10 Aug
2015
10 Aug
'15
3:43 p.m.
Hi,
This is a question for the sake of comprehension, as I actually solved
the problem with a workaround.
I am trying to get Kamailio working with a third party SIP provider. The
SIP server of this provider pings my Kamailio with OPTIONS messages.
Being located in a sub-network, the SIP messages are relayed to a router
(not a SIP router, just a gateway to the Internet) which is not
listening/sending on port 5060 but on 13377. When Kamailio answer to
OPTIONS, it send back the message to the router on the port 5060 which
is wrong. Here is the topology:
*Kamailio* *Router* *SIP Server*
/my.sip.domain 174.37.217.1 197.17.144.4/
| | ? <-------------------- 5060 |
| 5060 <---------------- 13377 | |
| 5060 ----------------−> 5060 | |
| | X |
You can see that, Kamailio answers to the wrong port, but I think this
is somewhat coherent since the SIP message says that the port 5060 is in
use. But still, I would have liked that the correct port was used:
*Kamailio* *Router* *SIP Server*
/my.sip.domain 174.37.217.1 197.17.144.4
/ | | ? <-------------------- 5060 |
| 5060 <---------------- 13377 | |
| 5060 ---------------−> 13377 | |
| | ? --------------------> 5060 |
But I do not understand where Kamailio is supposed to find the correct
port. Below are the transport frames, and SIP frames.
Kamailio receives:
Internet Protocol Version 4, Src: 174.37.217.1 (174.37.217.1), Dst:
172.16.8.61 (172.16.8.61)
Source: 174.37.217.1 (174.37.217.1)
Destination: 172.16.8.61 (172.16.8.61)
User Datagram Protocol, Src Port: 13377 (13377), Dst Port: sip (5060)
Source port: 13377 (13377)
Destination port: sip (5060)
OPTIONS sip:my.sip.domain:5060 SIP/2.0
Via: SIP/2.0/UDP 197.17.144.4:5060;branch=z9hG4bKb9340cb29ba
From: <sip:197.17.144.4>;tag=1797904074
To: <sip:my.sip.domain>
Date: Mon, 10 Aug 2015 10:01:51 GMT
Call-ID: c7f38580-5c817680-b94-38512c6(a)197.17.144.4
User-Agent: Cisco-CUCM10.5
CSeq: 101 OPTIONS
Contact: <sip:197.17.144.4:5060>
Max-Forwards: 0
Content-Length: 0
...and then sends:
Internet Protocol Version 4, Src: 172.16.8.61 (172.16.8.61), Dst:
174.37.217.1 (174.37.217.1)
Source: 172.16.8.61 (172.16.8.61)
Destination: 174.37.217.1 (174.37.217.1)
User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)
Source port: sip (5060)
Destination port: sip (5060)
SIP/2.0 200 OK
Via: SIP/2.0/UDP
197.17.144.4:5060;branch=z9hG4bKb9340cb29ba;received=174.37.217.1
From: <sip:197.17.144.4>;tag=1797904074
To: <sip:my.sip.domain>;tag=b27e1a1d33761e85846fc98f5f3a7e58.de7a
Call-ID: c7f38580-5c817680-b94-38512c6(a)197.17.144.4
CSeq: 101 OPTIONS
Allow: INVITE,ACK,BYE,CANCEL,INFO,OPTIONS,REFER,SUBSCRIBE,NOTIFY
Accept: */*
Accept-Encoding:
Accept-Language: en
Supported:
Server: kamailio (4.3.1 (x86_64/linux))
Content-Length: 0
We see clearly that the port is wrong here. But in the received SIP
frame, everything suggests that the correct port is 5060, and I do not
think Kamailio will look at the transport frame to send the response
back to the correct port. Am I correct stating this ? Maybe the Via
header should contain a port along with the IP address ?
I solved the problem by using TCP instead of UDP, as I know that since
the TCP connection is maintained, the port would be correct (because
imposed by the gateway).
I am sorry if the question does not directly relates to Kamailio, but
any explanation here would be appreciated, as I am a student trying to
learn how all this is working :)
Cheers,
Jean-Marie.