CTC Union ETU-01A, Installation And Operation Manual

Page: 17 / 144

Chapter 1. Introduction
11
November 2001
Multi-Frame Alignment Signal (MFAS)
MFAS framing uses Channel Associated Signaling (CAS)
to transmit A/B/C/D bit signaling information for each of 30
channels. This method uses the 32 time slot frame format with time
slot 0 for the FAS and time slot 16 for the Multi-Frame Alignment
Signal and the Channel Associated Signaling.
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.