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
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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
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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.
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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 np (1- (k -1)/ n) m = × » , for small p k 1- p k
P(En ) = P(En E n-1 )P(E n-1 )
= P(En E n-1 )P(E n-1 En-2 )LP(E1 E 0 )P(E0 ) m m m m n = × L e -m = e -m × n n -1 1 n! Known as Poisson distribution m n m n = ¥ = n n! m k k! n! m k k! Known as Erlang-B Formula åk = 0 åk =0
ECE/IUPUI 4-25
Intro to Computer Communication Networks
Blocking Probability
# trunks 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 1
0.1
0.01 Blocking Probability 10
9 0.001 8
0.0001 1 2 3 4 5 6 7 Erlang
ECE/IUPUI 4-26
13 Intro to Computer Communication Networks
Routing Control
Direct Trunk: for large traffic flow Indirect Path: for smaller flow thru tandem switches Alternative Path: Handle overflow
n What are the blocking probability of the alternative path? w Do not use the Erlang-B formula directly.
n Fairness between two paths: A-1-2-F and B-1-2-D
Tandem Tandem Switch 1 Switch 2 Indirect Path Alternative Path
Switch A Switch B Switch D Switch F
Switch C Switch E ECE/IUPUI 4-27
Intro to Computer Communication Networks
Overflow Control
Causes n Link failure: a cut in a wire (unidirectional failure or bidirectional failure) n Node failure: system failure, or sick components n Soft failure: Unexpected flow surge Symptoms n In normal condition: the more offered load, the more utilization n In overflow condition: the more offered load, the less utilization Goal n Maximize the system efficiency How To
n Allocate more resources carried load n Re-routing offered load n Control the choke, or terminate non-priority services Detection and Propagation n Need extra features or overheads n Using signaling or maintenance resources
ECE/IUPUI 4-28
14 Intro to Computer Communication Networks
Cellular Networks Frequency reuse
n adjacent cells cannot use the same frequency
n # of colors = reuse factor
n minimize the number of colors w graph coloring problem in a planar graph Handoff
n user can move from one cell to another, while continuing without interruption Home region
n area the service provides Roaming Base Stations n provide a service to out-of-home-region Signal power measurement Mobile Switching Center Frequency allocation
n 824-849 MHz for mobile-to-base (25MHz) 869-894 MHz for base-to-mobile (25MHz) w 832 channels (21 setup channels)
ECE/IUPUI 4-29
Intro to Computer Communication Networks
Satellite Networks
Geo-synchronous Earth Satellite
n 36,000 km, 270 ms round-trip time
n fixed location from the earth above equator n Application Spot beam
n Directional: focus in small area n Equipped with multiple antennas and multiple transponders
n Frequency re-use n Application Low -earth orbit satellite
n Cellular networks with 77 satellites (from Motolora) for global coverage w 750Km to 2000 Km, 2hr rotation w Each station adjust to the passing satellite w As a satellite pass over, a handoff is carried out to the next cell w Satellite acts as a switching node by inter-satellite link
ECE/IUPUI 4-30
15