receive and process bundled or fragmented data.
6.1 Transmission of DATA Chunks 6.1 Transmission of DATA Chunks
This document is specified as if there is a single retransmission This document is specified as if there is a single retransmission
timer per destination transport address, but implementations MAY have timer per destination transport address, but implementations MAY have
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A) At any given time, the data sender MUST NOT transmit new data to any A) At any given time, the data sender MUST NOT transmit new data to any
destination transport address if its peer's rwnd indicates that the destination transport address if its peer's rwnd indicates that the
peer has no buffer space (i.e. rwnd is 0, see Section 6.2.1). peer has no buffer space (i.e. rwnd is 0, see Section 6.2.1).
However, regardless of the value of rwnd (including if it is 0), However, regardless of the value of rwnd (including if it is 0),
the data sender can always have one DATA chunk in flight to the the data sender can always have one DATA chunk in flight to the
receiver if allowed by cwnd (see rule B below). This rule receiver if allowed by cwnd (see rule B below). This rule
allows the sender to probe for a change in rwnd that the sender allows the sender to probe for a change in rwnd that the sender
missed due to the SACK having been lost in transit from missed due to the SACK having been lost in transit from
the data receiver to the data sender. the data receiver to the data sender.
Internet draft Stream Control Transmission Protocol July 2000
B) At any given time, the sender MUST NOT transmit new data to a B) At any given time, the sender MUST NOT transmit new data to a
given transport address if it has cwnd or more bytes of data given transport address if it has cwnd or more bytes of data
outstanding to that transport address. outstanding to that transport address.
C) When the time comes for the sender to transmit, before sending C) When the time comes for the sender to transmit, before sending
new DATA chunks, the sender MUST first transmit any outstanding new DATA chunks, the sender MUST first transmit any outstanding
DATA chunks which are marked for retransmission (limited by the DATA chunks which are marked for retransmission (limited by the
current cwnd). current cwnd).
D) Then, the sender can send out as many new DATA chunks as Rule A and D) Then, the sender can send out as many new DATA chunks as Rule A and
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Note: The data sender SHOULD NOT use a TSN that is more than Note: The data sender SHOULD NOT use a TSN that is more than
2**31 - 1 above the beginning TSN of the current send window. 2**31 - 1 above the beginning TSN of the current send window.
6.2 Acknowledgement on Reception of DATA Chunks 6.2 Acknowledgement on Reception of DATA Chunks
The SCTP endpoint MUST always acknowledge the reception of each valid The SCTP endpoint MUST always acknowledge the reception of each valid
DATA chunk. DATA chunk.
The guidelines on delayed acknowledgement algorithm specified in The guidelines on delayed acknowledgement algorithm specified in
Internet draft Stream Control Transmission Protocol July 2000
Section 4.2 of [RFC2581] SHOULD be followed. Specifically, an Section 4.2 of [RFC2581] SHOULD be followed. Specifically, an
acknowledgement SHOULD be generated for at least every second packet acknowledgement SHOULD be generated for at least every second packet
(not every second DATA chunk) received, and SHOULD be generated within (not every second DATA chunk) received, and SHOULD be generated within
200 ms of the arrival of any unacknowledged DATA chunk. In some 200 ms of the arrival of any unacknowledged DATA chunk. In some
situations it may be beneficial for an SCTP transmitter to be more situations it may be beneficial for an SCTP transmitter to be more
conservative than the algorithms detailed in this document allow. conservative than the algorithms detailed in this document allow.
However, an SCTP transmitter MUST NOT be more aggressive than the However, an SCTP transmitter MUST NOT be more aggressive than the
following algorithms allow. following algorithms allow.
A SCTP receiver MUST NOT generate more than one SACK for every A SCTP receiver MUST NOT generate more than one SACK for every
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When an endpoint receives a SACK, it MAY use the Duplicate TSN When an endpoint receives a SACK, it MAY use the Duplicate TSN
information to determine if SACK loss is occurring. Further use of information to determine if SACK loss is occurring. Further use of
this data is for future study. this data is for future study.
The data receiver is responsible for maintaining its receive buffers. The data receiver is responsible for maintaining its receive buffers.
The data receiver SHOULD notify the data sender in a timely manner of The data receiver SHOULD notify the data sender in a timely manner of
changes in its ability to receive data. How an implementation manages changes in its ability to receive data. How an implementation manages
its receive buffers is dependent on many factors (e.g., Operating its receive buffers is dependent on many factors (e.g., Operating
System, memory management system, amount of memory, etc.). However, System, memory management system, amount of memory, etc.). However,
Internet draft Stream Control Transmission Protocol July 2000
the data sender strategy defined in Section 6.2.1 is based on the the data sender strategy defined in Section 6.2.1 is based on the
assumption of receiver operation similar to the following: assumption of receiver operation similar to the following:
A) At initialization of the association, the endpoint tells the A) At initialization of the association, the endpoint tells the
peer how much receive buffer space it has allocated to the peer how much receive buffer space it has allocated to the
association in the INIT or INIT ACK. The endpoint sets a_rwnd association in the INIT or INIT ACK. The endpoint sets a_rwnd
to this value. to this value.
B) As DATA chunks are received and buffered, decrement a_rwnd by B) As DATA chunks are received and buffered, decrement a_rwnd by
the number of bytes received and buffered. This is, in effect, the number of bytes received and buffered. This is, in effect,
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strategies in the data sender and thus in suboptimal performance. strategies in the data sender and thus in suboptimal performance.
The following example illustrates the use of delayed acknowledgements: The following example illustrates the use of delayed acknowledgements:
Endpoint A Endpoint Z Endpoint A Endpoint Z
{App sends 3 messages; strm 0} {App sends 3 messages; strm 0}
DATA [TSN=7,Strm=0,Seq=3] ------------> (ack delayed) DATA [TSN=7,Strm=0,Seq=3] ------------> (ack delayed)
(Start T3-rtx timer) (Start T3-rtx timer)
Internet draft Stream Control Transmission Protocol July 2000
DATA [TSN=8,Strm=0,Seq=4] ------------> (send ack) DATA [TSN=8,Strm=0,Seq=4] ------------> (send ack)
/------- SACK [TSN Ack=8,block=0] /------- SACK [TSN Ack=8,block=0]
(cancel T3-rtx timer) <-----/ (cancel T3-rtx timer) <-----/
... ...
... ...
DATA [TSN=9,Strm=0,Seq=5] ------------> (ack delayed) DATA [TSN=9,Strm=0,Seq=5] ------------> (ack delayed)
(Start T3-rtx timer) (Start T3-rtx timer)
... ...
{App sends 1 message; strm 1} {App sends 1 message; strm 1}
(bundle SACK with DATA) (bundle SACK with DATA)
/----- SACK [TSN Ack=9,block=0] \ /----- SACK [TSN Ack=9,block=0] \
/ DATA [TSN=6,Strm=1,Seq=2] / DATA [TSN=6,Strm=1,Seq=2]
(cancel T3-rtx timer) <------/ (Start T3-rtx timer) (cancel T3-rtx timer) <------/ (Start T3-rtx timer)
(ack delayed) (ack delayed)
... ...
(send ack) (send ack)
SACK [TSN Ack=6,block=0] -------------> (cancel T3-rtx timer) SACK [TSN Ack=6,block=0] -------------> (cancel T3-rtx timer)
Figure 5: Delayed Acknowledgment Example Figure 7: Delayed Acknowledgment Example
If an endpoint receives a DATA chunk with no user data (i.e., the If an endpoint receives a DATA chunk with no user data (i.e., the
Length field is set to 16) it MUST send an ABORT with error cause set Length field is set to 16) it MUST send an ABORT with error cause set
to "No User Data". to "No User Data".
An endpoint SHOULD NOT send a DATA chunk with no user data part. An endpoint SHOULD NOT send a DATA chunk with no user data part.
6.2.1 Processing a Received SACK 6.2.1 Processing a Received SACK
Each SACK an endpoint receives contains an a_rwnd value. This value Each SACK an endpoint receives contains an a_rwnd value. This value
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Since there is no explicit identifier that can be used to detect Since there is no explicit identifier that can be used to detect
out-of-order SACKs, the data sender must use heuristics to determine if a out-of-order SACKs, the data sender must use heuristics to determine if a
SACK is new. SACK is new.
An endpoint SHOULD use the following rules to calculate the rwnd, using the An endpoint SHOULD use the following rules to calculate the rwnd, using the
a_rwnd value, the Cumulative TSN Ack and Gap Ack Blocks in a received SACK. a_rwnd value, the Cumulative TSN Ack and Gap Ack Blocks in a received SACK.
A) At the establishment of the association, the endpoint A) At the establishment of the association, the endpoint
initializes the rwnd to the Advertised Receiver Window initializes the rwnd to the Advertised Receiver Window
Internet draft Stream Control Transmission Protocol July 2000
Credit (a_rwnd) the peer specified in the INIT or INIT ACK. Credit (a_rwnd) the peer specified in the INIT or INIT ACK.
B) Any time a DATA chunk is transmitted (or retransmitted) B) Any time a DATA chunk is transmitted (or retransmitted)
to a peer, the endpoint subtracts the data size of the to a peer, the endpoint subtracts the data size of the
chunk from the rwnd of that peer. chunk from the rwnd of that peer.
C) Any time a DATA chunk is marked for retransmission (via C) Any time a DATA chunk is marked for retransmission (via
either T3-rtx timer expiration (Section 6.3.3)or via fast either T3-rtx timer expiration (Section 6.3.3)or via fast
retransmit (Section 7.2.4)), add the data size of retransmit (Section 7.2.4)), add the data size of
those chunks to the rwnd. those chunks to the rwnd.
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peer endpoint. peer endpoint.
The computation and management of RTO in SCTP follows closely how The computation and management of RTO in SCTP follows closely how
TCP manages its retransmission timer. To compute the current RTO, an TCP manages its retransmission timer. To compute the current RTO, an
endpoint maintains two state variables per destination transport endpoint maintains two state variables per destination transport
address: SRTT (smoothed round-trip time) and RTTVAR (round-trip time address: SRTT (smoothed round-trip time) and RTTVAR (round-trip time
variation). variation).
6.3.1 RTO Calculation 6.3.1 RTO Calculation
Internet draft Stream Control Transmission Protocol July 2000
The rules governing the computation of SRTT, RTTVAR, and RTO are The rules governing the computation of SRTT, RTTVAR, and RTO are
as follows: as follows:
C1) Until an RTT measurement has been made for a packet sent C1) Until an RTT measurement has been made for a packet sent
to the given destination transport address, set RTO to the to the given destination transport address, set RTO to the
protocol parameter 'RTO.Initial'. protocol parameter 'RTO.Initial'.
C2) When the first RTT measurement R is made, set SRTT <- R, C2) When the first RTT measurement R is made, set SRTT <- R,
RTTVAR <- R/2, and RTO <- SRTT + 4 * RTTVAR. RTTVAR <- R/2, and RTO <- SRTT + 4 * RTTVAR.
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C7) A maximum value may be placed on RTO provided it is at least C7) A maximum value may be placed on RTO provided it is at least
RTO.max seconds. RTO.max seconds.
There is no requirement for the clock granularity G used for computing There is no requirement for the clock granularity G used for computing
RTT measurements and the different state variables, other than: RTT measurements and the different state variables, other than:
G1) Whenever RTTVAR is computed, if RTTVAR = 0, then adjust G1) Whenever RTTVAR is computed, if RTTVAR = 0, then adjust
RTTVAR <- G. RTTVAR <- G.
