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Versions: 00 01 02 03 04 draft-ietf-tsvwg-rfc4960-errata

Network Working Group                                         R. Stewart
Internet-Draft                                             Netflix, Inc.
Intended status: Informational                                 M. Tuexen
Expires: January 9, 2017                Muenster Univ. of Appl. Sciences
                                                              M. Proshin
                                                                Ericsson
                                                            July 8, 2016


                       RFC 4960 Errata and Issues
                draft-tuexen-tsvwg-rfc4960-errata-04.txt

Abstract

   This document is a compilation of issues found since the publication
   of RFC4960 in September 2007 based on experience with implementing,
   testing, and using SCTP along with the suggested fixes.  This
   document provides deltas to RFC4960 and is organized in a time based
   way.  The issues are listed in the order they were brought up.
   Because some text is changed several times the last delta in the text
   is the one which should be applied.  In addition to the delta a
   description of the problem and the details of the solution are also
   provided.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 9, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Corrections to RFC 4960 . . . . . . . . . . . . . . . . . . .   3
     3.1.  Path Error Counter Threshold Handling . . . . . . . . . .   3
     3.2.  Upper Layer Protocol Shutdown Request Handling  . . . . .   4
     3.3.  Registration of New Chunk Types . . . . . . . . . . . . .   5
     3.4.  Variable Parameters for INIT Chunks . . . . . . . . . . .   6
     3.5.  CRC32c Sample Code on 64-bit Platforms  . . . . . . . . .   7
     3.6.  Endpoint Failure Detection  . . . . . . . . . . . . . . .   8
     3.7.  Data Transmission Rules . . . . . . . . . . . . . . . . .   9
     3.8.  T1-Cookie Timer . . . . . . . . . . . . . . . . . . . . .  10
     3.9.  Miscellaneous Typos . . . . . . . . . . . . . . . . . . .  11
     3.10. CRC32c Sample Code  . . . . . . . . . . . . . . . . . . .  15
     3.11. partial_bytes_acked after T3-rtx Expiration . . . . . . .  15
     3.12. Order of Adjustments of partial_bytes_acked and cwnd  . .  16
     3.13. HEARTBEAT ACK and the association error counter . . . . .  17
     3.14. Path for Fast Retransmission  . . . . . . . . . . . . . .  19
     3.15. Transmittal in Fast Recovery  . . . . . . . . . . . . . .  20
     3.16. Initial Value of ssthresh . . . . . . . . . . . . . . . .  20
     3.17. Automatically Confirmed Addresses . . . . . . . . . . . .  21
     3.18. Only One Packet after Retransmission Timeout  . . . . . .  22
     3.19. INIT ACK Path for INIT in COOKIE-WAIT State . . . . . . .  23
     3.20. Zero Window Probing and Unreachable Primary Path  . . . .  24
     3.21. Normative Language in Section 10  . . . . . . . . . . . .  25
     3.22. Increase of partial_bytes_acked in Congestion Avoidance .  29
     3.23. Inconsistency in Notifications Handling . . . . . . . . .  30
     3.24. SACK.Delay Not Listed as a Protocol Parameter . . . . . .  34
     3.25. Processing of Chunks in an Incoming SCTP Packet . . . . .  36
     3.26. CWND Increase in Congestion Avoidance Phase . . . . . . .  37
     3.27. Refresh of cwnd and ssthresh after Idle Period  . . . . .  39
     3.28. Window Updates After Receiver Window Opens Up . . . . . .  40
     3.29. Path of DATA and Reply Chunks . . . . . . . . . . . . . .  41
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  43
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  43
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  43
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  43
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  43
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  43



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   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  44

1.  Introduction

   This document contains a compilation of all defects found up until
   the publishing of this document for [RFC4960] specifying the Stream
   Control Transmission Protocol (SCTP).  These defects may be of an
   editorial or technical nature.  This document may be thought of as a
   companion document to be used in the implementation of SCTP to
   clarify errors in the original SCTP document.

   This document provides a history of the changes that will be compiled
   into a BIS document for [RFC4960].  It is structured similar to
   [RFC4460].

   Each error will be detailed within this document in the form of:

   o  The problem description,
   o  The text quoted from [RFC4960],
   o  The replacement text that should be placed into an upcoming BIS
      document,
   o  A description of the solution.

   Note that when reading this document one must use care to assure that
   a field or item is not updated further on within the document.  Each
   section should be applied in sequence to the original [RFC4960] since
   this document is a historical record of the sequential changes that
   have been found necessary at various inter-op events and through
   discussion on the list.

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  Corrections to RFC 4960

3.1.  Path Error Counter Threshold Handling

3.1.1.  Description of the Problem

   The handling of the 'Path.Max.Retrans' parameter is described in
   Section 8.2 and Section 8.3 of [RFC4960] in an Inconsistent way.
   Whereas Section 8.2 describes that a path is marked inactive when the
   path error counter exceeds the threshold, Section 8.3 says the path
   is marked inactive when the path error counter reaches the threshold.




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   This issue was reported as an Errata for [RFC4960] with Errata ID
   1440.

3.1.2.  Text Changes to the Document

   ---------
   Old text: (Section 8.3)
   ---------

   When the value of this counter reaches the protocol parameter
   'Path.Max.Retrans', the endpoint should mark the corresponding
   destination address as inactive if it is not so marked, and may also
   optionally report to the upper layer the change of reachability of
   this destination address.  After this, the endpoint should continue
   HEARTBEAT on this destination address but should stop increasing the
   counter.

   ---------
   New text: (Section 8.3)
   ---------

   When the value of this counter exceeds the protocol parameter
   'Path.Max.Retrans', the endpoint should mark the corresponding
   destination address as inactive if it is not so marked, and may also
   optionally report to the upper layer the change of reachability of
   this destination address.  After this, the endpoint should continue
   HEARTBEAT on this destination address but should stop increasing the
   counter.

3.1.3.  Solution Description

   The intended state change should happen when the threshold is
   exceeded.

3.2.  Upper Layer Protocol Shutdown Request Handling

3.2.1.  Description of the Problem

   Section 9.2 of [RFC4960] describes the handling of received SHUTDOWN
   chunks in the SHUTDOWN-RECEIVED state instead of the handling of
   shutdown requests from its upper layer in this state.

   This issue was reported as an Errata for [RFC4960] with Errata ID
   1574.







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3.2.2.  Text Changes to the Document

   ---------
   Old text: (Section 9.2)
   ---------

   Once an endpoint has reached the SHUTDOWN-RECEIVED state, it MUST NOT
   send a SHUTDOWN in response to a ULP request, and should discard
   subsequent SHUTDOWN chunks.

   ---------
   New text: (Section 9.2)
   ---------

   Once an endpoint has reached the SHUTDOWN-RECEIVED state, it MUST NOT
   send a SHUTDOWN in response to a ULP request, and should discard
   subsequent ULP shutdown requests.

3.2.3.  Solution Description

   The text never intended the SCTP endpoint to ignore SHUTDOWN chunks
   from its peer.  If it did the endpoints could never gracefully
   terminate associations in some cases.

3.3.  Registration of New Chunk Types

3.3.1.  Description of the Problem

   Section 14.1 of [RFC4960] should deal with new chunk types, however,
   the text refers to parameter types.

   This issue was reported as an Errata for [RFC4960] with Errata ID
   2592.

3.3.2.  Text Changes to the Document
















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   ---------
   Old text: (Section 14.1)
   ---------

   The assignment of new chunk parameter type codes is done through an
   IETF Consensus action, as defined in [RFC2434].  Documentation of the
   chunk parameter MUST contain the following information:

   ---------
   New text: (Section 14.1)
   ---------

   The assignment of new chunk type codes is done through an
   IETF Consensus action, as defined in [RFC2434].  Documentation of the
   chunk type MUST contain the following information:

3.3.3.  Solution Description

   Refer to chunk types as intended.

