[Kamailio-Devel] How does Kamailio match an ACK for a stateless [3456]XX replied by Kamailio itself?

[Alex Balashov]

Klaus Darilion wrote:
> 
> Iñaki Baz Castillo wrote:
>> El Lunes, 15 de Diciembre de 2008, Klaus Darilion escribió:
>>> AFAIK the sl module registers a callback. It can detect ACK
>>> corresponding to stateless responses by certain parameter - I think it
>>> is encoded in the totag.
>> Wouldn't be better the Via "branch" parameter? (the ACK for a negative reply 
>> has the same "branch" since it's part of the same transaction).
>> But there can be multiple's ACK with same To_tag (due to re-INVITE's during a 
>> dialog).
> 
> Maybe it is the branch parameter. I do not know. I only know that it 
> uses one of these parameters.

I believe it does use the Via branch parameter, along with host and 
port.  In tags.h:calc_crc_suffix():

/*! \brief
  * Generate variable part of to-tag for a request;
  * it will have length of CRC16_LEN, sufficiently
  * long buffer must be passed to the function */
static inline void calc_crc_suffix( struct sip_msg *msg, char *tag_suffix)
{
         int ss_nr;
         str suffix_source[3];

         ss_nr=2;
         if (msg->via1==0) return; /* no via, bad message */
         suffix_source[0]=msg->via1->host;
         suffix_source[1]=msg->via1->port_str;
         if (msg->via1->branch)
                 suffix_source[ss_nr++]=msg->via1->branch->value;
         crcitt_string_array( tag_suffix, suffix_source, ss_nr );
}


I would opine that this function should be renamed to be a little 
clearer that it applies to the to-tag specifically.  Otherwise, 
calculate CRC suffix of what?

-- 
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
Tel    : (+1) (678) 954-0670
Direct : (+1) (678) 954-0671
Mobile : (+1) (706) 338-8599