Internet draft Stream Control Transmission Protocol July 2000
Experience [ALLMAN99] has shown that finer clock granularities Experience [ALLMAN99] has shown that finer clock granularities
(<= 100 msec) perform somewhat better than more coarse granularities. (<= 100 msec) perform somewhat better than more coarse granularities.
6.3.2 Retransmission Timer Rules 6.3.2 Retransmission Timer Rules
The rules for managing the retransmission timer are as follows: The rules for managing the retransmission timer are as follows:
R1) Every time a DATA chunk is sent to any address (including R1) Every time a DATA chunk is sent to any address (including
a retransmission), if the T3-rtx timer of that address is not a retransmission), if the T3-rtx timer of that address is not
running, start it running so that it will expire after the RTO of running, start it running so that it will expire after the RTO of
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/ \ / \
(Re-start T3-rtx timer) <------/ \--> (ack delayed) (Re-start T3-rtx timer) <------/ \--> (ack delayed)
(ack delayed) (ack delayed)
... ...
{send ack} {send ack}
SACK [TSN Ack=6,Block=0] --------------> (Cancel T3-rtx timer) SACK [TSN Ack=6,Block=0] --------------> (Cancel T3-rtx timer)
.. ..
(send ack) (send ack)
(Cancel T3-rtx timer) <-------------- SACK [TSN Ack=8,Block=0] (Cancel T3-rtx timer) <-------------- SACK [TSN Ack=8,Block=0]
Figure 6 - Timer Rule Examples Figure 8 - Timer Rule Examples
6.3.3 Handle T3-rtx Expiration 6.3.3 Handle T3-rtx Expiration
Internet draft Stream Control Transmission Protocol July 2000
Whenever the retransmission timer T3-rtx expires for a destination Whenever the retransmission timer T3-rtx expires for a destination
address, do the following: address, do the following:
E1) For the destination address for which the timer expires, adjust its E1) For the destination address for which the timer expires, adjust its
ssthresh with rules defined in Section 7.2.3 and set the ssthresh with rules defined in Section 7.2.3 and set the
cwnd <- MTU. cwnd <- MTU.
E2) For the destination address for which the timer expires, set E2) For the destination address for which the timer expires, set
RTO <- RTO * 2 ("back off the timer"). The maximum value discussed RTO <- RTO * 2 ("back off the timer"). The maximum value discussed
in rule C7 above (RTO.max) may be used to provide an upper bound in rule C7 above (RTO.max) may be used to provide an upper bound
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(see Section 6.4.1): (see Section 6.4.1):
F1) Whenever an endpoint switches from the current destination F1) Whenever an endpoint switches from the current destination
transport address to a different one, the current retransmission transport address to a different one, the current retransmission
timers are left running. As soon as the endpoint transmits a packet timers are left running. As soon as the endpoint transmits a packet
containing DATA chunk(s) to the new transport address, start the containing DATA chunk(s) to the new transport address, start the
timer on that transport address, using the RTO value of the timer on that transport address, using the RTO value of the
destination address to which the data is being sent, if rule R1 destination address to which the data is being sent, if rule R1
indicates to do so. indicates to do so.
Internet draft Stream Control Transmission Protocol July 2000
6.4 Multi-homed SCTP Endpoints 6.4 Multi-homed SCTP Endpoints
An SCTP endpoint is considered multi-homed if there are more than one An SCTP endpoint is considered multi-homed if there are more than one
transport address that can be used as a destination address to reach transport address that can be used as a destination address to reach
that endpoint. that endpoint.
Moreover, the ULP of an endpoint shall select one of the multiple Moreover, the ULP of an endpoint shall select one of the multiple
destination addresses of a multi-homed peer endpoint as the primary destination addresses of a multi-homed peer endpoint as the primary
path (see Sections 5.1.2 and 10.1 for details). path (see Sections 5.1.2 and 10.1 for details).
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6.4.1 Failover from Inactive Destination Address 6.4.1 Failover from Inactive Destination Address
Some of the transport addresses of a multi-homed SCTP endpoint may Some of the transport addresses of a multi-homed SCTP endpoint may
become inactive due to either the occurrence of certain error become inactive due to either the occurrence of certain error
conditions (see Section 8.2) or adjustments from SCTP user. conditions (see Section 8.2) or adjustments from SCTP user.
When there is outbound data to send and the primary path becomes When there is outbound data to send and the primary path becomes
inactive (e.g., due to failures), or where the SCTP user explicitly inactive (e.g., due to failures), or where the SCTP user explicitly
requests to send data to an inactive destination transport address, requests to send data to an inactive destination transport address,
before reporting an error to its ULP, the SCTP endpoint should try to before reporting an error to its ULP, the SCTP endpoint should try to
Internet draft Stream Control Transmission Protocol July 2000
send the data to an alternate active destination transport address if send the data to an alternate active destination transport address if
one exists. one exists.
When retransmitting data, if the endpoint is multi-homed, it should When retransmitting data, if the endpoint is multi-homed, it should
consider each source-destination address pair in its retransmission consider each source-destination address pair in its retransmission
selection policy. When retransmitting the endpoint should attempt to selection policy. When retransmitting the endpoint should attempt to
pick the most divergent source-destination pair from the original pick the most divergent source-destination pair from the original
source-destination pair to which the packet was transmitted. source-destination pair to which the packet was transmitted.
Note: Rules for picking the most divergent source-destination pair Note: Rules for picking the most divergent source-destination pair
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the upper layer (after re-assembly if the user data is fragmented by the upper layer (after re-assembly if the user data is fragmented by
the data sender). the data sender).
This provides an effective way of transmitting "out-of-band" data in a This provides an effective way of transmitting "out-of-band" data in a
given stream. Also, a stream can be used as an "unordered" stream by given stream. Also, a stream can be used as an "unordered" stream by
simply setting the U flag to 1 in all DATA chunks sent through that simply setting the U flag to 1 in all DATA chunks sent through that
stream. stream.
IMPLEMENTATION NOTE: When sending an unordered DATA chunk, an IMPLEMENTATION NOTE: When sending an unordered DATA chunk, an
implementation may choose to place the DATA chunk in an outbound implementation may choose to place the DATA chunk in an outbound
Internet draft Stream Control Transmission Protocol July 2000
packet that is at the head of the outbound transmission queue if packet that is at the head of the outbound transmission queue if
possible. possible.
The 'Stream Sequence Number' field in a DATA chunk with U flag set to 1 The 'Stream Sequence Number' field in a DATA chunk with U flag set to 1
has no significance. The sender can fill it with arbitrary value, but has no significance. The sender can fill it with arbitrary value, but
the receiver MUST ignore the field. the receiver MUST ignore the field.
Note: When transmitting ordered and unordered data, an endpoint does Note: When transmitting ordered and unordered data, an endpoint does
not increment its Stream Sequence Number when transmitting a DATA not increment its Stream Sequence Number when transmitting a DATA
chunk with U flag set to 1. chunk with U flag set to 1.
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DATA [TSN=7,Strm=0,Seq=3] --------> X (lost) DATA [TSN=7,Strm=0,Seq=3] --------> X (lost)
DATA [TSN=8,Strm=0,Seq=4] ---------------> (gap detected, DATA [TSN=8,Strm=0,Seq=4] ---------------> (gap detected,
immediately send ack) immediately send ack)
/----- SACK [TSN Ack=6,Block=1, /----- SACK [TSN Ack=6,Block=1,
/ Strt=2,End=2] / Strt=2,End=2]
<-----/ <-----/
(remove 6 from out-queue, (remove 6 from out-queue,
and mark 7 as "1" missing report) and mark 7 as "1" missing report)
Figure 8 - Reporting a Gap using SACK Internet draft Stream Control Transmission Protocol July 2000
Figure 9 - Reporting a Gap using SACK
The maximum number of Gap Ack Blocks that can be reported within a The maximum number of Gap Ack Blocks that can be reported within a
single SACK chunk is limited by the current path MTU. When a single single SACK chunk is limited by the current path MTU. When a single
SACK can not cover all the Gap Ack Blocks needed to be reported due to SACK can not cover all the Gap Ack Blocks needed to be reported due to
the MTU limitation, the endpoint MUST send only one SACK, reporting the the MTU limitation, the endpoint MUST send only one SACK, reporting the
Gap Ack Blocks from the lowest to highest TSNs, within the size limit Gap Ack Blocks from the lowest to highest TSNs, within the size limit
set by the MTU, and leave the remaining highest TSN numbers set by the MTU, and leave the remaining highest TSN numbers
unacknowledged. unacknowledged.
6.8 Adler-32 Checksum Calculation 6.8 Adler-32 Checksum Calculation
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6.9 Fragmentation and Reassembly 6.9 Fragmentation and Reassembly
An endpoint MAY support fragmentation when sending DATA chunks, but An endpoint MAY support fragmentation when sending DATA chunks, but
MUST support reassembly when receiving DATA chunks. If an endpoint MUST support reassembly when receiving DATA chunks. If an endpoint
supports fragmentation, it MUST fragment a user message if the size of supports fragmentation, it MUST fragment a user message if the size of
the user message to be sent causes the outbound SCTP packet size to the user message to be sent causes the outbound SCTP packet size to
exceed the current MTU. If an implementation does not support exceed the current MTU. If an implementation does not support
fragmentation of outbound user messages, the endpoint must return an fragmentation of outbound user messages, the endpoint must return an
error to its upper layer and not attempt to send the user message. error to its upper layer and not attempt to send the user message.
Internet draft Stream Control Transmission Protocol July 2000
IMPLEMENTATION NOTE: In this error case, the Send primitive IMPLEMENTATION NOTE: In this error case, the Send primitive
discussed in Section 10.1 would need to return an error to the upper discussed in Section 10.1 would need to return an error to the upper
layer. layer.
If its peer is multi-homed, the endpoint shall choose a If its peer is multi-homed, the endpoint shall choose a
size no larger than the association Path MTU. The association Path size no larger than the association Path MTU. The association Path
MTU is the smallest Path MTU of all destination addresses. MTU is the smallest Path MTU of all destination addresses.
Note: Once a message is fragmented it cannot be re-fragmented. Note: Once a message is fragmented it cannot be re-fragmented.
Instead if the PMTU has been reduced, then IP fragmentation must be Instead if the PMTU has been reduced, then IP fragmentation must be
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partial delivery API (see Section 10), freeing some of its receive partial delivery API (see Section 10), freeing some of its receive
buffer space so that the rest of the message may be received. buffer space so that the rest of the message may be received.
6.10 Bundling 6.10 Bundling
An endpoint bundles chunks by simply including multiple chunks in one An endpoint bundles chunks by simply including multiple chunks in one
outbound SCTP packet. The total size of the resultant IP datagram, outbound SCTP packet. The total size of the resultant IP datagram,
including the SCTP packet and IP headers, MUST be less or equal to the including the SCTP packet and IP headers, MUST be less or equal to the
current Path MTU. current Path MTU.
Internet draft Stream Control Transmission Protocol July 2000
If its peer endpoint is multi-homed, the sending endpoint shall choose If its peer endpoint is multi-homed, the sending endpoint shall choose
a size no larger than the latest MTU of the current primary path. a size no larger than the latest MTU of the current primary path.
