Are you sure the error messages are printed for this ACK, because it has to be sent via UDP, not via WS, thus the messages seem to be unrelated.

Get the log messages with debug=3 in order to see what is happening.


On 6/22/13 9:10 AM, Jayesh Nambiar wrote:
Is it possible that this could be a problem in the script. But when I call using a normal SIP Client like X-Lite, it works well. This only happens when the request comes on websocket. Is there something to be handled specially when handling requests like ACK over websocket?
The reference is more or less taken from

--- Jayesh

On Wed, Jun 19, 2013 at 2:14 PM, Jayesh Nambiar <> wrote:
Hi Daniel,
I checked using the kamcmd command and I see the webrtc connection active. The ACK comes from the webrtc client but somehow kamailio is unable to create a via header and forward the request. The ACK coming from webrtc client is as follows:

Via: SIP/2.0/WS df7jal23ls0d.invalid;branch=z9hG4bKJ0Qsiuh94B2slPLp19qH;rport
From: "Jayesh"<>;tag=vsTKsfB1ZR8EkHTPqzyc
To: <>;tag=UQ9veX0vUg7QS
Contact: "Jayesh"<sip:1000001001@df7jal23ls0d.invalid;rtcweb-breaker=no;click2call=no;transport=ws>;+g.oma.sip-im;;language="en,fr"
Call-ID: 2c76d5ee-e9d0-7f22-8be2-76e80b4ab48b
CSeq: 42684 ACK
Content-Length: 0
Max-Forwards: 70
Proxy-Authorization: Digest username="1000001001",realm="",nonce="UcFsQ1HBaxc84k4N1J00fpVDj9G57x5p",uri="sip:1223@;transport=udp",response="5b18a2182c335315875224f2244fb48b",algorithm=MD5
User-Agent: IM-client/OMA1.0 sipML5-v1.2013.03.27
Organization: Doubango Telecom

Where is the Kamailio; is a freeswitch playing music and the request is received on which is kamailio acting as a websocket server.
Also the connection between Kamailio and Freeswitch is UDP. I am not able to use the websocket module just because of this small problem caused in signaling. Any help is really appreciated. Could it be related to the nathelper module?


--- Jayesh

On Tue, Jun 18, 2013 at 2:17 PM, Daniel-Constantin Mierla <> wrote:

On 6/14/13 4:52 PM, Jayesh Nambiar wrote:
Hello All,
I have a setup which is SIPML5 -> Kamailio(Websocket) -> Freeswitch. All I am trying to do is initiate a call from SIPML5 and Play a Music file from freeswitch. This works, but the call hangs up after 30 seconds due to ACK timeout from from the SIPML5.

What I can see is the SIPML5 from Chrome does send an ACK on websocket, but I see the following error in kamailio syslog:

via_builder(): TCP/TLS connection (id: 0) for WebSocket could not be found
ERROR: <core> [msg_translator.c:1725]: build_req_buf_from_sip_req(): could not create Via header
ERROR: <core> [forward.c:607]: forward_request(): ERROR: forward_request: building failed
ERROR: sl [sl_funcs.c:371]: sl_reply_error(): ERROR: sl_reply_error used: I'm terribly sorry, server error occurred (1/SL)

Can someone help me understand what I am missing here and why kamailio is not able to create a VIA header to forward this request towards freeswitch. I have built a simple config file by following as reference.

Any help in understanding this is really appreciated.
looks like the web rtc connection was down (closed by one side or interrupted by the network). You can check with kamcmd the list of active connections.


Daniel-Constantin Mierla -!/miconda -
Kamailio Advanced Training, San Francisco, USA - June 24-27, 2013
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Daniel-Constantin Mierla -!/miconda -