[Serusers] Re: [Serdev] Problem with Via Branch/Strange Looping Problem with ACK's

Alex Mack amack at fhm.edu
Wed May 4 14:32:19 CEST 2005


Hi Zeus!

Maybe there's a misunderstandiung: I for myself have no problem with 
looping packets but I've problems with ACKs and Via-HF with branch=0 - 
and that's the UAS (SER) to be blamed for. The UA sends a normal - and 
in my eyes correct - ACK after an 200 OK, and this ACK is forwarded by 
SER with a Via-HF containing "branch=0".

So far I didn't get a clue how I could take influence on SER writing bad 
branch parameters - even if I wanted SER to do that. IMHO branch=0 isn't 
legal according to the metioned sections of RFC3261.

I've attached a ethereal plaintext export of a call. Packet #13 is the 
ACK from the initiating UA to SER, packet #14 is the bad ACK with 
branch=0. Sorry for the crumbled view, but I have almost no influence on 
ethereal's export format.

Alex Mack

Zeus Ng schrieb:

>When I mention section 12.2, I was referring your UA, not SER. I do have a
>typo on alias as well.
>
>To better troubleshoot your problem, ser.cfg and debug would help. By
>looking at your ngrep, I believe there is something wrong with your ser.cfg.
>The ACK from SER to Asterisk should not have a Record-Route header added.
>
>
>
>  
>
>>-----Original Message-----
>>From: serdev-bounces at lists.iptel.org 
>>[mailto:serdev-bounces at lists.iptel.org] On Behalf Of Alex Mack
>>Sent: Wednesday, 4 May 2005 8:29 PM
>>To: Zeus Ng
>>Cc: serdev at lists.iptel.org; serusers at lists.iptel.org
>>Subject: Re: [Serusers] Re: [Serdev] Problem with Via 
>>Branch/Strange Looping Problem with ACK's
>>
>>
>>Hi Zeus!
>>
>>Zeus Ng schrieb:
>>
>>    
>>
>>>First, the ACK should follow section 12.2 (indeed 12.2.1.1), 
>>>      
>>>
>>Requests 
>>    
>>
>>>within a Dialog, not section 12.1.2 according to section 
>>>      
>>>
>>13.2.2.4, 2xx 
>>    
>>
>>>Responses.
>>>------
>>>The UAC core MUST generate an ACK request for each 2xx received from
>>>the transaction layer. The header fields of the ACK are constructed
>>>in the same way as for any request sent within a dialog
>>>------
>>> 
>>>
>>>      
>>>
>>I disagee: the SER is an UAS not an UAC.
>>IMHO, the concernig chapters are 16.6 subpoint 8 ("16.6 Request 
>>Forwarding"; "8. Add a Via header field value") and 8.1.1.7 ("8.1.1.7 
>>Via"). Both chapters state the UAS (SER) MUST add a Via with a branch 
>>parameter starting with the magic cookie "z9hG4bK".
>>
>>The ACK generated by the UAC looks good to me, anyway.
>>
>>    
>>
>>>Second, do you happened to have a line like this in your SER config.
>>>
>>>aliase=your_proxy_name:5080 or aliase=your_proxy_ip:5080?
>>>
>>> 
>>>
>>>      
>>>
>>Are you sure about the trailing 'e' in "aliase"? I've two 
>>alias-definitions (one for the IP, one for the realm) in my 
>>ser.cfg. But 
>>they don't have the port added. I've already added the ports in the 
>>listen statements.
>>
>>Alex Mack
>>
>>_______________________________________________
>>Serdev mailing list
>>serdev at lists.iptel.org
>>http://lists.iptel.org/mailman/listinfo/serdev
>>
>>
>>    
>>
>
>
>
>  
>

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