When bundling control chunks with DATA chunks, an endpoint MUST place When bundling control chunks with DATA chunks, an endpoint MUST place
control chunks first in the outbound SCTP packet. The transmitter control chunks first in the outbound SCTP packet. The transmitter
MUST transmit DATA chunks within a SCTP packet in increasing order of MUST transmit DATA chunks within a SCTP packet in increasing order of
TSN. TSN.
Note: Since control chunks must be placed first in a packet and Note: Since control chunks must be placed first in a packet and
since DATA chunks must be transmitted before SHUTDOWN or SHUTDOWN ACK since DATA chunks must be transmitted before SHUTDOWN or SHUTDOWN ACK
chunks, DATA chunks cannot be bundled with SHUTDOWN or SHUTDOWN ACK chunks, DATA chunks cannot be bundled with SHUTDOWN or SHUTDOWN ACK
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The congestion control algorithms used by SCTP are based on The congestion control algorithms used by SCTP are based on
[RFC2581]. This section describes how the algorithms defined in [RFC2581]. This section describes how the algorithms defined in
RFC2581 are adapted for use in SCTP. We first list differences in RFC2581 are adapted for use in SCTP. We first list differences in
protocol designs between TCP and SCTP, and then describe SCTP's protocol designs between TCP and SCTP, and then describe SCTP's
congestion control scheme. The description will use the same congestion control scheme. The description will use the same
terminology as in TCP congestion control whenever appropriate. terminology as in TCP congestion control whenever appropriate.
SCTP congestion control is always applied to the entire association, SCTP congestion control is always applied to the entire association,
and NOT to individual streams. and NOT to individual streams.
Internet draft Stream Control Transmission Protocol July 2000
7.1 SCTP Differences from TCP Congestion control 7.1 SCTP Differences from TCP Congestion control
Gap Ack Blocks in the SCTP SACK carry the same semantic meaning as the Gap Ack Blocks in the SCTP SACK carry the same semantic meaning as the
TCP SACK. TCP considers the information carried in the SACK as advisory TCP SACK. TCP considers the information carried in the SACK as advisory
information only. SCTP considers the information carried in the Gap Ack information only. SCTP considers the information carried in the Gap Ack
Blocks in the SACK chunk as advisory. In SCTP, any DATA chunk that has Blocks in the SACK chunk as advisory. In SCTP, any DATA chunk that has
been acknowledged by SACK, including DATA that arrived at the receiving been acknowledged by SACK, including DATA that arrived at the receiving
end out of order, are NOT considered fully delivered until the end out of order, are NOT considered fully delivered until the
Cumulative TSN Ack Point passes the TSN of the DATA chunk (i.e., the Cumulative TSN Ack Point passes the TSN of the DATA chunk (i.e., the
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notices a gap in the received sequence number, it waits until notices a gap in the received sequence number, it waits until
the gap is filled before delivering the data that was received the gap is filled before delivering the data that was received
with sequence numbers higher than that of the missing data. On with sequence numbers higher than that of the missing data. On
the other hand, SCTP can deliver data to its upper-layer the other hand, SCTP can deliver data to its upper-layer
protocol even if there is a gap in TSN if the Stream Sequence protocol even if there is a gap in TSN if the Stream Sequence
Numbers are in sequence for a particular stream (i.e., the Numbers are in sequence for a particular stream (i.e., the
missing DATA chunks are for a different stream) or if unordered missing DATA chunks are for a different stream) or if unordered
delivery is indicated. Although this does not affect cwnd, it delivery is indicated. Although this does not affect cwnd, it
might affect rwnd calculation. might affect rwnd calculation.
Internet draft Stream Control Transmission Protocol July 2000
7.2 SCTP Slow-Start and Congestion Avoidance 7.2 SCTP Slow-Start and Congestion Avoidance
The slow start and congestion avoidance algorithms MUST be used by an The slow start and congestion avoidance algorithms MUST be used by an
endpoint to control the amount of data being injected into the network. endpoint to control the amount of data being injected into the network.
The congestion control in SCTP is employed in regard to the The congestion control in SCTP is employed in regard to the
association, not to an individual stream. In some situations it association, not to an individual stream. In some situations it
may be beneficial for an SCTP sender to be more conservative than the may be beneficial for an SCTP sender to be more conservative than the
algorithms allow; however, an SCTP sender MUST NOT be more aggressive algorithms allow; however, an SCTP sender MUST NOT be more aggressive
than the following algorithms allow. than the following algorithms allow.
Like TCP, an SCTP endpoint uses the following three control variables Like TCP, an SCTP endpoint uses the following three control variables
to regulate its transmission rate. to regulate its transmission rate.
o Receiver advertised window size (rwnd, in bytes), which is set by o Receiver advertised window size (rwnd, in bytes), which is set by
the receiver based on its available buffer space for incoming the receiver based on its available buffer space for incoming
packets. packets.
Note: This variable is kept on the entire association. Note: This variable is kept on the entire association.
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network to determine the available capacity. The slow start algorithm network to determine the available capacity. The slow start algorithm
is used for this purpose at the beginning of a transfer, or after is used for this purpose at the beginning of a transfer, or after
repairing loss detected by the retransmission timer. repairing loss detected by the retransmission timer.
o The initial cwnd before data transmission or after a sufficiently o The initial cwnd before data transmission or after a sufficiently
long idle period MUST be <= 2*MTU. long idle period MUST be <= 2*MTU.
o The initial cwnd after a retransmission timeout MUST be no more o The initial cwnd after a retransmission timeout MUST be no more
than 1*MTU. than 1*MTU.
Internet draft Stream Control Transmission Protocol July 2000
o The initial value of ssthresh MAY be arbitrarily high (for example, o The initial value of ssthresh MAY be arbitrarily high (for example,
implementations MAY use the size of the receiver advertised window). implementations MAY use the size of the receiver advertised window).
o Whenever cwnd is greater than zero, the endpoint is allowed to have o Whenever cwnd is greater than zero, the endpoint is allowed to have
cwnd bytes of data outstanding on that transport address. cwnd bytes of data outstanding on that transport address.
o When cwnd is less than or equal to ssthresh an SCTP endpoint MUST use o When cwnd is less than or equal to ssthresh an SCTP endpoint MUST use
the slow start algorithm to increase cwnd (assuming the current the slow start algorithm to increase cwnd (assuming the current
congestion window is being fully utilized). If an incoming SACK congestion window is being fully utilized). If an incoming SACK
advances the Cumulative TSN Ack Point, cwnd MUST be increased by at advances the Cumulative TSN Ack Point, cwnd MUST be increased by at
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by 1*MTU per RTT if the sender has cwnd or more bytes of data by 1*MTU per RTT if the sender has cwnd or more bytes of data
outstanding for the corresponding transport address. outstanding for the corresponding transport address.
In practice an implementation can achieve this goal in the In practice an implementation can achieve this goal in the
following way: following way:
o partial_bytes_acked is initialized to 0. o partial_bytes_acked is initialized to 0.
o Whenever cwnd is greater than ssthresh, upon each SACK arrival that o Whenever cwnd is greater than ssthresh, upon each SACK arrival that
advances the Cumulative TSN Ack Point, increase partial_bytes_acked advances the Cumulative TSN Ack Point, increase partial_bytes_acked
Internet draft Stream Control Transmission Protocol July 2000
by the total number of bytes of all new chunks acknowledged in that by the total number of bytes of all new chunks acknowledged in that
SACK including chunks acknowledged by the new Cumulative TSN Ack and SACK including chunks acknowledged by the new Cumulative TSN Ack and
by Gap Ack Blocks. by Gap Ack Blocks.
o When partial_bytes_acked is equal to or greater than cwnd and before o When partial_bytes_acked is equal to or greater than cwnd and before
the arrival of the SACK the sender had cwnd or more bytes of data the arrival of the SACK the sender had cwnd or more bytes of data
outstanding (i.e., before arrival of the SACK, flightsize was greater outstanding (i.e., before arrival of the SACK, flightsize was greater
than or equal to cwnd), increase cwnd by MTU, and reset than or equal to cwnd), increase cwnd by MTU, and reset
partial_bytes_acked to (partial_bytes_acked - cwnd). partial_bytes_acked to (partial_bytes_acked - cwnd).
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a packet arrives carrying data until the hole is filled. a packet arrives carrying data until the hole is filled.
Whenever an endpoint receives a SACK that indicates some TSN(s) Whenever an endpoint receives a SACK that indicates some TSN(s)
missing, it SHOULD wait for 3 further miss indications (via subsequent missing, it SHOULD wait for 3 further miss indications (via subsequent
SACK's) on the same TSN(s) before taking action with regard to Fast SACK's) on the same TSN(s) before taking action with regard to Fast
Retransmit. Retransmit.
When the TSN(s) is reported as missing in the fourth consecutive SACK, When the TSN(s) is reported as missing in the fourth consecutive SACK,
the data sender shall: the data sender shall:
Internet draft Stream Control Transmission Protocol July 2000
1) Mark the missing DATA chunk(s) for retransmission, 1) Mark the missing DATA chunk(s) for retransmission,
2) Adjust the ssthresh and cwnd of the destination address(es) to which 2) Adjust the ssthresh and cwnd of the destination address(es) to which
the missing DATA chunks were last sent, according to the formula the missing DATA chunks were last sent, according to the formula
described in Section 7.2.3. described in Section 7.2.3.
3) Determine how many of the earliest (i.e., lowest TSN) DATA 3) Determine how many of the earliest (i.e., lowest TSN) DATA
chunks marked for retransmission will fit into a single packet, chunks marked for retransmission will fit into a single packet,
subject to constraint of the path MTU of the destination transport subject to constraint of the path MTU of the destination transport
address to which the packet is being sent. Call this value K. address to which the packet is being sent. Call this value K.
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An endpoint SHOULD apply these techniques, and SHOULD do so on a An endpoint SHOULD apply these techniques, and SHOULD do so on a
per-destination-address basis. per-destination-address basis.
There are 4 ways in which SCTP differs from the description in RFC 1191 There are 4 ways in which SCTP differs from the description in RFC 1191
of applying MTU discovery to TCP: of applying MTU discovery to TCP:
1) SCTP associations can span multiple addresses. 1) SCTP associations can span multiple addresses.
An endpoint MUST maintain separate MTU estimates for each An endpoint MUST maintain separate MTU estimates for each
destination address of its peer. destination address of its peer.
Internet draft Stream Control Transmission Protocol July 2000
2) Elsewhere in this document, when the term "MTU" is discussed, 2) Elsewhere in this document, when the term "MTU" is discussed,
it refers to the MTU associated with the destination address it refers to the MTU associated with the destination address
corresponding to the context of the discussion. corresponding to the context of the discussion.
3) Unlike TCP, SCTP does not have a notion of "Maximum Segment 3) Unlike TCP, SCTP does not have a notion of "Maximum Segment
Size". Accordingly, the MTU for each destination address Size". Accordingly, the MTU for each destination address
SHOULD be initialized to a value no larger than the link MTU SHOULD be initialized to a value no larger than the link MTU
for the local interface to which packets for that remote for the local interface to which packets for that remote
destination address will be routed. destination address will be routed.
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report back all outstanding user data remaining in its outbound queue. report back all outstanding user data remaining in its outbound queue.
The association is automatically closed when the peer endpoint The association is automatically closed when the peer endpoint
becomes unreachable. becomes unreachable.
