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

ECE/IUPUI Intro to Computer Communication Networks 4-2 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 B C A B C A B C A B C A MUX Trunk group

ECE/IUPUI Intro to Computer Communication Networks 4-3 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 ( KHz) supergroup – 5 groups, or 60 voice channels mastergroup – 5 or 10 supergroups.

ECE/IUPUI Intro to Computer Communication Networks 4-4 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. A2A2 A1A1 B2B2 B1B1 C2C2 C1C1 MUX A2A2 A1A1 B2B2 B1B1 C2C2 C1C1 DEMUX A2A2 A1A1 B2B2 B1B1 C2C2 C1C1

ECE/IUPUI Intro to Computer Communication Networks 4-5 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 = Mbps TDM Jargon in US and Canada DS1 – output of T-1 multiplexer DS2 – 4 DS1s DS3 – 7 DS2s (28 DS1s)  Mbps ( not 28*1.544= 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, Mbps ( not 32*64*64Kbps = Mbps!)

ECE/IUPUI Intro to Computer Communication Networks 4-6 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 LTE STE Path Line Section Mux R SONET Terminal Switch STE RR Mux STS PTE SONET Terminal Switch Section

ECE/IUPUI Intro to Computer Communication Networks 4-7 SONET Frame – 1 Basic SONET: STS frame/second, 9x90 bytes Bandwidth ? Questions Overheads on each sub-layer? How many voice telephones can be carried by STS-1? section overhead line overhead payload (SPE) (87) path overhead

ECE/IUPUI Intro to Computer Communication Networks 4-8 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

ECE/IUPUI Intro to Computer Communication Networks 4-9 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.

ECE/IUPUI Intro to Computer Communication Networks 4-10 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 Optical MUX Prism Optical deMUX Prism

ECE/IUPUI Intro to Computer Communication Networks 4-11 Assignment of Wavelengths CH IN NY DC SF LA DF 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?

ECE/IUPUI Intro to Computer Communication Networks 4-12 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. SwitchLink U U U Connection of inputs to outputs Control N N

ECE/IUPUI Intro to Computer Communication Networks 4-13 The Very First Switch - Human Switch

ECE/IUPUI Intro to Computer Communication Networks 4-14

ECE/IUPUI Intro to Computer Communication Networks 4-15 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 N 2 crosspoints N N … N-1

ECE/IUPUI Intro to Computer Communication Networks 4-16 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)n 2 =O(N 1.5 ) crosspoints What if k < 2n-1 ? What if links are multiplexed? Multicast ?

ECE/IUPUI Intro to Computer Communication Networks 4-17 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

ECE/IUPUI Intro to Computer Communication Networks 4-18 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. Batcher Sorting Network Banyan Network

ECE/IUPUI Intro to Computer Communication Networks 4-19 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 6=110 4=100 6=110

ECE/IUPUI Intro to Computer Communication Networks 4-20 Batcher Sorting Networks Each module sorts two numbers only. The network sorts 8 numbers. n external lines – nlog 2 n complexity. Test yourself with any combination of 0-7.

ECE/IUPUI Intro to Computer Communication Networks 4-21 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 Time Slot Interchange n input lines input frame output frame translation table

ECE/IUPUI Intro to Computer Communication Networks 4-22 Telephone Networks Area Code 202 Area Code 317 Local Exchange Carrier Area Code 317 Local Exchange Carrier 274 local telephone office Pedestal feeder cable Switch distribution cable Serving Area I/f TANDEM Local loop (local access) Transport Area interexchange carriers (IXC) Distribution Frame Serving Area I/f

ECE/IUPUI Intro to Computer Communication Networks 4-23 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.

ECE/IUPUI Intro to Computer Communication Networks 4-24 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 Fewer Trunks Many User Lines

ECE/IUPUI Intro to Computer Communication Networks 4-25 Principle of Poisson Process, 1 t N(t) all trunks busy λarrival rate (call/second) E[X]expected holding time (second/call) ξ λ*E[X], mead load to the system (Erlang) c the number of trunks μ ξ /c, the probability of a trunk occupied E k event of k trunk occupied P(E c )blocking probability, P B

ECE/IUPUI Intro to Computer Communication Networks 4-26 Erlang-B Formula Using M/M/c/c queuing model where a =λ / μ

ECE/IUPUI Intro to Computer Communication Networks 4-27 Blocking Probability # trunks Blocking Probability Erlang

ECE/IUPUI Intro to Computer Communication Networks 4-28 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 Tandem Switch 1 Switch B Switch C Switch A Tandem Switch 2 Switch F Switch E Switch D Indirect Path Alternative Path

ECE/IUPUI Intro to Computer Communication Networks 4-29 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 offered load carried load

ECE/IUPUI Intro to Computer Communication Networks 4-30 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 MHz for mobile-to-base (25MHz) MHz for base-to-mobile (25MHz)  832 channels (21 setup channels) Base Stations Mobile Switching Center

ECE/IUPUI Intro to Computer Communication Networks 4-31 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