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Session 4. Transmission Systems and the Telephone Network Multiplexing

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Session 4. Transmission Systems and the Telephone Network Multiplexing Session 4. Transmission Systems and the Telephone Network Dongsoo S. Kim Electrical and Computer Engineering Indiana U. Purdue U. Indianapolis Intro to Computer Communication Networks Multiplexing A A A Trunk A group B B B MUX MUX B C C C C Sharing of expensive network resources – wire, bandwidth, computation power, … Types of Multiplexing n Frequency-Division Multiplexing n Time-Division Multiplexing n Wavelength Division Multiplexing n Code-Division Multiplexing n Statistical Multiplexing ECE/IUPUI 4-2 1 Intro to Computer Communication Networks Frequency Division Multiplexing Bandwidth is divided into a number of frequency slots The very old technology n AM – 10 kHz/channel n FM – 200 kHz/channel n TV – 60 MHz/channel n Voice – 4 kHz/channel How It works n Each channel is raised in frequency by a different amount from others. n Combine them. n No two channels occupy the sample portion of the frequency spectrum Standards (almost) n group – 12 voice channel (60-108 KHz) n supergroup – 5 groups, or 60 voice channels n mastergroup – 5 or 10 supergroups. ECE/IUPUI 4-3 Intro to Computer Communication Networks Time-Division Multiplexing A single high-speed digital transmission Each connection produces a digital information The high-speed multiplexor picks the digital data in round-robin fashion. Each connection is assigned a fixed time-slot during connection setup. A 2 A 1 A 2 A 1 C 2 B 2 A 2 C 1 B 1 A 1 DEMUX B 2 B 1 MUX B 2 B 1 C 2 C 1 C 2 C 1 ECE/IUPUI 4-4 2 Intro to Computer Communication Networks Time-Division Multiplexing – Standards T-1 Carrier : 24 digital telephone n A frame consists of 24 slots, 8-bit per slot. n Each frame has a single bit overhead for framing. n Each connection 8K pulses. n Bandwidth = (24*8+1)*8000 = 1.544 Mbps TDM Jargon in US and Canada n DS1 – output of T-1 multiplexer n DS2 – 4 DS1s n DS3 – 7 DS2s (28 DS1s) w 44.736 Mbps ( not 28*1.544=43.232 Mbps!) TDM Jargon in Europe n E1 – 30/32 voice channels w 1 channel for signalling w 1 channel for framing and maintenance n E2 – 4 E1s n E3 – 4 E2s n E4 – 4 E3s, 139.264 Mbps ( not 32*64*64Kbps = 131.072Mbps!) ECE/IUPUI 4-5 Intro to Computer Communication Networks SONET – Synchronous Optical Networks to handle lower-level digital signals Goals n support different carrier n internationalization n multiplex different digital channels n OAM (Operation, Administration and Maintenance) It is synchronous – controlled by a master clock. Components – sub-layer n switches n multiplexers n repeater STS STS PTE LTE PTE STE STE STE SONET SONET Terminal Mux R R R Mux Terminal Switch Switch Section Section Section Section Line Path ECE/IUPUI 4-6 3 Intro to Computer Communication Networks SONET Frame – 1 Basic SONET: STS-1 n 8000 frame/second, 9x90 bytes n Bandwidth ? Questions n Overheads on each sub-layer? n How many voice telephones can be carried by STS-1? path overhead section overhead line overhead payload (SPE) (87) ECE/IUPUI 4-7 Intro to Computer Communication Networks SONET Frame – 2 Asynchronous payload to Synchronous frame n SPE can begin anywhere within the SONET frame, span two frames. n If a payload arrives at the source while a dummy SONET frame is being constructed, it can be inserted into the current frame. – ADM capability n Pointer – First two bytes of line overhead ECE/IUPUI 4-8 4 Intro to Computer Communication Networks Self Healing Ring in SONET Double ring, bi-directional ring in a normal operation. When the fibers b/w two nodes are broken, the ring wraps around. How about a node failure? Fault tolerance n What is the resource to provide the additional service? n What has been sacrificed? Applied in the FDDI ring architecture. ECE/IUPUI 4-9 Intro to Computer Communication Networks Wavelength Division Multiplexing Optical version of FDM n The space b/w wavelengths is wide State-of-art technology can multiplex about 200 wavelengths, called DWDM (Dense WDM) Topology of optical networks n Goal: All optical communication (no conversion to electrical to transmission) n Expensive optical devices – wavelength converter, optical switch, … n Many wavelengths, still limited n Transparent optical networks Major Difficulties in WDM n No storage n Difficulty in computation Optical MUX Optical deMUX Prism Prism ECE/IUPUI 4-10 5 Intro to Computer Communication Networks Assignment of Wavelengths Current Paths (Connections) n SF-NY, SF-LA, LA -DC, NY-DF, NY-DC We have only two colors, red and blue Each link cannot carry two same color Want to add a connection between NY and LA. How? NY SF CH DC IN LA DF ECE/IUPUI 4-11 Intro to Computer Communication Networks Networks with Switches Geographically widespread networks Information flow from source to destination