3.4.  Variable Parameters for INIT Chunks

3.4.1.  Description of the Problem

   Newlines in wrong places break the layout of the table of variable
   parameters for the INIT chunk in Section 3.3.2 of [RFC4960].

   This issue was reported as an Errata for [RFC4960] with Errata ID
   3291 and Errata ID 3804.

3.4.2.  Text Changes to the Document




















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   ---------
   Old text: (Section 3.3.2)
   ---------

   Variable Parameters                  Status     Type Value
   -------------------------------------------------------------
   IPv4 Address (Note 1)               Optional    5 IPv6 Address
   (Note 1)               Optional    6 Cookie Preservative
   Optional    9 Reserved for ECN Capable (Note 2)   Optional
   32768 (0x8000) Host Name Address (Note 3)          Optional
   11 Supported Address Types (Note 4)    Optional    12

   ---------
   New text: (Section 3.3.2)
   ---------

   Variable Parameters                  Status     Type Value
   -------------------------------------------------------------
   IPv4 Address (Note 1)               Optional    5
   IPv6 Address (Note 1)               Optional    6
   Cookie Preservative                 Optional    9
   Reserved for ECN Capable (Note 2)   Optional    32768 (0x8000)
   Host Name Address (Note 3)          Optional    11
   Supported Address Types (Note 4)    Optional    12

3.4.3.  Solution Description

   Fix the formatting of the table.

3.5.  CRC32c Sample Code on 64-bit Platforms

3.5.1.  Description of the Problem

   The sample code for computing the CRC32c provided in [RFC4960]
   assumes that a variable of type unsigned long uses 32 bits.  This is
   not true on some 64-bit platforms (for example the ones using LP64).

   This issue was reported as an Errata for [RFC4960] with Errata ID
   3423.

3.5.2.  Text Changes to the Document










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   ---------
   Old text: (Appendix C)
   ---------

   unsigned long
   generate_crc32c(unsigned char *buffer, unsigned int length)
   {
     unsigned int i;
     unsigned long crc32 = ~0L;

   ---------
   New text: (Appendix C)
   ---------

   unsigned long
   generate_crc32c(unsigned char *buffer, unsigned int length)
   {
     unsigned int i;
     unsigned long crc32 = 0xffffffffL;

3.5.3.  Solution Description

   Use 0xffffffffL instead of ~0L which gives the same value on
   platforms using 32 bits or 64 bits for variables of type unsigned
   long.

3.6.  Endpoint Failure Detection

3.6.1.  Description of the Problem

   The handling of the association error counter defined in Section 8.1
   of [RFC4960] can result in an association failure even if the path
   used for data transmission is available, but idle.

   This issue was reported as an Errata for [RFC4960] with Errata ID
   3788.

3.6.2.  Text Changes to the Document













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   ---------
   Old text: (Section 8.1)
   ---------

   An endpoint shall keep a counter on the total number of consecutive
   retransmissions to its peer (this includes retransmissions to all the
   destination transport addresses of the peer if it is multi-homed),
   including unacknowledged HEARTBEAT chunks.

   ---------
   New text: (Section 8.1)
   ---------

   An endpoint shall keep a counter on the total number of consecutive
   retransmissions to its peer (this includes data retransmissions
   to all the destination transport addresses of the peer if it is
   multi-homed), including the number of unacknowledged HEARTBEAT
   chunks observed on the path which currently is used for data
   transfer. Unacknowledged HEARTBEAT chunks observed on paths
   different from the path currently used for data transfer shall
   not increment the association error counter, as this could lead
   to association closure even if the path which currently is used for
   data transfer is available (but idle).

3.6.3.  Solution Description

   A more refined handling for the association error counter is defined.

3.7.  Data Transmission Rules

3.7.1.  Description of the Problem

   When integrating the changes to Section 6.1 A) of [RFC2960] as
   described in Section 2.15.2 of [RFC4460] some text was duplicated and
   became the final paragraph of Section 6.1 A) of [RFC4960].

   This issue was reported as an Errata for [RFC4960] with Errata ID
   4071.

3.7.2.  Text Changes to the Document











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   ---------
   Old text: (Section 6.1 A))
   ---------
   The sender MUST also have an algorithm for sending new DATA chunks
   to avoid silly window syndrome (SWS) as described in [RFC0813].
   The algorithm can be similar to the one described in Section
   4.2.3.4 of [RFC1122].

   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
   receiver if allowed by cwnd (see rule B below).  This rule allows
   the sender to probe for a change in rwnd that the sender missed
   due to the SACK having been lost in transit from the data receiver
   to the data sender.

   ---------
   New text: (Section 6.1 A))
   ---------

   The sender MUST also have an algorithm for sending new DATA chunks
   to avoid silly window syndrome (SWS) as described in [RFC0813].
   The algorithm can be similar to the one described in Section
   4.2.3.4 of [RFC1122].

3.7.3.  Solution Description

   Last paragraph of Section 6.1 A) removed as intended in
   Section 2.15.2 of [RFC4460].

3.8.  T1-Cookie Timer

3.8.1.  Description of the Problem

   Figure 4 of [RFC4960] illustrates the SCTP association setup.
   However, it incorrectly shows that the T1-init timer is used in the
   COOKIE-ECHOED state whereas the T1-cookie timer should have been used
   instead.

   This issue was reported as an Errata for [RFC4960] with Errata ID
   4400.

3.8.2.  Text Changes to the Document









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   ---------
   Old text: (Section 5.1.6, Figure 4)
   ---------

   COOKIE ECHO [Cookie_Z] ------\
   (Start T1-init timer)         \
   (Enter COOKIE-ECHOED state)    \---> (build TCB enter ESTABLISHED
                                         state)
                                  /---- COOKIE-ACK
                                 /
   (Cancel T1-init timer, <-----/
    Enter ESTABLISHED state)

   ---------
   New text: (Section 5.1.6, Figure 4)
   ---------

   COOKIE ECHO [Cookie_Z] ------\
   (Start T1-cookie timer)       \
   (Enter COOKIE-ECHOED state)    \---> (build TCB enter ESTABLISHED
                                         state)
                                  /---- COOKIE-ACK
                                 /
   (Cancel T1-cookie timer, <---/
    Enter ESTABLISHED state)

3.8.3.  Solution Description

   Change the figure such that the T1-cookie timer is used instead of
   the T1-init timer.

3.9.  Miscellaneous Typos

3.9.1.  Description of the Problem

   While processing [RFC4960] some typos were not catched.

3.9.2.  Text Changes to the Document













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   ---------
   Old text: (Section 1.6)
   ---------

   Transmission Sequence Numbers wrap around when they reach 2**32 - 1.
   That is, the next TSN a DATA chunk MUST use after transmitting TSN =
   2*32 - 1 is TSN = 0.

   ---------
   New text: (Section 1.6)
   ---------

   Transmission Sequence Numbers wrap around when they reach 2**32 - 1.
   That is, the next TSN a DATA chunk MUST use after transmitting TSN =
   2**32 - 1 is TSN = 0.

   ---------
   Old text: (Section 3.3.10.9)
   ---------

   No User Data: This error cause is returned to the originator of a

   DATA chunk if a received DATA chunk has no user data.

   ---------
   New text: (Section 3.3.10.9)
   ---------

   No User Data: This error cause is returned to the originator of a
   DATA chunk if a received DATA chunk has no user data.





















