Signaling Compression
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The document outlines the Signaling Compression (SigComp) agenda, detailing its architecture, core functions, and applications, particularly for SIP (Session Initiation Protocol). It discusses compression mechanisms, including state management, negative acknowledgment, and relevant RFCs that define SigComp standards and requirements. Additionally, it highlights how SigComp reduces different types of application protocol messages while preserving significant protocol details during transit.
Signaling Compression
- 2. Agenda ●Core SigComp ●Negative Acknowledgment ●SigComp for SIP ●SigComp in P-CSCF ●Testing SigComp
- 3. What is SigComp? ●A Solution to compress application protocols ●Applied on any request - response type application ○Eg. SIP, RTSP etc. ●Independent of compression algorithm ●Defined in RFC 3320
- 4. Why SigComp? ●Protocols like SIP are text based ●Engineered for bandwidth rich link ●Transmission delay is significant ○Increases call setup time ●Bandwidth savings is not a main goal
- 8. Compartment
- 9. Compartment ●Stores SigComp parameters ●Stores states corresponding to a compartment ●Stores feedback item ●Maintained in State Handler
- 10. States ●A State is a plain string ○Can be uniquely identified by a state identifier ●Statically Created ○SIP/SDP Static Dictionary (RFC 3485) ○Presence Static Dictionary (RFC 5119) ●Dynamically Created ○Created dynamically during compression
- 11. SigComp Parameters ●SigComp Version ●Decompression memory size (DMS) ●State memory size (SMS) ●Cycles per bit (CPB) ●Locally available states
- 12. SigComp Callflow
- 14. Compressor Dispatcher ●Interfaces with application ○Compress a message ○Close a compartment ●Accepts message & Compartment ID from application ●Invokes appropriate Compressor ●Receives compressed message from Compressor ●Performs "byte stuffing" if required ●Sends the compressed message
- 15. Decompressor Dispatcher ●Interfaces with application ○Returns decompressed message ○Accept compartment ID to save states ●Receives compressed message from network ●Removes "byte stuffing" if required ●Invokes a single instance of UDVM per message ●Receives the decompressed message from UDVM
- 16. Compressor ●Compresses the message ●Interacts with State handler ○Create unacknowledged states ○Access saved states ○Access requested feedback data
- 17. State Handler ●Compartment maintenance ○Create compartment ○Add/Delete state to/from compartment ○Add/Access requested feedback in a compartment ●State maintenance ○Access state given state identifier
- 18. UDVM ●Virtual Machine to run SigComp bytecode ●Designed solely for the purpose of running decompression algorithms
- 19. Negative Acknowledgment for SigComp ●Version 2.0 of SigComp ●Handle decompression failure ○Generate NACK on decompression failure ○NACK carries all the failure details to correct the compartment ●Make adjustments to compartment on receipt of NACK ●Defined in RFC 4077
- 20. SigComp for SIP ●Defined in RFC 3486 & 5049 ●Demultiplex SigComp & SIP message ○First 5 bits of SigComp message is '11111' ●Mechanism for SIP entity to report its willingness to support SigComp ●SigComp requirements for a SIP entity
- 21. SigComp Requirements RFC 5049 3GPP TS 24.229 Minimum DMS 8 kB 8 kB Minimum SMS 2 kB 4 kB Minimum CPB 16 16 SigComp Version 2.0 2.0 Locally Available States SIP/SDP (RFC 3485) SIP/SDP (RFC 3485) Presence (RFC 5112)
- 22. 'comp=sigcomp' parameter ○SIP URI parameter ○ sip:alice@atlanta.com;comp=sigcomp ○Via header parameter ○ Via: SIP/2.0/UDP server1.foo.com:5060;branch=z9hG4bK87a7; comp=sigcomp
- 23. When to Compress? ●Route target has 'comp=sigcomp' parameter ○For response, Via header is route target ○For request, Route header or Request URI is route target ●'comp=sigcomp' is just a request to accept SigComp message ○For eg. We do not compress messages towards core network side even if the route target has 'comp=sigcomp'
- 24. Willingness to support SigComp ●Add 'comp=sigcomp' parameter in Via header ●Add 'comp=sigcomp' parameter in Record- Route ●An OPTIONS request send to proxy should return 200 ok with 'comp=sigcomp' in Contact header
- 25. References ●RFC 3320 (Core SigComp) ●RFC 3321 (SigComp Implementation) ●RFC 3485 (SIP/SDP Static Dictionary) ●RFC 3486 (Compressing SIP) ●RFC 4077 (NACK) ●RFC 5119 (Presence Static Dictionary)