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report of PTCL internship
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     EWSD Local Exchange: EWSD  ( E  lektronisches W   ähl  s   ystem D  igital   in German, Electronic Digital Switching System/Electronic World Switch Digital in English) is one of the most widely installed telephone exchange systems in the world. EWSD can work as a local or tandem switch or combined local/tandem, and for landline, or mobile phones. It is manufactured by Siemens AG, who claims that EWSD switches perform switching for over 160 million subscriber lines in more than 100 countries. ― DeTeWe ‖  bought its first EWSD under license in 1985 for remote switching. Bosch built its first EWSD as a local exchange in 1986. Deutsche Telekom formerly Deutsche Bundes post, the largest German telephone company, uses EWSD and System 12 (Alcatel), the former more than the latter. EWSD was introduced in 1975 as a sequel of the E  lektronisches W   ähl  s   ystem (  A nalog) , which was using analogue technology only. Hardware:   General Information: The hardware of an EWSD system is organized in subsystems that are linked through uniform interfaces. The Digital Line Unit (DLU) combines a number of analogue and digital subscriber lines. Max 952 Subscriber lines can be connected to one DLU. The DLU is connected to the Line/Trunk Group (LTG). The Line / Trunk Group (LTG) not only terminates Digital Line Units (DLUs) but It is also linked to:   Other exchanges   Digital Switching Board (DSB). The Switching System (SN) provides the inter-connections between two subscriber lines. To handles the Signalling System No.7, the EWSD exchange requires a Subsystem Common Channel Signalling Network Controller (CCNC). Since the processing workload is distributed over several microprocessors within the EWSD system, a common processor for Coordination tasks is extremely useful. These functions are handled by the Coordination Processor (CP). The CP consists of the:    Coordination Processor (CP)    External Memory (EM)    Operation and Maintenance Terminal (OMT)    System Panel (SYP)    Message Buffer (MB)    Central Clock Generator (CCG)    Load Distribution In order to reduce the workload of the Coordination Processor (CP) and to achieve faster processing times, some processing functions are distributed over autonomous control devices. Since the EWSD subsystems independently execute all necessary tasks within their respective areas, they require their own control devices such as the:  DLU: ã  Digital Line Unit Controller (DLUC) LTG: ã  Group Processors (GP) SN: ã  Switch Group Control (SGC) SYP: ã  System Panel Control (SYPC) MB: ã  Message Buffer Control (MBC) CCNC: ã  Common Channel Network Processor (CCNP) Main subsystems are:    CP (Central Processor)    MB (Message Buffer)    CCNC (Common Channel Network Control)    LINE (Analog Line Group)    LTG (Line Trunk Group)    DLU (Digital Line Unit)    SN (Switching Network)    PA (ISDN Primary Access)    PDC (Primary Digital Carrier) All system units are redundant so the inactive side can take over immediately in case of an error.DLU handles analog and ISDN lines and includes codes for analog lines, one of the  BORSCHT   functions for subscriber lines. Digital signals are assigned a time slot. DLU concentrates traffic onto a Line B unit, as well as Primary ISDN and V5.2 connections. Supervision and address signaling (dial pulse, DTMF) are also integrated in the DLU. ForPCM30 (E-1) connections to other exchanges, Line C Units are used, which also handle signaling including SS7, MFC R2 signaling, IKZ (dial pulse), and E&M.  The Switching Network consists of 4 space division stages of 16x16 switches, and a time division section with 16 stages of 4x4 switches. Control is provided by the CP Co-ordination Processor. There are the following kinds of Co-ordination Processors:    CP103 with max 22,000 call attempts in the busy hour    CP112 with max 60,000 call attempts in the busy hour    CP113D with max one million call attempts in the busy hour    CP113C with max six million call attempts in the busy hour    CP113E with max ten million call attempts in the busy hour Software: The software of EWSD is called APS (Automatic Program System). The APS is on a hard drive and includes the operating system, developed by Siemens in cooperation with Bosch. It is predominantly written in the CHILL language. Application software is switch specific and serves among other things traffic management, path search, and call charging. Support software serves translating programs, binding modules as well as administration of libraries for generating data. Operating and data communication software serve for co-operation of maintenance centers and switching centers. Technical Data:     Number of access lines: to 250,000     Number of feeder lines: 240,000    Traffic connection: 25,200    Call attempts in busy hour: 10 million    Operating voltages: -48V -60V -90V    Rate zones: 127, for each zone of 6 tariffs    Tariff change-over at 15 minute intervals    Space requirement with 10,000 access lines: 35 square meters Switching Network: The actual switching process that establishing a call connection between two subscribers takes place in the hardware subsystem called switching Network (SN).SN consist of Time Stages and Space Stages. A time stage consists of Time Stage Module (TSM) and space stage consist of Space Stage Module (SSM).    The main components of a SN are: Time Stages: In time stages octets to be switched change time slot and highway according to their destination. Space Stages: In space stages they change highway without changing time slots Switch Group Control (SGC) Connection paths through the time & space stages are switched by the SGC in accordance with the switching information from the CP. Packet Switching and Circuit Switching: Packet Switching: Packet-switched and circuit-switched networks use two different technologies for sending messages and data from one point to another. Each has its advantages and disadvantages depending on what you are trying to do. In packet-based networks, the message gets broken into small data packets. These packets are sent out from the computer and they travel around the network seeking out the most efficient route to travel as circuits become available. This does not necessarily mean that they seek out the shortest route. Each packet may go a different route from the others . Advantages:    Security    Bandwidth used to full potential   AccessDLUDLUCLTGGPLTGGPCommon ChannelSignalingCCNCCCNPCoordinationE MSYPSYPCM BMBCO M TC C GCP Switching S N 0S N 1S G CS G CS D CS D CS D CS D C
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