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Push to Talk and 7925 phones

I have the following lab setup in place to test Cisco 7925 IP phones with Singlewire's Pust to Talk (PTT) application.

Lab Setup

WLC connected to a 3750 switch.

Single 1131AG access point registered with the WLC.

UCM version 8.6.2 with 9 x 7925 IP phones.

Singlewire PTT application running on a Windows 2003 server.

7925 phones have a dedicated WLAN and are registered with UCM. Normal phone to phone operation is ok.

Problem Symptoms

When I initiate a PTT session from any phone, the phones in the group all play the alerting sound and join the session.

••·                 I can see the phone displays changing from talking, listening, waiting ok. This is the correct behaviour.

••·                 When the first person in the session presses the talk button, no audio is heard. This is true when the first person who tries to talk is the session initiator or any of the called phones.

••·                 When a second attempt to talk is made from another phone in the session, audio is played successfully from that phone and subsequently from any phone in the session.

••·                 Using Wireshark I’ve captured packets between the WLC and the 3750 switch. In the scenario described above, I can see phones transmitting multicast packets to 239.0.1.188 ok, even when no audio is being played.

Further testing has revelaved another pattern in the behaviour:

Initiate the PTT session, all phones in the group play the alerting tone and are active in the session.
Wait for approximately 10 seconds before attempting to press the talk button any phone.
From any phone in the session, press the talk key and after about a one second delay, audio is played ok. Previously I had been pressing the talk key as soon as the session had been initiated, which is what a user would do in the real world.

This suggests that some kind of timer is at work here where, if I wait for 10 seconds before trying to talk, audio is played ok (albeit with a further one second delay).

If anyone has seen PTT deployed with UCM and 7925 phones I would like to hear about it.

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