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   ---------
   Old text: (Section 6.7, Figure 9)
   ---------

   Endpoint A                                    Endpoint Z {App
   sends 3 messages; strm 0} DATA [TSN=6,Strm=0,Seq=2] ----------
   -----> (ack delayed) (Start T3-rtx timer)

   DATA [TSN=7,Strm=0,Seq=3] --------> X (lost)

   DATA [TSN=8,Strm=0,Seq=4] ---------------> (gap detected,
                                               immediately send ack)
                                   /----- SACK [TSN Ack=6,Block=1,
                                  /             Start=2,End=2]
                           <-----/ (remove 6 from out-queue,
    and mark 7 as "1" missing report)

   ---------
   New text: (Section 6.7, Figure 9)
   ---------

   Endpoint A                                    Endpoint Z
   {App sends 3 messages; strm 0}
   DATA [TSN=6,Strm=0,Seq=2] ---------------> (ack delayed)
   (Start T3-rtx timer)

   DATA [TSN=7,Strm=0,Seq=3] --------> X (lost)

   DATA [TSN=8,Strm=0,Seq=4] ---------------> (gap detected,
                                               immediately send ack)
                                   /----- SACK [TSN Ack=6,Block=1,
                                  /             Strt=2,End=2]
                           <-----/
   (remove 6 from out-queue,
    and mark 7 as "1" missing report)
















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   ---------
   Old text: (Section 6.10)
   ---------
   An endpoint bundles chunks by simply including multiple chunks in one
   outbound SCTP packet.  The total size of the resultant IP datagram,

   including the SCTP packet and IP headers, MUST be less that or equal
   to the current Path MTU.

   ---------
   New text: (Section 6.10)
   ---------

   An endpoint bundles chunks by simply including multiple chunks in one
   outbound SCTP packet.  The total size of the resultant IP datagram,
   including the SCTP packet and IP headers, MUST be less than or equal
   to the current Path MTU.

   ---------
   Old text: (Section 10.1)
   ---------
   o  Receive Unacknowledged Message

      Format: RECEIVE_UNACKED(data retrieval id, buffer address, buffer
              size, [,stream id] [, stream sequence number] [,partial
              flag] [,payload protocol-id])

   ---------
   New text: (Section 10.1)
   ---------

   O) Receive Unacknowledged Message

      Format: RECEIVE_UNACKED(data retrieval id, buffer address, buffer
              size, [,stream id] [, stream sequence number] [,partial
              flag] [,payload protocol-id])















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   ---------
   Old text: (Appendix C)
   ---------
   ICMP2) An implementation MAY ignore all ICMPv6 messages where the
          type field is not "Destination Unreachable", "Parameter
          Problem",, or "Packet Too Big".

   ---------
   New text: (Appendix C)
   ---------

   ICMP2) An implementation MAY ignore all ICMPv6 messages where the
          type field is not "Destination Unreachable", "Parameter
          Problem", or "Packet Too Big".

3.9.3.  Solution Description

   Typos fixed.

3.10.  CRC32c Sample Code

3.10.1.  Description of the Problem

   The CRC32c computation is described in Appendix B of [RFC4960].
   However, the corresponding sample code and its explanation appears at
   the end of Appendix C, which deals with ICMP handling.

3.10.2.  Text Changes to the Document

   Move the sample code related to CRC32c computation and its
   explanation from the end of Appendix C to the end of Appendix B.

3.10.3.  Solution Description

   Text moved to the appropriate location.

3.11.  partial_bytes_acked after T3-rtx Expiration

3.11.1.  Description of the Problem

   Section 7.2.3 of [RFC4960] explicitly states that partial_bytes_acked
   should be reset to 0 after packet loss detecting from SACK but the
   same is missed for T3-rtx timer expiration.








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3.11.2.  Text Changes to the Document

   ---------
   Old text: (Section 7.2.3)
   ---------

   When the T3-rtx timer expires on an address, SCTP should perform slow
   start by:

   ssthresh = max(cwnd/2, 4*MTU)
   cwnd = 1*MTU

   ---------
   New text: (Section 7.2.3)
   ---------

   When the T3-rtx timer expires on an address, SCTP should perform slow
   start by:

   ssthresh = max(cwnd/2, 4*MTU)
   cwnd = 1*MTU
   partial_bytes_acked = 0

3.11.3.  Solution Description

   Specify that partial_bytes_acked should be reset to 0 after T3-rtx
   timer expiration.

3.12.  Order of Adjustments of partial_bytes_acked and cwnd

3.12.1.  Description of the Problem

   Section 7.2.2 of [RFC4960] is unclear about the order of adjustments
   applied to partial_bytes_acked and cwnd in the congestion avoidance
   phase.

3.12.2.  Text Changes to the Document














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   ---------
   Old text: (Section 7.2.2)
   ---------

   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 outstanding (i.e., before arrival of the SACK, flightsize
      was greater than or equal to cwnd), increase cwnd by MTU, and
      reset partial_bytes_acked to (partial_bytes_acked - cwnd).

   ---------
   New text: (Section 7.2.2)
   ---------

   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 outstanding (i.e., before arrival of the SACK, flightsize
      was greater than or equal to cwnd), partial_bytes_acked is reset
      to (partial_bytes_acked - cwnd). Next, cwnd is increased by MTU.

3.12.3.  Solution Description

   The new text defines the exact order of adjustments of
   partial_bytes_acked and cwnd in the congestion avoidance phase.

3.13.  HEARTBEAT ACK and the association error counter

3.13.1.  Description of the Problem

   Section 8.1 and Section 8.3 of [RFC4960] prescribe that the receiver
   of a HEARTBEAT ACK must reset the association overall error counter.
   In some circumstances, e.g.  when a router discards DATA chunks but
   not HEARTBEAT chunks due to the larger size of the DATA chunk, it
   might be better to not clear the association error counter on
   reception of the HEARTBEAT ACK and reset it only on reception of the
   SACK to avoid stalling the association.

3.13.2.  Text Changes to the Document













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   ---------
   Old text: (Section 8.1)
   ---------

   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
   ACK is received from the peer endpoint.

   ---------
   New text: (Section 8.1)
   ---------

   The counter shall be reset each time a DATA chunk sent to that peer
   endpoint is acknowledged (by the reception of a SACK). When a
   HEARTBEAT ACK is received from the peer endpoint, the counter should
   also be reset. The receiver of the HEARTBEAT ACK may choose not to
   clear the counter if there is outstanding data on the association.
   This allows for handling the possible difference in reachability
   based on DATA chunks and HEARTBEAT chunks.

   ---------
   Old text: (Section 8.3)
   ---------

   Upon the receipt of the HEARTBEAT ACK, the sender of the HEARTBEAT
   should clear the error counter of the destination transport address
   to which the HEARTBEAT was sent, and mark the destination transport
   address as active if it is not so marked.  The endpoint may
   optionally report to the upper layer when an inactive destination
   address is marked as active due to the reception of the latest
   HEARTBEAT ACK.  The receiver of the HEARTBEAT ACK must also clear the
   association overall error count as well (as defined in Section 8.1).

   ---------
   New text: (Section 8.3)
   ---------

   Upon the receipt of the HEARTBEAT ACK, the sender of the HEARTBEAT
   should clear the error counter of the destination transport address
   to which the HEARTBEAT was sent, and mark the destination transport
   address as active if it is not so marked. The endpoint may
   optionally report to the upper layer when an inactive destination
   address is marked as active due to the reception of the latest
   HEARTBEAT ACK. The receiver of the HEARTBEAT ACK should also clear
   the association overall error counter (as defined in Section 8.1).






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3.13.3.  Solution Description

   The new text provides a possibility to not reset the association
   overall error counter when a HEARTBEAT ACK is received if there are
   valid reasons for it.

3.14.  Path for Fast Retransmission

3.14.1.  Description of the Problem

   [RFC4960] clearly describes where to retransmit data that is timed
   out when the peer is multi-homed but the same is not stated for fast
   retransmissions.

