STATION ID - 7047/3.12 9x Datakit Network FOR OFFICIAL USE ONLY This is a 9x system, restricted to authorized persons and for official 9x business only. Anyone using this system, network or data is subject to being monitored at any time for system administration and for identifying unauthorized users or system misuse. Anyone using this system expressly consents to such monitoring and is advised that any evidence of criminal activity revealed through such monitoring may be provided to law enforcement for prosecution. Local UK Digital Switching Systems and Line Tests by gr1p In the late 1990s in the UK there are really only two types of Switching systems that are used at local level, however in extreem rural areas, such as the Remote Scottish Highlands, the old Electronic Switches may sitll be in use. These Electronic switches (TXEs) which were used in the past throughout the whole country have been slowly replaced by the newer digital systems which at one time were only installed in the major cities where they catered for the increasingly large call volume both from business and residential lines very efficiently. There are two types of Digital Systems which are used at local level to deal with the majority of calls, System X and the newer variant, System Y which is based on AXE10 style technology. There are however other Digital Systems that are used to control other networks which aren't necessarily on a local level such as 5ESS which is used for the DDSN (Digitally Derived Service Network) which controls the 0800/0500/0891 service networks, the freefone numbers, premium rate numbers etc. 0800 and 0500 numbers are the equivalent of US 800/888 numbers, and 0891 numbers are the equivalent of US 900 numbers. The Basic principles of working within the Digital Systems are the same between the two due to the fact that System Y was based on the original System X. System X was set to be installed over 100% of the UK as the prime local digital switching system until this was deamed to be unfair due to the fact that one company would have a total hold over the Switching Market and not allow any other companies to compete in the market so a company called Ericsson produced AXE, a rival digital fone exchange system, the AXE10 class system was chosen by BT to be installed throughout the main cities in the UK and this forms the local BT System Y digital switching system. System X technology was soon outdated after release due to the fact that it was designed and produced by a consultive committee who were slow at releasing its first model and by this time AXE10 had been designed and unveiled and it saw a vast technological improvement on System X incorporating more digitally advanced extras such a improved CLASS Technology (essentially Caller ID technology) while at the same time keeping the fundamental backbone on which SystemX is based. The detailed workings within the system, whether X or Y, are seperated into particular modules, with each module dealing with a specific function at a certain stage of the switching process. It all starts on a local level with smaller modules within the exchange process performing tasks which make up the larger modules within the system ensuring that the whole process runs smoothly. A lot of processes make up for the local level of the system, which is really the most important part of the system. The lowest level is where the meeting point for the lines is formed, these meeting places are called Remote Concentrator Units (RCUs), these are where a very large number of lines meet and basically form your locally telco depot. The step up from RCUs are the Digital Local Exchanges (DLEs) which host all the RCUs in the area and form for a much wider distribution area, say, over the area of quite a few miles. The wide distribution of these DLEs into smaller areas, with the use of RCUs makes for a much more organised and proficient system of switching and exchange. The higher level switching of calls is dealt with by the Digital Switching Unit (DSU) which deals with a high volume of calls in an area, for example, the size of a large city. The Digital Switching Units then distibution the switching of calls to the smaller Digital Main Switching Unit (DMSU) which controls the switching of calls on a smaller level and delegates calls even further down the scale to the Digital Local Switching Units (DLSUs) which forms the basis of call switching by making sure it reaches its destination by setting the call along to the right connections and Subsystem. A few important factors effect whether a call is switched to its destination perfectly. The main factor relies on the Call Processing Subsystem (CPS) which takes overall control over a local line, registering its state whether engaged, free or otherwise out of order. This function is very sophisticated and a fundamental part of the digital exchange as it is needed to ensure that harmony is achieved among the fonelines. The next needed function, or module, is Common Channel Signalling (CCS) which is the process British Telecom (BT) use to reserve a speech channel for switching and to enable the lines to coherantly exist without cross-overs etc, this is therefore the standard form of signalling on any digital system and is used successfully in countries that make use of a digital system of switching. Although BT have produced a method of packet cutting for signalling the voice along the channels to ensure perfect arrival. They use a method called Pulse Code Modulation (PCM) to cut down voice into smaller packets sending them down the channels, several calls are cut at the sent time and sent seperatly without confusion, as the modulation is programmed to be sensitive enough to control the lines and the differences between each without any problems. When all the modules that make up the Digital System are combined and put into functional order they work in harmony automatically with no problems and with great efficiency. If one module fails, the whole process fails, each module relies on another and they all deam equal importance in the system. There is a very easy way to find out which digital fone exchange type your area falls under. Just go to your home fone and tap in the following code. *#001# If you get the following answer:- 'No services in operation on this line' or a 'List of Services' then your local digital exchange is SYSTEM X. If you get the answer:- 'Sorry, you have dialled an invalid service c0de' then your local digital exchange type is SYSTEM Y. This System of Digital Switching is the main system which is installed in the UK today for local use. 5ESS is implemented, but has not been discussed in this file as it is implemented on the Digitally Derived Service Network which will be discussed at a later date. [eof]