Dialogic Media Gateway - DMG2000 no ringback tones sent

Symptom

Callers do not hear ringback tones when calling into Dialogic 2000 Media Gateways (DMG2000 Gateways) using a T1 WinkStart line ;  only silence is heard.

Reason for the issue / Background

There are several ways to configure DMG2000 Gateways for T1-CAS to collect DID digits; CPID type 1 and CPID type 2 with auto answer. Below is the trace that shows an incoming call CAS signaling with DMG set to CPID type 2 auto answer.

Incoming call signaled below.

013:05.360 [Tel-19    ] Prot     CAS Signaling   Rx: xF

DMG trace shows DMG2000 Gateway is configured auto answer below.

013:05.360 [Tel-19    ] Code     condAutoAnswerType2Cpid: YES

DMG sends a Wink.

013:05.360 [Tel-19    ] Prot     CAS Signaling   Tx: xF

013:05.648 [Tel-19    ] Prot     CAS Signaling   Tx: x0

DMG signals connect to T1 line.

013:05.936 [Tel-19    ] Code     t1casChangeCallState() 3b74c34 CONNECTED
013:05.936 [Tel-19    ] Event    Tone Detect Enabled (0xFF)
013:05.936 [Tel-19    ] Code     actOffHook
013:05.936 [Tel-19    ] Code     _t1casFsmDoHook - Sending Hook [off]
013:05.936 [Tel-19    ] Prot     CAS Signaling   Tx: xF

From the incoming call signaled to answered, it only takes about 600ms. This is not enough time for the DMG2000 Gateway to send ringback tones. The ringback tones only occur before the call is answered.

Solution

1. Configure the DMG2000 Gateway to use CPID type 1 (auto answer only available for type 2). 

2. Set Incoming Rings Before Answer to 2. 

This should allow enough time for the T1 line to send DTMF digits before the DMG2000 Gateway sends INVITE to the SIP end point. The DMG2000 Gateway will send the call to the SIP end point after 2 rings. The DMG2000 Gateway will also send ringback tones to the line until the SIP end point answers the SIP call.