3.14.2.  Text Changes to the Document

   ---------
   Old text: (Section 6.4)
   ---------

   Furthermore, when its peer is multi-homed, an endpoint SHOULD try to
   retransmit a chunk that timed out to an active destination transport
   address that is different from the last destination address to which
   the DATA chunk was sent.

   ---------
   New text: (Section 6.4)
   ---------


   Furthermore, when its peer is multi-homed, an endpoint SHOULD try to
   retransmit a chunk that timed out to an active destination transport
   address that is different from the last destination address to which
   the DATA chunk was sent.

   When its peer is multi-homed, an endpoint SHOULD send fast
   retransmissions to the same destination transport address where
   original data was sent to. If the primary path has been changed and
   original data was sent there before the fast retransmit, the
   implementation MAY send it to the new primary path.

3.14.3.  Solution Description

   The new text clarifies where to send fast retransmissions.







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3.15.  Transmittal in Fast Recovery

3.15.1.  Description of the Problem

   The Fast Retransmit on Gap Reports algorithm intends that only the
   very first packet may be sent regardless of cwnd in the Fast Recovery
   phase but rule 3) of [RFC4960], Section 7.2.4, misses this
   clarification.

3.15.2.  Text Changes to the Document

   ---------
   Old text: (Section 7.2.4)
   ---------

   3)  Determine how many of the earliest (i.e., lowest TSN) DATA chunks
       marked for retransmission will fit into a single packet, subject
       to constraint of the path MTU of the destination transport
       address to which the packet is being sent.  Call this value K.
       Retransmit those K DATA chunks in a single packet.  When a Fast
       Retransmit is being performed, the sender SHOULD ignore the value
       of cwnd and SHOULD NOT delay retransmission for this single
       packet.

   ---------
   New text: (Section 7.2.4)
   ---------

   3)  If not in Fast Recovery, determine how many of the earliest
       (i.e., lowest TSN) DATA chunks marked for retransmission will fit
       into a single packet, subject to constraint of the path MTU of
       the destination transport address to which the packet is being
       sent. Call this value K. Retransmit those K DATA chunks in a
       single packet. When a Fast Retransmit is being performed, the
       sender SHOULD ignore the value of cwnd and SHOULD NOT delay
       retransmission for this single packet.

3.15.3.  Solution Description

   The new text explicitly specifies to send only the first packet in
   the Fast Recovery phase disregarding cwnd limitations.

3.16.  Initial Value of ssthresh








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3.16.1.  Description of the Problem

   The initial value of ssthresh should be set arbitrarily high.  Using
   the advertised receiver window of the peer is inappropriate if the
   peer increases its window after the handshake.  Furthermore, use a
   higher requirements level, since not following the advice may result
   in performance problems.

3.16.2.  Text Changes to the Document

   ---------
   Old text: (Section 7.2.1)
   ---------

   o  The initial value of ssthresh MAY be arbitrarily high (for
      example, implementations MAY use the size of the receiver
      advertised window).

   ---------
   New text: (Section 7.2.1)
   ---------

   o  The initial value of ssthresh SHOULD be arbitrarily high (e.g.,
      to the size of the largest possible advertised window).

3.16.3.  Solution Description

   Use the same value as suggested in [RFC5681], Section 3.1, as an
   appropriate initial value.  Furthermore use the same requirements
   level.

3.17.  Automatically Confirmed Addresses

3.17.1.  Description of the Problem

   The Path Verification procedure of [RFC4960] prescribes that any
   address passed to the sender of the INIT by its upper layer is
   automatically CONFIRMED.  This however is unclear if only addresses
   in the request to initiate association establishment are considered
   or any addresses provided by the upper layer in any requests (e.g. in
   'Set Primary').

3.17.2.  Text Changes to the Document








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   ---------
   Old text: (Section 5.4)
   ---------

   1)  Any address passed to the sender of the INIT by its upper layer
      is automatically considered to be CONFIRMED.

   ---------
   New text: (Section 5.4)
   ---------

   1)  Any addresses passed to the sender of the INIT by its upper
      layer in the request to initialize an association is
      automatically considered to be CONFIRMED.

3.17.3.  Solution Description

   The new text clarifies that only addresses provided by the upper
   layer in the request to initialize an association are automatically
   confirmed.

3.18.  Only One Packet after Retransmission Timeout

3.18.1.  Description of the Problem

   [RFC4960] is not completely clear when it describes data transmission
   after T3-rtx timer expiration.  Section 7.2.1 does not specify how
   many packets are allowed to be sent after T3-rtx timer expiration if
   more than one packet fit into cwnd.  At the same time, Section 7.2.3
   has the text without normative language saying that SCTP should
   ensure that no more than one packet will be in flight after T3-rtx
   timer expiration until successful acknowledgment.  It makes the text
   inconsistent.

3.18.2.  Text Changes to the Document
















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   ---------
   Old text: (Section 7.2.1)
   ---------

   o  The initial cwnd after a retransmission timeout MUST be no more
      than 1*MTU.

   ---------
   New text: (Section 7.2.1)
   ---------

   o  The initial cwnd after a retransmission timeout MUST be no more
      than 1*MTU and only one packet is allowed to be in flight
      until successful acknowledgement.

3.18.3.  Solution Description

   The new text clearly specifies that only one packet is allowed to be
   sent after T3-rtx timer expiration until successful acknowledgement.

3.19.  INIT ACK Path for INIT in COOKIE-WAIT State

3.19.1.  Description of the Problem

   In case of an INIT received in the COOKIE-WAIT state [RFC4960]
   prescribes to send an INIT ACK to the same destination address to
   which the original INIT has been sent.  This text does not address
   the possibility of the upper layer to provide multiple remote IP
   addresses while requesting the association establishment.  If the
   upper layer has provided multiple IP addresses and only a subset of
   these addresses are supported by the peer then the destination
   address of the original INIT may be absent in the incoming INIT and
   sending INIT ACK to that address is useless.

3.19.2.  Text Changes to the Document
















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   ---------
   Old text: (Section 5.2.1)
   ---------

   Upon receipt of an INIT in the COOKIE-WAIT state, an endpoint MUST
   respond with an INIT ACK using the same parameters it sent in its
   original INIT chunk (including its Initiate Tag, unchanged).  When
   responding, the endpoint MUST send the INIT ACK back to the same
   address that the original INIT (sent by this endpoint) was sent.

   ---------
   New text: (Section 5.2.1)
   ---------

   Upon receipt of an INIT in the COOKIE-WAIT state, an endpoint MUST
   respond with an INIT ACK using the same parameters it sent in its
   original INIT chunk (including its Initiate Tag, unchanged). When
   responding, the following rules MUST be applied:

   1)  The INIT ACK MUST only be sent to an address passed by the upper
       layer in the request to initialize the association.

   2)  The INIT ACK MUST only be sent to an address reported in the
       incoming INIT.

   3)  The INIT ACK SHOULD be sent to the source address of the
       received INIT.

3.19.3.  Solution Description

   The new text requires sending INIT ACK to the destination address
   that is passed by the upper layer and reported in the incoming INIT.
   If the source address of the INIT fulfills it then sending the INIT
   ACK to the source address of the INIT is the preferred behavior.

3.20.  Zero Window Probing and Unreachable Primary Path

3.20.1.  Description of the Problem

   Section 6.1 of [RFC4960] states that when sending zero window probes,
   SCTP should neither increment the association counter nor increment
   the destination address error counter if it continues to receive new
   packets from the peer.  But receiving new packets from the peer does
   not guarantee peer's accessibility and, if the destination address
   becomes unreachable during zero window probing, SCTP cannot get a
   changed rwnd until it switches the destination address for probes.





