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Cisco MC3810 Multiservice Access Concentrators

Field Notice: Cisco MC3810 AAL2 Fax Modem Doesn't Work with Cisco IOS Software Versions 12.1(3)XH, 12.1(2)XH or 12.1(2)T


September 7, 2001



Products Affected

Product

Comments

MC3810

Cisco MC3810 Multiservice Access Router

Problem Description

Basic FAX/Modem upspeeding is not initiated when V.21/2100Hz tones are injected into an ATM Adaptation Layer 2 (AAL2) DS0. The resulting debug output shows many CODEC mismatch messages.

A sample network diagram is represented below.

fn14035.gif

Background

Due to internal version control conflicts, certain key elements necessary to allow AAL2 connections to upspeed to G.711 when fax or modem signals are detected have been omitted. As a result, upspeeding is not working.

Problem Symptoms

Basic FAX/Modem upspeeding is not initiated when V.21/2100Hz tones are injected into an AAL2 DS0.

Workaround/Solution

You can prevent upspeeding by restricting the PVC bandwidth on the CAC master. If this workaround is unacceptable, do not use Cisco IOS 12.1(2)T images for AAL2 connections.

The solution is to update the Cisco IOS version to 12.1(3)T or later.

DDTS

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DDTS

Description

CSCdr78184 (registered customers only)

FAX/Modem not upspeeding.

For More Information

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