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TELEPHONE NETWORK

TELEPHONE NETWORK. Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the plain old telephone system ( POTS ), was originally an analog system using analog signals to transmit voice.

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TELEPHONE NETWORK

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  1. TELEPHONE NETWORK Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the plain old telephone system (POTS), was originally an analog system using analog signals to transmit voice.

  2. Public Circuit Switched Network

  3. Telecomm Components • Subscriber • Devices attached to network • Local Loop • Subscriber loop • Connection to network • Exchange • Switching centers • Trunks • Branches between exchanges • Multiplexed

  4. A telephone system

  5. Circuit Establishment

  6. LATAs Local Access transport areas • US was divided into more than 200 LATAs in 1984. • Inside the LATA services are called Intra LATA services. Intra-LATA services are provided by local exchange carriers. Since 1996, there are two types of LEC s: incumbent local exchange carriers and competitive local exchange carriers.

  7. Switching offices in a LATA

  8. Inter LATA Services • The services between LATAs are handled by Interexchange carriers (IXCs). • These carriers sometimes called long distance companies. • Point of presence is the switching office to interact between IXC to LATA.

  9. Point of presences (POPs)

  10. Note The tasks of data transfer and signaling are separated in modern telephone networks: data transfer is done by one network, signaling by another.

  11. Routing • Many connections will need paths through more than one switch • Need to find a route • Efficiency • Resilience Types of Routing: - Static routing uses the same approach all the time -Dynamic routing allows for changes in routing depending on traffic

  12. Right through Alternate Routing • Possible routes between end offices predefined • Originating switch selects appropriate route • Routes listed in preference order • Different sets of routes may be used at different times

  13. Alternate Routing Diagram

  14. Own exchange routing Own exchange routing or distributed routing allows alternative routes to be chosen at the intermediate nodes

  15. Computer controlled routing Separate computers are used for signaling & some algorithms are decided to chose the appropriate path.

  16. Subscriber loop signalling: Subscriber to network, Depends on subscriber device and switch Intraexchange signalling: In the exchange or switching system Interexchange signalling: Signalling between the exchanges Location of Signalling

  17. Control Signaling Functions • Audible communication with subscriber • Transmission of dialed number • Indication that call can not be completed • Call ended indication • Signal to ring phone • Billing info • Equipment and trunk status info • Control of specialist equipment

  18. Control Signal Sequence • Both phones on hook • Subscriber lifts receiver (off hook) • End office switch signaled • Switch responds with dial tone • Caller dials number • If target not busy, send ringer signal to target subscriber • Feedback to caller • Ringing tone, engaged tone, unobtainable • Target accepts call by lifting receiver • Switch terminates ringing signal and ringing tone • Switch establishes connection • Connection release when Source subscriber hangs up

  19. Type of signaling • In channel signaling • Common channel signaling

  20. In Channel Signaling • Use same channel for signaling and call • Requires no additional transmission facilities • In band • Uses same frequencies as voice signal • Can go anywhere a voice signal can • Impossible to set up a call on a faulty speech path • Out of band • Uses the frequencies above the voice band but below the upper limit • Can be sent whether or not voice signals are present • Need extra hardware • Narrow bandwidth is available for signalling

  21. Drawbacks of In Channel Signaling • Limited transfer rate • Signalling capability is less • Delay between entering address (dialing) and connection • Overcome by use of common channel signaling

  22. Common Channel Signaling • Control signals carried over paths independent of voice channel • One control signal channel (Common control channel) can carry signals for a number of subscriber channels • Associated Mode • Common channel closely tracks interswitch trunks • Disassociated Mode • Additional nodes (signal transfer points) • Effectively two separate networks Quasiassociated Mode

  23. Common v. In Channel Signaling

  24. CommonChannelSignaling Modes

  25. Signalling standards by CCITT • Signalling number 1-7 have been adopted • The signalling systems SS1 to SS5 deal with inchannel signalling • SS6 & SS7 deals with common channel signalling

  26. Signaling System Number 7 (SS7) • Common channel signaling scheme • ISDN • Call control, remote control, management and maintenance • Reliable means of transfer of info in sequence • Will operate over analog and below 64k • Can work with digital SPC exchanges (Speed less than 64kbps) • Point to point terrestrial and satellite links

  27. SS7 Signaling Network Elements • Signaling point (SP) • Any point in the network capable of handling SS7 control message • Signal transfer point (STP) • A signaling point capable of routing control messages • Control plane • Responsible for establishing and managing connections • Information plane • Once a connection is set up, info is transferred in the information plane

  28. Data transfer and signaling networks

  29. Performance of Signaling Network • STP capacities • Number of signaling links that can be handled • Message transfer time • Throughput capacity • Network performance • Number of SPs • Signaling delays • Availability and reliability • Ability of network to provide services in the face of STP failures

  30. Layers in SS7

  31. Layers in SS7 • Physical layer : MTP Level1 : Uses various transmission media specifications • Data link Layer : MTP Level2:Source destination address, CRC, Packetizing • Network layer: MTP Level 3: Routing from source to destination • Transport Layer SCCP (Signaling connection control point): Special services TUP (Telephone user port): Responsible for setting up voice calls TCAP (Transaction capabilities application port) : Transfer of calls or services ISDN (Integrated services digital network) : Support services to ISDN network

  32. Softswitch Architecture • General purpose computer running software to make it a smart phone switch • Lower costs • Greater functionality • Packetizing of digitized voice data • Allowing voice over IP • Most complex part of telephone network switch is software controlling call process • Call routing • Call processing logic • Physical switching done by media gateway • Call processing done by media gateway controller

  33. Softswitch

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