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3.20.2.  Text Changes to the Document

   ---------
   Old text: (Section 6.1)
   ---------

   If the sender continues to receive new packets from the receiver
   while doing zero window probing, the unacknowledged window probes
   should not increment the error counter for the association or any
   destination transport address.  This is because the receiver MAY
   keep its window closed for an indefinite time.  Refer to Section
   6.2 on the receiver behavior when it advertises a zero window.

   ---------
   New text: (Section 6.1)
   ---------

   If the sender continues to receive SACKs from the peer
   while doing zero window probing, the unacknowledged window probes
   should not increment the error counter for the association or any
   destination transport address.  This is because the receiver MAY
   keep its window closed for an indefinite time.  Refer to Section
   6.2 on the receiver behavior when it advertises a zero window.

3.20.3.  Solution Description

   The new text clarifies that if the receiver continues to send SACKs,
   the sender of probes should not increment the error counter of the
   association and the destination address even if the SACKs do not
   acknowledge the probes.

3.21.  Normative Language in Section 10

3.21.1.  Description of the Problem

   Section 10 of [RFC4960] is informative and normative language such as
   MUST and MAY cannot be used there.  However, there are several places
   in Section 10 where MUST and MAY are used.

3.21.2.  Text Changes to the Document

   ---------
   Old text: (Section 10.1)
   ---------

   E) Send

    Format: SEND(association id, buffer address, byte count [,context]



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            [,stream id] [,life time] [,destination transport address]
            [,unordered flag] [,no-bundle flag] [,payload protocol-id] )
    -> result

   ...

   o  no-bundle flag - instructs SCTP not to bundle this user data with
      other outbound DATA chunks.  SCTP MAY still bundle even when this
      flag is present, when faced with network congestion.

   ---------
   New text: (Section 10.1)
   ---------

   E) Send

    Format: SEND(association id, buffer address, byte count [,context]
            [,stream id] [,life time] [,destination transport address]
            [,unordered flag] [,no-bundle flag] [,payload protocol-id] )
    -> result

   ...

   o  no-bundle flag - instructs SCTP not to bundle this user data with
      other outbound DATA chunks.  SCTP may still bundle even when this
      flag is present, when faced with network congestion.

   ---------
   Old text: (Section 10.1)
   ---------

   G) Receive

    Format: RECEIVE(association id, buffer address, buffer size
            [,stream id])
    -> byte count [,transport address] [,stream id] [,stream sequence
       number] [,partial flag] [,delivery number] [,payload protocol-id]

   ...

   o  partial flag - if this returned flag is set to 1, then this
      Receive contains a partial delivery of the whole message.  When
      this flag is set, the stream id and Stream Sequence Number MUST
      accompany this receive.  When this flag is set to 0, it indicates
      that no more deliveries will be received for this Stream Sequence
      Number.

   ---------



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   New text: (Section 10.1)
   ---------

   G) Receive

    Format: RECEIVE(association id, buffer address, buffer size
            [,stream id])
    -> byte count [,transport address] [,stream id] [,stream sequence
       number] [,partial flag] [,delivery number] [,payload protocol-id]

   ...

   o  partial flag - if this returned flag is set to 1, then this
      Receive contains a partial delivery of the whole message.  When
      this flag is set, the stream id and Stream Sequence Number must
      accompany this receive.  When this flag is set to 0, it indicates
      that no more deliveries will be received for this Stream Sequence
      Number.

   ---------
   Old text: (Section 10.1)
   ---------

   N) Receive Unsent Message

      Format: RECEIVE_UNSENT(data retrieval id, buffer address, buffer
              size [,stream id] [, stream sequence number] [,partial
              flag] [,payload protocol-id])

   ...

   o  partial flag - if this returned flag is set to 1, then this
      message is a partial delivery of the whole message.  When this
      flag is set, the stream id and Stream Sequence Number MUST
      accompany this receive.  When this flag is set to 0, it indicates
      that no more deliveries will be received for this Stream Sequence
      Number.

   ---------
   New text: (Section 10.1)
   ---------

   N) Receive Unsent Message

      Format: RECEIVE_UNSENT(data retrieval id, buffer address, buffer
              size [,stream id] [, stream sequence number] [,partial
              flag] [,payload protocol-id])




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   ...

   o  partial flag - if this returned flag is set to 1, then this
      message is a partial delivery of the whole message.  When this
      flag is set, the stream id and Stream Sequence Number must
      accompany this receive.  When this flag is set to 0, it indicates
      that no more deliveries will be received for this Stream Sequence
      Number.

   ---------
   Old text: (Section 10.1)
   ---------

   O) Receive Unacknowledged Message

      Format: RECEIVE_UNACKED(data retrieval id, buffer address, buffer
              size, [,stream id] [, stream sequence number] [,partial
              flag] [,payload protocol-id])

   ...

   o  partial flag - if this returned flag is set to 1, then this
      message is a partial delivery of the whole message.  When this
      flag is set, the stream id and Stream Sequence Number MUST
      accompany this receive.  When this flag is set to 0, it indicates
      that no more deliveries will be received for this Stream Sequence
      Number.

   ---------
   New text: (Section 10.1)
   ---------

   O) Receive Unacknowledged Message

      Format: RECEIVE_UNACKED(data retrieval id, buffer address, buffer
              size, [,stream id] [, stream sequence number] [,partial
              flag] [,payload protocol-id])

   ...

   o  partial flag - if this returned flag is set to 1, then this
      message is a partial delivery of the whole message.  When this
      flag is set, the stream id and Stream Sequence Number must
      accompany this receive.  When this flag is set to 0, it indicates
      that no more deliveries will be received for this Stream Sequence
      Number.





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3.21.3.  Solution Description

   The normative language is removed from Section 10.

3.22.  Increase of partial_bytes_acked in Congestion Avoidance

3.22.1.  Description of the Problem

   Two issues have been discovered with the partial_bytes_acked handling
   described in Section 7.2.2 of [RFC4960]:

   o  If the Cumulative TSN Ack Point is not advanced but the SACK chunk
      acknowledges new TSNs in the Gap Ack Blocks, these newly
      acknowledged TSNs are not considered for partial_bytes_acked
      although these TSNs were successfully received by the peer.
   o  Duplicate TSNs are not considered in partial_bytes_acked although
      they confirm that the DATA chunks were successfully received by
      the peer.

3.22.2.  Text Changes to the Document

   ---------
   Old text: (Section 7.2.2)
   ---------

   o  Whenever cwnd is greater than ssthresh, upon each SACK arrival
      that advances the Cumulative TSN Ack Point, increase
      partial_bytes_acked by the total number of bytes of all new chunks
      acknowledged in that SACK including chunks acknowledged by the new
      Cumulative TSN Ack and by Gap Ack Blocks.

   ---------
   New text: (Section 7.2.2)
   ---------

   o  Whenever cwnd is greater than ssthresh, upon each SACK arrival,
      increase partial_bytes_acked by the total number of bytes of all
      new chunks acknowledged in that SACK including chunks acknowledged
      by the new Cumulative TSN Ack, by Gap Ack Blocks and by the number
      of bytes of duplicated chunks reported in Duplicate TSNs.

3.22.3.  Solution Description

   Now partial_bytes_acked is increased by TSNs reported as duplicated
   as well as TSNs newly acknowledged in Gap Ack Blocks even if the
   Cumulative TSN Ack Point is not advanced.





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3.23.  Inconsistency in Notifications Handling

3.23.1.  Description of the Problem

   [RFC4960] uses inconsistent normative and non-normative language when
   describing rules for sending notifications to the upper layer.  E.g.
   Section 8.2 of [RFC4960] says that when a destination address becomes
   inactive due to an unacknowledged DATA chunk or HEARTBEAT chunk, SCTP
   SHOULD send a notification to the upper layer while Section 8.3 of
   [RFC4960] says that when a destination address becomes inactive due
   to an unacknowledged HEARTBEAT chunk, SCTP may send a notification to
   the upper layer.

