Raj JainThe Ohio State University1Fundamentals ofFundamentals ofTelecommunicationsTelecommunicationsRaj JainProfessor of CISThe Ohio State UniversityColumbus, OH 43210http://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 Multiplexingq Voice signal has a bandwidth of 4 kHzq Nyquist sampling theorem:Sample at twice the highest signal frequencyÞ Sample at 8 kHz Þ Sample every 125 msecq 256 levels Þ 8 bits per sample ´ 8000 samples/sec= 64 kbpsq 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 amplifiersRaj JainThe Ohio State University4TDM (Cont)TDM (Cont)q 1500/64 » 24 Þ Can multiplex approx.24 voice channels on that carrierÞ Telecommunication-1 carrier or T1 carrier.Named after the ANSI committee.Raj JainThe Ohio State University5T1 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❑ 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 Signalingq Initially, every 6th frame, the 8th bit ofeach 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.This is also known as 23B+D in ISDN.B = Bearer, D = Delta (or change).Raj JainThe Ohio State University7SubrateSubrate 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 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 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 University10Echo 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 University11X1 Y1 X2 Y2Y2X2Y1X1Guard timePropagation delayTime-CompressionTime-CompressionMultiplexingMultiplexingq Half-duplex transmissionq Central office and subscriber take turnsq Some time is allowed for propagation delay and forthe line to turn aroundq Wire rate is more than twice the signal rateRaj JainThe Ohio State University12Optical FiberOptical Fiberin the Local Loopin the Local Loopq Distribution network uses a star topologyq Feeder cables connect central office toremote nodes. Can be replaced via fiber.May multiplex using TDM or WDMq Active star remote node ⇒ It muxes/demuxes.q Passive star remote node ⇒ Subscriber muxes/demuxesCentralOfficeRemote NodeBundles of TPIndividual TPRaj JainThe Ohio State University13Circuit SwitchingCircuit Switchingq Three Phases: Circuit setup,Signal Transfer, Circuit Disconnectq Hierarchical System: Subscribers are connected tolocal exchanges (or end offices), which are connectedvia trunks to other tandem or toll switching centers.q Routing can be static or adaptive.Load independent or load dependent.Raj JainThe Ohio State University14SignalingSignalingq 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 University15Other 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 University16Types of Signaling Types of Signaling FnsFnsq Supervisory: To obtain resources toestablish/hold/release a connection.q Address: Identify destination. Subscriber to switch.Between switches.q Call information: Provide call status to the callingsubscriberq Network Management: Operation, troubleshooting,and maintenance of the network. Not directly involvedin call establishment/termination.q Signaling between a subscriber and the network isdifferent (simple) from that inside the network.Raj JainThe Ohio State University17q In-band signaling ⇒ Signaling over thesame channel as payloadq Out-of-band signaling ⇒ Separate channels forsignaling (but may be same physical circuits)q Common Channel Signaling (CCS)⇒ Separate circuits for signaling⇒ Allows several new functions, such as 800Signaling ChannelSignaling ChannelPayloadSignalingRaj JainThe Ohio State University18Signaling ModesSignaling Modesq Associated Mode: CCS follows the samepath as payloadq Nonassociated Mode: CCS uses a separate networkRaj JainThe Ohio State University19SummarySummaryq T1, DS1, DS3, ...q T1 Frames consist of 193 bits per 125 µs.q Echo cancellation is required if sharing the same wire-pair for both directions.q Optical fiber can be used to replace feeder cable.q Signaling: In band vs Common Channel, associated vsnon-associated..Raj JainThe Ohio State University20HomeworkHomeworkq Read