Session_02 - UT D CS 6386 Telecommunication Software Design...

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Unformatted text preview: UT D CS 6386 Telecommunication Software Design Session 02 The Telephone Network - PSTN Telecommunication Networks Long-haul NW Node A Access NW Node Z Terminal Equipment Terminal Equipment Node B Access NW 2 1 PSTNs - Public Switched Telephone Networks 3 Telephone Network Physical Components Three major physical components 1. Local loops (the last mile) (the mile) 2. Trunks (transmission) (transmission) 3. Switching offices (switching) (switching) End Office Toll Office Regional Office Local Loop Trunk Intertoll Trunk 4 2 PSTNs Equipment Customer Premise Equipment - CPE Network Equipment Switches Local (class 5) Tandem (class 4) International Gateway Transmission equipment (OC-192, cross-connect, Mux/DeMux, etc.) Signaling equipment (STP, SCP) OAM&P equipment (Billing, Monitoring equipment) Network equipment for carriers: carrier grade 5 CPE Customer Premise Equipment Phone sets Key systems Serve a small number of lines Limited features PBX - Private Branch Exchange Full switching function at customer premise Under control of customer CENTREX PBX functionality implemented as features in the Central Office 6 3 Conventional Call (PBX) PBX PSTN 7 Information Flow Helen's Phone Off Hook Dial Tone Key Strokes Ring Back Remove Ringback Conversation 8 PBX Mike's Phone Alert Signal Off Hook 4 Local Calling Tandem CO CO 9 Classic Telephone Hierarchy 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 Regional Center Sectional Center Primary Center Toll Center End Office 10 5 NA Telephone Network Topology 11 Typical Configuration Today IXC IXC Tandem Tandem CO CO 12 6 Signaling Overview 13 Signaling Categories 1. Supervision 2. Information 3. Address 4. Control 5. Alerting 14 7 Channel Associated Signaling VF Trunk Tandem VF Trunk Central Office Central Office 2 Wire Loop 2 Wire Loop Mary Richard 15 Channel Associated Signaling 4. Off-Hook 6. Send MF Digits Central Office 1. Off-Hook 3. Dial Digits 2. Dial Tone 5. Wink 7. Ack Wink 15. Off-Hook 9. Wink 11. Ack Wink 14. Off-Hook Central Office 12. Ring Called Party 8. Off-Hook 10. Send MF Digits Tandem 16. Conversation 13. Called Party Answers Mary Richard 16 8 Common Channel Signaling SS7 Signaling Link STP Tandem Central Office A VF Trunk Central Office B Mary 2 Wire Loop Richard 17 Common Channel Signaling STP 4. IAM to TANDEM via STP Tandem 5. Return ACM via STP 11. Send ANM to CO A via STP 6. Send IAM via STP 7. Return ACM to TANDEM via STP 10. Send ANM to TANDEM via STP Central Office A 1. Off-Hook 3. Dial Digits Central Office B 8. Ring Called Party 2. Dial Tone 12. Conversation 9. Called Party Answers Mary Richard 18 9 Elements of the SS7 Network IMTs SSP Signaling Links SSP STP STP Signaling Links SCP SCP 19 SS#7 Network Topology SSP Service Switching Point STP Signal Transfer Point SCP Service Control Point 20 10 Point Code Assignments 227 - 010 - 000 227 - 010 - 001 227 - 010 - 005 227 - 010 - 002 227 - 010 - 004 227 - 010 - 003 Note: STP is always XXX-XXX-000 21 Cluster Definition 227 - 010 - 000 227 - 020 - 000 227 - 030 - 000 227 - 050 - 000 227 - 040 - 000 227 - 080 - 000 227 - 060 - 000 227 - 070 - 000 22 11 Overview of Transmission in PSTNs 23 Transmission Data are entities that convey information and are being exchanged e.g. voice A signal is an encoded form of data using a physical mean E.g. voltage, fire and smoke Transmission is the act of propagating a signal along a medium guided media unguided media Two domain of signal Time Frequency 24 12 Communication Channel Tx Rx Transmitter Receiver Medium 25 Transmission Media Wireline (guided) String Copper Twisted pair Coax Fiber and laser Wireless (unguided) Sound Smoke and fires Light and mirrors Infrared Radio Frequency Microwave 26 13 Transmission of Bits What Involved From physics Electromagnetic wave propagation Energy From mathematics Coding theory Theorical limits of channel 27 