Modem Pass through to remote PBX

Unanswered Question
Sep 5th, 2010
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Dear All,

I would like to use the cisco router 3640 (with T1 card) and cisco 2621 (with 2 x FXS card) to simulate the network & pstn environment to test the modem pass through, here is the detail connection:

Analog Phone (Ext: 451660) <--> [FXS] Cisco Router 2621 <---- LAN ----> Router 3640 [T1] <--> [T1] PBX (Panasonic) <--> Analog Phone (Ext: 454820, Modem)

The dial-peer on the router 2621 & 3640 is working as I can call in/out from PBX analog phone, and I was success to connect the PC (with modem port, and use the hyperterminal, atdt454820) from Outside PC (with modem port, Ext: 451660).

But I was fail to dial-out from PBX analog phone (454820) to 451660.

From Cisco router 2600:

dial-peer voice 45166 voip
destination-pattern 45166.
modem passthrough nse codec g711ulaw redundancy
session target ipv4: (Router 3640)

From Cisco router 3640

dial-peer voice 454820 voip
destination-pattern 454820
modem passthrough nse codec g711ulaw redundancy
session target ipv4: (Router 2600)

Here is the link I try to follow to do:

I would like to know if there is any miss-configure or how can I troubleshoot (to find out the cause) which I cannot connect from PBX' PC.


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Steven Holl Tue, 09/07/2010 - 08:04
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  • Cisco Employee,

Note that anytime a call traverses a voice gateway, we match *two* dial-peers, not one.  We match one inbound, and one outbound.  In your scenario, if the FXS side originates the call, it would be:

fxs(inbound pots)router(outbound voip)----LAN-----(inbound voip)router(outbound pots)---T1

The algorithm for how this works is documented in this link.  I recommend having a few reads over this:

If you can get these debugs, I can take a deeper look into the failure:

debug voip ccapi inout

debug isdn q931

debug vpm sig

debug h225 asn1

debug h245 asn1

Collect these in the following manner:

Router(config)# service sequence
Router(config)# service timestamps debug datetime msec
Router(config)# logging buffered 10000000 7
Router(config)# no logging con
Router(config)# no logging mon
Router(config)# voice iec syslog

Router# term len 0

Router# sh logg

Also send the full configs of both gateways.



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