User Manual

ArchitectureNortel Networks Confidential 3–29
S8000/S8002/S8006 BTS Reference Manual
3.3.1.3 Concentration and routing
The concentration and routing functionality is performed by the master and slave
processing units. The master processing unit manages the board ressources. The
slave processing unit, which operates synchronously with the master unit, manages
one PCM, one HDLC link (for master–slave communication), and one RS232 link.
The master processing unit receives a external clock signal at 4.096 MHz and
generates a 33 MHz reference frequency. This frequency is supplied to the slave unit
so that it can be synchronous with the master unit.
3.3.2 Control of the alarm management unit
The CMCF manages the alarm management unit, the RECAL board, located
outside the CBCF Module.
The RECAL board collects internal and external alarms and routes them to the
CMCF, which routes to the BSC.
The communication between the CMCF and the RECAL is done using a LAPD
protocol link that uses a channel supported by time slot 25 of PCM0.
3.3.3 PCM Interface
Up to three CPCMI boards provide the interface between six external PCM links
(A–bis) and six Private PCMs used inside the CBCF Module.
The interface tasks corresponds to an electrical level translation and a frame format
conversion depending on the type of external PCM link (PCM E1, PCM T1, or
HDSL).
The external PCM interface has functional blocs that perform the following
functions:
conversion of analog signals on the A–bis interface and the logical signals of the
Framer part of the PCMI
management of the synchronization clock
transposition between the A–bis and the Private PCMs signals
3.3.3.1 Signalling interfaces
The CPCMI board uses the PCM and HDSL interfaces described below.
PCM A–bis interface
The E1 interface is compatible with the G703 Recommendation. Its impedance is
120 (two pairs of bidirectional symmetrical links) or 75 Ohms (coaxial cables).
The T1 interface is compatible with ANSI T1.403 and T1.102. Its impedance is
100 Ohms (two pairs of bidirectional symmetrical links).