draft-ietf-rohc-sigcomp-sip-08.txt   rfc5049.txt 
Robust Header Compression C. Bormann Network Working Group C. Bormann
Internet-Draft Universitaet Bremen TZI Request for Comments: 5049 Universitaet Bremen TZI
Intended status: Standards Track Z. Liu Category: Standards Track Z. Liu
Expires: March 19, 2008 Nokia Research Center Nokia Research Center
R. Price R. Price
EADS Defence and Security Systems EADS Defence and Security Systems Limited
Limited
G. Camarillo, Ed. G. Camarillo, Ed.
Ericsson Ericsson
September 20, 2007 December 2007
Applying Signaling Compression (SigComp) to the Session Initiation
Protocol (SIP)
draft-ietf-rohc-sigcomp-sip-08.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on March 19, 2008. Applying Signaling Compression (SigComp)
to the Session Initiation Protocol (SIP)
Copyright Notice Status of This Memo
Copyright (C) The IETF Trust (2007). This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract Abstract
This document describes some specifics that apply when Signaling This document describes some specifics that apply when Signaling
Compression (SigComp) is applied to the Session Initiation Protocol Compression (SigComp) is applied to the Session Initiation Protocol
(SIP), such as default minimum values of SigComp parameters, (SIP), such as default minimum values of SigComp parameters,
compartment and state management, and a few issues on SigComp over compartment and state management, and a few issues on SigComp over
TCP. Any implementation of SigComp for use with SIP must conform to TCP. Any implementation of SigComp for use with SIP must conform to
this document and SigComp, and in addition support the SIP and this document and SigComp, and in addition, support the SIP and
Session Description Protocol (SDP) static dictionary. Session Description Protocol (SDP) static dictionary.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology .....................................................3
3. Compliance with this Specification . . . . . . . . . . . . . . 3 3. Compliance with This Specification ..............................3
4. Minimum Values of SigComp Parameters for SIP/SigComp . . . . . 3 4. Minimum Values of SigComp Parameters for SIP/SigComp ............3
4.1. decompression_memory_size (DMS) for SIP/SigComp . . . . . 4 4.1. decompression_memory_size (DMS) for SIP/SigComp ............4
4.2. state_memory_size (SMS) for SIP/SigComp . . . . . . . . . 4 4.2. state_memory_size (SMS) for SIP/SigComp ....................4
4.3. cycles_per_bit (CPB) for SIP/SigComp . . . . . . . . . . . 5 4.3. cycles_per_bit (CPB) for SIP/SigComp .......................5
4.4. SigComp_version (SV) for SIP/SigComp . . . . . . . . . . . 5 4.4. SigComp_version (SV) for SIP/SigComp .......................5
4.5. locally available state (LAS) for SIP/SigComp . . . . . . 5 4.5. locally available state (LAS) for SIP/SigComp ..............5
5. Delimiting SIP Messages and SigComp Messages on the Same 5. Delimiting SIP Messages and SigComp Messages on the Same Port ...5
Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Continuous Mode over TCP ........................................6
6. Continuous Mode over TCP . . . . . . . . . . . . . . . . . . . 6 7. Too-Large SIP Messages ..........................................7
7. Too Large SIP Messages . . . . . . . . . . . . . . . . . . . . 7 8. SIP Retransmissions .............................................7
8. SIP Retransmissions . . . . . . . . . . . . . . . . . . . . . 7 9. Compartment and State Management for SIP/SigComp ................7
9. Compartment and State Management for SIP/SigComp . . . . . . . 7 9.1. Remote Application Identification ..........................8
9.1. Remote Application Identification . . . . . . . . . . . . 8 9.2. Identifier Comparison Rules ...............................10
9.2. Identifier Comparison Rules . . . . . . . . . . . . . . . 10 9.3. Compartment Opening and Closure ...........................11
9.3. Compartment Opening and Closure . . . . . . . . . . . . . 11 9.4. Lack of a Compartment .....................................13
9.4. Lack of a Compartment . . . . . . . . . . . . . . . . . . 13 10. Recommendations for Network Administrators ....................13
10. Recommendations for Network Administrators . . . . . . . . . . 13 11. Private Agreements ............................................14
11. Private Agreements . . . . . . . . . . . . . . . . . . . . . . 14 12. Backwards Compatibility .......................................14
12. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 14 13. Interactions with Transport Layer Security (TLS) ..............14
13. Interactions with TLS . . . . . . . . . . . . . . . . . . . . 14 14. Example .......................................................15
14. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 15. Security Considerations .......................................17
15. Security Considerations . . . . . . . . . . . . . . . . . . . 17 16. IANA Considerations ...........................................17
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 17. Acknowledgements ..............................................17
17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 18. References ....................................................18
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 18.1. Normative References .....................................18
18.1. Normative References . . . . . . . . . . . . . . . . . . . 18 18.2. Informative References ...................................19
18.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . . . 21
1. Introduction 1. Introduction
SigComp [RFC3320] is a solution for compressing messages generated by SigComp [RFC3320] is a solution for compressing messages generated by
application protocols. Although its primary driver is to compress application protocols. Although its primary driver is to compress
SIP [RFC3261] messages, the solution itself has been intentionally SIP [RFC3261] messages, the solution itself has been intentionally
designed to be application agnostic so that it can be applied to any designed to be application agnostic so that it can be applied to any
application protocol; this is denoted as ANY/SigComp. Consequently, application protocol; this is denoted as ANY/SigComp. Consequently,
many application dependent specifics are left out of the base many application-dependent specifics are left out of the base
standard. It is intended that a separate specification is used to standard. It is intended that a separate specification be used to
describe those specifics when SigComp is applied to a particular describe those specifics when SigComp is applied to a particular
application protocol. application protocol.
This document binds SigComp and SIP; this is denoted as SIP/SigComp. This document binds SigComp and SIP; this is denoted as SIP/SigComp.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
3. Compliance with this Specification 3. Compliance with This Specification
Any SigComp implementation that is used for the compression of SIP Any SigComp implementation that is used for the compression of SIP
messages MUST conform to this document, as well as to [RFC3320]. messages MUST conform to this document, as well as to [RFC3320].
Additionally, it must support the SIP/SDP static dictionary, as Additionally, it must support the SIP/SDP static dictionary, as
specified in [RFC3485], and the mechanism for discovering SigComp specified in [RFC3485], and the mechanism for discovering SigComp
support at the SIP layer, as specified in [RFC3486]. support at the SIP layer, as specified in [RFC3486].
4. Minimum Values of SigComp Parameters for SIP/SigComp 4. Minimum Values of SigComp Parameters for SIP/SigComp
In order to support a wide range of capabilities among endpoints In order to support a wide range of capabilities among endpoints
implementing SigComp, SigComp defines a few parameters to describe implementing SigComp, SigComp defines a few parameters to describe
SigComp behavior (see section 3.3 of [RFC3320]). For each parameter, SigComp behavior (see Section 3.3 of [RFC3320]). For each parameter,
[RFC3320] specifies a minimum value that any SigComp endpoint MUST [RFC3320] specifies a minimum value that any SigComp endpoint MUST
support for ANY/SigComp. Those minimum values were determined with support for ANY/SigComp. Those minimum values were determined with
the consideration of all imaginable devices in which SigComp may be the consideration of all imaginable devices in which SigComp may be
implemented. Scalability was also considered as a key factor. implemented. Scalability was also considered as a key factor.