Switch – Core network components Unlike LAN, the wires (links) are the expensive resource. Control Link Switch 1 1 2 2 3 3 U Connection . of inputs . to outputs . U . U N N ECE/IUPUI 4-12 6 Intro to Computer Communication Networks The Very First Switch - Human person2 Switch ECE/IUPUI 4-13 Intro to Computer Communication Networks First Automatic Switch – Crossbar Switch NxN array of crosspoints (switch elements) Can connect any input to any available output by closing the correcsponding crosspoints It is nonblocking - a compatible request is always satisfied. Scalability n N2 crosspoints 1 2 . N 1 2 … N-1 N ECE/IUPUI 4-14 7 Intro to Computer Communication Networks The First Multistage Switch (Clos Switch) 3 stages, or 2k+1 stage N inputs = n x r 1 1 1 Input, middle, output stage Link b/w each pair of input and 2 middle switch modules 2 2 Link b/w each pair of middle and output switch modules 3 Nonblocking if m=2n-1 3 3 2nr(2n-1)+(2n-1)n2 =O(N1.5) crosspoints 4 What if k < 2n-1 ? r r What if links are multiplexed? m Multicast ? ECE/IUPUI 4-15 Intro to Computer Communication Networks Simple Packet Switch – Knockout Switch Used in some ATM switches Header info in each packet addresses to output port Possible to destine multiple packets to same output simultaneously n Tournament and select one packet Multicast Scalability Input lines Broadcast Bus 1 2 3 4 Concentrator Output Queue 1 2 3 4 Output lines ECE/IUPUI 4-16 8 Intro to Computer Communication Networks Binary Switch – Batcher/Banyan Switch Batcher Network – Sort incoming cell based on destination address Banyan Network n There exists one path from an input line to an output line, so it is possible to route the packet by itself without a central controller (Self-routing). n Two incoming packets might collide. n If the packets are ordered at the input lines, no collision. Batcher Banyan Sorting Network Network ECE/IUPUI 4-17 Intro to Computer Communication Networks Banyan Networks Self-Routing n 0 – move to the first port in the switching module n 1 – move to the second port in the switching module Possible to collide if they are out of order 6=110 0 0 4=100 0 0 1 1 6=110 1 1 2 2 2 2 3 3 3 3 4=100 4 4 4 4 5 5 5 5 6 6 6 6 7 7 7 7 ECE/IUPUI 4-18 9 Intro to Computer Communication Networks Batcher Sorting Networks Each module sorts two numbers only. The network sorts 8 numbers. n external lines – nlog2n complexity. Test yourself with any combination of 0-7. ECE/IUPUI 4-19 Intro to Computer Communication Networks Time Division Switch (TDX) n input lines are scanned in sequence, and build a frame with n slots. Slot of fixed size TSI reorder the slots in a frame and produce an output frame ex) T -1 n a slot is one byte, a frame consists of 24 slots, 8000 frame/sec n input lines input frame output frame Time Slot 7 6 5 4 3 2 1 0 1 2 5 0 3 6 7 4 Interchange 0 4 1 7 2 6 3 3 translation 4 0 table 5 5 6 2 ECE/IUPUI 7 1 4-20 10 Intro to Computer Communication Networks Area Code 202 Telephone Networks TANDEM Local loop (local access) interexchange carriers (IXC) TANDEM Pedestal Area Code 317 Local Exchange Carrier Serving local telephone office Area I/f 274 569 distribution cable Switch Distribution Frame Serving Area I/f feeder cable 881 Transport Area ECE/IUPUI 4-21 Intro to Computer Communication Networks Telephone Networks Local Loop n Analog grade designed 100 years ago. n Where is the largest copper mine? n A pair of twisted wires for bi-directional w Separate wires for each direction between central offices. w Hybrid transformer – convert two pairs to one pair or vice versa. n Utilization is very low. n Fiber to the Home (FTTH) vs. Fiber to the curb (FTTC) Trunk between central offices n Replaced by fiber optic. n For the most of communication services. ECE/IUPUI 4-22 11 Intro to Computer Communication Networks Concentration Numerous users and expensive trunks. Infrequently used customer lines Dual goals n Maximize the utilization of the shared trunks n Maintain an acceptable blocking probability Undeterministic and random manner of connection requests n Modeling with mathematic n Probability and statistics n Infinite number of customers Poisson Process n Independent trial n Timely process Many User Fewer Lines Trunks ECE/IUPUI 4-23 Intro to Computer Communication Networks Principle of Poisson Process, 1 l = arrival rate (call/second) E[X ] = expected holding time (second/call) m = l × E[X ], mean load to the sytem (Erlang) n = the number of trunks p = m / n, probabilit y of one occupancy Ek = event of k occupied trunks P(En) = blocking probabilit y all trunks busy N(t) t ECE/IUPUI 4-24 12 Intro to Computer Communication Networks Principle of Poisson Process, 2 n n 0 n - p n -np -m P(E ) = çæ ÷ö(1- p) p = (1- p) » (e ) = e = e , for small p 0 è0ø ænö ç ÷(1- p) n-k p k P(E ) çk ÷ n -k +1 p R(k ) = k = è ø = × P(E k -1 ) æ n ö n-k +1 k -1 k 1- p ç ÷(1- p) p èk -1ø
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