[OpenSIPS-Users] [OpenSIPS-Devel] OpenSIPS @ SIPit - report and conclusions

[Maxim Sobolev]

Johansson Olle E wrote:
> 23 okt 2008 kl. 09.53 skrev Klaus Darilion:
> 
>> Remarks:
>> ● T1 timer is constant – RFC 3261 does not allow to be changed
>>
>> RFC 3261 says: ...T1 is an estimate of the round-trip time (RTT),  
>> and it
>> defaults to 500 ms....
>>
>> So, IMO it is valid to adopt T1 timer.
> 
> That's my conclusion as well. I actually do adopt the T1 to the known  
> RTT in Asterisk.

I agree. I can't imagine a single scenario where UAS could misbehave as 
a result of UAC using non-default T1 or vice versa. The most you can get 
is additional signaling propagation delay or bandwidth waste as a result 
of too late / too early retransmits. In this regard, underestimating RTT 
is probably better than overestimating, since in most cases signaling 
takes only tiny fraction of available bandwidth.

At the practical level, though, adapting T1 dynamically to match RTT is 
an error-prone process (unless you can gather and analyze significant 
statistics of exchange between two hosts) and therefore has a little 
utility IMHO.

Regards,
-- 
Maksym Sobolyev
Sippy Software, Inc.
Internet Telephony (VoIP) Experts
T/F: +1-646-651-1110
Web: http://www.sippysoft.com