However, some of the minimum values specified in [RFC3320] are too However, some of the minimum values specified in [RFC3320] are too
small to allow good performance for SIP message compression. small to allow good performance for SIP message compression.
Therefore, they are increased for SIP/SigComp as specified in the Therefore, they are increased for SIP/SigComp as specified in the
following sections. For completeness, those parameters that are the following sections. For completeness, those parameters that are the
same for SIP/SigComp as they are for ANY/SigComp are also listed. same for SIP/SigComp as they are for ANY/SigComp are also listed.
The new minimum values are specific to SIP/SigComp and, thus, do not The new minimum values are specific to SIP/SigComp and, thus, do not
apply to any other application protocols. A SIP/SigComp endpoint MAY apply to any other application protocols. A SIP/SigComp endpoint MAY
offer additional resources over and above the minimum values offer additional resources over and above the minimum values
specified in this document if available; these resources can be specified in this document if available; these resources can be
advertised to remote endpoints as described in section 9.4.9 of advertised to remote endpoints as described in Section 9.4.9 of
[RFC3320]. [RFC3320].
4.1. decompression_memory_size (DMS) for SIP/SigComp 4.1. decompression_memory_size (DMS) for SIP/SigComp
Minimum value for ANY/SigComp: 2048 bytes, as specified in section Minimum value for ANY/SigComp: 2048 bytes, as specified in Section
3.3.1 of [RFC3320]. 3.3.1 of [RFC3320].
Minimum value for SIP/SigComp: 8192 bytes. Minimum value for SIP/SigComp: 8192 bytes.
Reason: a DMS of 2048 bytes is too small for SIP message compression Reason: a DMS of 2048 bytes is too small for SIP message compression
as it seriously limits the compression ratio and even makes as it seriously limits the compression ratio and even makes
compression impossible for certain messages. For example, the compression impossible for certain messages. For example, the
condition set by [RFC3320] for SigComp over UDP means: C + 2*B + R + condition set by [RFC3320] for SigComp over UDP means: C + 2*B + R +
2*S + 128 < DMS (each term is described below). Therefore, if DMs is 2*S + 128 < DMS (each term is described below). Therefore, if DMS is
too small, at least one of C, B, R, or S will be severely restricted. too small, at least one of C, B, R, or S will be severely restricted.
On the other hand, DMS is memory that is only temporarily needed On the other hand, DMS is memory that is only temporarily needed
during decompression of a SigComp message (the memory can be during decompression of a SigComp message (the memory can be
reclaimed when the message has been decompressed). Therefore, a reclaimed when the message has been decompressed). Therefore, a
requirement of 8 KB should not cause any problem for an endpoint that requirement of 8 KB should not cause any problems for an endpoint
already implements SIP, SigComp, and applications that use SIP. that already implements SIP, SigComp, and applications that use SIP.
C size of compressed application message, depending on R C size of compressed application message, depending on R
B size of bytecode. Note: two copies -- one as part of the SigComp B size of bytecode. Note: two copies -- one as part of the
message and one in UDVM (Universal Decompressor Virtual Machine) SigComp message and one in UDVM (Universal Decompressor Virtual
memory. Machine) memory.
R size of circular buffer in UDVM memory R size of circular buffer in UDVM memory
S any additional state uploaded other than that created from the S any additional state uploaded other than that created from the
content of the circular buffer at the end of decompression content of the circular buffer at the end of decompression
(similar to B, two copies of S are needed) (similar to B, two copies of S are needed)
128 the smallest address in UDVM memory to copy bytecode to 128 the smallest address in UDVM memory to copy bytecode to
4.2. state_memory_size (SMS) for SIP/SigComp 4.2. state_memory_size (SMS) for SIP/SigComp
Minimum value for ANY/SigComp: 0 (zero) bytes, as specified in Minimum value for ANY/SigComp: 0 (zero) bytes, as specified in
section 3.3.1 of [RFC3320]. Section 3.3.1 of [RFC3320].
Minimum value for SIP/SigComp: 2048 bytes. Minimum value for SIP/SigComp: 2048 bytes.
Reason: a non-zero SMS allows an endpoint to upload a state in the Reason: a non-zero SMS allows an endpoint to upload a state in the
first SIP message sent to a remote endpoint without the uncertainty first SIP message sent to a remote endpoint without the uncertainty
of whether the remote endpoint will have enough memory to store such of whether the remote endpoint will have enough memory to store such
a state. A non-zero SMS obviously requires the SIP/SigComp a state. A non-zero SMS obviously requires the SIP/SigComp
implementation to keep state. Based on the observation that there is implementation to keep state. Based on the observation that there is
little gain from stateless SigComp compression, the assumption is little gain from stateless SigComp compression, the assumption is
that purely stateless SIP implementations are unlikely to provide a that purely stateless SIP implementations are unlikely to provide a
SigComp function. Stateful implementations should have little SigComp function. Stateful implementations should have little
problem to keep 2K additional state for each compartment (see problem to keep 2K additional state for each compartment (see Section
Section 9). 9).
Note: SMS is a parameter that applies to each individual compartment. Note: SMS is a parameter that applies to each individual compartment.
An endpoint MAY offer different SMS values for different compartments An endpoint MAY offer different SMS values for different compartments
as long as the SMS value is not less than 2048 bytes. as long as the SMS value is not less than 2048 bytes.
4.3. cycles_per_bit (CPB) for SIP/SigComp 4.3. cycles_per_bit (CPB) for SIP/SigComp
Minimum value for ANY/SigComp: 16, as specified in section 3.3.1 of Minimum value for ANY/SigComp: 16, as specified in Section 3.3.1 of
[RFC3320]. [RFC3320].
Minimum value for SIP/SigComp: 16 (same as above) Minimum value for SIP/SigComp: 16 (same as above).
4.4. SigComp_version (SV) for SIP/SigComp 4.4. SigComp_version (SV) for SIP/SigComp
For ANY/SigComp: 0x01, as specified in section 3.3.2 of [RFC3320]. For ANY/SigComp: 0x01, as specified in Section 3.3.2 of [RFC3320].
For SIP/SigComp: >= 0x02 (at least SigComp + NACK) For SIP/SigComp: >= 0x02 (at least SigComp + NACK).
