[SR-Users] Guidance building a WebRTC to Asterisk Intermediate Proxy

Peter Manley peter.manley at kombea.com
Sat Jun 26 00:44:11 CEST 2021


I'm working on building an RTP Proxy which will allow both regular SIP to SIP transactions and WebRTC to SIP transactions to an Asterisk Server.

SIP UAC < ---UDP/SIP --- > Kamailio/RTPEngine Proxy < ---UDP/SIP----- > Asterisk Server


WebRTC UAC < ---WSS--- > Kamailio/RTPEngine Proxy < ---UDP/SIP----- > Asterisk Server

The Kamailio/RTPEngine Proxy is stateless (does not use the tm or registerer modules), and uses the Path module to replace the Route header with a Path header.

It works grep for SIP/UDP to SIP/UDP transactions.

HOWEVER... It only partially works for WSS to SIP/UDP transactions. The REGISTER/401(Unauthorized), REGISTER/200(OK) transaction works well.

When the Asterisk server sends a SIP Options message, I get the following error:
Jun 25 15:47:03 VRTPENGINE kamailio[4953]: INFO: <script>: => OPTIONS < sip:l4umfumh at;transport=ws;alias= -> <null> (IP:
Jun 25 15:47:03 VRTPENGINE kamailio[4953]: WARNING: <core> [core/msg_translator.c:2815]: via_builder(): TCP/TLS connection (id: 0) for WebSocket could not be found
Jun 25 15:47:03 VRTPENGINE kamailio[4953]: ERROR: <core> [core/msg_translator.c:2003]: build_req_buf_from_sip_req(): could not create Via header
Jun 25 15:47:03 VRTPENGINE kamailio[4953]: ERROR: <core> [core/forward.c:550]: forward_request(): building failed
Jun 25 15:47:03 VRTPENGINE kamailio[4953]: WARNING: <core> [core/receive.c:425]: receive_msg(): error while trying script

It appears that the WebSocket corresponding to the WSS leg cannot be located when the request is initiated from the Asterisk Server.

Any thoughts on how I can get this to work in the other direction (Asterisk to Kamailio)? I've been looking at the WebRTC to SIP Client and Server (https://github.com/havfo/WEBRTC-to-SIP), but that doesn't quite do what I want it to do (i.e. it appears to act as a registrar server and doesn't forward REGISTER requests on to another registrar).

Thanks and regards,

Peter H. Manley, Ph.D.
Chief Software Architect
KomBea Corporation
3400 North Ashton Blvd, Suite 470<https://urldefense.proofpoint.com/v2/url?u=https-3A__maps.google.com_-3Fq-3D3400-2BNorth-2BAshton-2BBlvd-2C-2BSuite-2B470-2B-250D-250A-2BLehi-2C-2BUtah-2B84043-26entry-3Dgmail-26source-3Dg&d=DwMF-g&c=aXfg9j-An5sFdflqnjAj_USiCjXm5xEBIX8lTgWEt0U&r=ykVOlDeeWPn-JjTs8avieNrFskQ3kNzjf6_Jn_wG5HLeLIRsvzCN4-dJx6BFR4el&m=MMSIepRfj2CXVMH3CH8SghyPAoonRISMH__5bcNFPLM&s=C4toC0HQ2JwHKiamawbqvdjdidlwyhCP0XVneFagwkY&e=>
Lehi, Utah 84043<https://urldefense.proofpoint.com/v2/url?u=https-3A__maps.google.com_-3Fq-3D3400-2BNorth-2BAshton-2BBlvd-2C-2BSuite-2B470-2B-250D-250A-2BLehi-2C-2BUtah-2B84043-26entry-3Dgmail-26source-3Dg&d=DwMF-g&c=aXfg9j-An5sFdflqnjAj_USiCjXm5xEBIX8lTgWEt0U&r=ykVOlDeeWPn-JjTs8avieNrFskQ3kNzjf6_Jn_wG5HLeLIRsvzCN4-dJx6BFR4el&m=MMSIepRfj2CXVMH3CH8SghyPAoonRISMH__5bcNFPLM&s=C4toC0HQ2JwHKiamawbqvdjdidlwyhCP0XVneFagwkY&e=>

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