Isolating Network / Workstation Problems

David Zolotko
May 23, 1999

This document was drafted to assist in the isolation of Ethernet based communication problems. The following procedure can be used to troubleshoot both 10BaseT and 100BaseT networks that are using twisted pair (copper) wiring.

When to Use This Procedure

Use this procedure to isolate Ethernet communications used by workstations from the network devices such as switching hubs and routers. This will allow you to focus your troubleshooting efforts towards the device where the problem is originating.

A common scenario where you may wish to employ this procedure is when workstation users are complaining that data throughput rates or "network speeds" are too slow. You can find out if the problem is originating from the direction of the workstation or the direction of the network.

What You Need

Scitex Part Number: 605C70100. Category 5 rated crossover cable/ 7foot length. Add this to your tool kit as a troubleshooting tool.

Overview

Ethernet communication is based on the EIA/TIA 568A/B standard, which specifies which wire pairs in a twisted pair Ethernet cable carry the receive channel and which wire pairs carry the transmit channel. The delivery of the transmit data from the sender to the receive channel of the recipient is an internal function of the network hub.

A crossover cable simply has the transmit channel at one end wired to the receive channel at the other end, and vice versa. This allows you to connect two Ethernet devices together directly, without the need for a network hub.

With a crossover cable installed between two workstations, you can bypass the need for the network hub and you can measure data throughput rates between the suspect workstation and a known good workstation. Then compare the file transfer times between the network attached, and the crossover connected configurations and focus your troubleshooting in the direction of the problem.

Procedure

Before doing anything, select or create a file to use for data transfer speed testing. Typically a 40 to 50-MB file will work well. Use only this file for the transfer time tests.
Move the file to the workstation (from a known good workstation) across the network and time how long it took in seconds. (Send the file back also). Divide the file size in Kbytes by the transfer speed in seconds. This will give you data throughput in KB/sec.
Now remove the workstation in question from the network and link it to the known good workstation (also removed from the network) directly, using the crossover cable.
Transfer the same file in the same manner and record the transfer time once again. (check send and receive rates).
Compare the results. If the file transfer rate is significantly faster using the crossover cable, troubleshoot in the direction of the network. If the file transfer rate remains unchanged, troubleshoot towards the direction of the workstation

Common Problems:

Damaged network patch cables
Out of date NIC drivers/software
Mis-matched auto-negotiate settings
Transceivers with "SQE Test" enabled
Problem port on network hub
Network traffic congestion

Scitex Network Services Group