Note that this implies that the provisions of [RFC4077] apply. That Note that this implies that the provisions of [RFC4077] apply. That
is, decompression failures result in SigComp NACK messages sent back is, decompression failures result in SigComp NACK messages sent back
to the originating compressor. It also implies that the compressor to the originating compressor. It also implies that the compressor
need not make use of the methods detailed in Section 2.4 of [RFC4077] need not make use of the methods detailed in Section 2.4 of [RFC4077]
(Detecting Support for NACK); for example, it can use optimistic (Detecting Support for NACK); for example, it can use optimistic
compression methods right from the outset. compression methods right from the outset.
4.5. locally available state (LAS) for SIP/SigComp 4.5. locally available state (LAS) for SIP/SigComp
Minimum LAS for ANY/SigComp: none, see section 3.3.3 of [RFC3320]. Minimum LAS for ANY/SigComp: none, see Section 3.3.3 of [RFC3320].
Minimum LAS for SIP/SigComp: the SIP/SDP static dictionary as defined Minimum LAS for SIP/SigComp: the SIP/SDP static dictionary as defined
in [RFC3485]. in [RFC3485].
Note that, since support for the static SIP/SDP dictionary is Note that, since support for the static SIP/SDP dictionary is
mandatory, it does not need to be advertised. mandatory, it does not need to be advertised.
5. Delimiting SIP Messages and SigComp Messages on the Same Port 5. Delimiting SIP Messages and SigComp Messages on the Same Port
In order to limit the number of ports required by a SigComp-aware In order to limit the number of ports required by a SigComp-aware
endpoint, it is possible to allow both SigComp messages and 'vanilla' endpoint, it is possible to allow both SigComp messages and 'vanilla'
SIP messages (i.e. uncompressed SIP messages with no SigComp header) SIP messages (i.e., uncompressed SIP messages with no SigComp header)
to arrive on the same port. to arrive on the same port.
For a message-based transport such as UDP or SCTP, distinguishing For a message-based transport such as UDP or Stream Control
between SigComp and non-SigComp messages can be done per message. Transmission Protocol (SCTP), distinguishing between SigComp and
The receiving endpoint checks the first octet of the UDP/SCTP payload non-SigComp messages can be done per message. The receiving endpoint
to determine whether the message has been compressed using SigComp. checks the first octet of the UDP/SCTP payload to determine whether
If the MSBs (Most Significant Bits) of the octet are "11111" then the the message has been compressed using SigComp. If the MSBs (Most
message is considered to be a SigComp message and is parsed as per Significant Bits) of the octet are "11111", then the message is
[RFC3320]. If the MSBs of the octet take any other value, then the considered to be a SigComp message and is parsed as per [RFC3320].
message is assumed to be an uncompressed SIP message, and is passed If the MSBs of the octet take any other value, then the message is
directly to the application with no further effect on the SigComp assumed to be an uncompressed SIP message, and it is passed directly
layer. to the application with no further effect on the SigComp layer.
For a stream-based transport such as TCP, distinguishing between For a stream-based transport such as TCP, distinguishing between
SigComp and non-SigComp messages has to be done per connection. The SigComp and non-SigComp messages has to be done per connection. The
receiving endpoint checks the first octet of the TCP data stream to receiving endpoint checks the first octet of the TCP data stream to
determine whether the stream has been compressed using SigComp. If determine whether the stream has been compressed using SigComp. If
the MSBs of the octet are "11111" then the stream is considered to the MSBs of the octet are "11111", then the stream is considered to
contain SigComp messages and is parsed as per [RFC3320]. If the MSBs contain SigComp messages and is parsed as per [RFC3320]. If the MSBs
of the octet take any other value, then the stream is assumed to of the octet take any other value, then the stream is assumed to
contain uncompressed SIP messages, and is passed directly to the contain uncompressed SIP messages, and it is passed directly to the
application with no further effect on the SigComp layer. Note that application with no further effect on the SigComp layer. Note that
SigComp message delimiters MUST NOT be used if the stream contains SigComp message delimiters MUST NOT be used if the stream contains
uncompressed SIP messages. uncompressed SIP messages.
Applications MUST NOT mix SIP messages and SigComp messages on a Applications MUST NOT mix SIP messages and SigComp messages on a
single TCP connection. If the TCP connection is used to carry single TCP connection. If the TCP connection is used to carry
SigComp messages then all messages sent over the connection MUST have SigComp messages, then all messages sent over the connection MUST
a SigComp header and be delimited by the use of 0xFFFF as described have a SigComp header and be delimited by the use of 0xFFFF, as
in [RFC3320]. described in [RFC3320].
Section 11 of [RFC4896] details a simple set of bytecodes, intended Section 11 of [RFC4896] details a simple set of bytecodes, intended
to be "well-known", that implement a null decompression algorithm. to be "well-known", that implement a null decompression algorithm.
These bytecodes effectively allow SigComp peers to send selected These bytecodes effectively allow SigComp peers to send selected
SigComp messages with uncompressed data. If a SIP implementation has SigComp messages with uncompressed data. If a SIP implementation has
reason to send both compressed and uncompressed SIP messages on a reason to send both compressed and uncompressed SIP messages on a
single TCP connection, the compressor can be instructed to use these single TCP connection, the compressor can be instructed to use these
bytecodes to send uncompressed SIP messages that are also valid bytecodes to send uncompressed SIP messages that are also valid
SigComp messages. SigComp messages.
6. Continuous Mode over TCP 6. Continuous Mode over TCP
Continuous Mode is a special feature of SigComp, which is designed to Continuous Mode is a special feature of SigComp, which is designed to
improve the overall compression ratio for long-lived connections. improve the overall compression ratio for long-lived connections.
Its use requires pre-agreement between the SigComp compressor and Its use requires pre-agreement between the SigComp compressor and
decompressor. Continuous mode is not used with SIP/SigComp. decompressor. Continuous mode is not used with SIP/SigComp.
Reason: continuous mode requires the transport itself to provide a Reason: continuous mode requires the transport itself to provide a
certain level of protection against denial of service attacks. TCP certain level of protection against denial-of-service attacks. TCP
alone is not considered to provide enough protection. alone is not considered to provide enough protection.
7. Too Large SIP Messages 7. Too-Large SIP Messages
SigComp does not support the compression of messages larger than 64k. SigComp does not support the compression of messages larger than 64k.
Therefore, if a SIP application sending compressed SIP messages to Therefore, if a SIP application sending compressed SIP messages to
another SIP application over a transport connection (e.g., a TCP another SIP application over a transport connection (e.g., a TCP
connection) needs to send a SIP message larger than 64k, the SIP connection) needs to send a SIP message larger than 64k, the SIP
application MUST NOT send the message over the same TCP connection. application MUST NOT send the message over the same TCP connection.
The SIP application SHOULD send the message over a different The SIP application SHOULD send the message over a different
transport connection (to do this, the SIP application may need to transport connection (to do this, the SIP application may need to
establish a new transport connection). establish a new transport connection).
skipping to change at page 7, line 29 skipping to change at page 7, line 29
taking into account any SigComp states that may have been created or taking into account any SigComp states that may have been created or
invalidated since the previous transmission. Implementations MUST invalidated since the previous transmission. Implementations MUST
NOT cache the result of compressing the message and retransmit such a NOT cache the result of compressing the message and retransmit such a
cached result. cached result.