   This makes the text inconsistent.

3.23.2.  Text Changes to the Document

   The following cahnge is based on the change described in Section 3.6.

































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   ---------
   Old text: (Section 8.1)
   ---------

   An endpoint shall keep a counter on the total number of consecutive
   retransmissions to its peer (this includes data retransmissions
   to all the destination transport addresses of the peer if it is
   multi-homed), including the number of unacknowledged HEARTBEAT
   chunks observed on the path which currently is used for data
   transfer. Unacknowledged HEARTBEAT chunks observed on paths
   different from the path currently used for data transfer shall
   not increment the association error counter, as this could lead
   to association closure even if the path which currently is used for
   data transfer is available (but idle). If the value of this
   counter exceeds the limit indicated in the protocol parameter
   'Association.Max.Retrans', the endpoint shall consider the peer
   endpoint unreachable and shall stop transmitting any more data to it
   (and thus the association enters the CLOSED state).  In addition, the
   endpoint MAY report the failure to the upper layer and optionally
   report back all outstanding user data remaining in its outbound
   queue.  The association is automatically closed when the peer
   endpoint becomes unreachable.

   ---------
   New text: (Section 8.1)
   ---------

   An endpoint shall keep a counter on the total number of consecutive
   retransmissions to its peer (this includes data retransmissions
   to all the destination transport addresses of the peer if it is
   multi-homed), including the number of unacknowledged HEARTBEAT
   chunks observed on the path which currently is used for data
   transfer. Unacknowledged HEARTBEAT chunks observed on paths
   different from the path currently used for data transfer shall
   not increment the association error counter, as this could lead
   to association closure even if the path which currently is used for
   data transfer is available (but idle). If the value of this
   counter exceeds the limit indicated in the protocol parameter
   'Association.Max.Retrans', the endpoint shall consider the peer
   endpoint unreachable and shall stop transmitting any more data to it
   (and thus the association enters the CLOSED state).  In addition, the
   endpoint SHOULD report the failure to the upper layer and optionally
   report back all outstanding user data remaining in its outbound
   queue.  The association is automatically closed when the peer
   endpoint becomes unreachable.

   The following changes are based on [RFC4960].




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   ---------
   Old text: (Section 8.2)
   ---------

   When an outstanding TSN is acknowledged or a HEARTBEAT sent to that
   address is acknowledged with a HEARTBEAT ACK, the endpoint shall
   clear the error counter of the destination transport address to which
   the DATA chunk was last sent (or HEARTBEAT was sent).  When the peer
   endpoint is multi-homed and the last chunk sent to it was a
   retransmission to an alternate address, there exists an ambiguity as
   to whether or not the acknowledgement should be credited to the
   address of the last chunk sent.  However, this ambiguity does not
   seem to bear any significant consequence to SCTP behavior.  If this
   ambiguity is undesirable, the transmitter may choose not to clear the
   error counter if the last chunk sent was a retransmission.

   ---------
   New text: (Section 8.2)
   ---------

   When an outstanding TSN is acknowledged or a HEARTBEAT sent to that
   address is acknowledged with a HEARTBEAT ACK, the endpoint shall
   clear the error counter of the destination transport address to which
   the DATA chunk was last sent (or HEARTBEAT was sent), and SHOULD
   also report to the upper layer when an inactive destination address
   is marked as active. When the peer endpoint is multi-homed and the
   last chunk sent to it was a retransmission to an alternate address,
   there exists an ambiguity as to whether or not the acknowledgement
   should be credited to the address of the last chunk sent. However,
   this ambiguity does not seem to bear any significant consequence to
   SCTP behavior. If this ambiguity is undesirable, the transmitter may
   choose not to clear the error counter if the last chunk sent was a
   retransmission.

   ---------
   Old text: (Section 8.3)
   ---------

   When the value of this counter reaches the protocol parameter
   'Path.Max.Retrans', the endpoint should mark the corresponding
   destination address as inactive if it is not so marked, and may also
   optionally report to the upper layer the change of reachability of
   this destination address.  After this, the endpoint should continue
   HEARTBEAT on this destination address but should stop increasing the
   counter.

   ---------
   New text: (Section 8.3)



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   ---------

   When the value of this counter exceeds the protocol parameter
   'Path.Max.Retrans', the endpoint should mark the corresponding
   destination address as inactive if it is not so marked, and SHOULD
   also report to the upper layer the change of reachability of this
   destination address.  After this, the endpoint should continue
   HEARTBEAT on this destination address but should stop increasing the
   counter.

   ---------
   Old text: (Section 8.3)
   ---------

   Upon the receipt of the HEARTBEAT ACK, the sender of the HEARTBEAT
   should clear the error counter of the destination transport address
   to which the HEARTBEAT was sent, and mark the destination transport
   address as active if it is not so marked.  The endpoint may
   optionally report to the upper layer when an inactive destination
   address is marked as active due to the reception of the latest
   HEARTBEAT ACK.  The receiver of the HEARTBEAT ACK must also clear the
   association overall error count as well (as defined in Section 8.1).

   ---------
   New text: (Section 8.3)
   ---------

   Upon the receipt of the HEARTBEAT ACK, the sender of the HEARTBEAT
   should clear the error counter of the destination transport address
   to which the HEARTBEAT was sent, and mark the destination transport
   address as active if it is not so marked. The endpoint SHOULD
   report to the upper layer when an inactive destination address
   is marked as active due to the reception of the latest
   HEARTBEAT ACK. The receiver of the HEARTBEAT ACK should also clear
   the association overall error counter (as defined in Section 8.1).

   ---------
   Old text: (Section 9.2)
   ---------

   An endpoint should limit the number of retransmissions of the
   SHUTDOWN chunk to the protocol parameter 'Association.Max.Retrans'.
   If this threshold is exceeded, the endpoint should destroy the TCB
   and MUST report the peer endpoint unreachable to the upper layer (and
   thus the association enters the CLOSED state).

   ---------
   New text: (Section 9.2)



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   ---------

   An endpoint should limit the number of retransmissions of the
   SHUTDOWN chunk to the protocol parameter 'Association.Max.Retrans'.
   If this threshold is exceeded, the endpoint should destroy the TCB
   and SHOULD report the peer endpoint unreachable to the upper layer
   (and thus the association enters the CLOSED state).

   ---------
   Old text: (Section 9.2)
   ---------

   The sender of the SHUTDOWN ACK should limit the number of
   retransmissions of the SHUTDOWN ACK chunk to the protocol parameter
   'Association.Max.Retrans'.  If this threshold is exceeded, the
   endpoint should destroy the TCB and may report the peer endpoint
   unreachable to the upper layer (and thus the association enters the
   CLOSED state).

   ---------
   New text: (Section 9.2)
   ---------

   The sender of the SHUTDOWN ACK should limit the number of
   retransmissions of the SHUTDOWN ACK chunk to the protocol parameter
   'Association.Max.Retrans'. If this threshold is exceeded, the
   endpoint should destroy the TCB and SHOULD report the peer endpoint
   unreachable to the upper layer (and thus the association enters the
   CLOSED state).

3.23.3.  Solution Description

   The inconsistencies are removed by using consistently SHOULD.

3.24.  SACK.Delay Not Listed as a Protocol Parameter

3.24.1.  Description of the Problem

   SCTP as specified in [RFC4960] supports delaying SACKs.  The timer
   value for this is a parameter and Section 6.2 of [RFC4960] specifies
   a default and maximum value for it.  However, defining a name for
   this parameter and listing it in the table of protocol parameters in
   Section 15 of [RFC4960] is missing.