The counter shall be reset each time a DATA chunk sent to that peer The counter shall be reset each time a DATA chunk sent to that peer
endpoint is acknowledged (by the reception of a SACK), or a HEARTBEAT- endpoint is acknowledged (by the reception of a SACK), or a HEARTBEAT-
ACK is received from the peer endpoint. ACK is received from the peer endpoint.
8.2 Path Failure Detection 8.2 Path Failure Detection
Internet draft Stream Control Transmission Protocol July 2000
When its peer endpoint is multi-homed, an endpoint should keep a error When its peer endpoint is multi-homed, an endpoint should keep a error
counter for each of the destination transport addresses of the peer counter for each of the destination transport addresses of the peer
endpoint. endpoint.
Each time the T3-rtx timer expires on any address, or when a HEARTBEAT Each time the T3-rtx timer expires on any address, or when a HEARTBEAT
sent to an idle address is not acknowledged within a RTO, the error sent to an idle address is not acknowledged within a RTO, the error
counter of that destination address will be incremented. When the counter of that destination address will be incremented. When the
value in the error counter exceeds the protocol parameter value in the error counter exceeds the protocol parameter
'Path.Max.Retrans' of that destination address, the endpoint should 'Path.Max.Retrans' of that destination address, the endpoint should
mark the destination transport address as inactive, and a notification mark the destination transport address as inactive, and a notification
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By default, an SCTP endpoint shall monitor the reachability of the By default, an SCTP endpoint shall monitor the reachability of the
idle destination transport address(es) of its peer by sending a idle destination transport address(es) of its peer by sending a
HEARTBEAT chunk periodically to the destination transport HEARTBEAT chunk periodically to the destination transport
address(es). address(es).
A destination transport address is considered "idle" if no new chunk A destination transport address is considered "idle" if no new chunk
which can be used for updating path RTT (usually including first which can be used for updating path RTT (usually including first
transmission DATA, INIT, COOKIE ECHO, HEARTBEAT etc.) and no transmission DATA, INIT, COOKIE ECHO, HEARTBEAT etc.) and no
HEARTBEAT has been sent to it within the current heartbeat period of HEARTBEAT has been sent to it within the current heartbeat period of
that address. This applies to both active and inactive destination that address. This applies to both active and inactive destination
Internet draft Stream Control Transmission Protocol July 2000
addresses. addresses.
The upper layer can optionally initiate the following functions: The upper layer can optionally initiate the following functions:
A) Disable heartbeat on a specific destination transport address of a A) Disable heartbeat on a specific destination transport address of a
given association, given association,
B) Change the HB.interval, B) Change the HB.interval,
C) Re-enable heartbeat on a specific destination transport address of C) Re-enable heartbeat on a specific destination transport address of
a given association, and, a given association, and,
D) Request an on-demand HEARTBEAT on a specific destination transport D) Request an on-demand HEARTBEAT on a specific destination transport
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optionally report to the upper layer when an inactive destination optionally report to the upper layer when an inactive destination
address is marked as active due to the reception of the latest address is marked as active due to the reception of the latest
HEARTBEAT ACK. The receiver of the HEARTBEAT ACK must also HEARTBEAT ACK. The receiver of the HEARTBEAT ACK must also
clear the association overall error count as well (as defined clear the association overall error count as well (as defined
in section 8.1). in section 8.1).
The receiver of the HEARTBEAT ACK should also perform an RTT The receiver of the HEARTBEAT ACK should also perform an RTT
measurement for that destination transport address using the time measurement for that destination transport address using the time
value carried in the HEARTBEAT ACK chunk. value carried in the HEARTBEAT ACK chunk.
Internet draft Stream Control Transmission Protocol July 2000
On an idle destination address that is allowed to heartbeat, a HEARTBEAT On an idle destination address that is allowed to heartbeat, a HEARTBEAT
chunk is RECOMMENDED to be sent once per RTO of that destination chunk is RECOMMENDED to be sent once per RTO of that destination
address plus the protocol parameter 'HB.interval' , with address plus the protocol parameter 'HB.interval' , with
jittering of +/- 50%, and exponential back-off of the RTO if the jittering of +/- 50%, and exponential back-off of the RTO if the
previous HEARTBEAT is unanswered. previous HEARTBEAT is unanswered.
A primitive is provided for the SCTP user to change the HB.interval A primitive is provided for the SCTP user to change the HB.interval
and turn on or off the heartbeat on a given destination address. The and turn on or off the heartbeat on a given destination address. The
heartbeat interval set by the SCTP user is added to the RTO of that heartbeat interval set by the SCTP user is added to the RTO of that
destination (including any exponential backoff). Only one heartbeat destination (including any exponential backoff). Only one heartbeat
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4) If the packet contains a COOKIE ECHO in the first chunk, process it 4) If the packet contains a COOKIE ECHO in the first chunk, process it
as described in Section 5.1. Otherwise, as described in Section 5.1. Otherwise,
5) If the packet contains a SHUTDOWN ACK chunk, the receiver should 5) If the packet contains a SHUTDOWN ACK chunk, the receiver should
respond to the sender of the OOTB packet with a SHUTDOWN COMPLETE. respond to the sender of the OOTB packet with a SHUTDOWN COMPLETE.
When sending the SHUTDOWN COMPLETE, the receiver of the OOTB packet When sending the SHUTDOWN COMPLETE, the receiver of the OOTB packet
must fill in the Verification Tag field of the outbound packet with must fill in the Verification Tag field of the outbound packet with
the Verification Tag received in the SHUTDOWN ACK and set the the Verification Tag received in the SHUTDOWN ACK and set the
T-bit in the Chunk Flags to indicate that no TCB was found. T-bit in the Chunk Flags to indicate that no TCB was found.
Internet draft Stream Control Transmission Protocol July 2000
Otherwise, Otherwise,
6) If the packet contains a SHUTDOWN COMPLETE chunk, the receiver 6) If the packet contains a SHUTDOWN COMPLETE chunk, the receiver
should silently discard the packet and take no further action. should silently discard the packet and take no further action.
Otherwise, Otherwise,
7) If the receiver is in COOKIE-ECHOED or COOKIE-WAIT state the procedures 7) If the packet contains a "Stale cookie" ERROR or a COOKIE ACK
in section 5 SHOULD be followed. Otherwise,
8) If the packet contains a "Stale cookie" ERROR or a COOKIE ACK
the SCTP Packet should be silently discarded. Otherwise, the SCTP Packet should be silently discarded. Otherwise,
9) The receiver should respond to the sender of the OOTB packet with 8) The receiver should respond to the sender of the OOTB packet with
an ABORT. When sending the ABORT, the receiver of the OOTB packet an ABORT. When sending the ABORT, the receiver of the OOTB packet
MUST fill in the Verification Tag field of the outbound packet MUST fill in the Verification Tag field of the outbound packet
with the value found in the Verification Tag field of the OOTB with the value found in the Verification Tag field of the OOTB
packet and set the T-bit in the Chunk Flags to indicate that no packet and set the T-bit in the Chunk Flags to indicate that no
TCB was found. After sending this ABORT, the receiver of the TCB was found. After sending this ABORT, the receiver of the
OOTB packet shall discard the OOTB packet and take no further OOTB packet shall discard the OOTB packet and take no further
action. action.
8.5 Verification Tag 8.5 Verification Tag
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set to 0, it should verify that the packet contains only an INIT set to 0, it should verify that the packet contains only an INIT
chunk. Otherwise, the receiver MUST silently discard the packet. chunk. Otherwise, the receiver MUST silently discard the packet.
B) Rules for packet carrying ABORT: B) Rules for packet carrying ABORT:
- The endpoint shall always fill in the Verification Tag field of the - The endpoint shall always fill in the Verification Tag field of the
outbound packet with the destination endpoint's tag value if it outbound packet with the destination endpoint's tag value if it
is known. is known.
- If the ABORT is sent in response to an OOTB packet, the endpoint - If the ABORT is sent in response to an OOTB packet, the endpoint
Internet draft Stream Control Transmission Protocol July 2000
MUST follow the procedure described in Section 8.4. MUST follow the procedure described in Section 8.4.
- The receiver MUST accept the packet if the Verification Tag - The receiver MUST accept the packet if the Verification Tag
matches either its own tag, OR the tag of its peer. Otherwise, the matches either its own tag, OR the tag of its peer. Otherwise, the
receiver MUST silently discard the packet and take no further receiver MUST silently discard the packet and take no further
action. action.
C) Rules for packet carrying SHUTDOWN COMPLETE: C) Rules for packet carrying SHUTDOWN COMPLETE:
- When sending a SHUTDOWN COMPLETE, if the receiver of the SHUTDOWN - When sending a SHUTDOWN COMPLETE, if the receiver of the SHUTDOWN
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no further action. An endpoint MUST ignore the SHUTDOWN COMPLETE if no further action. An endpoint MUST ignore the SHUTDOWN COMPLETE if
it is not in the SHUTDOWN-ACK-SENT state. it is not in the SHUTDOWN-ACK-SENT state.
D) Rules for packet carrying a COOKIE ECHO D) Rules for packet carrying a COOKIE ECHO
- When sending a COOKIE ECHO, the endpoint MUST use the value of the - When sending a COOKIE ECHO, the endpoint MUST use the value of the
Initial Tag received in the INIT ACK. Initial Tag received in the INIT ACK.
- The receiver of a COOKIE ECHO follows the procedures in Section 5. - The receiver of a COOKIE ECHO follows the procedures in Section 5.
E) Rules for packet carrying a SHUTDOWN ACK
- If the receiver is in COOKIE-ECHOED or COOKIE-WAIT state the procedures
in section 8.4 SHOULD be followed, in other words it should be
treated as an Out Of The Blue packet.
9. Termination of Association 9. Termination of Association
An endpoint should terminate its association when it exits from An endpoint should terminate its association when it exits from
service. An association can be terminated by either abort or service. An association can be terminated by either abort or
shutdown. An abort of an association is abortive by definition in that shutdown. An abort of an association is abortive by definition in that
any data pending on either end of the association is discarded and NOT any data pending on either end of the association is discarded and NOT
delivered to the peer. A shutdown of an association is considered a delivered to the peer. A shutdown of an association is considered a
graceful close where all data in queue by either endpoint is delivered graceful close where all data in queue by either endpoint is delivered
to the respective peers. However, in the case of a shutdown, SCTP does to the respective peers. However, in the case of a shutdown, SCTP does
not support a half-open state (like TCP) wherein one side may continue not support a half-open state (like TCP) wherein one side may continue
sending data while the other end is closed. When either endpoint sending data while the other end is closed. When either endpoint
performs a shutdown, the association on each peer will stop accepting performs a shutdown, the association on each peer will stop accepting
new data from its user and only deliver data in queue at the time of new data from its user and only deliver data in queue at the time of
sending or receiving the SHUTDOWN chunk. sending or receiving the SHUTDOWN chunk.
9.1 Abort of an Association 9.1 Abort of an Association
Internet draft Stream Control Transmission Protocol July 2000
When an endpoint decides to abort an existing association, it When an endpoint decides to abort an existing association, it
shall send an ABORT chunk to its peer endpoint. The sender MUST fill shall send an ABORT chunk to its peer endpoint. The sender MUST fill
in the peer's Verification Tag in the outbound packet and MUST NOT in the peer's Verification Tag in the outbound packet and MUST NOT
bundle any DATA chunk with the ABORT. bundle any DATA chunk with the ABORT.
