CIT’s ISDN Troubleshooting

## Copyright © 1999 Boson Software

Written by kevin@boson.com

## ISDN Switch Types:

- Valid ISDN switch types include: basic-1tr6, basic-5ess, basic-dms 100, basic-net 3, basic-ni, basic-ts 013, ntt, and vn3.

ISDN Status:

- The SHOW ISDN STATUS command is very useful in ISDN troubleshooting, because it displays status information about layers 1-3. ISDN Layer 2 is up, when its status is MULTIPLE-FRAME-ESTABLISHED.

- ISDN uses Link Access Procedure on the D channel (LAPD) to verify that signaling and control information is being received. ISDN has two layer 3 specifications: q.930 and q.931. These protocols perform such features as connection establishment and termination.

ISDN Protocols:

- ISDN protocols beginning with the letter E describe using ISDN on the existing telephone network. Protocols beginning with the letter I describe concepts, terminology, and services. Protocols beginning with the letter Q describe switching and signaling.

ISDN Reference Points:

R: The reference point between non-ISDN equipment and a terminal adapter (TA).

S: The reference point between user terminals and a network termination type 2 (NT2) device.

T: The reference point between network termination type 1 (NT1) devices and network termination type 2 (NT2) devices.

U: The reference point between network termination type 1 (NT1) devices and the carrier's ISDN switch.

ISDN BRI:

BRI has 2 64kbps B channels (called "bearer channels") for data and 1 16 kbps D channel for signaling.