The reason for this behavior is that it is impossible to know whether The reason for this behavior is that it is impossible to know whether
the failure causing the retransmission occurred on the message being the failure causing the retransmission occurred on the message being
retransmitted or on the response to that message. If the response retransmitted or on the response to that message. If the response
was lost, any state changes effected by the first instance of the was lost, any state changes effected by the first instance of the
retransmitted message would already have taken place. If these state retransmitted message would already have taken place. If these state
changes removed a state that the previously-transmitted message changes removed a state that the previously transmitted message
relied upon, then retransmission of the same compressed message would relied upon, then retransmission of the same compressed message would
lead to a decompression failure. lead to a decompression failure.
Note that a SIP retransmission may be caused by the original message Note that a SIP retransmission may be caused by the original message
or its response being lost by a decompression failure. In this case, or its response being lost by a decompression failure. In this case,
a NACK will have been sent by the decompressor to the compressor, a NACK will have been sent by the decompressor to the compressor,
which may use the information in this NACK message to adjust its which may use the information in this NACK message to adjust its
compression parameters. Note that, on an unreliable transport, such compression parameters. Note that, on an unreliable transport, such
a NACK message may still be lost, so if a compressor used some form a NACK message may still be lost, so if a compressor used some form
of optimistic compression it MAY want to switch to a method less of optimistic compression, it MAY want to switch to a method less
likely to cause any form of decompression failure when compressing a likely to cause any form of decompression failure when compressing a
SIP retransmission. SIP retransmission.
9. Compartment and State Management for SIP/SigComp 9. Compartment and State Management for SIP/SigComp
An application exchanging compressed traffic with a remote An application exchanging compressed traffic with a remote
application has a compartment that contains state information needed application has a compartment that contains state information needed
to compress outgoing messages and to decompress incoming messages. to compress outgoing messages and to decompress incoming messages.
To increase the compression efficiency, the application must assign To increase the compression efficiency, the application must assign
distinct compartments to distinct remote applications. distinct compartments to distinct remote applications.
skipping to change at page 8, line 16 skipping to change at page 8, line 16
SIP/SigComp applications identify remote applications by their SIP/ SIP/SigComp applications identify remote applications by their SIP/
SigComp identifiers. Each SIP/SigComp application MUST have a SIP/ SigComp identifiers. Each SIP/SigComp application MUST have a SIP/
SigComp identifier URN (Uniform Resource Name) that uniquely SigComp identifier URN (Uniform Resource Name) that uniquely
identifies the application. Usage of a URN provides a persistent and identifies the application. Usage of a URN provides a persistent and
unique name for the SIP/SigComp identifier. It also provides an easy unique name for the SIP/SigComp identifier. It also provides an easy
way to guarantee uniqueness. This URN MUST be persistent as long as way to guarantee uniqueness. This URN MUST be persistent as long as
the application stores compartment state related to other SIP/SigComp the application stores compartment state related to other SIP/SigComp
applications. applications.
A SIP/Sigcomp application SHOULD use a UUID (Universally Unique A SIP/SigComp application SHOULD use a UUID (Universally Unique
IDentifier) URN as its SIP/SigComp identifier, due to the IDentifier) URN as its SIP/SigComp identifier, due to the
difficulties in equality comparisons for other kinds of URNs. The difficulties in equality comparisons for other kinds of URNs. The
UUID URN [RFC4122] allows for non-centralized computation of a URN UUID URN [RFC4122] allows for non-centralized computation of a URN
based on time, unique names (such as a MAC address), or a random based on time, unique names (such as a Media Access Control (MAC)
number generator. If a URN scheme other than UUID is used, the URN address), or a random number generator. If a URN scheme other than
MUST be selected such that the application can be certain that no UUID is used, the URN MUST be selected such that the application can
other SIP/SigComp application would choose the same URN value. be certain that no other SIP/SigComp application would choose the
same URN value.
Note that the definition of SIP/SigComp identifier is similar to the Note that the definition of SIP/SigComp identifier is similar to the
definition of instance identifier in [I-D.ietf-sip-outbound]. One definition of instance identifier in [OUTBOUND]. One difference is
difference is that instance identifiers are only required to be that instance identifiers are only required to be unique within their
unique within their AoR (Address of Record) while SIP/SigComp AoR (Address of Record) while SIP/SigComp identifiers are required to
identifiers are required to be globally unique. be globally unique.
Even if instance identifiers are only required to be unique within Even if instance identifiers are only required to be unique within
their AoR, devices may choose to generate globally unique instance their AoR, devices may choose to generate globally unique instance
identifiers. A device with a globally unique instance identifier identifiers. A device with a globally unique instance identifier
SHOULD use its instance identifier as its SIP/SigComp identifier. SHOULD use its instance identifier as its SIP/SigComp identifier.
Using the same value for an entity's instance and SIP/SigComp Note: Using the same value for an entity's instance and
identifiers improves the compression ratio of header fields that SIP/SigComp identifiers improves the compression ratio of header
carry both identifiers (e.g., a Contact header field in a REGISTER fields that carry both identifiers (e.g., a Contact header field
request). in a REGISTER request).
Server farms that share SIP/SigComp state across servers MUST use the Server farms that share SIP/SigComp state across servers MUST use the
same SIP/SigComp identifier for all their servers. same SIP/SigComp identifier for all their servers.
SIP/SigComp identifiers are carried in the 'sigcomp-id' SIP URI SIP/SigComp identifiers are carried in the 'sigcomp-id' SIP URI
(Uniform Resource Identifier) or Via header field parameter. The (Uniform Resource Identifier) or Via header field parameter. The
'sigcomp-id' SIP URI parameter is a 'uri-parameter', as defined by 'sigcomp-id' SIP URI parameter is a 'uri-parameter', as defined by
the SIP ABNF (Augmented Backus-Naur Form, Section 25.1 of [RFC3261]). the SIP ABNF (Augmented Backus-Naur Form, Section 25.1 of [RFC3261]).
