[Freeswitch-users] SDP with double m=audio lines and with the same port

[Ján Füri]

Hello,

My freeswitch's INVITE sdp offers two m=audio lines. (RTP/SAVP and 
RTP/AVP).
That's OK, because I want it so ;)

But both use the same audio port number. **
Is that possible to change this behavior ? To use different audio port 
numbers for each m=audio line ...
Please check my example below. In SDP from my freeswitch, both m-lines 
have *m=audio **22284*.

The reason, why I want to change this is WebRTC and RTPengine. RTPengine 
changes this INVITEs to RTP/SAVPF.
And the changed RTP/SAVPF is then not acceptable for chrome browsers. 
Firefox works well (so far).
I already reported this to the RTPengine but they say the problem is 
with INVITE from freeswitch because the m-audio lines use the same port.

My example :
incoming calls -> Media Server (freeswitch) -> Kamailio (sip and 
websocket proxy) -> WebRTP and SIP clients

I have found a feature *media_webrtc=true* so I could avoid using 
rtpengine for webrtc clients (that would be really awesome), but then 
classic sip clients are offered only with RTP/SAVPF and most sip phones 
do not know RTP/SAVPF so the calls are rejected :(


INVITE SDP from freeswitch:

v=0.
o=SBC 1464589775 1464589776 IN IP4 <freeswitch-public-ip>.
s=SBC.
c=IN IP4 <freeswitch-public-ip>.
t=0 0.
*m=audio 22284 RTP/SAVP 8 0 9 3 18.*
a=rtpmap:8 PCMA/8000.
a=rtpmap:0 PCMU/8000.
a=rtpmap:9 G722/8000.
a=rtpmap:3 GSM/8000.
a=rtpmap:18 G729/8000.
a=rtcp:22285 IN IP4 <freeswitch-public-ip>.
a=crypto:1 AEAD_AES_256_GCM_8 
inline:Q/O+iUzZ9AZLcrADA7w/XcpkmuW6yArr1vsaWc0coTyWUIRLX2qfCA7XDAs.
a=crypto:2 AEAD_AES_128_GCM_8 inline:mBb/SmBuSQNSm8lC5giUfZMCv0ZYINvsQiX2sw.
a=crypto:3 AES_CM_256_HMAC_SHA1_80 
inline:ahOTNSsdmHLIOBqvUyGyNjd+gDfAE/+jA6w7XwzGWxBMjtzf5akXNvM/OGy0jQ.
a=crypto:4 AES_CM_192_HMAC_SHA1_80 
inline:k7002pXV/SUT7JHhZTYaMV5keUTp1EP57M4rcNZnAoZZzsceTXA.
a=crypto:5 AES_CM_128_HMAC_SHA1_80 
inline:bHcV4E/OnzMkNeaFplPWt4RELILYZeGlifnJNlRV.
a=crypto:6 AES_CM_256_HMAC_SHA1_32 
inline:zJkowU1tc5rQR5BPpg2m3eE97ZqXLFFJc1Agh89XuZynPFMrXhO266+eMZCd2A.
a=crypto:7 AES_CM_192_HMAC_SHA1_32 
inline:2DwGI3UAPsLFBS5sJBsc+pzEsITQwDHCvB0u7pK/XEE3G8swsrw.
a=crypto:8 AES_CM_128_HMAC_SHA1_32 
inline:Jen6Gm56Z+4RTRmfpXTpSpoG5bduyythl1j21a15.
a=crypto:9 AES_CM_128_NULL_AUTH 
inline:Nn83liGQY7eY8LGs9qz/7EoPiHOpRgwY8H7Ts/b5.
a=ptime:20.
*m=audio 22284 RTP/AVP 8 0 9 3 18.*
a=rtpmap:8 PCMA/8000.
a=rtpmap:0 PCMU/8000.
a=rtpmap:9 G722/8000.
a=rtpmap:3 GSM/8000.
a=rtpmap:18 G729/8000.
a=rtcp:22285 IN IP4 <freeswitch-public-ip>.
a=ptime:20.




INVITE SDP from RTPengine :

v=0
o=SBC 1464589775 1464589776 IN IP4 212.232.17.66
s=SBC
c=IN IP4 <rtpengine-public-ip>
t=0 0
*m=audio 31836 RTP/SAVPF 8 0 9 3 18*
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:9 G722/8000
a=rtpmap:3 GSM/8000
a=rtpmap:18 G729/8000
a=ptime:20
a=sendrecv
a=rtcp:31837
a=setup:actpass
a=fingerprint:sha-1 
11:76:2D:2A:F7:0D:5A:23:9D:F6:0C:E7:4C:DF:1E:CB:BF:5D:76:4F
a=ice-ufrag:NauDcjVU
a=ice-pwd:AiHk6LF4tE0GElyFMWtLeod1wH
a=candidate:cE0FGbXWIfwj6OGD 1 UDP 2130706431 <rtpengine-public-ip> 
31836 typ host
a=candidate:cE0FGbXWIfwj6OGD 2 UDP 2130706430 <rtpengine-public-ip> 
31837 typ host
*m=audio 31866 RTP/SAVPF 8 0 9 3 18*
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:9 G722/8000
a=rtpmap:3 GSM/8000
a=rtpmap:18 G729/8000
a=ptime:20
a=sendrecv
a=rtcp:31867
a=setup:actpass
a=fingerprint:sha-1 
11:76:2D:2A:F7:0D:5A:23:9D:F6:0C:E7:4C:DF:1E:CB:BF:5D:76:4F
a=ice-ufrag:YxCyPhQV
a=ice-pwd:2vYt8YaMhIp2DSLPeYOKDqqBX0
a=candidate:cE0FGbXWIfwj6OGD 1 UDP 2130706431 <rtpengine-public-ip> 
31866 typ host
a=candidate:cE0FGbXWIfwj6OGD 2 UDP 2130706430 <rtpengine-public-ip> 
31867 typ host


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