Microsoft Teams Direct Routing - Non Media Bypass Mode

[Ehud_Bart]

Trying to enable SBC working with Microsoft Teams Direct routing in 2 modes of operation "Media Bypass" configured as TRUE / FALSE.

When SBC is working towards Teams configured with "Media Bypass" as true, calls establish OK.

But, when Teams configured with "Media Bypass" as false, calls fail.

Scenario a: SBC sends INVITE and replied with 488  "sdp parse error".

Scenario b: SBC replies with 200OK on INVITE and receives a BYE message from Teams.

On both mode of operation of "Media Bypass", SBC sends exactly the same messages.

Is there a difference in the SIP/SDP messages between these 2 modes of operations?

Are there Teams LOGs pointing out the root cause of the difference between the two modes?

[#2 · Accepted solution]

@Ehud_Bart 

There isn't much on the Teams side you can look at, but you should be able to look at the logs from the SBC side.  What SBC are you using?  Depending on the SBC there are additional configurations required there, such as on the AudioCodes line, you need to enable ICE Lite.

In terms of operational differences between the two, there will be ICE information in the messages that will announce media bypass support along with candidates.  These are not in the headers, but in the SIP body.  This is a sample of an INVITE that has the necessary headers for media bypass.

INVITE sip:+1234567890@sbc1.provider.tld:5061;user=phone;transport=tls SIP/2.0 
FROM: MYUSER <sip:+1098765432@sip.pstnhub.microsoft.com:5061;user=phone>;tag=3f2a4ff9b10449cfb8cd9d9f43a8e77b
TO: <sip:+1234567890@sbc1.provider.tld:5061;user=phone>
CSEQ: 1 INVITE
CALL-ID: abc123
MAX-FORWARDS: 70
VIA: SIP/2.0/TLS 52.114.132.46:5061;branch=z9hG4bK195f743f
RECORD-ROUTE: <sip:sip-du-a-us.pstnhub.microsoft.com:5061;transport=tls;lr>
CONTACT: <sip:api-du-c-usea.pstnhub.microsoft.com:443;x-i=aaa-bbb-ccc-ddd;x-c=abc123/d/8/abc123>
CONTENT-LENGTH: 1138
MIN-SE: 300
SUPPORTED: timer
USER-AGENT: Microsoft.PSTNHub.SIPProxy v.2020.3.2.6 i.USEA.1
CONTENT-TYPE: application/sdp
ALLOW: INVITE,ACK,OPTIONS,CANCEL,BYE,NOTIFY
SESSION-EXPIRES: 3600

v=0
o=- 93204 0 IN IP4 127.0.0.1
s=session
c=IN IP4 52.114.152.110
b=CT:10000000
t=0 0
m=audio 52592 RTP/SAVP 104 117 9 103 111 18 0 8 97 101 13 118
c=IN IP4 52.114.152.110
a=rtcp:52593
a=ice-ufrag:9X9v
a=ice-pwd:123abc
a=rtcp-mux
a=candidate:1 1 UDP 2130706431 52.114.152.110 52592 typ srflx raddr 10.0.136.99 rpor [Time:06-03@12:21:00.391]
t 52592 
a=candidate:1 2 UDP 2130705918 52.114.152.110 52593 typ srflx raddr 10.0.136.99 rport 52593
a=candidate:2 1 tcp-act 2121006078 52.114.152.110 49152 typ srflx raddr 10.0.136.99 rport 49152
a=candidate:2 2 tcp-act 2121006078 52.114.152.110 49152 typ srflx raddr 10.0.136.99 rport 49152
a=label:main-audio
a=mid:1
a=crypto:1 AES_CM_128_HMAC_SHA1_80 inline:XFBdTTZaQ4YRASWBQzNDuh4eN5ztKQfMJYJMWE1Q|2^31
a=sendrecv
a=rtpmap:104 SILK/16000
a=rtpmap:117 G722/8000/2
a=rtpmap:9 G722/8000
a=rtpmap:103 SILK/8000
a=rtpmap:111 SIREN/16000
a=fmtp:111 bitrate=16000
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 RED/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=rtpmap:13 CN/8000
a=rtpmap:118 CN/16000
a=ptime:20

In a non-media bypass world, the ICE and candidates will be missing.