An endpoint MUST NOT respond to any received packet that contains an An endpoint MUST NOT respond to any received packet that contains an
ABORT chunk (also see Section 8.4). ABORT chunk (also see Section 8.4).
An endpoint receiving an ABORT shall apply the special Verification Tag An endpoint receiving an ABORT shall apply the special Verification Tag
check rules described in Section 8.5.1. check rules described in Section 8.5.1.
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its peer (i.e. as the peer sends all of its queued DATA chunks) should its peer (i.e. as the peer sends all of its queued DATA chunks) should
clear the endpoint's retransmission count and restart the T2-Shutdown clear the endpoint's retransmission count and restart the T2-Shutdown
timer, giving its peer ample opportunity to transmit all of its queued timer, giving its peer ample opportunity to transmit all of its queued
DATA chunks that have not yet been sent. DATA chunks that have not yet been sent.
Upon the reception of the SHUTDOWN, the peer endpoint shall Upon the reception of the SHUTDOWN, the peer endpoint shall
- enter the SHUTDOWN-RECEIVED state, - enter the SHUTDOWN-RECEIVED state,
- stop accepting new data from its SCTP user - stop accepting new data from its SCTP user
Internet draft Stream Control Transmission Protocol July 2000
- verify, by checking the Cumulative TSN Ack field of the chunk, that - verify, by checking the Cumulative TSN Ack field of the chunk, that
all its outstanding DATA chunks have been received by the SHUTDOWN all its outstanding DATA chunks have been received by the SHUTDOWN
sender. sender.
Once an endpoint as reached the SHUTDOWN-RECEIVED state it MUST NOT Once an endpoint as reached the SHUTDOWN-RECEIVED state it MUST NOT
send a SHUTDOWN in response to a ULP request. And should discard send a SHUTDOWN in response to a ULP request. And should discard
subsequent SHUTDOWN chunks. subsequent SHUTDOWN chunks.
If there are still outstanding DATA chunks left, the SHUTDOWN receiver If there are still outstanding DATA chunks left, the SHUTDOWN receiver
shall continue to follow normal data transmission procedures defined in shall continue to follow normal data transmission procedures defined in
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subsequent SHUTDOWN chunks. subsequent SHUTDOWN chunks.
If there are still outstanding DATA chunks left, the SHUTDOWN receiver If there are still outstanding DATA chunks left, the SHUTDOWN receiver
shall continue to follow normal data transmission procedures defined in shall continue to follow normal data transmission procedures defined in
Section 6 until all outstanding DATA chunks are acknowledged; however, Section 6 until all outstanding DATA chunks are acknowledged; however,
the SHUTDOWN receiver MUST NOT accept new data from its SCTP user. the SHUTDOWN receiver MUST NOT accept new data from its SCTP user.
While in SHUTDOWN-SENT state, the SHUTDOWN sender MUST immediately While in SHUTDOWN-SENT state, the SHUTDOWN sender MUST immediately
respond to each received packet containing one or more DATA chunk(s) respond to each received packet containing one or more DATA chunk(s)
with a SACK, a SHUTDOWN chunk, and restart the T2-shutdown timer. with a SACK, a SHUTDOWN chunk, and restart the T2-shutdown timer.
If it has no more outstanding DATA chunks, the SHUTDOWN receiver shall If it has no more outstanding DATA chunks, the SHUTDOWN receiver shall
send a SHUTDOWN ACK and start a T2-shutdown timer of its own, entering send a SHUTDOWN ACK and start a T2-shutdown timer of its own, entering
the SHUTDOWN-ACK-SENT state. the SHUTDOWN-ACK-SENT state. If the timer expires, the endpoint must
re-send the SHUTDOWN ACK.
The sender of the SHUTDOWN ACK should limit the number of The sender of the SHUTDOWN ACK should limit the number of
retransmissions of the SHUTDOWN ACK chunk to the protocol parameter retransmissions of the SHUTDOWN ACK chunk to the protocol parameter
'Association.Max.Retrans'. If this threshold is exceeded the endpoint 'Association.Max.Retrans'. If this threshold is exceeded the endpoint
should destroy the TCB and may report the peer endpoint unreachable to should destroy the TCB and may report the peer endpoint unreachable to
the upper layer (and thus the association enters the CLOSED state). the upper layer (and thus the association enters the CLOSED state).
Upon the receipt of the SHUTDOWN ACK, the SHUTDOWN sender shall stop Upon the receipt of the SHUTDOWN ACK, the SHUTDOWN sender shall stop
the T2-shutdown timer, send a SHUTDOWN COMPLETE chunk to its the T2-shutdown timer, send a SHUTDOWN COMPLETE chunk to its
peer, and remove all record of the association. peer, and remove all record of the association.
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If an endpoint is in SHUTDOWN-ACK-SENT state and receives an INIT chunk If an endpoint is in SHUTDOWN-ACK-SENT state and receives an INIT chunk
(e.g., if the SHUTDOWN COMPLETE was lost) with source and destination (e.g., if the SHUTDOWN COMPLETE was lost) with source and destination
transport addresses (either in the IP addresses or in the INIT chunk) transport addresses (either in the IP addresses or in the INIT chunk)
that belong to this association, it should discard the INIT chunk and that belong to this association, it should discard the INIT chunk and
retransmit the SHUTDOWN ACK chunk. retransmit the SHUTDOWN ACK chunk.
Note: Receipt of an INIT with the same source and destination IP Note: Receipt of an INIT with the same source and destination IP
addresses as used in transport addresses assigned to an endpoint but addresses as used in transport addresses assigned to an endpoint but
with a different port number indicates the initialization of a with a different port number indicates the initialization of a
separate association. separate association.
Internet draft Stream Control Transmission Protocol July 2000
The sender of the INIT or COOKIE should respond to the receipt of a The sender of the INIT or COOKIE should respond to the receipt of a
SHUTDOWN-ACK with a stand-alone SHUTDOWN COMPLETE in an SCTP packet with the SHUTDOWN-ACK with a stand-alone SHUTDOWN COMPLETE in an SCTP packet with the
Verification Tag field of its common header set to the same tag that Verification Tag field of its common header set to the same tag that
was received in the SHUTDOWN ACK packet. This is considered an Out of was received in the SHUTDOWN ACK packet. This is considered an Out of
the Blue packet as defined in Section 8.4. The sender of the INIT lets the Blue packet as defined in Section 8.4. The sender of the INIT lets
T1-init continue running and remains in the COOKIE-WAIT or COOKIE-ECHOED state. T1-init continue running and remains in the COOKIE-WAIT or COOKIE-ECHOED state.
Normal T1-init timer expiration will cause the INIT or COOKIE chunk to be Normal T1-init timer expiration will cause the INIT or COOKIE chunk to be
retransmitted and thus start a new association. retransmitted and thus start a new association.
If a SHUTDOWN is received in COOKIE WAIT or COOKIE ECHOED states the If a SHUTDOWN is received in COOKIE WAIT or COOKIE ECHOED states the
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SCTP must perform to support inter-process communication. Individual SCTP must perform to support inter-process communication. Individual
implementations must define their own exact format, and may provide implementations must define their own exact format, and may provide
combinations or subsets of the basic functions in single calls. combinations or subsets of the basic functions in single calls.
A) Initialize A) Initialize
Format: INITIALIZE ([local port], [local eligible address list]) Format: INITIALIZE ([local port], [local eligible address list])
-> local SCTP instance name -> local SCTP instance name
This primitive allows SCTP to initialize its internal data structures This primitive allows SCTP to initialize its internal data structures
Internet draft Stream Control Transmission Protocol July 2000
and allocate necessary resources for setting up its operation and allocate necessary resources for setting up its operation
environment. Once SCTP is initialized, ULP can communicate environment. Once SCTP is initialized, ULP can communicate
directly with other endpoints without re-invoking this primitive. directly with other endpoints without re-invoking this primitive.
SCTP will return a local SCTP instance name to the ULP. SCTP will return a local SCTP instance name to the ULP.
Mandatory attributes: Mandatory attributes:
None. None.
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will be returned on successful establishment of the association. If will be returned on successful establishment of the association. If
SCTP is not able to open an SCTP association with the peer endpoint, SCTP is not able to open an SCTP association with the peer endpoint,
an error is returned. an error is returned.
Other association parameters may be returned, including the complete Other association parameters may be returned, including the complete
destination transport addresses of the peer as well as the outbound destination transport addresses of the peer as well as the outbound
stream count of the local endpoint. One of the transport address from stream count of the local endpoint. One of the transport address from
the returned destination addresses will be selected by the local the returned destination addresses will be selected by the local
endpoint as default primary path for sending SCTP endpoint as default primary path for sending SCTP
packets to this peer. The returned "destination transport addr packets to this peer. The returned "destination transport addr
Internet draft Stream Control Transmission Protocol July 2000
list" can be used by the ULP to change the default primary path or to list" can be used by the ULP to change the default primary path or to
force sending a packet to a specific transport address. force sending a packet to a specific transport address.
IMPLEMENTATION NOTE: If ASSOCIATE primitive is implemented as a IMPLEMENTATION NOTE: If ASSOCIATE primitive is implemented as a
blocking function call, the ASSOCIATE primitive can return blocking function call, the ASSOCIATE primitive can return
association parameters in addition to the association id upon association parameters in addition to the association id upon
successful establishment. If ASSOCIATE primitive is implemented as a successful establishment. If ASSOCIATE primitive is implemented as a
non-blocking call, only the association id shall be returned and non-blocking call, only the association id shall be returned and
association parameters shall be passed using the COMMUNICATION UP association parameters shall be passed using the COMMUNICATION UP
notification. notification.
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None. None.
D) Close D) Close
Format: ABORT(association id [, cause code]) Format: ABORT(association id [, cause code])
-> result -> result
Ungracefully closes an association. Any locally queued user data Ungracefully closes an association. Any locally queued user data
will be discarded and an ABORT chunk is sent to the peer. A success will be discarded and an ABORT chunk is sent to the peer. A success
code will be returned on successful abortion of the association. If code will be returned on successful abortion of the association. If
Internet draft Stream Control Transmission Protocol July 2000
attempting to abort the association results in a failure, an error attempting to abort the association results in a failure, an error
code shall be returned. code shall be returned.
Mandatory attributes: Mandatory attributes:
o association id - local handle to the SCTP association o association id - local handle to the SCTP association
Optional attributes: Optional attributes:
o cause code - reason of the abort to be passed to the peer. o cause code - reason of the abort to be passed to the peer.
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initiated to transport (i.e. sent to the destination via SCTP's initiated to transport (i.e. sent to the destination via SCTP's
send primitive) within the life time variable. However, the send primitive) within the life time variable. However, the
user data will be transmitted if SCTP has attempted to transmit a user data will be transmitted if SCTP has attempted to transmit a
chunk before the life time expired. chunk before the life time expired.
