WUSTL CIS 777 - Fundamentals of Telecommunications

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Fundamentals of TelecommunicationsOverviewTime Division MultiplexingPCM and Compandingm-Law and A-LawEcho Cancellation300 bps over Single PairLocal LoopMultiplexingT1 FrameT1 SignalingD4 and ESF Frame FormatsSubrate MultiplexingEuropean System: E1Digital TDM HierarchySignalingOther Signaling FunctionsTypes of Signaling FnsSignaling ChannelSignaling ModesSummaryHomeworkRaj JainThe Ohio State University3-1Fundamentals of Fundamentals of TelecommunicationsTelecommunicationsRaj JainProfessor of CIS The Ohio State UniversityColumbus, OH 43210These slides are available at:http://www.cse.ohio-state.edu/~jain/cis777-00/Raj JainThe Ohio State University3-2OverviewOverviewSingle phone conversation: m-Law and A-LawMultiplexing: T1 Framing, Signaling, Frame FormatsDigital TDM HierarchyEcho CancellationSignaling: Functions, modesRaj JainThe Ohio State University3-3Time Division MultiplexingTime Division MultiplexingVoice signal has a bandwidth of 4 kHz(300 Hz to 3300 Hz is transmitted on phone systems)Nyquist sampling theorem: Sample at twice the highest signal frequency  Sample at 8 kHz  Sample every 125 sec256 levels  8 bits per sample  8000 samples/sec = 64 kbpsRaj JainThe Ohio State University3-4PCM and CompandingPCM and CompandingAnalog voice to Digital Signal  Pulse code modulation (PCM)Difference between actual and transmitted level  Quantizing noise. More perceptible at low levels.  Expand the number of levels at low amplitudesCompress at high amplitudes = CompandingInput xOutput yRaj JainThe Ohio State University3-5-Law and A-Law-Law and A-LawIn North America: -Lawy = ln (1+x)/ln(1+),  = 255In Europe: A-Lawy = (1+ ln Ax)/(1+ ln A), A = 87.6Linear for small values of x (x < 1/ or x < 1/A) and logarithmic for larger values.Input xOutputyRaj JainThe Ohio State University3-6Echo CancellationEcho CancellationEcho Cancellation: Reflections from various distances along the path are estimated and subtracted from the received signal  144 kbps up to 4 kmProblem: Full duplex transmission over a single pairSolution 1: FDM for the two directions.  Only half of the bandwidth for each directionSolution 2: Use digital signal  Some part of the signal returns (echo). Near-end and far-end echoesTransmitterReceiver TransmitterReceiverNear-end Far-endRaj JainThe Ohio State University3-7300 bps over Single Pair300 bps over Single Pair300 bps modems (Bell 108 specification)Use frequency shift keying0 1070 Hz, 1  1270 Hz in one direction0  2025 Hz, 1  2225 Hz in the other direction1070 1270 2025 2225SignalStrengthFrequencyRaj JainThe Ohio State University3-8CentralOfficeRemote NodeBundles of TPIndividual TPLocal LoopLocal LoopDistribution network uses a star topology Hierarchical System: Subscribers are connected to local exchanges (or end offices), which are connected via trunks to other tandem or toll switching centers.Feeder cables connect central office to remote nodes. Can be replaced via fiber. May multiplex using TDM or WDMRaj JainThe Ohio State University3-9MultiplexingMultiplexingMultiple conversations  Multiple frequency bandsFrequency division multiplexing (FDM)Useful for analog signals.In 1962, telephone carrier cable between Bell System offices could carry approx 1.5 Mbps over a mile = Distance between manholes in large cities = Distance between amplifiers1500/64  24  Can multiplex approx. 24 voice channels on that carrier  Telecommunication-1 carrier or T1 carrier. Named after the ANSI committee.Raj JainThe Ohio State University3-10T1 FrameT1 FrameT1= 24 voice channels = Digital Service 1 = DS1Used time-division multiplexing:1 2 3 23 24Framing bitT1 Frame = 193 bits/125 sSimple Framing: Add 101010 (1 bit per frame)1 0 1 0 1Any other sequence  ResynchronizeRaj JainThe Ohio State University3-11T1 SignalingT1 SignalingOn-hook/off-hook or destination address = SignalingInitially, manual through operatorsLater through switchesIn T1-frames, initially, the 8th bit of every 6th frame in each channel was used for signaling8th bit is not reliable  Use only 7 bits per frame  56 kbpsIn the newer PRI (primary rate interface) format used with ISDN, the signaling information of 23 channels is combined into a separate 24th channel. Each user gets full 64 kbps.Raj JainThe Ohio State University3-12Frame # 193rd bit Use 193rdbit Use1 1 FT X FDL2 0 FS X CRC3 0 FT X FDL4 0 FS 0 FS5 1 FT X FDL6 1 FS X CRC7 0 FT X FDL8 1 FS 0 FS9 1 FT X FDL10 1 FS X CRC11 0 FT X FDL12 0 FS 1 FS13 X FDL14 X CRC15 X FDL16 0 FS17 X FDL18 X CRC19 X FDL20 1 FS21 X FDL22 X CRC23 X FDL24 1 FSD4 Format superframe = 12 FramesESF format extended superframe = 24 Frames FT = Terminal Framing BitFS = Multiframe AlignmentFDL = Datalink bit (M bit)CRC = Cyclic Redundancy Check bitX = Data dependent11109876*54321 12*193 bitsSuperframeD4 and ESF Frame FormatsD4 and ESF Frame FormatsRaj JainThe Ohio State University3-13Subrate MultiplexingSubrate MultiplexingUsed for data rates lower than 56 kbps.One bit of the 7 bits is used to indicate data rate6 bits per channel = 48 kbpsFive 9.6 kbps subchannelsTen 4.8 kbps subchannelsTwenty 2.4 kbps subchannelsFive subchannels  Subchannel 1 uses frames 1, 6, 11, ...Raj JainThe Ohio State University3-14European System: E1European System: E1European counter part of American T1Designed by Conference of Post and Telecommunications (CEPT)32 bytes per 125 s frame = 2.048 Mb/s30 channels are used for dataOne channel for synchronizationOne channel for signallingRaj JainThe Ohio State University3-15Digital TDM HierarchyDigital TDM HierarchyNorth America Europe JapanDS0 64 kbps 64 kbps 64 kbpsDS1 1.544 Mbps E1 2.048 Mbps J1 1.544 MbpsDS2 6.313 Mbps E2 8.448 Mbps J2 6.312 MbpsDS3 44.736 Mbps E3 34.368 Mbps J3 32.064 MbpsDS4 274.176 Mbps E4 139.264 Mbps J4 97.728 MbpsDS1C 3.152 Mbps E5 565.148 Mbps J5 397.200 MbpsRaj JainThe Ohio State University3-16SignalingSignalingSignal = ControlSignaling in telephone networks = Control messages in computer networksExamples: Connection setup request = Off-hook signal from telephone to switchConnection setup acknowledge = Dial toneDestination address = Pulse or tone dialingDestination busy = Busy toneDestination Available = Ringing toneRaj JainThe Ohio State University3-17Other Signaling Other Signaling


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WUSTL CIS 777 - Fundamentals of Telecommunications

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