Data Transmission - Ericsson EF738 Service Manual

System Introduction

Data Transmission

Many types of signalling are used between the different parts of the ETACS system.
The signalling has the following main objectives:
• MSC - MT
• MSC - BS
• MSC - MSC
• MSC - PSTN
• BS - MT
The messages and orders between the different units are sent in the form of so-
called words. All words have the same length. Each word is divided into a number
of fields, each of which contains a given type of information. The mobile telephone
has a systems section where the frames are coded and decoded. The transmission is
performed by means of FSK (Frequency Shift Key) modulation, where a logic 1 is
represented by a constant frequency above the carrier frequency of the transmitter.
A logic 0 is represented by a constant frequency below the carrier frequency. The
speed of transmission is 8 kbits/s.
10
- setting up and clearing of calls
- switching of call in progress
- updating
- ordering of power reduction
- remote control of base station
- transmission of alarm
- updating of subscriber register and roaming register
- transfer of call to roaming subscriber
- setting up of calls
- supervision of transmission quality