 (MTP) of the CCITT signalling system AXE can be equipped with either of two alternative central pro- No.7. cessors that are fully compatible on target code level, towards RPs Signalling system No.7, as specified by CCITT, is built up of two and I/O peripherals and may be changed or modified, even in parts, namely User Parts (UPs) and a common Message Transfer service. One is aimed for low cost, small physical volume and high Part (MTP). The task of the MTP is to transfer information reliably reliability whereas the other is aimed at high capacity requirement between UPs in different switches. The user parts belong to the applications. They have a similar logical and physical structure. Trunk and Signalling Subsystem, TSS. Each processor stores software in three logical stores. Programme The Traffic Control Subsystem, TCS, controls and supervises the Store (PS), Data Store (DS) and Reference Store (RS). set up of all calls. TCS stores and analyses digits received directly The operating system is structured to be largely hardware inde- from subscribers or via trunks and based on stored information pendent. It has functions for job monitoring, loading, function (analysis data) decides how the call is to be handled. change, automatic re-loading, storage allocation, size alteration of AXE applications and features 32/17 data files, programme correction, programme test, processor statis- The packaging system contributes to easy handling all the way: tics and handling of regional processors. during design, manufacture, installation and operation/mainten- The Regional Processor Subsystem, RPS, consists of a dimension- ance. able number of regional processors (RPs). The APT regional soft- ware units are stored and executed by RPS. The interwork between the central processor and the regional processors take place via a 32.10 AXE applications and features duplicated regional processor bus, RPB. The Maintenance Subsystem, MAS, supervises the proper oper- The concept of AXE is to provide one system for all network ation of A