Signaling Compression


Signaling compression, or SigComp, is a compression method designed especially for compression of text-based communication data as SIP or RTSP. SigComp had originally been defined in RFC 3320 and was later updated with RFC 4896. A Negative Acknowledgement Mechanism for Signaling Compression is defined in RFC 4077. The SigComp work is performed in the ROHC working group in the transport area of the IETF.

Overview

SigComp specifications describe a compression schema that is located in between the application layer and the transport layer. It is implemented upon a virtual machine configuration which executes a specific set of commands that are optimized for decompression purposes.
One strong point for SigComp is that the bytecode to decode messages can be sent over SigComp itself, so this allows to use any kind of compression schema given that it is expressed as bytecode for the UDVM. Thus any SigComp compatible device may use compression mechanisms that did not exist when it was released without any firmware change. Additionally, some decoders may be already been standardised, so SigComp may recall that code so it is not needed to be sent over the connection. To assure that a message is decodable the only requirement is that the UDVM code is available, so the compression of messages is executed off the virtual machine, and native code can be used.
As an independent system a mechanism to signal the application conversation, a compartment mechanism is used, so a given application may have any given number of different, independent conversations, while persisting all the session status.

General architecture

Related standards documents