User guide

loopback to be local or remote. With local loopback, the E1 interface can transmit packets

to the CSU, but receives its own transmission back again and ignores data from the CSU.

With remote loopback, packets sent from the CSU are received by the E1 interface,

forwarded if there is a valid route, and immediately retransmitted to the CSU.

Figure 1: Remote and Local E1 Loopback

To configure loopback capability on an E1 interface, include the loopback statement at

the [edit interfaces interface-name e1-options] hierarchy level:

[edit interfaces interface-name e1-options]

loopback (local | remote);

Packets can be looped on either the local router or the remote CSU.

To exchange BERT patterns between a local router and a remote router, include the

loopback remote statement in the interface configuration at the remote end of the link.

From the local router, you issue the test interface command.

For more information about configuring BERT, see “Interface Diagnostics” on page 87.

For more information about using operational mode commands to test interfaces, see

the CLI Explorer.

To turn off the loopback capability, remove the loopback statement from the configuration:

[edit]

user@host# delete interfaces e1-fpc/pic/port e1-options loopback

You can determine whether there is an internal problem or an external problem by

checking the error counters in the output of the show interface interface-name extensive

command:

user@host> show interfaces interface-name extensive

Example: Configuring E1 Loopback Capability

To determine whether a problem is internal or external, loop packets on both the local

and the remote router. To do this, include the no-keepalives and encapsulation cisco-hdlc

statements at the [edit interfaces interface-name] hierarchy level and the loopback local

statement at the [edit interfaces interface-name e1-options] hierarchy level.

With this configuration, the link stays up, so you can loop ping packets to a remote router.

The loopback local statement causes the interface to loop within the PIC just before the

data reaches the transceiver.

Chapter 2: E1 Interfaces