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Session 4. Transmission Systems and the Telephone Network

Session 4. Transmission Systems and the Telephone Network. Dongsoo S. Kim Electrical and Computer Engineering Indiana U. Purdue U. Indianapolis. A. A. A. A. Trunk group. B. B. B. MUX. MUX. B. C. C. C. C. Multiplexing.

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Session 4. Transmission Systems and the Telephone Network

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  1. Session 4. Transmission Systems and the Telephone Network Dongsoo S. Kim Electrical and Computer Engineering Indiana U. Purdue U. Indianapolis

  2. Intro to Computer Communication Networks A A A A Trunk group B B B MUX MUX B C C C C Multiplexing • Sharing of expensive network resources – wire, bandwidth, computation power, … • Types of Multiplexing • Frequency-Division Multiplexing • Time-Division Multiplexing • Wavelength Division Multiplexing • Code-Division Multiplexing • Statistical Multiplexing

  3. Intro to Computer Communication Networks Frequency Division Multiplexing • Bandwidth is divided into a number of frequency slots • The very old technology • AM – 10 kHz/channel • FM – 200 kHz/channel • TV – 60 MHz/channel • Voice – 4 kHz/channel • How It works • Each channel is raised in frequency by a different amount from others. • Combine them. • No two channels occupy the sample portion of the frequency spectrum • Standards (almost) • group – 12 voice channel (60-108 KHz) • supergroup – 5 groups, or 60 voice channels • mastergroup – 5 or 10 supergroups.

  4. 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. A2 A1 A2 A1 C2 B2 A2 C1 B1 A1 MUX DEMUX B2 B1 B2 B1 C2 C1 C2 C1

  5. Intro to Computer Communication Networks Time-Division Multiplexing – Standards • T-1 Carrier : 24 digital telephone • A frame consists of 24 slots, 8-bit per slot. • Each frame has a single bit overhead for framing. • Each connection 8K pulses. • Bandwidth = (24*8+1)*8000 = 1.544 Mbps • TDM Jargon in US and Canada • DS1 – output of T-1 multiplexer • DS2 – 4 DS1s • DS3 – 7 DS2s (28 DS1s) • 44.736 Mbps ( not 28*1.544=43.232 Mbps!) • TDM Jargon in Europe • E1 – 30/32 voice channels • 1 channel for signalling • 1 channel for framing and maintenance • E2 – 4 E1s • E3 – 4 E2s • E4 – 4 E3s, 139.264 Mbps ( not 32*64*64Kbps = 131.072Mbps!)

  6. Intro to Computer Communication Networks SONET – Synchronous Optical Networks • to handle lower-level digital signals • Goals • support different carrier • internationalization • multiplex different digital channels • OAM (Operation, Administration and Maintenance) • It is synchronous – controlled by a master clock. • Components – sub-layer • switches • multiplexers • repeater STS PTE STS PTE LTE STE STE STE SONET Terminal Switch SONET Terminal Switch Mux Mux R R R Section Section Section Section Line Path

  7. Intro to Computer Communication Networks path overhead section overhead line overhead payload (SPE) (87) SONET Frame – 1 • Basic SONET: STS-1 • 8000 frame/second, 9x90 bytes • Bandwidth ? • Questions • Overheads on each sub-layer? • How many voice telephones can be carried by STS-1?

  8. Intro to Computer Communication Networks SONET Frame – 2 • Asynchronous payload to Synchronous frame • SPE can begin anywhere within the SONET frame, span two frames. • 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 • Pointer – First two bytes of line overhead

  9. 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 • What is the resource to provide the additional service? • What has been sacrificed? • Applied in the FDDI ring architecture.

  10. Intro to Computer Communication Networks Optical MUX Prism Optical deMUX Prism Wavelength Division Multiplexing • Optical version of FDM • The space b/w wavelengths is wide • State-of-art technology can multiplex about 200 wavelengths, called DWDM (Dense WDM) • Topology of optical networks • Goal: All optical communication (no conversion to electrical to transmission) • Expensive optical devices – wavelength converter, optical switch, … • Many wavelengths, still limited • Transparent optical networks • Major Difficulties in WDM • No storage • Difficulty in computation

  11. Intro to Computer Communication Networks NY SF CH DC IN LA DF Assignment of Wavelengths • Current Paths (Connections) • SF-NY, SF-LA, LA-DC, NY-DF, NY-DC • We have only two colors, red and blue • Each link can not carry two same color • Want to add a connection between NY and LA. How?

  12. Intro to Computer Communication Networks Control Link Switch Connection of inputs to outputs 1 1 2 2 U 3 3 . . . . . . U U N N 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.

  13. Intro to Computer Communication Networks Switch The Very First Switch - Human

  14. Intro to Computer Communication Networks

  15. Intro to Computer Communication Networks 1 2 . . . N N-1 2 N … 1 First Automatic Switch – Crossbar Switch • N xN 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 • N2 crosspoints

  16. Intro to Computer Communication Networks The First Multistage Switch (Clos Switch) • 3 stages, or 2k+1 stage • N inputs = n x r • Input, middle, output stage • Link b/w each pair of input and middle switch modules • Link b/w each pair of middle and output switch modules • Nonblocking if m=2n-1 • 2nr(2n-1)+(2n-1)n2=O(N1.5) crosspoints • What if k < 2n-1 ? • What if links are multiplexed? • Multicast ?

