[OpenSIPS-Users] Message compression in OpenSIPS 1.12

[Răzvan Crainea]

Hi all,

The first topic presented in the last public meeting[1] was related to 
Message compression - the idea is to reduce the size of the SIP messages 
to avoid UDP fragmentationor to save bandwidth and processing power.

This topic was split in two parts:

1) SIP-wise changes over the messages (RFC3261 compliant -> supported by 
all user agents)
     a) function that converts all header names to the short form (i.e. 
 From -> f, Call-ID -> i, etc.). A single function will be exported in 
the script that will be called for the requests that should use the 
short form.
     b) function that joins together headers that support multiple 
bodies (i.e. Record-Route, Via, Contact, etc.). There will be a function 
that indicates whether the outgoing request should merge these headers 
in a single one. An example of usage is when having two Via headers such 
as the following example:

Via: SIP/2.0/UDP bigbox3.site3.atlanta.com;branch=z9hG4bK77ef4c2312983.1
Via: SIP/2.0/UDP pc33.atlanta.com;branch=z9hG4bKnashds8

These headers will be merged in a single header:

     Via: SIP/2.0/UDP 
bigbox3.site3.atlanta.com;branch=z9hG4bK77ef4c2312983.1, SIP/2.0/UDP 
pc33.atlanta.com;branch=z9hG4bKnashds8

     c)delete irrelevant headers: create a new function that is used to 
delete certain headers that are not mandatory in the SIP protocol. By 
default, all headers but the mandatory ones are deleted. However, the 
function should receive a headers whitelist as a parameter: a list of 
headers that should not be deleted because they might be useful for the 
platform or end-users.

     comp_delete_headers("X-Source-IP|User-Agent|Date");

     d) remove redefined SDP attributes: provide a function that removes 
attributes that are redefined for some of the static codecs. For 
example, consider the following SDP:

     m=audio 49230 RTP/AVP 0 98
     a=rtpmap:0 PCMU/8000
     a=rtpmap:98 L16/11025/2

The SDP above can be suppressed to the following form:

     m=audio 49230 RTP/AVP 0 98
     a=rtpmap:98 L16/11025/2


2)Compressing the SIP message (using gzip). The idea is to take the SDP 
body and several headers that are not used in the routing logic, 
compress them, apply a base64 transformation and add to the message's 
body. A use case for this is a platform that has several edge servers 
(SBCs) and a few core instances - when entering the platform the message 
compression should be applied and then sent to the core servers. Inside 
the core networks, the messages should be carried in the compressed 
format to reduce the bandwidth. When leaving the network, the message 
has to be decompressed and forwarded to the next gateway without any 
compression, since the other equipments might not understand them.
There will be several functions exported in the script:

     a) compress_msg("1","Header1|Header2"); compresses the body of the 
message and listed headers
     b) decompress_msg(); decompress both headers and body

What do you think about this approach? Is this something you find 
useful? Since we don't have a final decision for this topic, we are 
looking for more input from you guys.Anybody is welcome to throw any 
kind of useful feedback on this matter, so don't be shy!

[1] http://www.opensips.org/Community/IRCmeeting20140827

Best regards,

-- 
Răzvan Crainea
OpenSIPS Solutions
www.opensips-solutions.com