[asterisk-users] SIP response time in Asterisk

[Raj Jain]

> In what amount of time does "100 Trying message" have to be 
> sent to asterisk?  I see asterisk retransmitting the INVITE 
> message multiple times before receiving the "100 Trying message".

The INVITEs are retransmitted based on a timer T1, which starts at a default
of 500 ms and then exponentially backoffs and caps at 64*T1. The first
INVITE retransmission is supposed to happen in 500 ms. However, Asterisk has
a minor bug in this place. Asterisk sends the first INVITE retransmission
after 1 second instead of 500 ms. 

This means Asterisk will wait for a second for a response such as 100 Trying
before it will start retransmitting the INVITE. Asterisk will retransmit the
INVITE after 1, 1, 2, 4, 8, 16, 32 seconds (ideally, this should be 500ms,
1, 2, 4, 8, 16, 32) from the start if it doesn't see a response.

Raj



> 
> 
> --- David Boyd <dboyd at ignitetrx.com> wrote:
> 
> > On Fri, 2007-10-26 at 11:12 -0700, John Riek wrote:
> > > I need to know how fast a sip device needs to
> > respond
> > > to an INVITE sip message from asterisk before
> > asterisk
> > > retransmits the INVITE message again.
> > > 
> > > Thanks
> > Snip  ---
> > 
> > 
> > 
> > 
> > 7.2.1 INVITE received
> > 
> >    When an INVITE request is received by the gateway, a "100 Trying"
> >    response MAY be sent back to the SIP network indicating that the
> >    gateway is handling the call.
> > 
> >    The necessary hardware resources for the media stream MUST be
> >    reserved in the gateway when the INVITE is received, since an IAM
> >    message cannot be sent before the resource reservation 
> (especially
> >    TCIC selection) takes place.  Typically the resources 
> consist of a
> >    time slot in an E1/T1 and an RTP/UDP port on the IP side.  
> > Resources
> >    might also include any quality-of-service provisions (although no
> >    such practices are recommended in this document).
> > **********
> >    After sending the IAM the timer T7 is started. 
> > The default value of
> >    T7 is between 20 and 30 seconds.  The gateway goes to 
> the 'Trying'
> >    state.
> > **********
> > 
> > 
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