[OpenSER-Devel] Possible bug in the tm module in the presence of packet loss/branches

[Klaus Darilion]

Dan Pascu schrieb:
> On Thursday 06 March 2008, Maxim Sobolev wrote:
>> The issue at hand has lead me to discovering the problem, which is hard
>> to observe, but the problem itself IMHO is important one and by no
>> means non-existing in the real world. As I said in the other message,
>> I've seen this issue many times before in normal conditions, but
>> attributed it to some kind of CPE failure. This could also happen not
>> only due to network problems but due to UDP packets loss when server is
>> loaded. Run "netstat -su" on the any more or less loaded Linux server
>> running OpenSER and see how many UDP packets are getting dropped every
>> second ("packet receive errors" item).
> 
> Udp:
>     219469376 packets received
>     154 packets to unknown port received.
>     16936 packet receive errors
>     261877247 packets sent
> 
> This is from a box which is loaded close to the limit of the number of 
> users a single box can handle. Yet the packet loss is only 0.0077%, which 
> is insignificant and can be dealt with by the retransmission mechanism.
> 
> My issue with what you're proposing is that it tries to modify the SIP 
> callflow to something no specified in the RFC, to solve a non-SIP 
> problem. I also do not like the idea that the proxy would keep 
> retransmitting on a branch after the originator has canceled the call.

If you really want to solve this I think the proper approach is using PRACK.

regards
klaus