CRC_Error.pdf

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NTM CRC Errors

Document ID: 10874

Introduction

Prerequisites

Requirements

Components Used

Conventions

Error Definition

Error Example

Troubleshoot

Related Information

Introduction

This document discusses Network Trunk Module (NTM) Cyclic Redundancy Check (CRC) errors.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.

The information in this document was created from the devices in a specific lab environment. All of the

devices used in this document started with a cleared (default) configuration. If your network is live, make sure

that you understand the potential impact of any command.

Conventions

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

Error Definition

This error applies to the IGX NTM with T1 and E1 backcards. The NTM with T1 backcard must beconfigured for Extended Superframe Framing (ESF).

The errors refer to CRC errors on the T1and E1 framing level and indicate a line quality problem. CRC errors

are a critical inservice performance measurement that detect bit errors with approximately 98 percent

accuracy. Possible CRC error causes include:

Hardware malfunction

Loose or unconnected shield ground wires

Bridge taps

Timing problems

Electrical interference


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For E1, the CRC4 multiframe uses four international bits for CRC4. The CRC4 information is provided in

timeslot 0 of the E1 which uses CRC4 multiframing. CRC4 detects bit errors in a block of data with high

accuracy. CPE performs CRC4 calculations on the E1to guarantee data quality.

Error Example

The likely location of the equipment errors is highlighted in yellow.

Troubleshoot

These troubleshooting activities are intrusive. Complete these steps in a maintenance window only:

If the user traffic is affected.

Or

Ifdsptrks indicates an error condition still persists, such as when the trunk is not in ClearOK.

Both ends of the trunk must be active while you troubleshoot.

Issue the dsptrks command to verify that the trunk is active.

If the trunk number is not displayed in the dsptrks screen, the trunk is not active. To activate a trunk,

issue the uptrk command.

1.

Check the cable connection between the trunk card and the next upstream device.

Note: The term upstream refers to the relative position of a piece of transmission equipment in the

network.

The NTM is:

Downstream from the nearest piece of transmission equipment in the receive direction.a.

Upstream from the nearest piece of transmission equipment in the transmit direction.

Typically, the next upstream device is the local channel service unit (CSU) or network

termination (NT). If the dsptrks display indicates no errors at the remote IGX, a oneway

problem exists.

An example of such a problem is when the physcial link received towards the local trunk has

a problem but the transmission direction works properly.

b.

2.

To check the local cable, leave it connected to the trunk card but you must remove it from the CSU or

NT.

3.


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Put a loopback plug on the disconnected end of the cable. If the dsptrkerrs stops to

increment CRC errors, then the cablefunctions properly.

a.

Before you proceed, monitor dsptrkerrs for a few minutes.b.

You must make sure the signal strength is sufficient.

You must check to see if the maximum line length is not exceeded.a.

For T1 trunks, issue the cnftrk command in order to configure the line buildout (LBO). .

LBO compensates for the loss in decibels based on the distance from the trunk card to thefirst repeater in the circuit. A longer distance from the device to the repeater requires a boost

to the signal strength on the circuit to compensate for loss over that distance.

b.

4.

Check the CSU or NT for proper function.5.

Ask your Telco to check the line.6.

If the problem persists after you use these steps to troubleshoot, contact Cisco Technical Support.

Related Information

How to Distinguish Between Different IGX NTM Models

IGX 8400 NTM Trunk Errors Definition

Downloads WAN Switching Software

International Telephony Union (ITU) Recommendation G.704

Cisco WAN Switching Solutions Cisco Documentation

Guide to New Names and Colors for WAN Switching Products

Technical Support Cisco Systems

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Updated: Apr 30, 2009 Document ID: 10874

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CRC_Error.pdf