Cisco 700 Series ISDN Access Routers

Document ID: 10262

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
Problem
Background
Description
Solution
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Introduction

A problem was introduced in the 4.1(1) software release for Cisco 700 Series Routers when using Cisco Fast Step version 1.00 to configure the router on NI-1 ISDN switch types.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

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

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Problem

A Cisco 700 Series Router might not respond to Cisco Fast Step version 1.00 if configured for an NI-1 switch type. This problem only occurs if you use Cisco Fast Step version 1.00 to configure the router.

Background

For NI-1 switch types, IOC compliance dictates that when an ISDN device is first powered on, the device must wait a random interval that ranges between 1 and 300 seconds before it registers its SPIDs. This interval, known as the T-WAIT time, exists to protect the telco switch from a flood of SPID registrations if devices all power on at the same time (as in a power outage situation).

Description

4.1(1) software implements the T-WAIT interval both upon power up and whenever the router1s switch type configuration is changed to NI-1. The latter causes problems for Cisco Fast Step users.

Cisco Fast Step configures the router with the switch type, SPIDs, and so on, and then waits up to 70 seconds for SPID validation before it allows the user to proceed. This causes a problem because the T-WAIT interval for NI-1 switch types is a random value between 1 to 300 seconds. If the T-WAIT interval exceeds Cisco Fast Step1s 70 second window, Cisco Fast Step times-out with a SPID registration error.

The impact of the T-WAIT period is minimal and transparent to the end users if the console is used to configure the router instead of Cisco Fast Step. This message appears on the console to inform the user that the router is in T-WAIT and that the T-WAIT interval can be bypassed by initiating a call.

Please wait for T-WAIT timer to expire in __ seconds Make a call to bypass this timer

For Cisco Fast Step 1.00 users, the T-WAIT period cannot be bypassed because calls cannot be placed until SPIDs are registered.

Note: There is no indication that the router is in T-WAIT other than through the command line interface.

Solution

• Cisco Fast Step version 1.01 places an outgoing call to force the router to bypass the T-WAIT period if the 700 Series Router is configured for an NI-1 switch type.

• Possible engineering fix in 4.2 to implement T-WAIT only upon power up and not force T-WAIT on simple switch-type configuration changes.

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