The following is its ABNF [RFC4234]: The following is its ABNF [RFC4234]:
skipping to change at page 9, line 46 skipping to change at page 9, line 47
Call-ID: 3c26700c1adb-lu1lz5ri5orr Call-ID: 3c26700c1adb-lu1lz5ri5orr
CSeq: 215196 REGISTER CSeq: 215196 REGISTER
Max-Forwards: 70 Max-Forwards: 70
Contact: <sip:2145550500@192.0.2.247:2078; Contact: <sip:2145550500@192.0.2.247:2078;
sigcomp-id=urn:uuid:2e5fdc76-00be-4314-8202-1116fa82a473>; sigcomp-id=urn:uuid:2e5fdc76-00be-4314-8202-1116fa82a473>;
q=1.0; expires=3600; q=1.0; expires=3600;
+sip.instance="<urn:uuid:2e5fdc76-00be-4314-8202-1116fa82a473>" +sip.instance="<urn:uuid:2e5fdc76-00be-4314-8202-1116fa82a473>"
Content-Length: 0 Content-Length: 0
SIP messages are matched with remote application identifiers as SIP messages are matched with remote application identifiers as
follows. follows:
Outgoing requests: the remote application identifier is the SIP/ Outgoing requests: the remote application identifier is the SIP/
SigComp identifier of the URI to which the request is sent. If SigComp identifier of the URI to which the request is sent. If
the URI does not contain a SIP/SigComp identifier, the remote the URI does not contain a SIP/SigComp identifier, the remote
application identifier is the IP address plus port of the datagram application identifier is the IP address plus port of the datagram
carrying the request for connection-less transport protocols, and carrying the request for connectionless transport protocols, and
the transport connection (e.g., a TCP connection) carrying the the transport connection (e.g., a TCP connection) carrying the
request for connection-oriented transport protocols (this is to request for connection-oriented transport protocols (this is to
support legacy SIP/SigComp applications). support legacy SIP/SigComp applications).
Incoming responses: the remote application identifier is the same as Incoming responses: the remote application identifier is the same as
that of the previously-sent request that initiated the transaction that of the previously sent request that initiated the transaction
to which the response belongs. to which the response belongs.
Incoming requests: the remote application identifier is the SIP/ Incoming requests: the remote application identifier is the SIP/
SigComp identifier of the top-most Via entry. If the Via header SigComp identifier of the top-most Via entry. If the Via header
field does not contain a SIP/SigComp identifier, the remote field does not contain a SIP/SigComp identifier, the remote
application identifier is the source IP address plus port of the application identifier is the source IP address plus port of the
datagram carrying the request for connection-less transport datagram carrying the request for connectionless transport
protocols, and the transport connection (e.g., a TCP connection) protocols, and the transport connection (e.g., a TCP connection)
carrying the request for connection-oriented transport protocols carrying the request for connection-oriented transport protocols
(this is to support legacy SIP/SigComp applications). (this is to support legacy SIP/SigComp applications).
Outgoing responses: the remote application identifier is the same as Outgoing responses: the remote application identifier is the same as
that of the previously-received request that initiated the that of the previously received request that initiated the
transaction to which the response belongs. Note that, due to transaction to which the response belongs. Note that, due to
standard SIP Via header field processing, this identifier will be standard SIP Via header field processing, this identifier will be
present in the top-most Via entry in such responses (as long as it present in the top-most Via entry in such responses (as long as it
was present in the top-most Via entry of the previously-received was present in the top-most Via entry of the previously received
request). request).
A SIP/SigComp application placing its URI with the 'comp=sigcomp' A SIP/SigComp application placing its URI with the 'comp=sigcomp'
parameter in a header field MUST add a 'sigcomp-id' parameter with parameter in a header field MUST add a 'sigcomp-id' parameter with
its SIP/SigComp identifier to that URI. its SIP/SigComp identifier to that URI.
A SIP/SigComp application generating its own Via entry containing the A SIP/SigComp application generating its own Via entry containing the
'comp=sigcomp' parameter MUST add a 'sigcomp-id' parameter with its 'comp=sigcomp' parameter MUST add a 'sigcomp-id' parameter with its
SIP/SigComp identifier to that Via entry. SIP/SigComp identifier to that Via entry.
skipping to change at page 10, line 49 skipping to change at page 10, line 51
9.2. Identifier Comparison Rules 9.2. Identifier Comparison Rules
Equality comparisons between SIP/SigComp identifiers are performed Equality comparisons between SIP/SigComp identifiers are performed
using the rules for URN equality that are specific to the scheme in using the rules for URN equality that are specific to the scheme in
the URN. If the element performing the comparisons does not the URN. If the element performing the comparisons does not
understand the URN scheme, it performs the comparisons using the understand the URN scheme, it performs the comparisons using the
lexical equality rules defined in RFC 2141 [RFC2141]. Lexical lexical equality rules defined in RFC 2141 [RFC2141]. Lexical
equality may result in two URNs being considered unequal when they equality may result in two URNs being considered unequal when they
are actually equal. In this specific usage of URNs, the only element are actually equal. In this specific usage of URNs, the only element
which provides the URN is the SIP/SigComp application identified by that provides the URN is the SIP/SigComp application identified by
that URN. As a result, the SIP/SigComp application SHOULD provide that URN. As a result, the SIP/SigComp application SHOULD provide
lexically equivalent URNs in each registration it generates. This is lexically equivalent URNs in each registration it generates. This is
likely to be normal behavior in any case; applications are not likely likely to be normal behavior in any case; applications are not likely
to modify the value of their SIP/SigComp identifiers so that they to modify the value of their SIP/SigComp identifiers so that they
remain functionally equivalent yet lexicographically different from remain functionally equivalent yet lexicographically different from
previous identifiers. previous identifiers.
9.3. Compartment Opening and Closure 9.3. Compartment Opening and Closure
SIP applications need to know when to open a new compartment and when SIP applications need to know when to open a new compartment and when
to close it. The lifetime of SIP/SigComp compartments is linked to to close it. The lifetime of SIP/SigComp compartments is linked to
registration state. Compartments are opened at SIP registration time registration state. Compartments are opened at SIP registration time
and are typically closed when the registration expires or is and are typically closed when the registration expires or is
canceled. canceled.
Note that linking the lifetime of SIP/SigComp compartments to Note: Linking the lifetime of SIP/SigComp compartments to
registration state limits the applicability of this specification. registration state limits the applicability of this specification.
In particular, SIP user agents that do not register but, for In particular, SIP user agents that do not register but, for
example, only handle PUBLISH or SUBSCRIBE/NOTIFY transactions are example, only handle PUBLISH or SUBSCRIBE/NOTIFY transactions are
not able create SIP/SigComp compartments following this not able create SIP/SigComp compartments following this
specification. Previous revisions of this specification also specification. Previous revisions of this specification also
defined compartments valid during a SIP transaction or a SIP defined compartments valid during a SIP transaction or a SIP
dialog. Those compartments covered all possible SIP entities, dialog. Those compartments covered all possible SIP entities,
including those that do not handle REGISTER transactions. including those that do not handle REGISTER transactions.
However, it was decided to eliminate those types of compartments However, it was decided to eliminate those types of compartments
because the complexity they introduced (e.g., edge proxy servers because the complexity they introduced (e.g., edge proxy servers
were required to keep dialog state) was higher than the benefits were required to keep dialog state) was higher than the benefits
they brought in most deployment scenarios. they brought in most deployment scenarios.
Usually, any states created during the lifetime of a compartment will Usually, any states created during the lifetime of a compartment will
be "logically" deleted when the compartment is closed. As described be "logically" deleted when the compartment is closed. As described
in section 6.2 of [RFC3320], a logical deletion can become a physical in Section 6.2 of [RFC3320], a logical deletion can become a physical
deletion only when no compartment continues to exist that created the deletion only when no compartment continues to exist that created the
(same) state. (same) state.
