Command Reference Guide

3Com Router 5000 Family and Router 6000 Family sendloopcode ● 299
Command Reference
In LLB mode, all 193 bits (one synchronization bit and 192 effective bandwidth bits) in
a T1 PCM frame are looped back. In PLB mode, however, only 192 effective
bandwidth bits are looped back.
The format of loopback code can be compliant with ANSI T1.403 or AT&T TR 54016.
In SF framing, LLB code is sent using the effective bandwidth (slots 1 through 24). In
ESF framing, both LLB code and PLB code are sent/received in the FDL in ESF frames.
This command is used in conjunction with the far-end T1 device. The far-end device
must be able to set loopback mode depending on the detected loopback code. The
sending of remote loopback control code can last five minutes without affecting the
operation of other interfaces.
You can use this command only when the far-end CT1/PRI interface can automatically
detect loopback request code from the network.