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

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 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

MUXMUX

Trunkgroup

ECE/IUPUI


4-3

Frequency Division MultiplexingBandwidth is divided into a number of frequency slotsThe 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.

ECE/IUPUI


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.

A2 A1

B2 B1

C2 C1

MUXA2 A1B2 B1C2 C1

DEMUX

A2 A1

B2 B1

C2 C1

ECE/IUPUI


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 = 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!)

ECE/IUPUI


4-6

SONET – Synchronous Optical Networks

to handle lower-level digital signalsGoals

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

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 – 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?

sectionoverhead

lineoverhead

payload (SPE) (87)

path overhead

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4-8

SONET Frame – 2Asynchronous 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

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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 tolerance

What is the resource to provide the additional service? What has been sacrificed?

Applied in the FDDI ring architecture.

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4-10

Wavelength Division MultiplexingOptical version of FDM

The space b/w wavelengths is wideState-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 MUXPrism

Optical deMUXPrism

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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 blueEach link can not carry two same colorWant to add a connection between NY and LA. How?

ECE/IUPUI


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

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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 crosspointsIt is nonblocking - a compatible request is always satisfied.Scalability

N2 crosspoints

N

1 2

1

N

2...

… N-1

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4-16

The First Multistage Switch (Clos Switch)

3 stages, or 2k+1 stageN inputs = n x r Input, 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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4-17

Simple Packet Switch – Knockout Switch

Used in some ATM switchesHeader info in each packet addresses to output portPossible to destine multiple packets to same output simultaneously

Tournament and select one packetMulticastScalability

1

2

3

4

1 2 3 4

Input lines

Output lines

Concentrator

OutputQueue

Broadcast Bus

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4-18

Binary Switch – Batcher/Banyan Switch

Rearrangeably nonblocking switchBatcher Network – Sort incoming cell based on destination addressBanyan 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.

BatcherSortingNetwork

BanyanNetwork

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4-19

Banyan NetworksSelf-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

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

ECE/IUPUI


4-20

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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4-21

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-1

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

ECE/IUPUI


4-22

Telephone NetworksArea Code 202Area Code 202

Area Code 317 Local Exchange Carrier

Area Code 317 Local 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

ECE/IUPUI


4-23

Telephone NetworksLocal 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


4-24

ConcentrationNumerous users and expensive trunks.Infrequently used customer linesDual 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

FewerTrunks

ManyUserLines

ECE/IUPUI


4-25

Principle of Poisson Process, 1

t

N(t)all trunks busy

λ arrival rate (call/second)E[X] expected holding time (second/call)ξ λ*E[X], mead load to the system (Erlang)c the number of trunksμ ξ /c , the probability of a trunk occupiedEk event of k trunk occupiedP(Ec ) blocking probability, PB

ECE/IUPUI


4-26

Erlang-B Formula

c

k

k

C

B

kac

aP

0!!

Using M/M/c/c queuing model

where a=λ / μ

ECE/IUPUI


4-27

Blocking Probability

0.0001

0.001

0.01

0.1

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

# trunks

Blo

ckin

g P

rob

ab

ility

1 2 3 4 5 6 7

8

9

10

Erlang

ECE/IUPUI


4-28

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

TandemSwitch 1

Switch B

Switch C

Switch A

TandemSwitch 2

Switch F

Switch E

Switch D

Indirect Path Alternative Path

ECE/IUPUI


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

carr

ied

load

ECE/IUPUI


4-30

Cellular NetworksFrequency 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 measurementFrequency 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

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4-31

Satellite NetworksGeo-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

Documents

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