User Manual

Architecture
Nortel Networks Confidential
3–6
PE/DCL/DD/0063
411–9001–063
Standard 12.07/EN September 2000
GSM/BSS V12
The private PCM TS number of the O&M channel of a DRX (or e–DRX) is
unvarying in a given gateway configuration. This TS number acts as the DRX (or
e–DRX) address for the gateway/DRX (or e–DRX) link.
O&M data are sent only on the O&M channel of the DRX (or e–DRX) selected on
the bus. Only the data received on this O&M channel are redirected to the O&M bus.
The GSM TIME channel
This one–way logical channel transports the GSM time signal to each DRX (or
e–DRX). It is carried by bit 7 of TS 31 of the Private PCM. The transmission speed
of the resulting transmission channel is 8 kbit/s.
A correction value is sent to each DRX (or e–DRX) over the OML link of the Private
PCM. This value corresponds to the delays caused by propagation. Each DRX (or
e–DRX) can therefore locally regenerate a synchronous GSM TIME bus with the
BCF subsystem bus.
The refresh period must be a multiple of an occurrence between the GSM time base
(577 µs) and the PCM time base (125 µs). The selected refresh period is 60 ms.
Such a 60–ms frame contains three parts:
Synchronization flag Useful data Filler bits
3.1.3.3 GSM TIME bus
Principle
The GSM Time bus is a V11 serial bus used in the BCF Unit to link the SYNC and
GTW boards.
The data it conveys define the “local BTS time”. The serial format includes a flag
to detect any break in the link. Moreover it provides a “strobe” every 577 µs that
accurately matches the start of each time slot.
Interface signals
The GSM TIME bus supports three types of signals. These three signals, which are
generated by the synchronization unit, are transmitted in differential mode.