  17. 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 • Tournament and select one packet • Multicast • Scalability

  18. Intro to Computer Communication Networks Batcher Sorting Network Banyan Network Binary Switch – Batcher/Banyan Switch • Rearrangeably nonblocking switch • Batcher Network – Sort incoming cell based on destination address • Banyan Network • 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). • Two incoming packets might collide. • If the packets are ordered at the input lines, no collision.

  19. Intro to Computer Communication Networks 6=110 4=100 6=110 4=100 Banyan Networks • Self-Routing • 0 – move to the first port in the switching module • 1 – move to the second port in the switching module • Possible to collide if they are out of order

  20. 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.

  21. Intro to Computer Communication Networks n input lines Time Slot Interchange input frame output frame 1 7 6 2 5 5 4 0 3 3 2 6 1 7 0 4 0 4 1 7 2 6 3 3 4 0 5 5 6 2 translation table 7 1 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 • a slot is one byte, a frame consists of 24 slots, 8000 frame/sec

  22. Area Code 202 Intro to Computer Communication Networks TANDEM Local loop (local access) interexchange carriers (IXC) Area Code 317 Local Exchange Carrier TANDEM Pedestal 569 Serving Area I/f local telephone office 274 distribution cable Distribution Frame Switch 881 Serving Area I/f feeder cable Transport Area Telephone Networks

  23. Intro to Computer Communication Networks Telephone Networks • Local Loop • Analog grade designed 100 years ago. • Where is the largest copper mine? • A pair of twisted wires for bi-directional • Separate wires for each direction between central offices. • Hybrid transformer – convert two pairs to one pair or vice versa. • Utilization is very low. • Fiber to the Home (FTTH) vs. Fiber to the curb (FTTC) • Trunk between central offices • Replaced by fiber optic. • For the most of communication services.

  24. Intro to Computer Communication Networks Many User Lines Fewer Trunks Concentration • Numerous users and expensive trunks. • Infrequently used customer lines • Dual goals • Maximize the utilization of the shared trunks • Maintain an acceptable blocking probability • Undeterministic and random manner of connection requests • Modeling with mathematic • Probability and statistics • Infinite number of customers • Poisson Process • Independent trial • Timely process

  25. Intro to Computer Communication Networks all trunks busy N(t) t Principle of Poisson Process, 1 λ arrival rate (call/second) E[X] expected holding time (second/call) ξλ*E[X], mead load to the system (Erlang) c the number of trunks μ ξ/c , the probability of a trunk occupied Ekevent of k trunk occupied P(Ec) blocking probability, PB

  26. Intro to Computer Communication Networks Erlang-B Formula where a=λ / μ Using M/M/c/c queuing model

  27. Intro to Computer Communication Networks # trunks Blocking Probability 10 9 8 7 1 6 2 3 4 5 Erlang Blocking Probability

  28. Intro to Computer Communication Networks Tandem Switch 1 Tandem Switch 2 Alternative Path Indirect Path Switch A Switch B Switch D Switch F Switch C Switch E Routing Control • Direct Trunk: for large traffic flow • Indirect Path: for smaller flow thru tandem switches • Alternative Path: Handle overflow • What are the blocking probability of the alternative path? • Do not use the Erlang-B formula directly. • Fairness between two paths: A-1-2-F and B-1-2-D

  29. Intro to Computer Communication Networks carried load offered load Overflow Control • Causes • Link failure: a cut in a wire (unidirectional failure or bidirectional failure) • Node failure: system failure, or sick components • Soft failure: Unexpected flow surge • Symptoms • In normal condition: the more offered load, the more utilization • In overflow condition: the more offered load, the less utilization • Goal • Maximize the system efficiency • How To • Allocate more resources • Re-routing • Control the choke, or terminate non-priority services • Detection and Propagation • Need extra features or overheads • Using signaling or maintenance resources

  30. Intro to Computer Communication Networks Cellular Networks • Frequency reuse • adjacent cells cannot use the same frequency • # of colors = reuse factor • minimize the number of colors • graph coloring problem in a planar graph • Handoff • user can move from one cell to another, while continuing without interruption • Home region • area the service provides • Roaming • provide a service to out-of-home-region • Signal power measurement • Frequency allocation • 824-849 MHz for mobile-to-base (25MHz)869-894 MHz for base-to-mobile (25MHz) • 832 channels (21 setup channels) Base Stations Mobile SwitchingCenter

  31. Intro to Computer Communication Networks Satellite Networks • Geo-synchronous Earth Satellite • 36,000 km, 270 ms round-trip time • fixed location from the earth above equator • Application • Spot beam • Directional: focus in small area • Equipped with multiple antennas and multiple transponders • Frequency re-use • Application • Low-earth orbit satellite • Cellular networks with 77 satellites (from Motolora) for global coverage • 750Km to 2000 Km, 2hr rotation • Each station adjust to the passing satellite • As a satellite pass over, a handoff is carried out to the next cell • Satellite acts as a switching node by inter-satellite link

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