CTC Union EOe-1, User Manual

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Chapter 1. Introduction
6
1.3 E1 signal structure
The E1 line operates at a nominal rate of 2.048Mbps. The
data transferred over the E1 line is transmitted transparently as a
bit stream in Unframed E1 mode.
E1 line signal
The basic E1 line signal is coded using the Alternate Mark
Inversion (AMI) or HDB3 rule.
In the AMI format, "ones" are alternately transmitted as
positive and negative pulse, whereas "zeros" are transmitted as a
zero voltage level. AMI is not used in most 2.048Mbps
transmissions because synchronization loss occurs during long
strings of data zeros."
In the HDB3 format, a string of four consecutive zeros is
replaced with a substitute string of pulses containing an
intentional bipolar violation. The HDB3 code substitutions
provide high pulse density so that the receiving equipment is able
to maintain synchronization with the received signal.