_\'/_[ Gwhan Burn'in Haxorz ]_\'/_ The UK PSTN an overview. SYSTEM X/X LOCAL AXE hybrid. _\'/_gBH Throughout the UK, BT implement system x (a digital switching system operated on a hierarchical chain of network operation groups). In this article I am going to explain some of the myths about the UK phone system, and expand on a few things that "they" would'nt want you to know. 1st, well look at the different facilities that are offered to internal BT staff within the X LOCAL network. (Customer Line Testing on Digital Exchanges...) Automatic Exchange Billing/Direct Transfer of Accounting in SYSTEM X, the mechanical subscribers meter is replaced by "software". The subscribers meter then becomes an area of "memory" allocated to each subscriber, and is incremented after each call in much the same way as the old meter was "stepped" after every unit. These individual areas of "memory" within the exchange, can be "read out" automatically and the information transfered to the Accounts Department in a very short period of time. This brings us on to the "REMOTE ACCESS" privaleges of the BT engineer, depending on level of clearnace. Manipulation of Exchange Equipment from a central point. For example, taking faulty equipment out of service, or making subscribers temporary out of service (TOS) for non-payment of bills. Monitoring Exchange Performance.. to ensure that faults in the exchange equipment do not effect service to other customers. Monitoring Network Performance - to ensure that defciencies or faults in the Network do not affect service. All these facilities can be controled from a central point. This central point can control a number of exchanges and can be situated virtually anywhere. (Network MASTER PLAN...) Network Structure. The UK Digital Network consists of several different types of Excahnges formaing the Trunk Network, TN and the Local Network, LN. The Trunk Network consists of 54 Digital Main Switching Units (DMSU) System X exchanges which are FULLY interconnected. Each of these exchanges has a number of Digital Local Switching Units (DLSU) conencted to it and the DMSU catchment area encompasess several old group Switching Centre Areas. The Local Network is divided into cells.. These "cells", contain a MINIMUM of two Digital Local Switching Units (DLSU) one a System X Exchange and the other an AXE10 Exchange. One of these Exchanges is used as the Digital Cell Centre Exchange (DCCE) and has access to the DMSU via its Digital Distribution Frame. The other Exchange also uses the DCCEs Frame for access to the DMSU. Remote Concentrator Units (RCU) are conencted to the DLSU's for their own system type. Where Analogue Local Exchanges have been replaced by several concentrators this is known by BT's internal staff as a Remote Concentrator Centre (RCC). In isolated/rurral areas of the UK, such as certain areas of Scotland, UXD5 exchanges are still in place. So, here is a diagram of what the UK SYSTEM X network plan looks like... (fear the ascii) ....................... _____ . | ALE | . |_____| . : > Non Switched | . = > Non Swicched _____ _|____ . ______ | RCU |__| DLSU | . | | |_____| | DCCE |--------| DMSU | |______| . |______| ............................... _____ | | . : | . | RCU |____| | . : | . _____ _____ |_____| | . : | . | RCU | | RCU | | . : | . |_____| |_____| Local Call | . : | . | | ..............|........ : | . | | | : | . | | | _:__|_ . __|___ __|___ |__________| |==========.==| DLSU |======| DLSU | | DMSU |__________.__| DCCE |______| DLE | |______| . |______| |______| : | . | : | . | Local Call : | ......|........................ : | | : | | _:__|_ | | | | | DMSU |________________| |______| In this diagram, the RCU's could also be RSS's, or more comonly known as AXE 10... Here is a brief explanation of the different sections of this diagram.. DMSU == Digital Main Switching Units, these exchanges provide the fully interconnected Trunk Network. Each DMSU catachment area comprises of several old GSC areas. The DMSU switches traffic both between and within the catchment area. DLSU == Digital Local Switching Unit. The DLSU is a general term for a digital local proccessor exchange. It provides a service for its customers. It can also provide other facilities dependant on its role as either DCCE or a DLE. DCCE == Digital Cell Centre Exchange. This is the exchange that provides a service for its own customers and act as a "parent" for the RCU's. It can act as a parrent for anolouge exchanges, terminating analouge line plant and performing call charging as required. It concentrates, and then forwards traffic to the DMSU's for parented Analouge Local Exchagnes (ALE) without their own DMSU links. The DCCE also switches Tandem Traffic between other DLSU's. DLE == Digital Local Exchange. This is a DLSU which may host RCU's and also act as a parent for those ALE's which have been replaced bt RCU's parented upon the DLE. (As Above). RCU == Remote Concentrator Unit. These are connected to the DLSU and are considered as part of the DLSU which it is conencted to. UXD5 == This is the digital exchange developed from the CDSS1 (Monarch) PABX. DJSU == Digital Junction Switching Unit. This is a switching unit situated in a high telephone density local network which performs a tandem switching function, but has NO customer conenctions. TXD identification... An alternative method of labelling types of exchanges is by number. This number forms part of the exchanges Network Nodal Identity, which appears on ALL documents specific to the particulr exchange. Some examples of the TXD numbers/identification... TXD NUMBER EXCHANGE -------------------------------- 3 RCU [ SYSTEM X ] 5 UXD5 6-9 DLSU [ SYSTEM X ] 13 DMSU 14 DJSU 30 OSSU 31 OCHC 53 RCU [ AXE 10 ] 56-59 DLSU [ AXE 10 ] 80-86 OMC THE OMU ALL BT Digital Exchanges are served by an Operations and Maintenance Centre (OMC). An OMC is the computer equipment required ro collect data from exchanges and is served by a number of users... Traffic, Sales, Operation and Maintenance Unit (OMU) etc.. An OMU is the office where engineers monitor the performance of the exchanges, and recieve the data collected by the OMC. There are sometimes more than one OMU connected to each OMC. The OMU is an office containing visual display TERMINALS which are connected to the Operations and Maintenance Centre (OMC). The OMU staff can send or recieve information via the OMC to control the exchanges conencted to it. The OMU hierarchy is as follows... ISOS == In Service Operational Support PSG == Product Support Group (BT Headquaters) DSG == District Suppoer Group (BT District staff) OMU == Operations and Maintenance Unit (BT OMU staff) The OMU staff... System Manager == The system manager has overall responsibility for the operation of the OMC computer and its terminal network. OMU Manager == The Operations and Maintenance Unit Manager (UM) has an overall responsibility for all exchanges controlled by his/her OMU. Maintenance Control Officer (MCO) == Is responsible for making sure that all tasks and routines have been carried out. This is achived will the help of the Maintenance Officers. His/Her job is also reffered to as the Task Co-ordinating Duty (TCD). Maintenance Officer (MO) == This dude is responsible for dealing with and clearing tasks pressented to him by the MCO. There are three types of Local System X exchange. They are... Digital Principle Local Exchange (DPLE), Large Local Exchange (LLE), Medium Local Exchange (MLE). THE END... (OF THE BEGGINING). _\'/_gBH.