A SigComp endpoint may offer to keep a state created upon request A SigComp endpoint may offer to keep a state created upon request
from a SigComp peer endpoint beyond the default lifetime of a from a SigComp peer endpoint beyond the default lifetime of a
compartment (i.e., beyond the duration of its associated compartment (i.e., beyond the duration of its associated
registration). This may be used to improve compression efficiency of registration). This may be used to improve compression efficiency of
subsequent SIP messages generated by the same remote application at subsequent SIP messages generated by the same remote application at
the SigComp peer endpoint. To indicate that such state will continue the SigComp peer endpoint. To indicate that such state will continue
to be available, the SigComp endpoint can inform its peer SigComp to be available, the SigComp endpoint can inform its peer SigComp
endpoint by announcing the (partial) state ID in the returned SigComp endpoint by announcing the (partial) state ID in the returned SigComp
parameters at the end of the registration that was supposed to limit parameters at the end of the registration that was supposed to limit
the lifetime of the SigComp state. That signals the state will be the lifetime of the SigComp state. That signals the state will be
maintained. The mandatory support for the SigComp Negative maintained. The mandatory support for the SigComp Negative
Acknowledgement (NACK) Mechanism [RFC4077] in SIP/SigComp ensures Acknowledgement (NACK) Mechanism [RFC4077] in SIP/SigComp ensures
that it is possible to recover from synchronization errors regarding that it is possible to recover from synchronization errors regarding
compartment lifetimes. compartment lifetimes.
As an operational concern, bugs in the compartment management As an operational concern, bugs in the compartment management
implementation are likely to lead to sporadic, hard to diagnose implementation are likely to lead to sporadic, hard-to-diagnose
failures. Decompressors may therefore want to cache old state and, failures. Decompressors may therefore want to cache old state and,
if still available, allow access while logging diagnostic if still available, allow access while logging diagnostic
information. Both compressors and decompressors use the SigComp information. Both compressors and decompressors use the SigComp
Negative Acknowledgement (NACK) Mechanism [RFC4077] to recover from Negative Acknowledgement (NACK) Mechanism [RFC4077] to recover from
situations where such old state may no longer be available. situations where such old state may no longer be available.
A REGISTER transaction causes an application to open a new A REGISTER transaction causes an application to open a new
compartment to be valid for the duration of the registration compartment to be valid for the duration of the registration
established by the REGISTER transaction. established by the REGISTER transaction.
skipping to change at page 12, line 33 skipping to change at page 12, line 36
application identifier. application identifier.
These compartments MAY be closed if the REGISTER request is responded These compartments MAY be closed if the REGISTER request is responded
with a non-2xx final response, or when the registration expires or is with a non-2xx final response, or when the registration expires or is
canceled. However, applications MAY also choose to keep these canceled. However, applications MAY also choose to keep these
compartments open for a longer period of time, as discussed compartments open for a longer period of time, as discussed
previously. For a given successful registration, applications SHOULD previously. For a given successful registration, applications SHOULD
NOT close their associated compartments until the registration is NOT close their associated compartments until the registration is
over. over.
A SIP network can be configured so that regular SIP traffic to and Note: A SIP network can be configured so that regular SIP traffic
from a user agent traverses a different set of proxies than the to and from a user agent traverses a different set of proxies than
initial REGISTER transaction. The path the REGISTER transaction the initial REGISTER transaction. The path the REGISTER
follows is typically determined by configuration data. The path transaction follows is typically determined by configuration data.
subsequent requests traverse is determined by the Path [RFC3327] The path subsequent requests traverse is determined by the Path
and the Service-Route [RFC3308] header fields in the REGISTER [RFC3327] and the Service-Route [RFC3308] header fields in the
transaction and by the Record-Route and the Route header fields in REGISTER transaction and by the Record-Route and the Route header
dialog-creating transactions. Previous revisions of this document fields in dialog-creating transactions. Previous revisions of
supported the use of different paths for different types of this document supported the use of different paths for different
traffic. However, for simplicity reasons, this document now types of traffic. However, for simplicity reasons, this document
assumes that networks using compression are configured so that now assumes that networks using compression will be configured so
subsequent requests follow the same path as the initial REGISTER that subsequent requests follow the same path as the initial
transaction. Section 10 provides network administrators with REGISTER transaction in order to achieve the best possible
recommendations so that they can configure they networks properly. compression. Section 10 provides network administrators with
recommendations so that they can configure the networks properly.
If, following the rules above, a SIP application is supposed to open If, following the rules above, a SIP application is supposed to open
a compartment for a remote application identifier for which it a compartment for a remote application identifier for which it
already has a compartment (e.g., the SIP application registers already has a compartment (e.g., the SIP application registers
towards a second registrar using the same edge proxy server as for towards a second registrar using the same edge proxy server as for
its registration towards its first registrar), the SIP application its registration towards its first registrar), the SIP application
MUST use the already existing compartment. That is, the SIP MUST use the already existing compartment. That is, the SIP
application MUST NOT open a new compartment. application MUST NOT open a new compartment.
9.4. Lack of a Compartment 9.4. Lack of a Compartment
The use of stateless compression (i.e., compression without a The use of stateless compression (i.e., compression without a
compartment) is not typically worthwhile and may even result in compartment) is not typically worthwhile and may even result in
message expansion. Therefore, if a SIP application does not have a message expansion. Therefore, if a SIP application does not have a
compartment for a message it needs to send, it MAY choose not to compartment for a message it needs to send, it MAY choose not to
compress it even in the presence of the comp=sigcomp parameter. compress it even in the presence of the 'comp=sigcomp' parameter.
Section Section 5 describes how a SIP application can send compressed Section 5 describes how a SIP application can send compressed and
and uncompressed messages over the same TCP connection. Note that uncompressed messages over the same TCP connection. Note that RFC
RFC 3486 [RFC3486] states the following: 3486 [RFC3486] states the following:
"If the next-hop URI contains the parameter comp=sigcomp, the "If the next-hop URI contains the parameter comp=sigcomp, the
client SHOULD compress the request using SigComp" client SHOULD compress the request using SigComp".
Experience since RFC 3486 [RFC3486] was written has shown that Experience since RFC 3486 [RFC3486] was written has shown that
stateless compression is, in most cases, not worthwhile. That is why stateless compression is, in most cases, not worthwhile. That is why
now it is not recommended to use it any longer. it is not recommended to use it any longer.
10. Recommendations for Network Administrators 10. Recommendations for Network Administrators
Network administrators can configure their networks so that the Network administrators can configure their networks so that the
compression efficiency achieved is increased. The following compression efficiency achieved is increased. The following
recommendations help network administrators perform their task. recommendations help network administrators perform their task.
