[asterisk-users] ISDN30 Timing Sources

[Jon Morgan]

Hi All,

I have a query regarding timing issues on a back-to-back asterisk setup we have here in the UK.  Let me explain.

We have a 2 port Digium TE220P card, one span is configured to connect to our ISDN30 provider (British Telecom), the other span connects to our internal PBX.  Here's the zaptel.conf snip:

span=1,1,0,ccs,hdb3,crc4
bchan=1-15
dchan=16
bchan=17-31

span=2,0,0,ccs,hdb3,crc4
bchan=32-46
dchan=47
bchan=48-62

We bridge the two legs of the call together in order to perform some magic (recording, etc.).  Our problem is that we occasionally get call quality problems such as breaks in the call, one way audio, clicks and pops on the line, etc.

I checked for information with regard to these quality issues and have found possible solutions ranging from echo training to timing issues.

Now, my question is, do we have the timing sources configured correctly on our spans above?  As you can see, we've set span 1 to make the equipment at the far end of the E1/T1 link the preferred source of the master clock and disabled span 2 so it's never a source of timing but is this correct?

I've seen other configuration such as the following:

span=1,1,0,ccs,hdb3,crc4
bchan=1-15
dchan=16
bchan=17-31

span=2,1,0,ccs,hdb3,crc4
bchan=32-46
dchan=47
bchan=48-62

Would adding span 2 as a timing source maybe fix our clicking issues?

Kindest Regards,

Jon Morgan

Jon Morgan
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