Chapter 12. ISDN BRI Troubleshooting

From a technology prospective, most of the ISDN fundamentals are covered in the previous chapters of this part. This chapter provides you with a systematic approach to ISDN troubleshooting and demonstrates the suggested layer-by-layer approach to ISDN problems. The approach requires you to start from the physical layer and go up, layer by layer and protocol by protocol, to identify potential issues. This chapter covers the following common issues:

• Troubleshooting the physical layer

• Troubleshooting the data link layer

• Troubleshooting the network layer

• Troubleshooting the Point-to-Point Protocol (PPP), including link control protocol (LCP), authentication, Network Control Protocol (NCP), and the termination of connections

• Troubleshooting MLP, PPP, callback, and MMP

• Troubleshooting telephone interfaces