No Teams voicemail message from vodafone mobile: AudioCodes / Teams Media Bypass


Call from Vodafone mobile <->AudioCodes <-> Teams (Forward to Voicemail)

The caller does not hear a team voicemail announcement. This problem only occurs with calls from vodafone mobile. The scenario could not be reproduced for all other providers tested.

In the debug recording of the audiocodes, the rtp stream of teams towards Vodafone could be listened to.

The filter could be created based on the ports and RTP traffic.

(acdr.ext.src_port == 8840 and rtp)

Since the AudioCodes passes on the RTP stream accordingly, a ticket was opened with Vodafone. After a short time, we also received a corresponding answer.

The problem at this point is that TEAMS seems to send the RTP packets following in certain constellations:

Problem is the CSRC marker 1, the R4 media gateways cannot do that. In comparison, all other known RTP packets from the sender have the marker 0.

Frame 235: 220 bytes on wire (1760 bits), 220 bytes captured (1760 bits)
Linux cooked capture
Internet Protocol Version 4, Src:, Dst:
User Datagram Protocol, Src Port: 49074, Dst Port: 55174
Real-Time Transport Protocol
[Stream setup by SDP (frame 117)]
10.. .... = Version: RFC 1889 Version (2)
..0. .... = Padding: False
...0 .... = Extension: False
.... 0001 = Contributing source identifiers count: 1
1... .... = Marker: True
Payload type: ITU-T G.711 PCMA (8)
Sequence number: 4668
[Extended sequence number: 70204]
Timestamp: 1178996717
Synchronization Source identifier: 0xc21ccacf (3256666831)
Contributing Source identifiers (1 items)
CSRC item 0: 0x1
Payload: d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5d5...

This makes only so far teams installations and is not understood on the media gateway to the Vodafone mobile network and thus the voicemail announcement is not heard.

This parameter is expected to be 0 by default. Here this parameter should be either set to 0 or removed completely and thus this should work for mobile networks.

D,H, This parameter indicates that in the call several streams are expected but in the end there is only one stream, which leads to the problem.

When disabling the media bypass, this parameter is set to the default value.

So (as far as I know) this problem only occurs in connection with Media Bypass and Vodafone as SIP provider.

To set the tag of the CSRC to 0, the switch in the IP Profile was set.

This regenerates the RTP streams in the direction of the provider, but also requires that enough transcoding resources (inform of hardware or licenses) are available. The subsequent test was successful.

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