Cisco Catalyst 4000 Series Switches

Document ID: 5241

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
Problem
Solution
Related Information

Introduction

This document provides a Cisco IOS® Software command that resolves T1 controller slips caused by conflicting clock sources on the motherboard of the Cisco Access Gateway Module for the Catalyst 4000 family switches. Excessive slips might cause poor voice quality and incomplete fax or modem calls.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on these software and hardware versions:

• Cisco Access Gateway Module for the Catalyst 4000 family switches

Conventions

For more information on document conventions, refer to the Cisco Technical Tips Conventions.

Problem

Slips might occur in any VWIC E1/T1 controller in the Cisco Access Gateway module connected to telco or PBX. This will not happen if the same VWIC is installed in a Cisco 2600/3600 chassis.

The TDM clock reference on the Cisco Access Gateway module can be derived from one of seven sources. These are the free running on-board clock and two recovered clock sources from each VIC slot that contains an E1/T1 card. The default reference is the on-board clock.

Solution

The frame-clock-select command can be used to select one of the E1/T1 ports as the primary reference.

Use frame-clock-select <priority E1/T1 slot/port>, where priority 1 is the primary reference.

For example: frame-clock-select 1 T1 2/0 sets the clock recovered from T1 controller 2/0 as the primary clock.

Related Information

• Voice Technology Support
• Voice and IP Communications Product Support
• Recommended Reading: Troubleshooting Cisco IP Telephony
• Technical Support - Cisco Systems