Fundamentals of TelecommunicationsSlide 2Time Division MultiplexingTDM (Cont)T1 FrameT1 SignalingSubrate MultiplexingDigital TDM Hierarchy300 bps over Single PairEcho CancellationTime-Compression MultiplexingOptical Fiber in the Local LoopCircuit SwitchingSignalingOther Signaling FunctionsTypes of Signaling FnsSignaling ChannelSignaling ModesSummaryHomeworkRaj JainThe Ohio State University1Fundamentals of Fundamentals of TelecommunicationsTelecommunicationsRaj JainProfessor of CIS The Ohio State UniversityColumbus, OH 43210http://www.cse.ohio-state.edu/~jain/Raj JainThe Ohio State University2Time Division Multiplexing T1, T3, DS1, E1T1 FramingEcho CancellationSignalingOverviewRaj JainThe Ohio State University3Time Division MultiplexingTime Division MultiplexingVoice signal has a bandwidth of 4 kHz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 kbps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 amplifiersRaj JainThe Ohio State University4TDM (Cont)TDM (Cont)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 University5T1 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Framing: Add 101010 (1 bit per frame)Frame 1 Frame 0 Frame 1 Frame 0 Frame 1Any other sequence  ResynchronizeRaj JainThe Ohio State University6T1 SignalingT1 SignalingInitially, every 6th frame, the 8th bit of 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. This is also known as 23B+D in ISDN. B = Bearer, D = Delta (or change).Raj JainThe Ohio State University7Subrate 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 University8Digital 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 University9300 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 University10Echo 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 University11X1 Y1 X2 Y2Y2X2Y1X1Guard timePropagation delayTime-Compression Time-Compression MultiplexingMultiplexingHalf-duplex transmissionCentral office and subscriber take turns Some time is allowed for propagation delay and for the line to turn aroundWire rate is more than twice the signal rateRaj JainThe Ohio State University12Optical Fiber Optical Fiber in the Local Loopin the Local LoopDistribution network uses a star topologyFeeder cables connect central office to remote nodes. Can be replaced via fiber. May multiplex using TDM or WDMActive star remote node  It muxes/demuxes. Passive star remote node  Subscriber muxes/demuxesCentralOfficeRemote NodeBundles of TPIndividual TPRaj JainThe Ohio State University13Circuit SwitchingCircuit SwitchingThree Phases: Circuit setup, Signal Transfer, Circuit DisconnectHierarchical System: Subscribers are connected to local exchanges (or end offices), which are connected via trunks to other tandem or toll switching centers.Routing can be static or adaptive.Load independent or load dependent.Raj JainThe Ohio State University14SignalingSignaling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 University15Other Signaling Other Signaling FunctionsFunctionsTransmission of dialed number between switchesTransmission of information between switches indicating that a call cannot be completedTransmission of billing informationTransmission of information for diagnosing and isolating failuresControl of satellite channelsRaj JainThe Ohio State University16Types of Signaling FnsTypes of Signaling FnsSupervisory: To obtain resources to establish/hold/release a connection. Address: Identify destination. Subscriber to switch. Between switches.Call information: Provide call status to the calling subscriberNetwork Management: Operation, troubleshooting, and maintenance of the network. Not directly involved in call establishment/termination.Signaling between a subscriber and the network is different (simple) from that inside the network.Raj JainThe Ohio State University17In-band signaling  Signaling over the same channel as payloadOut-of-band signaling  Separate channels for signaling (but may be same physical circuits)Common Channel Signaling (CCS)  Separate circuits for signaling Allows several new functions, such as 800Signaling ChannelSignaling ChannelPayloadSignalingRaj JainThe Ohio State University18Signaling ModesSignaling