Signaling Compression (SigComp) Corrections and Clarifications
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From: The IESG <firstname.lastname@example.org> To: IETF-Announce <email@example.com> Cc: Internet Architecture Board <firstname.lastname@example.org>, RFC Editor <email@example.com>, rohc mailing list <firstname.lastname@example.org>, rohc chair <email@example.com> Subject: Protocol Action: 'Implementer's Guide for SigComp' to Proposed Standard The IESG has approved the following document: - 'Implementer's Guide for SigComp ' <draft-ietf-rohc-sigcomp-impl-guide-11.txt> as a Proposed Standard This document is the product of the Robust Header Compression Working Group. The IESG contact persons are Magnus Westerlund and Lars Eggert. A URL of this Internet-Draft is: http://www.ietf.org/internet-drafts/draft-ietf-rohc-sigcomp-impl-guide-11.txt
Technical Summary This document describes common misinterpretations and some ambiguities in the Signalling Compression Protocol (SigComp), and offers guidance to developers to clarify any resultant problems. Working Group Summary This document has grown through concerns from implementers. The final document has been reviewed by the WG, and there is WG consensus that the document should now be published as an RFC. Document Quality There are several independent implementations of SigComp, which are in general already implemented according to this document. Personnel Document Sheperd for this document is Lars-Erik Jonsson, and Magnus Westerlund is the Responsible Area Director. Note to RFC Editor First page header: NEW: Updates: RFC 3320, RFC 3321, RFC 3485 (once approved) Title: OLD: Implementer's Guide for SigComp NEW: Signaling Compression (SigComp) Corrections and Clarifications Abstract: OLD: This document (if approved) clarifies and corrects text in the following updated RFCs: RFC 3320, RFC 3321, RFC 3485. NEW: This document updates the following RFCs: RFC 3320, RFC 3321, RFC 3485. Section 1: OLD: "in section 3.4" refers to section 3.4 of this document "in section RFC-3320:3.4 refers to section 3.4 of RFC 3320  NEW: "in section 3.4" refers to section 3.4 of this document "in section RFC3320-3.4" refers to section 3.4 of RFC 3320  Section 2.1, First paragraph: OLD: SigComp  states that the default Decompression Memory Size (DMS) is 2K. The UDVM memory size is defined in section RFC3320:7 to be (DMS - sizeof (sigcomp_msg)) for messages transported over UDP and (DMS / 2) for those transported over TCP. NEW: SigComp  states that the default Decompression Memory Size (DMS) is 2K. The UDVM memory size is defined in section RFC3320-7 to be (DMS - sizeof (sigcomp_msg)) for messages transported over UDP and (DMS / 2) for those transported over TCP. Section 12, final paragraph OLD: These are seen to be relatively low cost bugs as only these 5 strings are affected and they are only affected under certain conditions. NEW: This document does not correct the dictionary, as any changes to the dictionary itself would be non-backwards-compatible, and require all implementations to maintain two different copies of the dictionary. Such a cost is far too high for a bug that is trivial to work around and has negligible effect on compression ratios. Instead, we point out the flaw so as to allow implementers to avoid any consequent problems. Specifically: if the bytecodes sent to a remote endpoint contain instructions that load only a sub-portion of the SIP/SDP dictionary, then the input stream provided to those bytecodes cannot reference any of these five offsets in the offset table unless the corresponding string portion of the dictionary has also been loaded. For example, if bytecodes loaded only the first three priorities of the dictionary (both string and offset table), use of the offset for "send" (at 0x089d) would be valid; however, use of the offset for "phone" (at 0x00f2) would not. Please replace all occurances of "Sigcomp" with "SigComp".