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tdm gateway modem passthrough

Hi! The problem is the following: the customer had a TDM PBX connected to PSTN through E1 PRI. After implementing IP-telephony we installed Cisco3825 with 2 PRIs on vwics (1st facing PSTN, 2nd facing local PBX) to host applications and allow PSTN access from voip peers. The problem is that modem calls from modems attached to PBX towards PSTN have become unstable, loosing connection after ~1 min. Gateway sees it as normal clearing on local modem side. In this case gateway 3825 simply switches calls from one PRI to the other, but it brings in this problem. What could be done to solve it? There is no modem detection implemented anywhere now and I don't know why adding one voice switch could lead to that. Any suggestions would be appreciated.

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Hall of Fame Super Gold

Re: tdm gateway modem passthrough

Configure network-clock-participate and network-clock-select 1 for the interface to PSTN.

Configure clock source internal for the interface going to PBX.

2 REPLIES
Hall of Fame Super Gold

Re: tdm gateway modem passthrough

Configure network-clock-participate and network-clock-select 1 for the interface to PSTN.

Configure clock source internal for the interface going to PBX.

New Member

Re: tdm gateway modem passthrough

Thanks, Paolo!

Somehow I missed the "select" command.

I did set "clock source int" on PBX controller and "clock source line" on PSTN controller and I thought the gateway would prefer line source if given, but oddly it prefers internal until explicitly configured to prefer selected clock source.

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