Dialogic Voice Cards - Minor audio corruption may occur while playing or recording on some JCT channels
Symptom
Minor audio corruption lasting about 4 to 60 ms may occur while playing or recording on some channels of a Dialogic JCT Series Media Board. This corruption may manifest itself as either a small loss of data or a repeat of previous data. Typically, these anomalies are not detectable by the human ear, but may cause issues with automated algorithms that are processing the data (for example: DTMF detectors, FSK transmission).
Reason for the issue
The issue is caused by the way that some JCT voice devices may share a communication path with signaling devices. The signaling messages have a higher priority when communicating with the host so, if there are a large number of messages present, this may create an under-run condition where the voice device buffers are not serviced in a timely manner. This may cause the firmware to start to 'replay' or 'overwrite' a buffer causing some data to be repeated or silence to be played out on the line until the under-run is resolved and the buffers are serviced.
Often, these anomalies only last a few milliseconds (4-20) but the duration will depend on the signaling load on the DTI device.
This issue does not apply to all voice devices on the system. Only voice devices that share memory space with signaling DTI devices may be affected. You can check if any voice devices are sharing memory with signaling devices by looking at the voxcfg file located in the <Dialogic install path>\Dialogic\cfg\ directory. Voice cards that share the same virtual ID as the dti may be affected.
For example, the voxcfg may contain the following entries:
#
# Board Type - D/300JCT-E1 #2 in slot 2/6
#
dxxxB1 4 2060007 C E2000000 2000 22 SPAN 50715
dxxxB2 4 2060007 C E2002000 2000 22 SPAN 50716
dxxxB3 4 2060007 C E2004000 2000 22 SPAN 50717
dxxxB4 4 2060007 C E2006000 2000 22 SPAN 50718
dxxxB5 4 2060007 C E2000000 2000 2 SPAN 50719
dtiB1 30 2060007 T E2000000 2000 2 E1SPAN 50720
dxxxB6 4 2060007 C E2002000 2000 2 SPAN 50721
dxxxB7 4 2060007 C E2004000 2000 2 SPAN 50722
dxxxB8 2 2060007 C E2006000 2000 2 SPAN 50723
In this case, dtiB1 has an ID of 2, and dxxxB5-dxxxB8 also share that same ID. This means that the 16 voice devices dxxxB5C1 – dxxxB8C4 may be affected by corruption when there is signaling traffic on dtiB1.
Fix / Solution
This is a permanent architectural limitation on the Dialogic JCT Series Media Boards.
Workaround
One way to minimize the impact of this issue is to not use the play or record functions to transmit data or DTMF information. If DTMF tones are to be transmitted then dx_dial may be used. If data is being transmitted then non-affected voice devices may be used. (dxxxB1-dxxxB4 in the above example).
Product List
Dialogic JCT Series Media Boards