Product specifications

Chapter 1. Introduction
12
May 2011
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.
1.6 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.
HDB3 (High Density Bipolar of order 3 code) is a telecommunications line code mainly used
in Japan, Europe and Australia and is based on AMI. It is also very similar to the B8ZS
encoding used in T-1 lines. 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.
E1 link line coding
The ETU-01A supports two E1 line codes:
AMI coding.
HDB3 coding.
E1 framing formats
The ETU-01A supports five frame formats:
Unframed
FAS (CCS, PCM-31)
FAS (CCS, PCM-31) + CRC4 (PCM-31C)
MFAS (CAS, PCM-30)
MFAS (CAS, PCM-30) + CRC4 (PCM-30C)