IMPLEMENTATION NOTE: In order to better support the data lifetime IMPLEMENTATION NOTE: In order to better support the data lifetime
option, the transmitter may hold back the assigning of the TSN option, the transmitter may hold back the assigning of the TSN
number to an outbound DATA chunk to the last moment. And, for number to an outbound DATA chunk to the last moment. And, for
implementation simplicity, once a TSN number has been assigned the implementation simplicity, once a TSN number has been assigned the
sender should consider the send of this DATA chunk as committed, sender should consider the send of this DATA chunk as committed,
Internet draft Stream Control Transmission Protocol July 2000
overriding any lifetime option attached to the DATA chunk. overriding any lifetime option attached to the DATA chunk.
o destination transport address - specified as one of the destination o destination transport address - specified as one of the destination
transport addresses of the peer endpoint to which this packet transport addresses of the peer endpoint to which this packet
should be sent. Whenever possible, SCTP should use this destination should be sent. Whenever possible, SCTP should use this destination
transport address for sending the packets, instead of the current transport address for sending the packets, instead of the current
primary path. primary path.
o unorder flag - this flag, if present, indicates that the user o unorder flag - this flag, if present, indicates that the user
would like the data delivered in an unordered fashion to the peer would like the data delivered in an unordered fashion to the peer
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Optional attributes: Optional attributes:
o source transport address - optionally, some implementations may o source transport address - optionally, some implementations may
allow you to set the default source address placed in all allow you to set the default source address placed in all
outgoing IP datagrams. outgoing IP datagrams.
G) Receive G) Receive
Format: RECEIVE(association id, buffer address, buffer size Format: RECEIVE(association id, buffer address, buffer size
[,stream id]) [,stream id])
Internet draft Stream Control Transmission Protocol July 2000
-> byte count [,transport address] [,stream id] [,stream sequence -> byte count [,transport address] [,stream id] [,stream sequence
number] [,partial flag] [,delivery number] [,payload protocol-id] number] [,partial flag] [,delivery number] [,payload protocol-id]
This primitive shall read the first user message in the SCTP in-queue This primitive shall read the first user message in the SCTP in-queue
into the buffer specified by ULP, if there is one available. The size into the buffer specified by ULP, if there is one available. The size
of the message read, in bytes, will be returned. It may, depending on of the message read, in bytes, will be returned. It may, depending on
the specific implementation, also return other information such as the the specific implementation, also return other information such as the
sender's address, the stream id on which it is received, whether there sender's address, the stream id on which it is received, whether there
are more messages available for retrieval, etc. For ordered messages, are more messages available for retrieval, etc. For ordered messages,
their stream sequence number may also be returned. their stream sequence number may also be returned.
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Format: STATUS(association id) Format: STATUS(association id)
-> status data -> status data
This primitive should return a data block containing the following This primitive should return a data block containing the following
information: information:
association connection state, association connection state,
destination transport address list, destination transport address list,
destination transport address reachability states, destination transport address reachability states,
current receiver window size, current receiver window size,
Internet draft Stream Control Transmission Protocol July 2000
current congestion window sizes, current congestion window sizes,
number of unacknowledged DATA chunks, number of unacknowledged DATA chunks,
number of DATA chunks pending receipt, number of DATA chunks pending receipt,
primary path, primary path,
most recent SRTT on primary path, most recent SRTT on primary path,
RTO on primary path, RTO on primary path,
SRTT and RTO on other destination addresses, etc. SRTT and RTO on other destination addresses, etc.
Mandatory attributes: Mandatory attributes:
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address. Default interval is the RTO of the destination address. address. Default interval is the RTO of the destination address.
J) Request HeartBeat J) Request HeartBeat
Format: REQUESTHEARTBEAT(association id, destination transport Format: REQUESTHEARTBEAT(association id, destination transport
address) address)
-> result -> result
Instructs the local endpoint to perform a HeartBeat on the specified Instructs the local endpoint to perform a HeartBeat on the specified
destination transport address of the given association. The returned destination transport address of the given association. The returned
Internet draft Stream Control Transmission Protocol July 2000
result should indicate whether the transmission of the HEARTBEAT result should indicate whether the transmission of the HEARTBEAT
chunk to the destination address is successful. chunk to the destination address is successful.
Mandatory attributes: Mandatory attributes:
o association id - local handle to the SCTP association o association id - local handle to the SCTP association
o destination transport address - the transport address of the o destination transport address - the transport address of the
association on which a heartbeat should be issued. association on which a heartbeat should be issued.
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o failure threshold - the new value of 'Path.Max.Retrans' for the o failure threshold - the new value of 'Path.Max.Retrans' for the
destination address. destination address.
M) Set Protocol Parameters M) Set Protocol Parameters
Format: SETPROTOCOLPARAMETERS(association id, [,destination transport Format: SETPROTOCOLPARAMETERS(association id, [,destination transport
address,] protocol parameter list) address,] protocol parameter list)
-> result -> result
This primitive allows the local SCTP to customize the protocol This primitive allows the local SCTP to customize the protocol
Internet draft Stream Control Transmission Protocol July 2000
parameters. parameters.
Mandatory attributes: Mandatory attributes:
o association id - local handle to the SCTP association o association id - local handle to the SCTP association
o protocol parameter list - The specific names and values of the o protocol parameter list - The specific names and values of the
protocol parameters (e.g., Association.Max.Retrans [see Section 14]) protocol parameters (e.g., Association.Max.Retrans [see Section 14])
that the SCTP user wishes to customize. that the SCTP user wishes to customize.
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o payload protocol-id - The 32 bit unsigned integer that was sent to o payload protocol-id - The 32 bit unsigned integer that was sent to
be sent to the peer indicating the type of payload protocol of the be sent to the peer indicating the type of payload protocol of the
received data. received data.
O) Receive unacknowledged message O) Receive unacknowledged message
Format: RECEIVE_UNACKED(data retrieval id, buffer address, buffer size, Format: RECEIVE_UNACKED(data retrieval id, buffer address, buffer size,
[,stream id] [, stream sequence number] [,partial flag] [,stream id] [, stream sequence number] [,partial flag]
[,payload protocol-id]) [,payload protocol-id])
Internet draft Stream Control Transmission Protocol July 2000
o data retrieval id - The identification passed to the ULP in the o data retrieval id - The identification passed to the ULP in the
failure notification. failure notification.
o buffer address - the memory location indicated by the ULP to store o buffer address - the memory location indicated by the ULP to store
the received message. the received message.
o buffer size - the maximum size of data to be received, in bytes. o buffer size - the maximum size of data to be received, in bytes.
Optional attributes: Optional attributes:
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A) DATA ARRIVE notification A) DATA ARRIVE notification
SCTP shall invoke this notification on the ULP when a user message is SCTP shall invoke this notification on the ULP when a user message is
successfully received and ready for retrieval. successfully received and ready for retrieval.
The following may be optionally be passed with the notification: The following may be optionally be passed with the notification:
o association id - local handle to the SCTP association o association id - local handle to the SCTP association
Internet draft Stream Control Transmission Protocol July 2000
o stream id - to indicate which stream the data is received on. o stream id - to indicate which stream the data is received on.
B) SEND FAILURE notification B) SEND FAILURE notification
If a message can not be delivered SCTP shall invoke this notification If a message can not be delivered SCTP shall invoke this notification
on the ULP. on the ULP.
The following may be optionally be passed with the notification: The following may be optionally be passed with the notification:
o association id - local handle to the SCTP association o association id - local handle to the SCTP association
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COMMUNICATION UP notification is optional at the association COMMUNICATION UP notification is optional at the association
initiator's side. initiator's side.
The following shall be passed with the notification: The following shall be passed with the notification:
o association id - local handle to the SCTP association o association id - local handle to the SCTP association
o status - This indicates what type of event has occurred o status - This indicates what type of event has occurred
o destination transport address list - the complete set of transport o destination transport address list - the complete set of transport
Internet draft Stream Control Transmission Protocol July 2000
addresses of the peer addresses of the peer
o outbound stream count - the maximum number of streams allowed to be o outbound stream count - the maximum number of streams allowed to be
used in this association by the ULP used in this association by the ULP
o inbound stream count - the number of streams the peer endpoint o inbound stream count - the number of streams the peer endpoint
has requested with this association (this may not be the same has requested with this association (this may not be the same
number as 'outbound stream count'). number as 'outbound stream count').
E) COMMUNICATION LOST notification E) COMMUNICATION LOST notification
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o error info - this indicates the type of error and optionally some o error info - this indicates the type of error and optionally some
additional information received through the ERROR chunk. additional information received through the ERROR chunk.
G) RESTART notification G) RESTART notification
When SCTP detects that the peer has restarted, it may send When SCTP detects that the peer has restarted, it may send
this notification to its ULP. this notification to its ULP.
The following can be passed with the notification: The following can be passed with the notification:
Internet draft Stream Control Transmission Protocol July 2000
o association id - local handle to the SCTP association o association id - local handle to the SCTP association
H) SHUTDOWN COMPLETE notification H) SHUTDOWN COMPLETE notification
When SCTP completes the shutdown procedures (section 9.2) this When SCTP completes the shutdown procedures (section 9.2) this
notification is passed to the upper layer. notification is passed to the upper layer.
The following can be passed with the notification: The following can be passed with the notification:
o association id - local handle to the SCTP association o association id - local handle to the SCTP association
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11.2.2 Protecting against Data Corruption in the Network 11.2.2 Protecting against Data Corruption in the Network
Where the risk of undetected errors in datagrams delivered by the lower Where the risk of undetected errors in datagrams delivered by the lower
layer transport services is considered to be too great, additional layer transport services is considered to be too great, additional
integrity protection is required. If this additional protection were integrity protection is required. If this additional protection were
provided in the application-layer, the SCTP header would remain provided in the application-layer, the SCTP header would remain
vulnerable to deliberate integrity attacks. While the existing SCTP vulnerable to deliberate integrity attacks. While the existing SCTP
mechanisms for detection of packet replays are considered sufficient mechanisms for detection of packet replays are considered sufficient
for normal operation, stronger protections are needed to protect SCTP for normal operation, stronger protections are needed to protect SCTP
when the operating environment contains significant risk of deliberate when the operating environment contains significant risk of deliberate
Internet draft Stream Control Transmission Protocol July 2000
attacks from a sophisticated adversary. attacks from a sophisticated adversary.
In order to promote software code-reuse, to avoid re-inventing the In order to promote software code-reuse, to avoid re-inventing the
wheel, and to avoid gratuitous complexity to SCTP, the IP wheel, and to avoid gratuitous complexity to SCTP, the IP
Authentication Header [RFC2402] SHOULD be used when the threat Authentication Header [RFC2402] SHOULD be used when the threat
environment requires stronger integrity protections, but does not environment requires stronger integrity protections, but does not
require confidentiality. require confidentiality.
A widely implemented BSD Sockets API extension exists for applications A widely implemented BSD Sockets API extension exists for applications
to request IP security services, such as AH or ESP from an operating to request IP security services, such as AH or ESP from an operating
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A blind attack is one where the attacker is unable to intercept or A blind attack is one where the attacker is unable to intercept or
otherwise see the content of data flows passing to and from the target otherwise see the content of data flows passing to and from the target
SCTP node. Blind denial of service attacks may take the form of SCTP node. Blind denial of service attacks may take the form of
flooding, masquerade, or improper monopolization of services. flooding, masquerade, or improper monopolization of services.
11.2.4.1 Flooding 11.2.4.1 Flooding
The objective of flooding is to cause loss of service and incorrect The objective of flooding is to cause loss of service and incorrect
behavior at target systems through resource exhaustion, interference behavior at target systems through resource exhaustion, interference
Internet draft Stream Control Transmission Protocol July 2000
with legitimate transactions, and exploitation of buffer-related with legitimate transactions, and exploitation of buffer-related
software bugs. Flooding may be directed either at the SCTP node or at software bugs. Flooding may be directed either at the SCTP node or at
resources in the intervening IP Access Links or the Internet. resources in the intervening IP Access Links or the Internet.
