[SR-Users] question regarding rtpengine and ICE candidate selection

[Andrew Chen]

Hi all,

I was wondering if someone can help me understand how the ICE parameter
works in the rtpengine module works.

So basically our client does an ICE candidate lookup and grabs a list of
them and applies it to the INVITE that gets sent to the Kamailio.  The list
looks like this:

2020-12-03T18:05:46.456030+00:00 ashmainkama51 kamailio[22147]:
a=candidate:3373280875 1 udp 2122262783
2001:8a0:78fc:7000:e1d7:e93:3c50:ee71 59827 typ host generation 0
network-id 2 network-cost 10
2020-12-03T18:05:46.456057+00:00 ashmainkama51 kamailio[22147]:
a=candidate:3040609428 1 udp 2122197247
2001:8a0:78fc:7000:d979:bf75:dbc0:69f 59828 typ host generation 0
network-id 3 network-cost 10
2020-12-03T18:05:46.456081+00:00 ashmainkama51 kamailio[22147]:
a=candidate:1681997092 1 udp 2122129151 192.168.1.66 59829 typ host
generation 0 network-id 1 network-cost 10
2020-12-03T18:05:46.456106+00:00 ashmainkama51 kamailio[22147]:
a=candidate:2274611867 1 tcp 1518283007
2001:8a0:78fc:7000:e1d7:e93:3c50:ee71 9 typ host tcptype active generation
0 network-id 2 network-cost 10
2020-12-03T18:05:46.456131+00:00 ashmainkama51 kamailio[22147]:
a=candidate:4223662180 1 tcp 1518217471
2001:8a0:78fc:7000:d979:bf75:dbc0:69f 9 typ host tcptype active generation
0 network-id 3 network-cost 10
2020-12-03T18:05:46.456155+00:00 ashmainkama51 kamailio[22147]:
a=candidate:717406676 1 tcp 1518149375 192.168.1.66 9 typ host tcptype
active generation 0 network-id 1 network-cost 10
2020-12-03T18:05:46.456180+00:00 ashmainkama51 kamailio[22147]:
a=candidate:2130547417 1 udp 8199935 206.81.191.27 61165 typ relay raddr
85.247.0.121 rport 53091 generation 0 network-id 1 network-cost 10


In the rtpengine_offer, I have this:

rtpengine_offer("ICE=force DTLS=passive replace-session-connection
replace-origin external internal");

What i am trying to do is to tell the freeswitch endpoint to use rtpengine
as ICE candidate and I see in the SDP this is happening:

a=candidate:6296910676 1 udp 659136 206.81.191.52 52766 typ host generation
0

Btw..206.81.191.52 is a separate AWS instance running rtpengine binary.

On the rtpengine_answer, I tell the remote client side the same thing..use
rtpengine as your ICE candidate:

rtpengine_answer("ICE=force DTLS=passive replace-session-connection
replace-origin internal external");

and this is snippet from 200 OK:

a=candidate:6296910676 1 udp 659136 206.81.191.52 52766 typ host generation
0

Question:

Why does the rtpengine logs still show that it's trying to use
2001:8a0:78fc:7000:e1d7:e93:3c50:ee71 as RTP candidate in this scenario?

Dec  3 18:05:47 ashmainrtpe42 rtpengine[8505]: DEBUG:
[ep1sbnkk9tikhg4kpmot]: Forward to sink endpoint:
2001:8a0:78fc:7000:e1d7:e93:3c50:ee71:59827 (RTP seq 25423 TS 0)

I thought ICE=force will handle such adjustments so that all rtp is handled
by the rtpengine to our client and bypass the STUN server?



Thanks.

-- 
Andy Chen
Sr. Telephony Lead Engineer
achen@ <achen at thinkingphones.com>fuze.com

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