[SR-Users] Transport protocol related question - how to bind a dialog to a negotiated transport protocol

[Daniel-Constantin Mierla]

Hello,

the request within dialogs are sent to the address in the Contact header 
of the request/response creating the dialog. In you trace, the SUBSCRIBE 
has a Contact with no transport, the default one being UDP.

Of course, a higher priority than Contact in sending would be 
Record-Route, but it is not the case of your example.

In other words, SIP allows to create dialogs on one transport and 
request a follow up on another transport. Even the response to a request 
can have different destination (ip, port or protocol) than the address 
from where the request was sent, Via header specifying where it should 
be sent.

Cheers,
Daniel

On 11/06/14 21:32, Klaus Feichtinger wrote:
> Hello,
>
> I wonder if it is allowed using transport protocol UDP for SIP NOTIFY 
> requests (which are generated by Kamailio/presence module), when the 
> SUBSCRIBE dialog was established using TCP as transport protocol.
> In other words: this is a principal question if it is allowed changing 
> the transport protocol for in-dialog transactions e.g. from TCP to 
> UDP. Initially I rather thought that in-dialog transactions shall use 
> the same transport protocol as the dialog itself (e.g. SIP INFO 
> requests within a standard media session), except the message would be 
> too big for UDP, where a change to TCP is recommended.
>
> Can anybody give me a hint, if the current behaviour of Kamailio is 
> correct or not? Or - how can I bind Kamailio to a specific transport 
> protocol (for messages that are created by modules themselves)? 
> Kamailio is sending NOTIFY requests with UDP, even when the 
> subscription was done with TCP (see excerpt below).
>
> 09:58:10.360749 IP (tos 0x0, ttl 64, id 35302, offset 0, flags [DF], 
> proto TCP (6), length 444) 10.1.1.14.37883 > 10.1.1.44.5060: P, cksum 
> 0x1cb3 (correct), 1:393(392) ack 1 win 457 <nop,nop,timestamp 
> 624699305 795715664>
> SUBSCRIBE sip:116006 at 10.1.1.44;transport=TCP SIP/2.0
> Via: SIP/2.0/TCP 10.1.1.14:5070;rport;branch=z9hG4bK1540213071
> From: <sip:1 at 10.1.1.14:5070>;tag=620071678
> To: <sip:116006 at 10.1.1.44;transport=TCP>
> Call-ID: 449986375
> CSeq: 20 SUBSCRIBE
> Contact: <sip:1 at 10.1.1.14:37883>
> Max-Forwards: 70
> Expires: 1200
> Event: presence
> Content-Length: 0
>
>
> 09:58:10.361324 IP (tos 0x10, ttl 64, id 65438, offset 0, flags [DF], 
> proto TCP (6), length 431) 10.1.1.44.5060 > 10.1.1.14.37883: P, cksum 
> 0x29fb (correct), 1:380(379) ack 393 win 215 <nop,nop,timestamp 
> 795715792 624699305>
> SIP/2.0 202 OK
> Via: SIP/2.0/TCP 10.1.1.14:5070;rport=37883;branch=z9hG4bK1540213071
> From: <sip:1 at 10.1.1.14:5070>;tag=620071678
> To: 
> <sip:116006 at 10.1.1.44;transport=TCP>;tag=4f7a7e54f75c89f5b968c90011d693b5-9eed
> Call-ID: 449986375
> CSeq: 20 SUBSCRIBE
> Expires: 1200
> Contact: <sip:10.1.1.44:5060;transport=tcp>
> Content-Length: 0
>
>
> 09:58:10.361507 IP (tos 0x10, ttl 64, id 32295, offset 0, flags 
> [none], proto UDP (17), length 484) 10.1.1.44.5060 > 10.1.1.14.37883: 
> SIP, length: 456
> NOTIFY sip:1 at 10.1.1.14:37883 SIP/2.0
> Via: SIP/2.0/UDP 
> 10.1.1.44;branch=z9hG4bKc408.509e6347000000000000000000000000.0
> To: sip:1 at 10.1.1.14;tag=620071678
> From: sip:116006 at 10.1.1.44;tag=4f7a7e54f75c89f5b968c90011d693b5-9eed
> CSeq: 2 NOTIFY
> Call-ID: 449986375
> Content-Length: 0
> User-Agent: kamailio (4.0.4 (i386/linux))
> Max-Forwards: 70
> Event: presence
> Contact: <sip:10.1.1.44:5060;transport=tcp>
> Subscription-State: active;expires=1200
>
> Thx
> Klaus
>
>
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-- 
Daniel-Constantin Mierla - http://www.asipto.com
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda

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