Where the latter entities are the target, flooding will manifest Where the latter entities are the target, flooding will manifest
itself as loss of network services, including potentially the breach itself as loss of network services, including potentially the breach
of any firewalls in place. of any firewalls in place.
In general, protection against flooding begins at the equipment In general, protection against flooding begins at the equipment
design level, where it includes measures such as: design level, where it includes measures such as:
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attack on a third party by sending large numbers of INITs to random attack on a third party by sending large numbers of INITs to random
hosts containing the host name of the target. In addition to the hosts containing the host name of the target. In addition to the
strain on DNS resources, this could also result in large numbers of strain on DNS resources, this could also result in large numbers of
INIT ACKs being sent to the target. One method to protect against this INIT ACKs being sent to the target. One method to protect against this
type of attack is to verify that the IP addresses received from DNS type of attack is to verify that the IP addresses received from DNS
include the source IP address of the original INIT. If the list of IP include the source IP address of the original INIT. If the list of IP
addresses received from DNS does not include the source IP address of addresses received from DNS does not include the source IP address of
the INIT, the endpoint MAY silently discard the INIT. This last option the INIT, the endpoint MAY silently discard the INIT. This last option
will not protect against the attack against the DNS. will not protect against the attack against the DNS.
11.2.4.2 Masquerade 11.2.4.2 Blind Masquerade
Internet draft Stream Control Transmission Protocol July 2000
Masquerade can be used to deny service in several ways: Masquerade can be used to deny service in several ways:
- by tying up resources at the target SCTP node to which the - by tying up resources at the target SCTP node to which the
impersonated node has limited access. For example, the target node impersonated node has limited access. For example, the target node
may by policy permit a maximum of one SCTP association with the may by policy permit a maximum of one SCTP association with the
impersonated SCTP node. The masquerading attacker may attempt to impersonated SCTP node. The masquerading attacker may attempt to
establish an association purporting to come from the impersonated establish an association purporting to come from the impersonated
node so that the latter cannot do so when it requires it. node so that the latter cannot do so when it requires it.
- by deliberately allowing the impersonation to be detected, - by deliberately allowing the impersonation to be detected,
thereby provoking counter-measures which cause the impersonated node thereby provoking counter-measures which cause the impersonated node
to be locked out of the target SCTP node. to be locked out of the target SCTP node.
- by interfering with an established association by inserting - by interfering with an established association by inserting
extraneous content such as a SHUTDOWN request. extraneous content such as a SHUTDOWN request.
SCTP reduces the risk of masquerade attacks through IP spoofing by use SCTP reduces the risk of blind masquerade attacks through IP spoofing
of the four-way startup handshake. Because the initial exchange is by use of the four-way startup handshake. Man-in-the-middle masqurade
memoryless, no lockout mechanism is triggered by masquerade attacks. attacks are discussed in Section 11.3 below. Because the initial exchange
is memoryless, no lockout mechanism is triggered by blind masquerade attacks.
In addition, the INIT ACK containing the State Cookie is transmitted In addition, the INIT ACK containing the State Cookie is transmitted
back to the IP address from which it received the INIT. Thus the back to the IP address from which it received the INIT. Thus the
attacker would not receive the INIT ACK containing the State Cookie. attacker would not receive the INIT ACK containing the State Cookie.
SCTP protects against insertion of extraneous packets into the flow of SCTP protects against insertion of extraneous packets into the flow of
an established association by use of the Verification Tag. an established association by use of the Verification Tag.
Logging of received INIT requests and abnormalities such as Logging of received INIT requests and abnormalities such as
unexpected INIT ACKs might be considered as a way to detect patterns unexpected INIT ACKs might be considered as a way to detect patterns
of hostile activity. However, the potential usefulness of such of hostile activity. However, the potential usefulness of such
logging must be weighed against the increased SCTP startup logging must be weighed against the increased SCTP startup
processing it implies, rendering the SCTP node more vulnerable to processing it implies, rendering the SCTP node more vulnerable to
flooding attacks. Logging is pointless without the establishment of flooding attacks. Logging is pointless without the establishment of
operating procedures to review and analyze the logs on a routine operating procedures to review and analyze the logs on a routine
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adjoining SCTP node. SCTP user applications should be capable of adjoining SCTP node. SCTP user applications should be capable of
detecting large volumes of illegitimate or "no-op" messages within a detecting large volumes of illegitimate or "no-op" messages within a
given association and either logging or terminating the association as given association and either logging or terminating the association as
a result, based on local policy. a result, based on local policy.
11.3 Protection against Fraud and Repudiation 11.3 Protection against Fraud and Repudiation
The objective of fraud is to obtain services without authorization The objective of fraud is to obtain services without authorization
and specifically without paying for them. In order to achieve this and specifically without paying for them. In order to achieve this
objective, the attacker must induce the SCTP user application at the objective, the attacker must induce the SCTP user application at the
Internet draft Stream Control Transmission Protocol July 2000
target SCTP node to provide the desired service while accepting target SCTP node to provide the desired service while accepting
invalid billing data or failing to collect it. Repudiation is a invalid billing data or failing to collect it. Repudiation is a
related problem, since it may occur as a deliberate act of fraud or related problem, since it may occur as a deliberate act of fraud or
simply because the repudiating party kept inadequate records of simply because the repudiating party kept inadequate records of
service received. service received.
Potential fraudulent attacks include interception and misuse of Potential fraudulent attacks include interception and misuse of
authorizing information such as credit card numbers, blind authorizing information such as credit card numbers, blind
masquerade and replay, and man-in-the middle attacks which modify masquerade and replay, and man-in-the middle attacks which modify
the packets passing through a target SCTP association in real time. the packets passing through a target SCTP association in real time.
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The interception attack is countered by the confidentiality measures The interception attack is countered by the confidentiality measures
discussed in Section 11.2.3 above. discussed in Section 11.2.3 above.
Section 11.2.4.2 describes how SCTP is resistant to blind masquerade Section 11.2.4.2 describes how SCTP is resistant to blind masquerade
attacks, as a result of the four-way startup handshake and the attacks, as a result of the four-way startup handshake and the
Verification Tag. The Verification Tag and TSN together are Verification Tag. The Verification Tag and TSN together are
protections against blind replay attacks, where the replay is into an protections against blind replay attacks, where the replay is into an
existing association. existing association.
However, SCTP does not protect against man-in-the-middle attacks However, SCTP does not protect against man-in-the-middle attacks
where the attacker is able to intercept and alter the packets sent where the attacker is able to intercept and alter the packets sent
and received in an association. Where a significant possibility of and received in an association. For example, the INIT ACK will have
such attacks is seen to exist, or where possible repudiation is an sufficient information sent on the wire for an adversary in the middle
to hijack an existing SCTP association. Where a significant possibility
of such attacks is seen to exist, or where possible repudiation is an
issue, the use of the IPSEC AH service is recommended to ensure both issue, the use of the IPSEC AH service is recommended to ensure both
the integrity and the authenticity of the SCTP packets passed. the integrity and the authenticity of the SCTP packets passed.
SCTP also provides no protection against attacks originating at or SCTP also provides no protection against attacks originating at or
beyond the SCTP node and taking place within the context of an beyond the SCTP node and taking place within the context of an
existing association. Prevention of such attacks should be covered existing association. Prevention of such attacks should be covered
by appropriate security policies at the host site, as discussed in by appropriate security policies at the host site, as discussed in
Section 11.2.1. Section 11.2.1.
12. Recommended Transmission Control Block (TCB) Parameters 12. Recommended Transmission Control Block (TCB) Parameters
skipping to change at page 101, line 37 skipping to change at page 103, line 4
Associations: A list of current associations and mappings to the Associations: A list of current associations and mappings to the
data consumers for each association. This may be in data consumers for each association. This may be in
the form of a hash table or other implementation the form of a hash table or other implementation
dependent structure. The data consumers may be process dependent structure. The data consumers may be process
identification information such as file descriptors, identification information such as file descriptors,
named pipe pointer, or table pointers dependent on how named pipe pointer, or table pointers dependent on how
SCTP is implemented. SCTP is implemented.
Secret Key: A secret key used by this endpoint to compute the MAC. Secret Key: A secret key used by this endpoint to compute the MAC.
Internet draft Stream Control Transmission Protocol July 2000
This SHOULD be a cryptographic quality random number with This SHOULD be a cryptographic quality random number with
a sufficient length. Discussion in [RFC1750] can be a sufficient length. Discussion in [RFC1750] can be
helpful in selection of the key. helpful in selection of the key.
Address List: The list of IP addresses that this instance has bound. Address List: The list of IP addresses that this instance has bound.
This information is passed to one's peer(s) in INIT and This information is passed to one's peer(s) in INIT and
INIT ACK chunks. INIT ACK chunks.
SCTP Port: The local SCTP port number the endpoint is bound to. SCTP Port: The local SCTP port number the endpoint is bound to.
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Peer Rwnd : Current calculated value of the peer's rwnd. Peer Rwnd : Current calculated value of the peer's rwnd.
Next TSN : The next TSN number to be assigned to a new DATA chunk. Next TSN : The next TSN number to be assigned to a new DATA chunk.
: This is sent in the INIT or INIT ACK chunk to the peer : This is sent in the INIT or INIT ACK chunk to the peer
: and incremented each time a DATA chunk is assigned a : and incremented each time a DATA chunk is assigned a
: TSN (normally just prior to transmit or during : TSN (normally just prior to transmit or during
: fragmentation). : fragmentation).
Last Rcvd : This is the last TSN received in sequence. This value is Last Rcvd : This is the last TSN received in sequence. This value is
Internet draft Stream Control Transmission Protocol July 2000
TSN : set initially by taking the peer's Initial TSN, TSN : set initially by taking the peer's Initial TSN,
: received in the INIT or INIT ACK chunk, and : received in the INIT or INIT ACK chunk, and
: subtracting one from it. : subtracting one from it.
Mapping : An array of bits or bytes indicating which out of Mapping : An array of bits or bytes indicating which out of
Array : order TSN's have been received (relative to the Array : order TSN's have been received (relative to the
: Last Rcvd TSN). If no gaps exist, i.e. no out of order : Last Rcvd TSN). If no gaps exist, i.e. no out of order
: packets have been received, this array will be set to all : packets have been received, this array will be set to all
: zero. This structure may be in the form of a circular : zero. This structure may be in the form of a circular
: buffer or bit array. : buffer or bit array.
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Error count : The current error count for this destination. Error count : The current error count for this destination.
Error : Current error threshold for this destination i.e. Error : Current error threshold for this destination i.e.
Threshold : what value marks the destination down if Error count Threshold : what value marks the destination down if Error count
: reaches this value. : reaches this value.
cwnd : The current congestion window. cwnd : The current congestion window.
ssthresh : The current ssthresh value. ssthresh : The current ssthresh value.
Internet draft Stream Control Transmission Protocol July 2000
RTO : The current retransmission timeout value. RTO : The current retransmission timeout value.
SRTT : The current smoothed round trip time. SRTT : The current smoothed round trip time.