For a given user agent, the route sets for incoming requests (created For a given user agent, the route sets for incoming requests (created
by a Path header field) and for outgoing requests (created by a by a Path header field) and for outgoing requests (created by a
Service-Route header field) are typically the same. However, Service-Route header field) are typically the same. However,
skipping to change at page 14, line 29 skipping to change at page 14, line 34
12. Backwards Compatibility 12. Backwards Compatibility
SigComp has a number of parameters that can be configured per SigComp has a number of parameters that can be configured per
endpoint. This document specifies a profile for SigComp when used endpoint. This document specifies a profile for SigComp when used
for SIP compression that further constrains the range that some of for SIP compression that further constrains the range that some of
these parameters may take. Examples of this are Decompressor Memory these parameters may take. Examples of this are Decompressor Memory
Size, State Memory Size, and SigComp Version (support for NACK). Size, State Memory Size, and SigComp Version (support for NACK).
Additionally, this document specifies how SIP/SigComp applications Additionally, this document specifies how SIP/SigComp applications
should perform compartment mapping. should perform compartment mapping.
When this document was written, there already were a few existing When this document was written, there were already a few existing
SIP/SigComp deployments. The rules in this document have been SIP/SigComp deployments. The rules in this document have been
designed to maximize interoperability with those legacy SIP/SigComp designed to maximize interoperability with those legacy SIP/SigComp
implementations. Nevertheless, implementers should be aware that implementations. Nevertheless, implementers should be aware that
legacy SIP/SigComp implementations may not conform to this legacy SIP/SigComp implementations may not conform to this
specification. Examples of problems with legacy applications would specification. Examples of problems with legacy applications would
be smaller DMS than mandated in this document, lack of NACK support, be smaller DMS than mandated in this document, lack of NACK support,
or a different compartment mapping. or a different compartment mapping.
13. Interactions with TLS 13. Interactions with Transport Layer Security (TLS)
Endpoints exchanging SIP traffic over a TLS [RFC4346] connection can Endpoints exchanging SIP traffic over a TLS [RFC4346] connection can
use the compression provided by TLS. Two endpoints exchanging SIP/ use the compression provided by TLS. Two endpoints exchanging SIP/
SigComp traffic over a TLS connection that provides compression need SigComp traffic over a TLS connection that provides compression need
to first compress the SIP messages using SigComp and, then, pass them to first compress the SIP messages using SigComp and then pass them
to the TLS layer, which will compress them again. When receiving to the TLS layer, which will compress them again. When receiving
data, the processing order is reversed. data, the processing order is reversed.
However, compressing messages twice this way does not typically bring However, compressing messages this way twice does not typically bring
significant gains. Once a message is compressed using SigComp, TLS significant gains. Once a message is compressed using SigComp, TLS
is not usually able to compress it further. Therefore, TLS will is not usually able to compress it further. Therefore, TLS will
normally only be able to compress SigComp code sent between normally only be able to compress SigComp code sent between
compressor and decompressor. Since the gain of having SigComp code compressor and decompressor. Since the gain of having SigComp code
compressed should be in most cases minimal, it is NOT RECOMMENDED compressed should be minimal in most cases, it is NOT RECOMMENDED to
using TLS compression when SigComp compression is being used. use TLS compression when SigComp compression is being used.
14. Example 14. Example
Figure 1 shows an example message flow where the user agent and the Figure 1 shows an example message flow where the user agent and the
outbound proxy exchange compressed SIP traffic. Compressed messages outbound proxy exchange compressed SIP traffic. Compressed messages
are marked with a (c). are marked with a (c).
User Agent Outbound Proxy Registrar User Agent Outbound Proxy Registrar
|(1) REGISTER (c) | | |(1) REGISTER (c) | |
skipping to change at page 15, line 47 skipping to change at page 15, line 50
| |------------------------------> | |------------------------------>
|(11) BYE (c) | | |(11) BYE (c) | |
|---------------->| | |---------------->| |
| |(12) BYE | | |(12) BYE |
| |------------------------------> | |------------------------------>
| |(13) 200 OK | | |(13) 200 OK |
| |<------------------------------ | |<------------------------------
|(14) 200 OK (c) | | |(14) 200 OK (c) | |
|<----------------| | |<----------------| |
Figure 1: Example message flow Figure 1: Example Message Flow
The user agent in Figure 1 is initially configured (e.g., using the The user agent in Figure 1 is initially configured (e.g., using the
SIP configuration framework [I-D.ietf-sipping-config-framework]) with SIP configuration framework [CONFIG]) with the URI of its outbound
the URI of its outbound proxy. That URI contains the outbound proxy. That URI contains the outbound proxy's SIP/SigComp
proxy's SIP/SigComp identifier, referred to as 'Outbound-id', in a identifier, referred to as 'Outbound-id', in a 'sigcomp-id'
'sigcomp-id' parameter. parameter.
When the user agent sends an initial REGISTER request (1) to the When the user agent sends an initial REGISTER request (1) to the
outbound proxy's URI, the user agent opens a new compartment for outbound proxy's URI, the user agent opens a new compartment for
'Outbound-id'. This compartment will be valid, at least, for the 'Outbound-id'. This compartment will be valid for the duration of
duration of the registration. the registration, at least.
On receiving this REGISTER request (1), the outbound proxy opens a On receiving this REGISTER request (1), the outbound proxy opens a
new compartment for the SIP/SigComp identifier that appears in the new compartment for the SIP/SigComp identifier that appears in the
'sigcomp-id' parameter of the top-most Via entry. This identifier, 'sigcomp-id' parameter of the top-most Via entry. This identifier,
which is the user agent's SIP/SigComp identifier, is referred to as which is the user agent's SIP/SigComp identifier, is referred to as
'UA-id'. The compartment opened by the outbound proxy will be valid, 'UA-id'. The compartment opened by the outbound proxy will be valid
at least, for the duration of the registration. The outbound proxy for the duration of the registration, at least. The outbound proxy
adds Path header field with its own URI, which contains the adds a Path header field with its own URI, which contains the
'Outbound-id' SIP/SigComp identifier, to the REGISTER request and 'Outbound-id' SIP/SigComp identifier, to the REGISTER request and
relays it to the registrar (2). relays it to the registrar (2).
When the registrar receives the REGISTER request (2), it constructs When the registrar receives the REGISTER request (2), it constructs
the route future incoming requests (to the user agent) will follow the route future incoming requests (to the user agent) will follow
using the Contact and the Path header fields. Future incoming using the Contact and the Path header fields. Future incoming
requests will traverse the outbound proxy before reaching the user requests will traverse the outbound proxy before reaching the user
agent. agent.
The registrar also constructs the route future outgoing requests The registrar also constructs the route future outgoing requests
skipping to change at page 17, line 14 skipping to change at page 17, line 14
Since this URI's SIP/SigComp identifier 'Outbound-id' matches that of Since this URI's SIP/SigComp identifier 'Outbound-id' matches that of
the compartment created before, this compartment is used to compress the compartment created before, this compartment is used to compress
the INVITE request. the INVITE request.
