User guide

96 RealCT Direct API Developer Guide
Chapter 4: E1 Networking
Organizing Frames into CEPT Multiframes
The E1 frames are organized into CEPT multiframes. Each
multiframe consists of 16 E1 frames, as Figure 20 shows.
Within the multiframes, timeslots 0 and 16 of each frame carry
a specific pattern of information.
Figure 20. A CEPT Multiframe
Timeslot 0
Timeslot 0 carries framing and CRC information. The bit
patterns alternate every other frame.
In even frames, bits 2-8 follow the framing synchronization
pattern: 0011011. The first bit carries cyclic redundancy
check (CRC) data.
In odd frames, the first bit is a CRC alignment signal, the
second bit is always 1, the third bit carries alarm
information, and the remaining bits are reserved.
Table 17 shows the bit patterns for odd and even timeslot 0 in a
CEPT multiframe. The multiframe is divided into two
sub-multiframes of eight frames each.
0
0
1
1
2
2
313029
28
01100111
8-bit timeslot
E1 Frame 125 S
CEPT Multiframe
34
5
6
7
8 9 10 11 12 13
14 15