System Administration Guide: Network Services

Fixing Leased-Line Problems

The most common problem with leased lines is poor performance. In most situations, you need to work with the telephone company to fix the problem.

Table 21–6 Common Leased-Line Problems




The link does not start. 

CSU biopolar violations (CSU BPVs) can be the cause. One end of the link is set up for AMI lines. The other end is set up for ESF bit–8 zero substitute (B8Zs). 

If you are in the United States or Canada, you can directly fix this problem from the menu of the CSU/DSU. Check the CSU/DSU manufacturer's documentation for details.

In other locales, the provider might be responsible for fixing CSU BPVs. 

The link has poor performance. 

The pppd debug output shows CRC errors when sustained traffic is on the link. Your line might have a clocking problem, caused by misconfigurations between the telephone company and your network.

Contact the telephone company to ensure that “loop clocking” is in use. 

On some unstructured leased lines, you might have to supply clocking. North American users should use loop clocking.