2.2
Functional Operation
2.2.1
General
See §1.1.
2.2.2
E1 Framing
E1 is a 2.048 Mbps bi-directional (full duplex) link through which the data is transported in a
digital way in frames. One frame consists of 32 time slots (Figure 5). Timeslot 0 is used for
framing and synchronization, and time slot 16 for signaling. The bandwidth of one time slot
is 64 kbps (=8 bits/125 µs). One frame thus consists of 32*8 = 256 bits and lasts
125 µs. Typically 16 frames are packed together in one multiframe.
NOTE:
Multiframe = future support;
Frame = 125 µs = 32 time slots
Bit slot
Time slot
Frame
Figure 5 E1 Framing
2.2.3
E1 Coding: AMI, HDB3
AMI, HDB3 are different types of line coding. HDB3 is used in E1. The 2-OLS module supports
HDB3 for E1. HDB3 is an enhancement of AMI. For this reason, AMI is mentioned here as
well.
As the E1 link has no separate clock transmission, the receiver will derive the clock from the
incoming data stream. A minimum density of logical ones is required in order to guarantee a
faultless clock recovery. This is achieved basically by AMI which encodes the data stream
with bipolar violations. A more enhanced and better encoding is HDB3 which enhances the
AMI stream by replacing successive zeros:
E1
HDB3: replace four successive zeros with a fixed bit pattern ‘000V’ or ‘B00V’;
A ‘B’ and ‘V’ can either be ‘-‘ or ‘+’. Which pattern is used depends on the amount of ‘+’ and
‘-‘ already received from send on the link.
...0000...
...000V...
...B00V...
Figure 6 HDB3 Encoding
F
0
1
2
S
16
31
F = Framing
S = Signaling
1
16 1
Multiframe = 2 ms
E1: HDB3 Encoding
:
replace 4 zeros with 000V or B00V
Interface Module PTN-2-OLS with E1/PTN-2-OLS with T
Release 01 02/2018
9
