[SR-Users] NO_DTLS_FINGERPRINT when calling from webrtc to webrtc client

Daniel-Constantin Mierla miconda at gmail.com
Wed Sep 17 09:35:37 CEST 2014


I would add the RTP-WebRTC gateway between SIP Kamailio and SIP UAC, 
from resources point of view, it is the only leg that needs 

Otherwise, you can try to work with two rtpengine instances (sets) in WS 
Kamailio, one to use for ws client to proxy and the other one for the 
leg from proxy to ws client. It will be a communication between them 
with classic rtp, both having towards ws client webrtc. It has the 
drawback of decryption and encryption done two times for the same call. 
You would need to add rtpengine set id in record-route to be able to 
handle properly the re-INVITE, BYE, etc.

Another option that I would use is to send a negative reply from SIP 
kamailio, catch that in failure_route in WS Kamailio and engace there 
the rtpengine with proper flags. E.g., you assume it is going to be 
webrtc-to-webrtc, so no encryption/decryption added first time invite 
comes from WS client. You forward to SIP kamailio, which based on 
location, if it discovers that the callee is classic SIP-RTP, will send 
a 4xx back to WS Kamailio -- you end previous rtpengine session and 
engage it again with new flags (use branch route for managing rtpengine 
-- like it is done in default kamailio.cfg for rtpproxy).


On 15/09/14 20:30, Paweł Sternal wrote:
> Hi. Another topic about WebRTC, websockets with kamailio and rtpengine 
> ;-)
> My problem is how to distinguish a call to WS UAC and how to SIP UAC 
> in scenarios:
> 1) WS client1 -> WS kamailio -> SIP kamailio -> SIP UAC
> 2) WS client1 -> WS kamailio -> SIP kamailio -> WS kamailio -> WS client2
> WS kamailio is a proxy, SIP kamailio is a registrar
> When "WS client1" is calling to "123123" WS kamailio doesn't know if 
> "123123" was registered from "WS client2" or from SIP UAC.
> I have in this case rtpengine_manage("....... RTP/AVP"), but when 
> INVITE is returned to WS kamailio? RTP/SAVPF?
> Probably it is obvious, however...
> When WS client2 reply with 200OK, rtpengine_manage("..... ICE=force") 
> to WS client1 SDP is sent without a:fingerprint. sipml5 dumps warning:
> message: "Could not negotiate answer SDP; cause = NO_DTLS_FINGERPRINT
> I tried different combinations... and I'm stuck :/
> Regards
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Daniel-Constantin Mierla
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
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