session 4. transmission systems and the telephone...

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Session 4. Transmission Systems and the Telephone Network

Dongsoo S. KimElectrical and Computer EngineeringIndiana 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 Multiplexingn Frequency-Division Multiplexingn Time-Division Multiplexingn Wavelength Division Multiplexingn Code-Division Multiplexing n Statistical Multiplexing

B

C

A

B

C

A

B

C

A

B

C

A

MUXMUX

Trunkgroup

2

ECE/IUPUI


4-3

Frequency Division MultiplexingBandwidth is divided into a number of frequency slotsThe very old technologyn AM – 10 kHz/channeln FM – 200 kHz/channeln TV – 60 MHz/channeln Voice – 4 kHz/channel

How It worksn 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 channelsn mastergroup – 5 or 10 supergroups.

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4-4

Time-Division MultiplexingA single high-speed digital transmissionEach connection produces a digital informationThe 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

B2 B1

C 2 C 1

MUXA 2 A 1B2 B1C 2 C 1

DEMUX

A 2 A 1

B2 B1

C 2 C 1

3

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4-5

Time-Division Multiplexing – StandardsT-1 Carrier : 24 digital telephonen 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 Canadan DS1 – output of T-1 multiplexern DS2 – 4 DS1s

n DS3 – 7 DS2s (28 DS1s) w 44.736 Mbps ( not 28*1.544=43.232 Mbps!)

TDM Jargon in Europen E1 – 30/32 voice channels

w 1 channel for signallingw 1 channel for framing and maintenance

n E2 – 4 E1s

n E3 – 4 E2sn E4 – 4 E3s, 139.264 Mbps ( not 32*64*64Kbps = 131.072Mbps!)

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4-6

SONET – Synchronous Optical Networksto handle lower-level digital signalsGoalsn support different carriern internationalizationn multiplex different digital channelsn OAM (Operation, Administration and Maintenance)

It is synchronous – controlled by a master clock .

Components – sub-layern switchesn multiplexersn repeater

STSPTE LTE

STE

Path

Line

Section Section

Mux RSONET

TerminalSwitch

STE STE

R R Mux

STSPTE

SONETTerminalSwitch

SectionSection

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4-7

SONET Frame – 1Basic SONET: STS-1n 8000 frame/second, 9x90 bytesn Bandwidth ?

Questionsn Overheads on each sub-layer?n How many voice telephones can be carried by STS-1?

sectionoverhead

lineoverhead

payload (SPE) (87)

path overhead

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4-8

SONET Frame – 2Asynchronous payload to Synchronous framen 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 capabilityn Pointer – First two bytes of line overhead

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4-9

Self Healing Ring in SONETDouble 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 tolerancen What is the resource to provide the additional service?n What has been sacrificed?

Applied in the FDDI ring architecture.

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4-10

Wavelength Division MultiplexingOptical version of FDMn 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 limitedn Transparent optical networks

Major Difficulties in WDMn No storagen Difficulty in computation

Optical MUXPrism

Optical deMUXPrism

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4-11

Assignment of Wavelengths

CH

IN

NY

DC

SF

LA

DF

Current Paths (Connections)n SF-NY, SF -LA, LA -DC, NY -DF, NY -DC

We have only two colors, red and blueEach link cannot carry two same colorWant to add a connection between NY and LA. How?

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4-12

Networks with SwitchesGeographically widespread networksInformation flow from source to destinationSwitch – Core network componentsUnlike LAN, the wires (links) are the expensive resource.

SwitchLink

U

U

U

Connectionof inputs to outputs

Control

123

N

123

N

.

.

.

.

.

.

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4-13

The Very First Switch - Human

person2

Switch

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4-14

First Automatic Switch – Crossbar Switch

NxN array of crosspoints (switch elements)Can connect any input to any available output by closing the correcsponding crosspointsIt is nonblocking - a compatible request is always satisfied.Scalabilityn N2 crosspoints

N

1 2

1

N

2...

… N -1

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4-15

The First Multistage Switch (Clos Switch)3 stages, or 2k+1 stageN inputs = n x rInput, middle, output stageLink b/w each pair of input and middle switch modulesLink b/w each pair of middle and output switch modulesNonblocking if m=2n-12nr(2n-1)+(2n-1)n2

=O(N1.5) crosspointsWhat if k < 2n-1 ?What if links are multiplexed?Multicast ?

1

2

3

4

m

1

2

3

r

1

2

3

r

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4-16

Simple Packet Switch – Knockout SwitchUsed in some ATM switchesHeader info in each packet addresses to output portPossible to destine multiple packets to same output simultaneouslyn Tournament and select one packet

MulticastScalability

1

2

3

4

1 2 3 4

Input lines

Output lines

Concentrator

OutputQueue

Broadcast Bus

9

ECE/IUPUI


4-17

Binary Switch – Batcher/Banyan SwitchBatcher Network – Sort incoming cell based on destination addressBanyan Networkn 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.