   This issue was reported as an Errata for [RFC4960] with Errata ID
   4656.





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3.24.2.  Text Changes to the Document

   ---------
   Old text: (Section 6.2)
   ---------

   An implementation MUST NOT allow the maximum delay to be configured
   to be more than 500 ms.  In other words, an implementation MAY lower
   this value below 500 ms but MUST NOT raise it above 500 ms.

   ---------
   New text: (Section 6.2)
   ---------

   An implementation MUST NOT allow the maximum delay (protocol
   parameter 'SACK.Delay') to be configured to be more than 500 ms.
   In other words, an implementation MAY lower the value of
   SACK.Delay below 500 ms but MUST NOT raise it above 500 ms.

   ---------
   Old text: (Section 15)
   ---------

   The following protocol parameters are RECOMMENDED:

      RTO.Initial - 3 seconds
      RTO.Min - 1 second
      RTO.Max - 60 seconds
      Max.Burst - 4
      RTO.Alpha - 1/8
      RTO.Beta - 1/4
      Valid.Cookie.Life - 60 seconds
      Association.Max.Retrans - 10 attempts
      Path.Max.Retrans - 5 attempts (per destination address)
      Max.Init.Retransmits - 8 attempts
      HB.interval - 30 seconds
      HB.Max.Burst - 1

   ---------
   New text: (Section 15)
   ---------

   The following protocol parameters are RECOMMENDED:

      RTO.Initial - 3 seconds
      RTO.Min - 1 second
      RTO.Max - 60 seconds
      Max.Burst - 4



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      RTO.Alpha - 1/8
      RTO.Beta - 1/4
      Valid.Cookie.Life - 60 seconds
      Association.Max.Retrans - 10 attempts
      Path.Max.Retrans - 5 attempts (per destination address)
      Max.Init.Retransmits - 8 attempts
      HB.interval - 30 seconds
      HB.Max.Burst - 1
      SACK.Delay - 200 milliseconds

3.24.3.  Solution Description

   The parameter was given a name and added to the list of protocol
   parameters.

3.25.  Processing of Chunks in an Incoming SCTP Packet

3.25.1.  Description of the Problem

   There are a few places in [RFC4960] where the receiver of a packet
   must discard it while processing the chunks of the packet.  It is
   unclear whether the receiver has to rollback state changes already
   performed while processing the packet or not.

   The intention of [RFC4960] is to process an incoming packet chunk by
   chunk and do not perform any prescreening of chunks in the received
   packet so the receiver must only discard a chunk causing discard and
   all further chunks.

3.25.2.  Text Changes to the Document

   ---------
   Old text: (Section 3.2)
   ---------

   00 -  Stop processing this SCTP packet and discard it, do not
         process any further chunks within it.

   01 -  Stop processing this SCTP packet and discard it, do not
         process any further chunks within it, and report the
         unrecognized chunk in an 'Unrecognized Chunk Type'.

   ---------
   New text: (Section 3.2)
   ---------

   00 -  Stop processing this SCTP packet, discard the unrecognized
         chunk and all further chunks.



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   01 -  Stop processing this SCTP packet, discard the unrecognized
         chunk and all further chunks, and report the unrecognized
         chunk in an 'Unrecognized Chunk Type'.

   ---------
   Old text: (Section 11.3)
   ---------

   It is helpful for some firewalls if they can inspect just the first
   fragment of a fragmented SCTP packet and unambiguously determine
   whether it corresponds to an INIT chunk (for further information,
   please refer to [RFC1858]).  Accordingly, we stress the requirements,
   stated in Section 3.1, that (1) an INIT chunk MUST NOT be bundled
   with any other chunk in a packet, and (2) a packet containing an INIT
   chunk MUST have a zero Verification Tag.  Furthermore, we require
   that the receiver of an INIT chunk MUST enforce these rules by
   silently discarding an arriving packet  with an INIT chunk that is
   bundled with other chunks or has a non-zero verification tag and
   contains an INIT-chunk.

   ---------
   New text: (Section 11.3)
   ---------

   It is helpful for some firewalls if they can inspect just the first
   fragment of a fragmented SCTP packet and unambiguously determine
   whether it corresponds to an INIT chunk (for further information,
   please refer to [RFC1858]).  Accordingly, we stress the requirements,
   stated in Section 3.1, that (1) an INIT chunk MUST NOT be bundled
   with any other chunk in a packet, and (2) a packet containing an INIT
   chunk MUST have a zero Verification Tag.  Furthermore, we require
   that the receiver of an INIT chunk MUST enforce these rules by
   silently discarding the INIT chunk and all further chunks if the INIT
   chunk is bundled with other chunks or the packet has a non-zero
   verification tag.

3.25.3.  Solution Description

   The new text makes it clear that chunks can be processed from the
   beginning to the end and no rollback or pre-screening is required.

3.26.  CWND Increase in Congestion Avoidance Phase

3.26.1.  Description of the Problem

   [RFC4960] in Section 7.2.2 prescribes to increase cwnd by 1*MTU per
   RTT if the sender has cwnd or more bytes of outstanding data to the
   corresponding address in the Congestion Avoidance phase.  However,



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   this is described without normative language.  Moreover,
   Section 7.2.2 includes an algorithm how an implementation can achieve
   it but this algorithm is underspecified and actually allows
   increasing cwnd by more than 1*MTU per RTT.

3.26.2.  Text Changes to the Document

   ---------
   Old text: (Section 7.2.2)
   ---------

   When cwnd is greater than ssthresh, cwnd should be incremented by
   1*MTU per RTT if the sender has cwnd or more bytes of data
   outstanding for the corresponding transport address.

   ---------
   New text: (Section 7.2.2)
   ---------

   When cwnd is greater than ssthresh, cwnd should be incremented by
   1*MTU per RTT if the sender has cwnd or more bytes of data
   outstanding for the corresponding transport address. The basic
   guidelines for incrementing cwnd during congestion avoidance are:

   o  SCTP MAY increment cwnd by 1*MTU.

   o  SCTP SHOULD increment cwnd by one 1*MTU once per RTT when
      the sender has cwnd or more bytes of data outstanding for
      the corresponding transport address.

   o  SCTP MUST NOT increment cwnd by more than 1*MTU per RTT.

   ---------
   Old text: (Section 7.2.2)
   ---------

   o  Whenever cwnd is greater than ssthresh, upon each SACK arrival
      that advances the Cumulative TSN Ack Point, increase
      partial_bytes_acked by the total number of bytes of all new chunks
      acknowledged in that SACK including chunks acknowledged by the new
      Cumulative TSN Ack and by Gap Ack Blocks.

   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 outstanding (i.e., before arrival of the SACK, flightsize
      was greater than or equal to cwnd), increase cwnd by MTU, and
      reset partial_bytes_acked to (partial_bytes_acked - cwnd).




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   ---------
   New text: (Section 7.2.2)
   ---------

   o  Whenever cwnd is greater than ssthresh, upon each SACK arrival,
      increase partial_bytes_acked by the total number of bytes of all
      new chunks acknowledged in that SACK including chunks acknowledged
      by the new Cumulative TSN Ack, by Gap Ack Blocks and by the number
      of bytes of duplicated chunks reported in Duplicate TSNs.

   o  When partial_bytes_acked is greater than cwnd and before the
      arrival of the SACK the sender had less bytes of data outstanding
      than cwnd (i.e., before arrival of the SACK, flightsize was less
      than cwnd), reset partial_bytes_acked to cwnd.

   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 outstanding (i.e., before arrival of the SACK, flightsize
      was greater than or equal to cwnd), partial_bytes_acked is reset
      to (partial_bytes_acked - cwnd). Next, cwnd is increased by MTU.

