Signaling Compression (SigComp) is a standards based solution to compress request-response based protocols. This presentation talks about using SigComp to compress SIP messages.

1. Signaling Compression
(SigComp)

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

5. A Simple Compression

6. A Simple Decompression

7. SigComp Architecture

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

13. SigComp Architecture

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)