BatcherSortingNetwork

BanyanNetwork

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4-18

Banyan NetworksSelf-Routingn 0 – move to the first port in the switching modulen 1 – move to the second port in the switching module

Possible to collide if they are out of order

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

6=110

4=100

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

4=1006=110

10

ECE/IUPUI


4-19

Batcher Sorting NetworksEach module sorts two numbers only.The network sorts 8 numbers.n external lines – nlog2n complexity.Test yourself with any combination of 0-7.

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4-20

Time Division Switch (TDX)n input lines are scanned in sequence, and build a frame with n slots.Slot of fixed sizeTSI reorder the slots in a frame and produce an output frameex) T -1n a slot is one byte, a frame consists of 24 slots, 8000 frame/sec

7 6 5 4 3 2 1 0

76

5

4

3

21

0

01234567

1 2 5 0 3 6 7 4Time Slot

Interchange

n input lines

input frame output frame

translation table

11

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4-21

Telephone Networks

Area Code 202

Area Code 317Local Exchange Carrier

274local telephone office

Pedestal

feeder cable

Switch

distribution cable

Serving Area I/f

881

569

TANDEM

TANDEM

Local loop (local access)

Transport Area

interexchange carriers (IXC)

Dis

trib

uti

on

Fra

me

Serving Area I/f

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4-22

Telephone NetworksLocal Loopn 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 officesn Replaced by fiber optic.n For the most of communication services.

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ECE/IUPUI


4-23

ConcentrationNumerous users and expensive trunks.Infrequently used customer linesDual goalsn Maximize the utilization of the shared trunksn Maintain an acceptable blocking probability

Undeterministic and random manner of connection requestsn Modeling with mathematicn Probability and statisticsn Infinite number of customers

Poisson Processn Independent trialn Timely process

FewerTrunks

ManyUserLines

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4-24

Principle of Poisson Process, 1

yprobabilit blocking )( trunksoccupied ofevent

occupancy one ofy probabilit ,/ trunksofnumber the

(Erlang) sytem the toloadmean ,][ll)(second/ca timeholding expected][

nd)(call/seco rate arrival

====

⋅===

n

k

EPkE

npn

XEXE

µ

λµ

λ

t

N(t)all trunks busy

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ECE/IUPUI


4-25

Principle of Poisson Process, 2peeepppnEP npnpnn smallfor ,)()1()1(0)( 0

0µ−−− ==≈−=−

=

pkp

nkknp

pp

kkn

ppk

n

ppkn

EPEP

kRkkn

kkn

k

k

smallfor ,1

)/)1(1(

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)1(1

)1(

)()(

)(111

µ≈

−−−

⋅=

−⋅

+−=

−

−

−

==−+−

−

−

∑∑ =

∞

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⋅=−

⋅=

=

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k

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nnnn

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001211

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!!!!

!11

)()()()(

)()()(

µ

µ

µ

µ

µµµµ µµL

L

Known as Poisson distribution

Known as Erlang-B Formula

ECE/IUPUI


4-26

Blocking Probability

0.0001

0.001

0.01

0.1

11 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

# trunks

Bloc

king

Pro

babi

lity

1 2 3 4 5 6 7

8

9

10

Erlang

14

ECE/IUPUI


4-27

Routing ControlDirect Trunk: for large traffic flowIndirect Path: for smaller flow thru tandem switchesAlternative Path: Handle overflown 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

TandemSwitch 1

Switch B

Switch C

Switch A

TandemSwitch 2

Switch F

Switch E

Switch D

Indirect Path Alternative Path

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4-28

Overflow Control Causesn Link failure: a cut in a wire (unidirectional failure or bidirectional failure)n Node failure: system failure, or sick componentsn Soft failure: Unexpected flow surge

Symptomsn In normal condition: the more offered load, the more utilizationn In overflow condition: the more offered load, the less utilization

Goaln Maximize the system efficiency

How Ton Allocate more resources n Re-routingn Control the choke, or terminate non-priority services

Detection and Propagationn Need extra features or overheadsn Using signaling or maintenance resources

offered load

carr

ied

load

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ECE/IUPUI


4-29

Cellular NetworksFrequency reusen adjacent cells cannot use the same frequencyn # of colors = reuse factor

n minimize the number of colorsw graph coloring problem in a planar graph

Handoffn user can move from one cell to another, while

continuing without interruption

Home regionn area the service provides

Roamingn provide a service to out-of-home-region

Signal power measurementFrequency allocationn 824-849 MHz for mobile-to-base (25MHz)

869-894 MHz for base-to-mobile (25MHz)w 832 channels (21 setup channels)

Base Stations

Mobile SwitchingCenter

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4-30

Satellite NetworksGeo-synchronous Earth Satelliten 36,000 km, 270 ms round-trip timen fixed location from the earth above equatorn Application

Spot beamn Directional: focus in small arean Equipped with multiple antennas and multiple transpondersn Frequency re-usen Application

Low-earth orbit satelliten Cellular networks with 77 satellites (from Motolora) for global coverage

w 750Km to 2000 Km, 2hr rotation

w Each station adjust to the passing satellitew 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

session 4. transmission systems and the telephone...

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