On receiving the INVITE request (5), the outbound proxy Record Routes On receiving the INVITE request (5), the outbound proxy Record Routes
and relays the INVITE request (6) forward. The outbound proxy Record and relays the INVITE request (6) forward. The outbound proxy Record
Routes to ensure that all SIP messages related to this new dialog are Routes to ensure that all SIP messages related to this new dialog are
routed through the outbound proxy. routed through the outbound proxy.
Finally the dialog is terminated by a BYE transaction (11) that also Finally, the dialog is terminated by a BYE transaction (11) that also
traverses the outbound proxy. traverses the outbound proxy.
15. Security Considerations 15. Security Considerations
The same security considerations as described in [RFC3320] apply to The same security considerations as described in [RFC3320] apply to
this document. Note that keeping SigComp states longer than the this document. Note that keeping SigComp states longer than the
duration of a SIP dialog should not pose new security risks because duration of a SIP dialog should not pose new security risks because
the state has been allowed to be created in the first place. the state has been allowed to be created in the first place.
16. IANA Considerations 16. IANA Considerations
The IANA is requested to register the 'sigcomp-id' Via header field The IANA has registered the 'sigcomp-id' Via header field parameter,
parameter, which is defined in Section 9.1, under the Header Field which is defined in Section 9.1, under the Header Field Parameters
Parameters and Parameter Values subregistry within the SIP Parameters and Parameter Values subregistry within the SIP Parameters registry:
registry:
Predefined Predefined
Header Field Parameter Name Values Reference Header Field Parameter Name Values Reference
---------------------------- --------------- --------- --------- ---------------------------- --------------- --------- ---------
Via sigcomp-id No [RFCxxxx] Via sigcomp-id No [RFC5049]
The IANA is requested to register the 'sigcomp-id' SIP URI parameter, The IANA has registered the 'sigcomp-id' SIP URI parameter, which is
which is defined in Section 9.1, under the SIP/SIPS URI Parameters defined in Section 9.1, under the SIP/SIPS URI Parameters subregistry
subregistry within the SIP Parameters registry: within the SIP Parameters registry:
Parameter Name Predefined Values Reference Parameter Name Predefined Values Reference
-------------- ----------------- --------- -------------- ----------------- ---------
sigcomp-id No [RFCxxxx] sigcomp-id No [RFC5049]
Note to the RFC Editor: please, substitute RFCxxxx with the RFC
number this document will get.
17. Acknowledgements 17. Acknowledgements
The authors would like to thank the following people for their The authors would like to thank the following people for their
comments and suggestions: Jan Christoffersson, Joerg Ott, Mark West, comments and suggestions: Jan Christoffersson, Joerg Ott, Mark West,
Pekka Pessi, Robert Sugar, Jonathan Rosenberg, Robert Sparks, Juergen Pekka Pessi, Robert Sugar, Jonathan Rosenberg, Robert Sparks, Juergen
Schoenwaelder, and Tuukka Karvonen. Abigail Surtees and Adam Roach Schoenwaelder, and Tuukka Karvonen. Abigail Surtees and Adam Roach
performed thorough reviews of this document. performed thorough reviews of this document.
18. References 18. References
skipping to change at page 18, line 51 skipping to change at page 18, line 43
Description Protocol (SDP) Static Dictionary for Signaling Description Protocol (SDP) Static Dictionary for Signaling
Compression (SigComp)", RFC 3485, February 2003. Compression (SigComp)", RFC 3485, February 2003.
[RFC3486] Camarillo, G., "Compressing the Session Initiation [RFC3486] Camarillo, G., "Compressing the Session Initiation
Protocol (SIP)", RFC 3486, February 2003. Protocol (SIP)", RFC 3486, February 2003.
[RFC4077] Roach, A., "A Negative Acknowledgement Mechanism for [RFC4077] Roach, A., "A Negative Acknowledgement Mechanism for
Signaling Compression", RFC 4077, May 2005. Signaling Compression", RFC 4077, May 2005.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122, Unique IDentifier (UUID) URN Namespace", RFC 4122, July
July 2005. 2005.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC4234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Specifications: ABNF", RFC 4234, October 2005. Syntax Specifications: ABNF", RFC 4234, October 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006. (TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4896] Surtees, A., West, M., and A. Roach, "Signaling [RFC4896] Surtees, A., West, M., and A. Roach, "Signaling
Compression (SigComp) Corrections and Clarifications", Compression (SigComp) Corrections and Clarifications", RFC
RFC 4896, June 2007. 4896, June 2007.
18.2. Informative References 18.2. Informative References
[I-D.ietf-sipping-config-framework] [CONFIG] Petrie, D. and S. Channabasappa, "A Framework for Session
Petrie, D. and S. Channabasappa, "A Framework for Session Initiation Protocol User Agent Profile Delivery", Work in
Initiation Protocol User Agent Profile Delivery", Progress, June 2007.
draft-ietf-sipping-config-framework-12 (work in progress),
June 2007.
[I-D.ietf-sip-outbound] [OUTBOUND] Jennings, C. and R. Mahy, "Managing Client Initiated
Jennings, C. and R. Mahy, "Managing Client Initiated
Connections in the Session Initiation Protocol (SIP)", Connections in the Session Initiation Protocol (SIP)",
draft-ietf-sip-outbound-08 (work in progress), March 2007. Work in Progress, March 2007.
Authors' Addresses Authors' Addresses
Carsten Bormann Carsten Bormann
Universitaet Bremen TZI Universitaet Bremen TZI
Postfach 330440 Postfach 330440
Bremen D-28334 Bremen D-28334
Germany Germany
Phone: +49 421 218 7024 Phone: +49 421 218 63921
Fax: +49 421 218 7000 Fax: +49 421 218 7000
Email: cabo@tzi.org EMail: cabo@tzi.org
Zhigang Liu Zhigang Liu
Nokia Research Center Nokia Research Center
955 Page Mill Road 955 Page Mill Road
Palo Alto, CA 94304 Palo Alto, CA 94304
USA USA
Phone: +1 650 796 4578 Phone: +1 650 796 4578
Email: zhigang.c.liu@nokia.com EMail: zhigang.c.liu@nokia.com
Richard Price Richard Price
EADS Defence and Security Systems Limited EADS Defence and Security Systems Limited
Meadows Road Meadows Road
Queensway Meadows Queensway Meadows
Newport, Gwent NP19 4SS Newport, Gwent NP19 4SS
Phone: +44 (0)1633 637874 Phone: +44 (0)1633 637874
Email: richard.price@eads.com EMail: richard.price@eads.com
Gonzalo Camarillo (editor) Gonzalo Camarillo (editor)
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: Gonzalo.Camarillo@ericsson.com EMail: Gonzalo.Camarillo@ericsson.com
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
skipping to change at page 21, line 44 skipping to change at line 910
attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
 End of changes. 76 change blocks. 
201 lines changed or deleted 171 lines changed or added

This html diff was produced by rfcdiff 1.34. The latest version is available from http://tools.ietf.org/tools/rfcdiff/