[SR-Users] No ACK from MS Teams

Thu Feb 11 08:31:27 CET 2021

Dear List

Hope this email finds you all well.

I have followed the below tutorial on how to integrate Kamailio with MS
Teams

https://skalatan.de/en/blog/kamailio-sbc-teams

However i have been facing an issue with MS Teams with direct routing where
MS Teams does not send back an ACK after a 200 OK.

The current inbound call flow is the following:

*MS Teams ==> Kamailio==>Asterisk*

Once Asterisk answers with 200 OK we send this 200 OK back to MS Teams
however, MS Teams just doesn't answer back with ACK and call drops.

The below trace shows the INVITE coming from MS Teams and the 200 OK we
send back.

||||||||||||||||||||
====================
tag: rcv
pid: 26135
process: 23
time: 1613025911.983278
date: Thu Feb 11 08:45:11 2021
proto: tls ipv4
srcip: 52.114.132.46
srcport: 4352
dstip: SBC_IP_ADDR
dstport: 5061
~~~~~~~~~~~~~~~~~~~~
INVITE sip:+357XXXXXXXX at SBC-FQDN:5061;user=phone;transport=tls SIP/2.0
FROM: Phillip Kyriacou<sip:+357XXXXXXXX at sip.pstnhub.microsoft.com:5061
;user=phone>;tag=c3da9477e05d45fca31c24a155af3318
TO: <sip:+357XXXXXXXX at SBC-FQDN:5061;user=phone>
CSEQ: 1 INVITE
CALL-ID: 9cb9a2f3144e594c87bccda76791c28e
MAX-FORWARDS: 70
VIA: SIP/2.0/TLS 52.114.132.46:5061;branch=z9hG4bK0cf2c45
RECORD-ROUTE: <sip:sip-du-a-us.pstnhub.microsoft.com:5061;transport=tls;lr>
CONTACT: <sip:api-du-b-euwe.pstnhub.microsoft.com:443
;x-i=6e5254d9-79c2-4657-b54b-68791aa8e81f;x-c=9cb9a2f3144e594c87bccda76791c28e/d/10/e21a
6ff7125e4cbd91e75ec687fd4c5d>
CONTENT-LENGTH: 1097
MIN-SE: 300
SUPPORTED: timer
USER-AGENT: Microsoft.PSTNHub.SIPProxy v.2021.2.9.1 i.USEA.7
CONTENT-TYPE: application/sdp
ALLOW: INVITE,ACK,OPTIONS,CANCEL,BYE,NOTIFY
SESSION-EXPIRES: 3600

v=0
o=- 170239 0 IN IP4 127.0.0.1
s=session
c=IN IP4 52.113.40.94
b=CT:10000000
t=0 0
m=audio 51414 RTP/SAVP 104 9 103 111 18 0 8 97 101 13 118
c=IN IP4 52.113.40.94
a=rtcp:51415
a=ice-ufrag:BwFs
a=ice-pwd:sFyvnfQ9iH101E80ZKjCxi9+
a=rtcp-mux
a=candidate:1 1 UDP 2130706431 52.113.40.94 51414 typ srflx raddr
10.0.137.19 rport 51414
a=candidate:1 2 UDP 2130705918 52.113.40.94 51415 typ srflx raddr
10.0.137.19 rport 51415
a=candidate:2 1 tcp-act 2121006078 52.113.40.94 49152 typ srflx raddr
10.0.137.19 rport 49152
a=candidate:2 2 tcp-act 2121006078 52.113.40.94 49152 typ srflx raddr
10.0.137.19 rport 49152
a=label:main-audio
a=mid:1
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:Igc2LVM9FH5kQtkRpHw99H5SB7Rd7eKzJy4gdWJg|2^31
a=sendrecv
a=rtpmap:104 SILK/16000
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

||||||||||||||||||||
====================
tag: snd
pid: 26086
process: 6
time: 1613025917.726664
date: Thu Feb 11 08:45:17 2021
proto: tls ipv4
srcip: SBC_IP_ADDR
srcport: 5061
dstip: 52.114.132.46
dstport: 5061
~~~~~~~~~~~~~~~~~~~~
SIP/2.0 200 OK
Via: SIP/2.0/TLS 52.114.132.46:5061;branch=z9hG4bK0cf2c45
Record-Route:
<sip:SBC-IP-ADDR:5060;ftag=c3da9477e05d45fca31c24a155af3318;lr=on>
Record-Route:
<sip:SBC-FQDN:5061;transport=tls;ftag=c3da9477e05d45fca31c24a155af3318;lr=on>
Record-Route: <sip:sip-du-a-us.pstnhub.microsoft.com:5061;transport=tls;lr>
From: Phillip Kyriacou<sip:+357XXXXXXX at sip.pstnhub.microsoft.com:5061
;user=phone>;tag=c3da9477e05d45fca31c24a155af3318
To: <sip:+357XXXXXXXX at SBC-FQDN:5061;user=phone>;tag=as659924a4
Call-ID: 9cb9a2f3144e594c87bccda76791c28e
CSeq: 1 INVITE
Server: MediaGW V1.0
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO,
PUBLISH, MESSAGE
Supported: replaces, timer
Session-Expires: 1800;refresher=uas
Contact: <sip:357XXXXXXXX at ASTERISK_PUBLIC_IP:5060>
Content-Type: application/sdp
Require: timer
Content-Length: 339

v=0
o=root 411266324 411266324 IN IP4 ASTERISK_PUBLIC_IP
s=ASTERISK
c=IN IP4 ASTERISK_PUBLIC_IP
t=0 0
m=audio 14416 RTP/SAVP 0 8 101
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:9PcaAGjbemJKTERlFTcVwmLRQoDSEQPxX0L1a6RF
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=maxptime:150
a=sendrecv
||||||||||||||||||||

Am I doing anything wrong here that MS Teams wont respond to my 200 OK? The
Kamailio SBC is showing active on MS Teams and Kamailio dispatcher shows
all the MS Team hubs as AP. I also can't see any errors in the log file

My TLS cfg has the following:
======================

*[server:default]method = TLSv1.2+verify_certificate =
yesrequire_certificate = yesprivate_key =
/etc/letsencrypt/live/sbc.intelligentsupport.eu/privkey.pem
<http://sbc.intelligentsupport.eu/privkey.pem>certificate =
/etc/letsencrypt/live/sbc.intelligentsupport.eu/fullchain.pem
<http://sbc.intelligentsupport.eu/fullchain.pem>ca_list =
/etc/ssl/certs/ca-certificates.crt*

*[client:default]method = TLSv1.2+verify_certificate =
yesrequire_certificate = yesprivate_key =
/etc/letsencrypt/live/sbc.intelligentsupport.eu/privkey.pem
<http://sbc.intelligentsupport.eu/privkey.pem>certificate =
/etc/letsencrypt/live/sbc.intelligentsupport.eu/fullchain.pem
<http://sbc.intelligentsupport.eu/fullchain.pem>ca_list =
/etc/ssl/certs/ca-certificates.crt*

Thanks very much in advance!

Phillip
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