System information
FCD 901 48
Issue R2A, 07.2009
XMP1 Release 5.5 System Description
Frame Structure and Synchronization
Page 2-4 Proprietary Information Aastra
2.2 Frame Structure and Synchronization
2.2.1 Frame structure
In the time-division multiplex procedure, the analog signals to be
transmitted are first sampled, quantized and encoded. These analog
signals are telephone signals (limited from 300 Hz to 3400 Hz) which are
sampled at a rate of f
A
= 8000 Hz, i.e. the amplitude of the analog signal is
sampled once every 125s.
The sampling results are quantized and encoded to form 8-bit words. This
pulse code modulation (PCM) has a bit rate of 64 kbit/s. Since the
bandwidth of the transmission paths is considerably wider than that required
for this bit rate, several PCM signals can be combined to a PCM multiplex
signal of a higher bit rate. The encoded sampling values of the different
input signals are thus transmitted one after the other.
The XMP1 system is appropriate for handling signals of both KZU and DSK
modules.
It combines 30 x 64 kbit/s digital signals (channels) + 2 kbit/s or
31 x 64 kbit/s digital signals to one PCM 2.048 Mbit/s multiplex signal on the
ports.
Each 125 s frame transmits 32 channels, 8 bits being allocated to each of
them.
30 (31) of these 32 channels available are used for transmitting traffic
information. Two channels are required for transmitting the frame alignment
signal or service digits and signalling information.
The first time slot (time slot 0) of the frame includes the frame alignment
signal and service digits by turns. The frame alignment signal is required for
synchronizing the transmit and receive sections of the PCM transmission
system. The service digits include information on fault conditions and bit
error ratios.
The signalling information is transmitted in time slot 16 of each pulse frame.
It includes the signalling pulses for two voice channels. Thus, 15 frames are
required for transmitting the signalling information of all voice channels. A
total of 16 frames are combined to one multiframe, the additional frame
available being required for transmitting the multiframe alignment signal
and service digits.
The multiframe has a duration of 16 x 125 s = 2 ms.
The pulse frame is in compliance with ITU-T Rec. G.704.