red for No.7 signalling is known as an LIU7. Each Trunk Modules (TM) are used for analogue trunk or junction con- LIU7 will provide message discrimination, routing and distribution nections to DMS. The TM encodes and multiplexes incoming for one No.7 signalling link. The signalling link enters the LIU7 as speech from a maximum of 30 analogue circuits into a digital format a 64 kbit/s (single channel) link which may have been derived from incorporating the line supervisory and control signals. Outgoing a multiplexer connected to a PDTC or directly from the PDTC as a speech and signals are demultiplexed and decoded into their respec- DSO (digital speech - no channels) link. tive speech and signalling information on each circuit. A range of different analogue signalling systems may be supported by selecting The LPP may be used to support Signalling Transfer Point (STP) different interface circuit packs. working. A variation on the TM is the Maintenance Trunk Module (MTM) It is the architecture of the LPP which not only provides the which has all the functions of a TM card and interfaces a maximum capabilities for advanced features and services of the future, but also of 28 service circuits (tones, alarms, etc.) and test equipments. the ability to process the large volume of intelligent messaging 32/22 Telephone exchanges 2 to 6 X 30 Ch links per LCM To other Up to 20 x 30 Ch ports per LGC Up to 640 lines per LCM SWITCH 3 to 16 30 Ch links Up to 10 LCM per LGC Up to Up to 600 Up to channels lines channels Figure 32.14 DMS line concentration required whilst maintaining the necessary firewalls to ensure total ral are delegated to local processors in the relevant sub system. A network integrity. central control (DMS-Core) co-ordinates call processing including In first generation systems, No.7 signalling is supported by Mess- the interactions between the Switching Network and the Peripheral age Switching Buffers and associated Signalling Terminals perfor- Modules. (See Figure 32.15.) ming a similar function to the LPP. 