on with DMS 32/24 32.10 AXE applications and features 32/17 This page intentionally left blank Introduction 32/3 32.1 Introduction The TXE2 system Chapter 31 introduced the principles of switching systems. There TXE2 is designed for use as a small local exchange. Its capacity is are currently many switches being used throughout the world. A limited basically by the number of busy hour calls it can handle. The large number of these are analogue, although they are gradually theoretical maximum capacity of a TXE2 unit is 240 erlangs of total being converted over to digital switching systems. traffic (i.e. originating, terminating and tandem) and the multiple is In this chapter some of the switches in current use are described. determined by the total traffic per line; typically a single unit of TXE2 can serve from two to three thousand lines. The lower limit It is not the intention to provide a comprehensive description of these switches, but rather to cover their architecture, and show how is basically an economic one and could be about 200 lines in they implement the basic switching functions. Because of space circumstances where the growth rate is fairly large. limitations only a few of the many major switches are described. Normally a TXE2 will be installed as a single unit within the These are the TXE analogue switch from STC, part of Northern stated capacities for lines and traffic. Should either of these grow Telecom; the System 12 switch, originally from ITT but now being beyond the capacity of the single unit, a second unit may be coupled developed by Alcatel Bell; the AXE switch from Ericsson; and the to the first to double the exchange capacity. In exceptional circum- DMS switch from Northern Telecom. stances, growth beyond the capacity of two exchange units could be met by using unit switching equipment to combine three or more exchange units. The TXE2 system may be divided into three main areas: TXE analogue exchanges 1. The switching area comprising three stages A, B and C in the The TXE2 and TXE4 anal