Specifications

Chapter 1. Introduction
15
1.7 Loopback Feature
The ETU01-Plus features V.54 diagnostic capabilities for performing local loop
back and remote digital loop back. The operator at either end of the line may test
both the ETU01-Plus and the line in the digital loop back mode. The loop back is
controlled by either a manual switch or by the V.35 DTE interface.
A front panel switch generates an internal 511 bit pseudo random test pattern,
according to ITU-T, for direct end-to-end integrity testing. The Error indicator flashes
for each bit error detected.
1.8 Typical System Applications
The fractional E1 data service is based on the assumption that the user data rate
is a fraction of the available E1 bandwidth, in multiples of 56K or 64K. In a typical
application (Figure 1.6), the ETU01-Plus is used to connect the synchronous user
DTEs over an E1 line.
Figure 1.6 E1 Point-to-Point Application
When connected in this fashion, one ETU01-Plus must have its clock set to
Internal Oscillator to provide a reference clock for the E1. The unit on the opposite
side of the E1 link will set its clocking to E1 Recovery.
Line coding, Framing, and Timeslot assignment must match on both sides. The
ETU01-Plus supports assigning timeslots in any order, from 1 to 31 (64Kbps to
1984Kbps) timeslots. When set to unframed, the ETU01-Plus provides full 2048Kbps
throughput between the V.35 DTE devices.
The ETU01U-Plus is not capable of fractional E1 operation and should be used
where only an unframed, transparent 2.048Kbps transmission is required.