T1: A Survival Guide

CSU/DSU Configuration

CSU/DSU configuration can be a frustrating affair for many reasons. Each vendor has a slightly different way of describing features, and terms in the manual may differ from the terms your telco uses. In many cases, your service provider or telco will include a CSU/DSU in the startup charges for a new line and will even pre-configure the CSU/DSU to work with the new line. Depending on the model, configuration can be frustrating. Some CSU/DSUs are configured with jumpers or DIP switches, and the cheapest ones even require a power-cycle to reread the jumper or switch settings. Higher-end CSU/DSUs have menu-driven configuration and are far easier to use.

While the array of configuration options may be bewildering, the following options are critically important and account for most of the problems you may see:

Framing

The choice is between SF and ESF, and the former is rare and getting rarer. This setting is supplied by the telco because it must match the telco equipment.

Line code/DS0 channel speed

These two settings are related. AMI encoding is almost always associated with 56k component DS0 channels, and B8ZS is always associated with 64k component DS0s. Depending on your CSU/DSU, configuration may be required for both line code and DS0 speed or just one of the two. Like framing, these settings are supplied by the telco.

Line build out

By the time a pulse reaches a T1 repeater, it is assumed that a certain amount of attenuation will have already occurred. T1 uses ...