[asterisk-users] Improving the speed of chan_sip

[Mark Michelson]

Pavel Jezek wrote:
> 
> Steve Murphy wrote:
>> Hello--
>>
>> Why do I target chan_sip for so much effort?  Because, 
>> it seems to me, chan_sip is probably the most used channel 
>> driver in the asterisk community!! (and, of course,
>> the zap/dahdi driver, is also pretty popular)
>>
>> I haven't had time to follow up on chan_sip, and I probably 
>> won't for several months. 
>>
>> But, if I had time, here is what I'd do:
>>
>> There are two ways to speed up chan_sip, and they are separate issues,
>> tied together on how many cpu cycles they use up:
>>
>> 1. Call setup/teardown (invites/hangups) -- limits the calls/sec
>> asterisk can handle.
>>   
> 
> one of the big issues in sip callsetup performance, that appears to me 
> in current trunk, is about 500ms delay in propagation SIP/OK message 
> between bridged parties
> eg.: one party answers call, send SIP/OK with SDP to asterisk, asterisk 
> then forwards it to other party, but with unacceptable delay about 500ms!
> this is so much, that users complaining about lost first word of speech 
> communication,
> I posted info about this to bugreport, that seems to be related to this, 
> look at my message:
> http://bugs.digium.com/view.php?id=12708#91173
> I also attach graph picture from wireshark, that clearly ilustrated, 
> where is problem.... (OK-SDP-delay.png )
> PJ
> 

If you check ast_answer in channel.c of trunk, you can see that it calls 
__ast_answer(chan, 500). The 500 there is a 500 ms delay that occurs before 
calling the channel's answer callback. In the case of SIP, this would indeed 
mean that there is a 500 ms delay between receiving the 200 OK from the callee 
and sending a 200 OK to the caller.

Mark Michelson