RTTVAR : The current RTT variation. RTTVAR : The current RTT variation.
partial : The tracking method for increase of cwnd when in partial : The tracking method for increase of cwnd when in
bytes acked : congestion avoidance mode (see Section 6.2.2) bytes acked : congestion avoidance mode (see Section 6.2.2)
state : The current state of this destination, i.e. DOWN, UP, state : The current state of this destination, i.e. DOWN, UP,
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-- through definition of additional parameter types, or -- through definition of additional parameter types, or
-- through definition of additional cause codes within -- through definition of additional cause codes within
ERROR chunks ERROR chunks
In the case where a particular ULP using SCTP desires to have its own In the case where a particular ULP using SCTP desires to have its own
ports, the ULP should be responsible for registering with IANA for ports, the ULP should be responsible for registering with IANA for
getting its ports assigned. getting its ports assigned.
13.1 IETF-defined Chunk Extension 13.1 IETF-defined Chunk Extension
Internet draft Stream Control Transmission Protocol July 2000
The definition and use of new chunk types is an integral part of The definition and use of new chunk types is an integral part of
SCTP. Thus, new chunk types are assigned by IANA through an SCTP. Thus, new chunk types are assigned by IANA through an
IETF Consensus action as defined in [RFC2434]. IETF Consensus action as defined in [RFC2434].
The documentation for a new chunk code type must include the following The documentation for a new chunk code type must include the following
information: information:
(a) A long and short name for the new chunk type; (a) A long and short name for the new chunk type;
(b) A detailed description of the structure of the chunk, which MUST (b) A detailed description of the structure of the chunk, which MUST
conform to the basic structure defined in Section 3.2; conform to the basic structure defined in Section 3.2;
(c) A detailed definition and description of intended use of each field (c) A detailed definition and description of intended use of each field
skipping to change at page 105, line 38 skipping to change at page 107, line 5
(d) Detailed description of the structure and content of data fields (d) Detailed description of the structure and content of data fields
which accompany this cause code. which accompany this cause code.
The initial word (32 bits) of a cause code parameter MUST conform to The initial word (32 bits) of a cause code parameter MUST conform to
the format shown in Section 3.3.10, i.e.: the format shown in Section 3.3.10, i.e.:
-- first two bytes contain the cause code value -- first two bytes contain the cause code value
-- last two bytes contain length of the Cause Parameter. -- last two bytes contain length of the Cause Parameter.
13.3 Payload Protocol Identifiers 13.3 Payload Protocol Identifiers
Internet draft Stream Control Transmission Protocol July 2000
Except for value 0 which is reserved by SCTP to indicate an Except for value 0 which is reserved by SCTP to indicate an
unspecified payload protocol identifier in a DATA chunk, SCTP will unspecified payload protocol identifier in a DATA chunk, SCTP will
not be responsible for standardizing or verifying any payload protocol not be responsible for standardizing or verifying any payload protocol
identifiers; SCTP simply receives the identifier from the upper layer identifiers; SCTP simply receives the identifier from the upper layer
and carries it with the corresponding payload data. and carries it with the corresponding payload data.
The upper layer, i.e., the SCTP user, SHOULD standardize any specific The upper layer, i.e., the SCTP user, SHOULD standardize any specific
protocol identifier with IANA if it is so desired. The use of any protocol identifier with IANA if it is so desired. The use of any
specific payload protocol identifier is out of the scope of SCTP. specific payload protocol identifier is out of the scope of SCTP.
skipping to change at page 106, line 36 skipping to change at page 108, line 4
16. Authors' Addresses 16. Authors' Addresses
Randall R. Stewart Tel: +1-815-479-8536 Randall R. Stewart Tel: +1-815-479-8536
24 Burning Bush Trail. EMail: rstewart@flashcom.net 24 Burning Bush Trail. EMail: rstewart@flashcom.net
Crystal Lake, IL 60012 Crystal Lake, IL 60012
USA USA
Qiaobing Xie Tel: +1-847-632-3028 Qiaobing Xie Tel: +1-847-632-3028
Motorola, Inc. EMail: qxie1@email.mot.com Motorola, Inc. EMail: qxie1@email.mot.com
1501 W. Shure Drive, #2309 1501 W. Shure Drive, #2309
Internet draft Stream Control Transmission Protocol July 2000
Arlington Heights, IL 60004 Arlington Heights, IL 60004
USA USA
Ken Morneault Tel: +1-703-484-3323 Ken Morneault Tel: +1-703-484-3323
Cisco Systems Inc. EMail: kmorneau@cisco.com Cisco Systems Inc. EMail: kmorneau@cisco.com
13615 Dulles Technology Drive 13615 Dulles Technology Drive
Herndon, VA. 20171 Herndon, VA. 20171
USA USA
Chip Sharp Tel: +1-919-392-3121 Chip Sharp Tel: +1-919-392-3121
skipping to change at page 107, line 38 skipping to change at page 109, line 5
4531G Boelter Hall 4531G Boelter Hall
Los Angeles, CA 90095-1596 Los Angeles, CA 90095-1596
USA USA
Vern Paxson Tel: +1-510-642-4274 x 302 Vern Paxson Tel: +1-510-642-4274 x 302
ACIRI EMail: vern@aciri.org ACIRI EMail: vern@aciri.org
1947 Center St., Suite 600, 1947 Center St., Suite 600,
Berkeley, CA 94704-1198 Berkeley, CA 94704-1198
USA USA
Internet draft Stream Control Transmission Protocol July 2000
17. References 17. References
[RFC768] Postel, J. (ed.), "User Datagram Protocol", RFC 768, August [RFC768] Postel, J. (ed.), "User Datagram Protocol", RFC 768, August
1980. 1980.
[RFC793] Postel, J. (ed.), "Transmission Control Protocol", RFC 793, [RFC793] Postel, J. (ed.), "Transmission Control Protocol", RFC 793,
September 1981. September 1981.
[RFC1123] Braden, R., "Requirements for Internet hosts - application [RFC1123] Braden, R., "Requirements for Internet hosts - application
and support.", RFC 1123, October 1989. and support.", RFC 1123, October 1989.
skipping to change at page 108, line 37 skipping to change at page 110, line 4
[RFC2409] D. Harkins, D. Carrel, "The Internet Key Exchange (IKE)", [RFC2409] D. Harkins, D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998. RFC 2409, November 1998.
[RFC2434] T. Narten, and H. Avestrand, "Guidelines for Writing an IANA [RFC2434] T. Narten, and H. Avestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs.", RFC2434, October 1998. Considerations Section in RFCs.", RFC2434, October 1998.
[RFC2460] Deering, S., and R. Hinden, "Internet Protocol, Version [RFC2460] Deering, S., and R. Hinden, "Internet Protocol, Version
6 (IPv6) Specification", RFC 2460, December 1998. 6 (IPv6) Specification", RFC 2460, December 1998.
[RFC2581] Allman, M., Paxson, V., and Stevens, W., "TCP Congestion [RFC2581] Allman, M., Paxson, V., and Stevens, W., "TCP Congestion
Internet draft Stream Control Transmission Protocol July 2000
Control", RFC 2581, April 1999. October 1994. Control", RFC 2581, April 1999. October 1994.
18. Bibliography 18. Bibliography
[ALLMAN99] Allman, M., and Paxson, V., "On Estimating End-to-End [ALLMAN99] Allman, M., and Paxson, V., "On Estimating End-to-End
Network Path Properties", Proc. SIGCOMM'99, 1999. Network Path Properties", Proc. SIGCOMM'99, 1999.
[FALL96] Fall, K., and Floyd, S., Simulation-based Comparisons of [FALL96] Fall, K., and Floyd, S., Simulation-based Comparisons of
Tahoe, Reno, and SACK TCP, Computer Communications Review, Tahoe, Reno, and SACK TCP, Computer Communications Review,
V. 26 N. 3, July 1996, pp. 5-21. V. 26 N. 3, July 1996, pp. 5-21.
skipping to change at page 109, line 37 skipping to change at page 111, line 4
RFC2481 details negotiation of ECN during the SYN and SYN-ACK stages RFC2481 details negotiation of ECN during the SYN and SYN-ACK stages
of a TCP connection. The sender of the SYN sets two bits in the of a TCP connection. The sender of the SYN sets two bits in the
TCP flags, and the sender of the SYN-ACK sets only 1 bit. The reasoning TCP flags, and the sender of the SYN-ACK sets only 1 bit. The reasoning
behind this is to assure both sides are truly ECN capable. For SCTP behind this is to assure both sides are truly ECN capable. For SCTP
this is not necessary. To indicate that an endpoint is ECN capable this is not necessary. To indicate that an endpoint is ECN capable
an endpoint SHOULD add to the INIT and or INIT ACK chunk the TLV an endpoint SHOULD add to the INIT and or INIT ACK chunk the TLV
reserved for ECN. This TLV contains no parameters, and thus has reserved for ECN. This TLV contains no parameters, and thus has
the following format: the following format:
0 1 2 3 0 1 2 3
Internet draft Stream Control Transmission Protocol July 2000
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Type = 32768 | Parameter Length = 4 | | Parameter Type = 32768 | Parameter Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ECN-Echo: ECN-Echo:
RFC 2481 details a specific bit for a receiver to send back in its RFC 2481 details a specific bit for a receiver to send back in its
TCP acknowledgements to notify the sender of the Congestion Experienced TCP acknowledgements to notify the sender of the Congestion Experienced
(CE) bit having arrived from the network. For SCTP this same indication (CE) bit having arrived from the network. For SCTP this same indication
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: The CWR is considered a Control chunk. Note: The CWR is considered a Control chunk.
Appendix B Alder 32 bit checksum calculation Appendix B Alder 32 bit checksum calculation
The Adler-32 checksum calculation given in this appendix is copied from The Adler-32 checksum calculation given in this appendix is copied from
[RFC1950]. [RFC1950].
Adler-32 is composed of two sums accumulated per byte: s1 is the sum Adler-32 is composed of two sums accumulated per byte: s1 is the sum
Internet draft Stream Control Transmission Protocol July 2000
of all bytes, s2 is the sum of all s1 values. Both sums are done of all bytes, s2 is the sum of all s1 values. Both sums are done
modulo 65521. s1 is initialized to 1, s2 to zero. The Adler-32 modulo 65521. s1 is initialized to 1, s2 to zero. The Adler-32
checksum is stored as s2*65536 + s1 in network byte order. checksum is stored as s2*65536 + s1 in network byte order.
The following C code computes the Adler-32 checksum of a data buffer. The following C code computes the Adler-32 checksum of a data buffer.
It is written for clarity, not for speed. The sample code is in the It is written for clarity, not for speed. The sample code is in the
ANSI C programming language. Non C users may find it easier to read ANSI C programming language. Non C users may find it easier to read
with these hints: with these hints:
& Bitwise AND operator. & Bitwise AND operator.
skipping to change at line 5860 skipping to change at line 6198
s2 = (s2 + s1) % BASE; s2 = (s2 + s1) % BASE;
} }
return (s2 << 16) + s1; return (s2 << 16) + s1;
} }
/* Return the adler32 of the bytes buf[0..len-1] */ /* Return the adler32 of the bytes buf[0..len-1] */
unsigned long adler32(unsigned char *buf, int len) unsigned long adler32(unsigned char *buf, int len)
{ {
return update_adler32(1L, buf, len); return update_adler32(1L, buf, len);
} }
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