Raj JainThe Ohio State University1Fundamentals ofFundamentals ofFundamentals ofTelecommunicationsTelecommunicationsTelecommunicationsRaj JainProfessor of CISThe Ohio State UniversityColumbus, OH [email protected]://www.cis.ohio-state.edu/~jain/Raj JainThe Ohio State University2q Time Division Multiplexing T1, T3, DS1, E1q T1 Framingq Echo Cancellationq SignalingOverviewRaj JainThe Ohio State University3Time Division MultiplexingTime Division MultiplexingTime Division Multiplexingq Voice signal has a bandwidth of 4 kHzq 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 kbpsq In 1962, telephone carrier (cable) between Bell System officescould carry approximately 1.5 Mbps over a mile = Distancebetween manholes in large cities = Distance betweenamplifiersq 1500/64 ≈ 24 ⇒ Can multiplex approximately 24 voicechannels on that carrier ⇒ Telecommunication-1 carrier or T1carrier. Named after the ANSI committee.Raj JainThe Ohio State University4T1 FrameT1 FrameT1 Frameq T1= 24 voice channels = Digital Service 1 = DS1q Used time-division multiplexing:1 2 3 23 24Framing bitT1 Frame = 193 bits/125 µsq Framing: Add 101010 (1 bit per frame)Frame 1 Frame 0 Frame 1 Frame 0 Frame 1q Any other sequence ⇒ ResynchronizeRaj JainThe Ohio State University5T1 SignalingT1 SignalingT1 Signalingq Initially, 8th bit of every channel was used for signalingq Now, every 6th frame, the 8th bit of each channel is used forsignalingq Net rate = (8 × 5+7)/(125 × 6) = 62.66 kbpsq For digital data service, 24th channel is used for sync bytewhich allows faster and more reliable frameresynchronization. 8th bit in each of the 23 channelsindicates whether the data is user’s or system controlq 8th bit is not reliable⇒ Use only 7 bits per frame ⇒ 56 kbpsq For mixture of voice and data, all 24 channels can be used.No sync bytes.Raj JainThe Ohio State University6Subrate MultiplexingSubrate MultiplexingSubrate Multiplexingq Used for data rates lower than 56 kbps.q One bit of the 7 bits is used to indicate data rateq 6 bits per channel = 48 kbpsq Five 9.6 kbps subchannelsq Ten 4.8 kbps subchannelsq Twenty 2.4 kbps subchannelsq Five subchannels ⇒ Subchannel 1 uses frames 1, 6, 11, ...Raj JainThe Ohio State University7DS1DS2Digital TDM HierarchyDigital TDM HierarchyDigital TDM HierarchyNorth America European JapanDS0 64 kbps 64 kbps 64 kbps1.544 Mbps E1 2.048 Mbps 1.544 Mbps6.313 Mbps E2 8.448 Mbps 6.312 MbpsDS3 44.736 Mbps E3 34.368 Mbps 32.064 MbpsDS4 274.176 Mbps E4 139.264 Mbps 97.728 MbpsE5 565.148 Mbps 397.200 MbpsDS1C 3.152 MbpsRaj JainThe Ohio State University8300 bps over Single Pair300 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 University9Echo CancellationEcho CancellationEcho Cancellationq Echo Cancellation: Estimate echo and subtract fromreceived signal. Transmitted signal is known. Reflectionsfrom various distances along the path are estimated andsubtracted from the received signal ⇒ 144 kbps up to 4 kmq Problem: Full duplex transmission over a single pairq Solution 1: Use different frequencies for the two directions.Only half of the bandwidth available for each directionq Solution 2: Use digital signal ⇒ Some part of the signalreturns (echo). Near-end and far-end echoesTransmitterReceiver TransmitterReceiverNear-end Far-endRaj JainThe Ohio State University10Time-Compression MultiplexingTime-Compression MultiplexingTime-Compression Multiplexingq Half-duplex transmissionq Central office and subscriber take turns for transmittingq Some time is allowed for propagation delay and for the lineto turn aroundq Wire rate is more than twice the signal rateX1 Y1 X2 Y2Y2X2Y1X1Guard timePropagation delayRaj JainThe Ohio State University11Optical Fiber in the Local LoopOptical Fiber in the Local LoopOptical Fiber in the Local Loopq Distribution network uses a star topologyq Feeder cables connect central office to remote nodesq Initially, feeder cables can be replaced via fiber. Maymultiplex using TDM or WDMq Active star Remote node ⇒ It multiplexes/demultiplexes.q Passive star remote node ⇒ Subscriber equipmentmultiplexes/demultiplexesCentralOfficeRemote NodeBundles of TPIndividual TPRaj JainThe Ohio State University12Circuit SwitchingCircuit SwitchingCircuit Switchingq Three Phases: Circuit setup, Signal Transfer, CircuitDisconnectq Hierarchical System: Subscribers are connected to localexchanges (or end offices), which are connected via trunksto other tandem or toll switching centers.q Routing can be static or adaptive.Load independent or load dependent.Raj JainThe Ohio State University13SignalingSignalingSignalingq Signal = Controlq Signaling in telephone networks= Control messages in computer networksq Examples:q Connection setup request= Off-hook signal from telephone to switchq Connection setup acknowledge = Dial toneq Destination address = Pulse or tone dialingq Destination busy = Busy toneq Destination Available = Ringing toneRaj JainThe Ohio State University14Other Signaling FunctionsOther Signaling FunctionsOther Signaling Functionsq Transmission of dialed number between switchesq Transmission of information between switches indicatingthat a call cannot be completedq Transmission of billing informationq Transmission of information for diagnosing and isolatingfailuresq Control of satellite channelsRaj JainThe Ohio State University15Types of Signaling FunctionsTypes of Signaling FunctionsTypes of Signaling Functionsq Supervisory: To obtain resources to establish/hold/release aconnection. Includes information sent back to thesubscriber's switch about the status of the call.q Address: Identify destination. Subscriber to switch.Between switches.q Call information: Provide call status to the callingsubscriberq Network Management: Operation, troubleshooting, andmaintenance of the network. Not directly involved in callestablishment/termination.q Signaling between a subscriber and the network is different(simple) from that inside the network.Raj JainThe Ohio State University16q In-band signaling ⇒ Signaling over the same channel aspayloadq Out-of-band signaling ⇒ Separate channels for signaling(but may be same physical circuits)q Common Channel