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New Member

full duplex fax?

Is it possible for a Cisco 2620XM to be misconfigured and cause faxes to run half duplex?

Symptom: fax pages dying at half the page, or simply coming through missing half the data. Fax seems to connect and go through successful...just missing data.

Topology: analog fax-->audiocodesFXS-->ethernet-->2620XM--PRI to PSTN

SIP based IP telephony with Audiocodes analog gateways. Anyone have any experience troubleshooting faxes across VoIP? Is there a command that needs to be issued at the dial-peer level to force full duplex? Seems like it would just know to do that...why would half duplex even be an option?




Re: full duplex fax?

would the 2651XM happen to have an AIM-voice-30 installed as the DSP resources ? If so , add the following commands :

network-clock-participate wic 0 <--if VWIC is in slot 0

network-clock-select 1 t1 0/0

(assuming the PRI is on port t1 0/0 , change config to match if necessary)

New Member

Re: full duplex fax?

2651 does not have an AIM voice card. 10/100 ethe for the IP leg of calls. PRI for voice to PSTN.

Thanks for the command..I've never heard of that one. I will look it up and see what it does. Might not apply to my situation...but always like to learn new commands.


Cisco Employee

Re: full duplex fax?

Few questions:

1) What type of Fax over ip protocol does Audiocodes support ?

2) Can you make a call from FXS port on Audiocodes analog gateway out to PRI and what type of voice quality do you have ?

3) What type of codec are you using between Audiocodes and Cisco ?

4) To cover all ground check your ethernet interface on 2620 and make sure you do not have any errors or collisions.

Normally in fax world you do not have 2 fax machines talking at the same time a single fax machine is who originates call sends data to terminating fax machines. The terminating fax machines usually negotiates capabilites with originating fax machines which we call it training. Once this is done the terminating fax machines collects data that is send from originating fax machines.

Hope that helps..



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