Raj JainThe Ohio State University1Fundamentals ofFundamentals ofTelecommunicationsTelecommunicationsRaj JainProfessor of CISThe Ohio State UniversityColumbus, OH 43210These slides are available at:http://www.cis.ohio-state.edu/~jain/cis777-99/Raj JainThe Ohio State University2q Single phone conversation: µ-Law and A-Lawq Multiplexing: T1 Framing, Signaling, Frame Formatsq Digital TDM Hierarchyq Echo Cancellationq Signaling: Functions, modesOverviewRaj JainThe Ohio State University3Summary Slide (Summary Slide (contcont.).)q HomeworkRaj JainThe Ohio State University4Time Division MultiplexingTime Division Multiplexingq Voice signal has a bandwidth of 4 kHz(300 Hz to 3300 Hz is transmitted on phone systems)q Nyquist sampling theorem:Sample at twice the highest signal frequency⇒ Sample at 8 kHz ⇒ Sample every 125 µsecq 256 levels ⇒ 8 bits per sample × 8000 samples/sec= 64 kbpsRaj JainThe Ohio State University5PCM and CompandingPCM and Compandingq Analog voice to Digital Signal⇒ Pulse code modulation (PCM)q 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 University6µµµµ-Law and A-Law-Law and A-Lawq In North America: µ-Lawy = ln (1+µx)/ln(1+µ), µ = 255q In Europe: A-Lawy = (1+ ln Ax)/(1+ ln A), A = 87.6q Linear for small values of x (x < 1/µ or x < 1/A)and logarithmic for larger values.Input xOutputyRaj JainThe Ohio State University7Echo CancellationEcho Cancellationq Echo Cancellation: Reflections from variousdistances along the path are estimated and subtractedfrom the received signal ⇒ 144 kbps up to 4 km❑ Problem: Full duplex transmission overa 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 thesignal returns (echo). Near-end and far-end echoesTransmitterReceiver TransmitterReceiverNear-end Far-endRaj JainThe Ohio State University8300 bps over Single Pair300 bps over Single Pairq 300 bps modems (Bell 108 specification)q 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 University9CentralOfficeRemote NodeBundles of TPIndividual TPLocal LoopLocal Loopq Distribution network uses a star topology⇒ Hierarchical System: Subscribers are connected tolocal exchanges (or end offices), which are connectedvia trunks to other tandem or toll switching centers.q Feeder cables connect central office toremote nodes. Can be replaced via fiber.May multiplex using TDM or WDMRaj JainThe Ohio State University10MultiplexingMultiplexingq Multiple conversations ⇒ Multiple frequency bandsFrequency division multiplexing (FDM)Useful for analog signals.q In 1962, telephone carrier cable between Bell Systemoffices could carry approx 1.5 Mbps over a mile= Distance between manholes in large cities= Distance between amplifiersq 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 University11T1 FrameT1 Frameq T1= 24 voice channels= Digital Service 1 = DS1q Used time-division multiplexing:1 2 3 23 24Framing bitT1 Frame = 193 bits/125 µs❑ Simple Framing: Add 101010 (1 bit per frame)Frame 1 Frame 0 Frame 1 Frame 0 Frame 1❑ Any other sequence ⇒ ResynchronizeRaj JainThe Ohio State University12T1 SignalingT1 Signalingq On-hook/off-hook or destination address = Signalingq Initially, manual through operatorsLater through switchesq In T1-frames, initially, the 8th bit of every 6th framein each channel was used for signalingq 8th bit is not reliable⇒ Use only 7 bits per frame ⇒ 56 kbpsq In the newer PRI (primary rate interface) format usedwith ISDN, the signaling information of 23 channelsis combined into a separate 24th channel.Each user gets full 64 kbps.Raj JainThe Ohio State University13Frame # 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 University14SubrateSubrate Multiplexing Multiplexingq Used for data rates lower than 56 kbps.q One bit of the 7 bits is used to indicatedata rateq 6 bits per channel = 48 kbpsm Five 9.6 kbps subchannelsm Ten 4.8 kbps subchannelsm Twenty 2.4 kbps subchannelsq Five subchannels ⇒ Subchannel 1 uses frames 1, 6,11, ...Raj JainThe Ohio State University15European System: E1European System: E1q European counter part of American T1q Designed by Conference of Post andTelecommunications (CEPT)q 32 bytes per 125 µs frame = 2.048 kb/s30 channels are used for dataOne channel for synchronizationOne channel for signallingRaj JainThe Ohio State University16Digital 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 University17SignalingSignalingq Signal = Controlq Signaling in telephone networks= Control messages in computer networksq Examples:m Connection setup request= Off-hook signal from telephone to switchm Connection setup acknowledge = Dial tonem Destination address = Pulse or tone dialingm Destination busy = Busy tonem Destination Available = Ringing toneRaj JainThe Ohio State University18Other SignalingOther SignalingFunctionsFunctionsq Transmission of dialed number betweenswitchesq Transmission of information between switchesindicating that a call cannot be completedq Transmission of billing informationq Transmission of information for diagnosing andisolating failuresq Control of satellite channelsRaj JainThe Ohio State University19Types of Signaling Types of Signaling FnsFnsq Supervisory: To obtain resources