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

[Maxim Sobolev]

Klaus Darilion wrote:
> 
> 
> 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.

Klaus,

PRACK has nothing to do with it. It is for reliable delivery of non-100 
provisional replies (i.e. 180, 183 etc). For 100 reliable delivery 
relies on INVITE retransmits.

-Maxim