unction block forms a continuous area in technical components within the framework of the system. the programme store. The start address to this area is also found by New technology, e.g. new components, may be introduced, mak- means of the reference store. The machine instruction list does not ing possible a continuous development of the system. AXE there- contain any operations which refer to an absolute address in the fore always represents state of the art technology. stores. Thus the programme part of a function block is also relocat- able. Each software signal to a function block is defined by a unique 32.9 AXE implementation symbolic number. In the software signal operation the block number for the receiving function block and the signal number in question One system for all applications is achieved through specified func- must be given in order to access a specific programme sequence, tions, grouped together to form subsystems. These may be com- (See Figure 32.9). First the function block number register is loaded bined to suit different applications. An AXE exchange is a with the block number. The function block start address is then combination of switching subsystems and control subsystems. Reference Programme store store Function Reference block Programme table number start Start address address for SW signal 1 Signal distribution table Software Start address Function block signal for SW signal n programme number Programme Figure 32.9 Addressing principle AXE implementation 32/15 APT Switching System APZ Control System MTS Mobile Telephony Subsystem RPS Regional Processor Subsystem SSS Subscriber Switching Subsystem CPS Central Processor Subsystem GSS Group Switch Subsystem RP Regional Processor TSS Trunk and Signalling Subsystem CP Central Processor CCS Common Channel Signalling Sub. MAU Maintenance Unit LSM Line Switch Module ST Signalling Terminal ETC Exchange Terminal Circuit Figure 32.10 AXE hardware structure 32.9.1 Switching system APT native accesses to the subscriber network, such as ISDN 30B