Signals Time Domain Concepts Continuous signal Various continuously over time Discrete signal Signal strength has a finite number of levels Periodic signal Repeated over time Aperiodic signal Not repeated over time 28 14 Signals Frequency Domain Concepts Spectrum The range of frequencies covered by the signal Absolute bandwidth The width of spectrum Effective bandwidth Often just bandwidth Narrow band of frequencies that contains most energy of the signal 29 Periodic Signals 30 15 Fourier Analysis Decomposition of periodic functions in the frequency domain Any periodic function g(t) with period T can be expressed as g(t) = 1/2 c + an sin (2nft) + bn cos (2nft) f = 1/T is the fundamental frequency 2f, 3f, 4f,......,nf are harmonics In reality we can NOT use infinite number of harmonics Signals are approximated by a finite number of harmonics Fourrier analysis helps understanding the effects of limited bandwidth on signals 31 Time Domain Frequency Domain 32 16 Transmission - Multiplexing A trunk can carries n separate channels of data Transmitter end A multiplexer combines inputs from n source lines and transmits them on the single trunk Receiver end A demultiplexer accepts data from the single trunk, separates the data according to channel and delivers them to the appropriate output lines MUX 1 trunk, n channels DEMUX n inputs n outputs 33 Multiplexing - FDM Frequency Division Multiplexing 34 17 Multiplexing - WDM # Power Power Power Fiber 1 spectrum Fiber 2 spectrum Spectrum on the shared fiber Prism or diffraction grating # Shared fiber Wavelength Division Multiplexing Variation of FDM used for optical fibers 35 Multiplexing - TDM Time Division Multiplexing Different channels given full bandwidth at different times TDM is widely used in telephone networks 36 18 Transmission PCM Voice Channel PCM : Pulse Code Modulation Basis for digital transmission of voice Analog voice signals are sampled at 8,000 times a second, each sample has 256 levels (8 bits) Thus each PCM voice channel requires 64 Kbps (or 64,000 bps) Quiz: What is the interval between two consecutive samples? In telephone parlance, one voice circuit (or channel) equals 64 Kbps 37 Transmission T1/E1 Trunk A trunk carries a number of voice channels How many? CCITT could not agree on international standards when PCM started In North America & Japan the smallest trunk is called T1 trunk 24 voice channels In Europe the equivalent is named E1 trunk 32 voice channels Quiz: what is bit rate of T1 trunks and E1 trunks respectively? 38 19 Transmission DS Hierarchy Digital Signal Number of Number previous level circuits DS0 DS1 24 DS2 4 DS3 7 Number of voice Bandwidth circuits 1 24 96 672 64 Kbps 1.544Mbps 6.312 Mbps 44.736 Mbps Multiplexed trunks can be multiplexed further US/Japan standard is called Digital Signaling hierarchy (DS) 39 Transmission RF - Radio Frequency Lower frequencies (longer wavelengths) Pass through objects well Do not propagate far power falls with the rate of 1/d3 in air d=distance Higher frequencies (shorter wavelengths) Propagate in straight lines Bounce off obstacles causing multipath interference and fading Propagate further than long wavelengths but may get absorbed by rain 40 20 Transmission - Satellites Geosynchronous ~36,000km above earth orbit ~24 hours appear to be "stationary" satellite Non-geosynchronous - Low NonEarth Orbit (LEO) 750km up Iridium project for satellite telephones (77 >66) ground station ocean ground station 41 Transmission Impairments Received signal may differ from signal transmitted due to channel impairments Causes of impairments Attenuation Distortion Delay Noise Fading (wireless) 42 21 Transmission Signals Analog vs Digital Which is better for communications? 43 22 ...
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This note was uploaded on 09/01/2008 for the course CS 6386 taught by Professor Nguyen during the Summer '08 term at University of Texas at Dallas, Richardson.

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