3.26.3.  Solution Description

   The basic guidelines for incrementing cwnd during congestion
   avoidance phase are added into Section 7.2.2.  The guidelines include
   the normative language and are aligned with [RFC5681].

   The algorithm from Section 7.2.2 is improved to not allow increasing
   cwnd by more than 1*MTU per RTT.

3.27.  Refresh of cwnd and ssthresh after Idle Period

3.27.1.  Description of the Problem

   [RFC4960] prescribes to adjust cwnd per RTO if the endpoint does not
   transmit data on a given transport address.  In addition to that, it
   prescribes to set cwnd to the initial value after a sufficiently long
   idle period.  The latter is excessive.  Moreover, it is unclear what
   is a sufficiently long idle period.

   [RFC4960] doesn't specify the handling of ssthresh in the idle case.
   If ssthres is reduced due to a packet loss, ssthresh is never
   recovered.  So traffic can end up in Congestion Avoidance all the
   time, resulting in a low sending rate and bad performance.  The
   problem is even more serious for SCTP because in a multi-homed SCTP
   association traffic switch back to the previously failed primary path
   will also lead to the situation where traffic ends up in Congestion
   Avoidance.



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3.27.2.  Text Changes to the Document

   ---------
   Old text: (Section 7.2.1)
   ---------

   o  The initial cwnd before DATA transmission or after a sufficiently
      long idle period MUST be set to min(4*MTU, max (2*MTU, 4380
      bytes)).

   ---------
   New text: (Section 7.2.1)
   ---------

   o  The initial cwnd before DATA transmission MUST be set to
      min(4*MTU, max (2*MTU, 4380 bytes)).

   ---------
   Old text: (Section 7.2.1)
   ---------

   o  When the endpoint does not transmit data on a given transport
      address, the cwnd of the transport address should be adjusted to
      max(cwnd/2, 4*MTU) per RTO.

   ---------
   New text: (Section 7.2.1)
   ---------
   o  When the endpoint does not transmit data on a given transport
      address, the cwnd of the transport address should be adjusted to
      max(cwnd/2, 4*MTU) per RTO. At the first cwnd adjustment, the
      ssthresh of the transport address should be adjusted to the cwnd.

3.27.3.  Solution Description

   A rule about cwnd adjustment after a sufficiently long idle period is
   removed.

   The text is updated to refresh ssthresh after the idle period.  When
   the idle period is detected, the cwnd value is stored to the ssthresh
   value.

3.28.  Window Updates After Receiver Window Opens Up








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3.28.1.  Description of the Problem

   The sending of SACK chunks for window updates is only indirectly
   referenced in [RFC4960], Section 6.2, where it is stated that an SCTP
   receiver must not generate more than one SACK for every incoming
   packet, other than to update the offered window.

   However, the sending of window updates when the receiver window opens
   up is necessary to avoid performance problems.

3.28.2.  Text Changes to the Document

   ---------
   Old text: (Section 6.2)
   ---------

   An SCTP receiver MUST NOT generate more than one SACK for every
   incoming packet, other than to update the offered window as the
   receiving application consumes new data.

   ---------
   New text: (Section 6.2)
   ---------

   An SCTP receiver MUST NOT generate more than one SACK for every
   incoming packet, other than to update the offered window as the
   receiving application consumes new data. When the window opens
   up, an SCTP receiver SHOULD send additional SACK chunks to update
   the window even if no new data is received. The receiver MUST avoid
   sending large burst of window updates.



3.28.3.  Solution Description

   The new text makes clear that additional SACK chunks for window
   updates may be sent as long as excessive bursts are avoided.

3.29.  Path of DATA and Reply Chunks

3.29.1.  Description of the Problem

   Section 6.4 of [RFC4960] describes the transmission policy for multi-
   homed SCTP endpoints.  However, there are the following issues with
   it:

   o  It states that a SACK should be sent to the source address of an
      incoming DATA.  However, it is known that other SACK policies



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      (e.g. sending SACKs always to the primary path) may be more
      beneficial in some situations.
   o  Initially it states that an endpoint should always transmit DATA
      chunks to the primary path.  Then it states that the rule for
      transmittal of reply chunks should also be followed if the
      endpoint is bundling DATA chunks together with the reply chunk
      which contradicts with the first statement to always transmit DATA
      chunks to the primary path.  Some implementations were having
      problems with it and sent DATA chunks bundled with reply chunks to
      a different destination address than the primary path that caused
      many gaps.

3.29.2.  Text Changes to the Document

---------
Old text: (Section 6.4)
---------

An endpoint SHOULD transmit reply chunks (e.g., SACK, HEARTBEAT ACK,
etc.) to the same destination transport address from which it
received the DATA or control chunk to which it is replying.  This
rule should also be followed if the endpoint is bundling DATA chunks
together with the reply chunk.

However, when acknowledging multiple DATA chunks received in packets
from different source addresses in a single SACK, the SACK chunk may
be transmitted to one of the destination transport addresses from
which the DATA or control chunks being acknowledged were received.

---------
New text: (Section 6.4)
---------

An endpoint SHOULD transmit reply chunks (e.g., INIT ACK, COOKIE ACK,
HEARTBEAT ACK, etc.) in response to control chunks to the same
destination transport address from which it received the control
chunk to which it is replying.

The selection of the destination transport address for packets containing
SACK chunks is implementation dependent. However, an endpoint SHOULD NOT vary
the destination transport address of a SACK when it receives DATA chunks
from the same source address.

When acknowledging multiple DATA chunks received in packets
from different source addresses in a single SACK, the SACK chunk MAY
be transmitted to one of the destination transport addresses from
which the DATA or control chunks being acknowledged were received.




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3.29.3.  Solution Description

   The SACK transmission policy is left implementation dependent but it
   is specified to not vary the destination address of a packet
   containing a SACK chunk unless there are reasons for it as it may
   negatively impact RTT measurement.

   A confusing statement that prescribes to follow the rule for
   transmittal of reply chunks when the endpoint is bundling DATA chunks
   together with the reply chunk is removed.

4.  IANA Considerations

   This document does not require any actions from IANA.

5.  Security Considerations

   This document does not add any security considerations to those given
   in [RFC4960].

6.  Acknowledgments

   The authors wish to thank Pontus Andersson, Eric W.  Biederman,
   Cedric Bonnet, Lionel Morand, Jeff Morriss, Karen E.  E.  Nielsen,
   Tom Petch and Julien Pourtet for their invaluable comments.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              RFC 4960, DOI 10.17487/RFC4960, September 2007,
              <http://www.rfc-editor.org/info/rfc4960>.

7.2.  Informative References

   [RFC2960]  Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
              Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
              Zhang, L., and V. Paxson, "Stream Control Transmission
              Protocol", RFC 2960, DOI 10.17487/RFC2960, October 2000,
              <http://www.rfc-editor.org/info/rfc2960>.





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   [RFC4460]  Stewart, R., Arias-Rodriguez, I., Poon, K., Caro, A., and
              M. Tuexen, "Stream Control Transmission Protocol (SCTP)
              Specification Errata and Issues", RFC 4460,
              DOI 10.17487/RFC4460, April 2006,
              <http://www.rfc-editor.org/info/rfc4460>.

   [RFC5681]  Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
              Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
              <http://www.rfc-editor.org/info/rfc5681>.

Authors' Addresses

   Randall R. Stewart
   Netflix, Inc.
   Chapin, SC  29036
   United States

   Email: randall@lakerest.net


   Michael Tuexen
   Muenster University of Applied Sciences
   Stegerwaldstrasse 39
   48565 Steinfurt
   Germany

   Email: tuexen@fh-muenster.de


   Maksim Proshin
   Ericsson
   Kistavaegen 25
   Stockholm  164 80
   Sweden

   Email: mproshin@tieto.mera.ru















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