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Faxes and Modems, WS-6624 - not working

According to the release notes for CM 3.1,


CSCdu84212 Modem connections on C6624 FXS are a low speed or unreliable.

Workaround: None exists.

Which is exactly the problem I'm having.

The release notes for 3.1.2(a) show that this is still unresolved.


Cat6509, CM3.1(1), WS-6624, connection to the outside terminating on WS-6608 T1 PRI.

Most outbound modem connections are not connecting, and if they do it's 2400 baud. The biggest problem is some mainframe modems that have had their instruction manuals turn to dust a long ago and are strapped for 9600 baud. The modems train with the distant end and then just give up after continually retrying for about 60 seconds.

If there is no solution to the WS-6624 FXS issue, then what IP Telephony FXS device _does_ provide reliable fax and modem connectivity?

The WS-6624 is supposed to have some sort of "modem pass through" configuration. The docs say that it's dynamically changing the DSPs (removing VAD, changing jitter settings, etc) when it sees a modem connection. Somethings not working right, and there's nothing obvious in the CM gateway config screen or at the enable prompt on the Cat.

Cisco Employee

Re: Faxes and Modems, WS-6624 - not working

The loads for the 6624 that fix this bug are included in the 3.1(2a) upgrade. Looks like the bug report itself needs to be updated to show this. If you are running 3.1(1) then you should be fine to run the upgrade. If you are running 3.0, then beware of CSCdv43128.

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