Protocol Action: The Session Initiation Protocol (SIP) and Session Description Protocol (SDP) static dictionary for Signaling Compression (SigComp) to Proposed Standard

[The IESG <[e-mail]>]

The IESG has approved publication of the following Internet-Drafts as
Proposed Standards:

o The Session Initiation Protocol (SIP) and Session Description Protocol
  (SDP) static dictionary for Signaling Compression (SigComp)
	<draft-ietf-sipping-sigcomp-sip-dictionary-05.txt> 

o Compressing the Session Initiation Protocol
	<draft-ietf-sip-compression-02.txt>

These documents are the product of the Session Initiation Proposal
Investigation Working Group and the Session Initiation Protocol Working
Group.

The IESG contact persons are Scott Bradner and Allison Mankin.

 
Technical Summary
 
The static dictionary specification is specified for loading into a
device for use by Signalling Compression (SigComp), RFC 3320 in order
to achieve higher efficiency. It is based on an analysis of the
Session Initiation Protocol (SIP), RFC 3261, which as a text-based
protocol for initiating and managing communication sessions, can be
very well compressed by using Signaling Compression (SigComp).
Similarly, the Session Description Protocol (SDP), RFC 2327, is a
text-based protocol intended for describing multimedia sessions for
the purposes of session announcement, session invitation, and other
forms of multimedia session initiation. The dictionary is compression
algorithm independent.


The SIP compression specication defines a parameter of the SIP or SIPS
url and VIA header, comp=sigcomp, that indicates that compression should
be done. This is set by knowledge of being on an air interface, and
a mechanism is defined for ensuring symmetric compression.

Data integrity must be provided by SIP security so that gratuitous
compression or decompression is not hacked, and the Security
Considerations should describe use of S/MIME integrity for this
purpose; they mention the threat, but not the existing remedies.
(RFC-Editor note coming).

 
Working Group Summary
 
The working group had some controversy over the tradeoff of the
large amount of compression gain from having the dictionary versus
its use of memory (8K) in a small device. The authors explicitly
asked for feedback during Working and IETF Last Call and received
largely positive support. Other results were supportive of advancement.
 
Protocol Quality
 
The documents were reviewed for the IESG by Allison Mankin.
Prototype implementations supporting the compression benefits
have been carried out by two of the dictionary authors.


RFC Editor Note:

Please add a reference to RFC 2119 to the normative references of
these specifications.

In the abstract of draft-ietf-sipping-sigcomp-sip-dictionary, 
please substitute the RFC numbers for the references (which are 
improper abstract style). SIGCOMP has a fast track RFC number.


Additional RFC-Editor note for draft-ietf-sipping-sigcomp-sip-dictionary:

 Old:
       Each entry contains the string that actually occurs in the 
	 dictionary, its priority (see below), its offset from the first 
	 octet and its length (both in hexadecimal), and one or more 
	 references that elucidate why this string is expected to occur 
	 in SIP/SDP messages.

 New:
       Each entry contains the string that actually occurs in the 
	 dictionary, its priority (see below), its offset from the first 
	 octet and its length (both in hexadecimal), and one or more 
	 references that elucidate why this string is expected to occur 
	 in SIP/SDP messages. [Add:] Note: Length in this document 
	 always refers to octets.


 Old:

     Len: the length of the string (in hexadecimal)

 New: 

     Len: the length of the string (in octets, in hexadecimal)