Lgw 2 e Chapter 4 Presentation

7/30/2019 Lgw 2 e Chapter 4 Presentation

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Chapter 4Circuit-Switching

NetworksMultiplexing

SONETTransport NetworksCircuit Switches

The Telephone NetworkSignaling

Traffic and Overload Control in Telephone NetworksCellular Telephone Networks


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Circuit Switching Networksz End-to-end dedicated circuits between clients

z Client can be a person or equipment (router or switch)z Circuit can take different forms

z Dedicated path for the transfer of electrical currentz Dedicated time slots for transfer of voice samplesz Dedicated frames for transfer of Nx51.84 Mbps signalsz Dedicated wavelengths for transfer of optical signals

z Circuit switching networks require:z Multiplexing & switching of circuitsz Signaling & control for establishing circuits

z These are the subjects covered in this chapter


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(a) A switch provides the network to a cluster of users, e.g.a telephone switch connects a local community

(b) A multiplexer connects two access networks, e.g. a highspeed line connects two switches

Accessnetwork

Network

How a network grows


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Metropolitan network Aviewed as Network A of Access Subnetworks

National network viewedas Network of RegionalSubnetworks (including A)

A

National &International

Network of RegionalSubnetworks

(a)

(b)

A

Network of

AccessSubnetworks

dc

ba

A

Metropolitan

1*

a

c

b

d

2

34

A Network Keeps Growing

z Very high-speed lines


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NetworksMultiplexing


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z Multiplexing involves the sharing of a transmission channel(resource) by several connections or information flows

z

Channel = 1 wire, 1 optical fiber, or 1 frequency bandz Significant economies of scale can be achieved by combining

many signals into onez Fewer wires/pole; fiber replaces thousands of cables

z Implicit or explicit information is required to demultiplex theinformation flows.

Multiplexing

B B

C C

A A

B

C

A

B

C

A(a) (b)

MUX MUX

SharedChannel


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(b) Combinedsignal fits into

channelbandwidth

Frequency-Division Multiplexingz Channel divided into frequency slots

z

Guard bandsrequiredz AM or FM radio

stationsz TV stations in

air or cablez Analog

telephonesystems

Cf

B f

Af

W u

W u

0

0

0 W u

A CB

f W 0

(a) Individual

signals occupyWu Hz


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(a) Each signaltransmits 1 unit

every 3 T seconds

(b) Combinedsignal transmits1 unit every T

seconds

Time-Division Multiplexing

t A1 A23T 0T 6T

t B

1B

2

3T 0T 6T

t C 1 C2

3T 0T 6T

B1 C1 A2 C2B2 A1 t 0T 1T 2T 3T 4T 5T 6T

z High-speed digital channel divided into time slots

z Framingrequired

z Telephonedigitaltransmission

z Digitaltransmission inbackbonenetwork


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T-Carrier Systemz Digital telephone system uses TDM.z PCM voice channel is basic unit for TDM

z 1 channel = 8 bits/sample x 8000 samples/sec. = 64 kbpsz T-1 carrier carries Digital Signal 1 (DS-1) that

combines 24 voice channels into a digital stream:

Bit Rate = 8000 frames/sec. x (1 + 8 x 24) bits/frame= 1.544 Mbps

2

24

1 1

2

24

24 b1 2 . . .b2322

Frame

24 . . .

. . .

MUX MUX

Framing bit


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North American Digital

Multiplexing Hierarchy

z DS0, 64 Kbps channelz DS1, 1.544 Mbps channelz DS2, 6.312 Mbps channelz DS3, 44.736 Mbps channelz DS4, 274.176 Mbps channel

1

24

1

4

1

7

1

6

..

..

.

.

.

.

Mux

Mux

Mux

Mux

DS1 signal, 1.544Mbps

DS2 signal, 6.312Mbps

DS3 signal, 44.736Mpbs

DS4 signal

274.176Mbps

24 DS04 DS1

7 DS2

6 DS3


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CCITT Digital Hierarchy

1

30

1

4

1

1

4

..

..

.

.

.

.

Mux

Mux

Mux

Mux

2.048 Mbps

8.448 Mbps

34.368 Mpbs

139.264 Mbps

64 Kbps

z CCITT digital hierarchy based on 30 PCM channels

z E1, 2.048 Mbps channelz E2, 8.448 Mbps channelz E3, 34.368 Mbps channelz E4, 139.264 Mbps channel


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12345 12345

t MUX

Clock Synch & Bit Slipsz Digital streams cannot be kept perfectly synchronizedz Bit slips can occur in multiplexers

Slow clock results in late bitarrival and bit slip


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Pulse Stuffingz Pulse Stuffing: synchronization to avoid data loss due to slipsz Output rate > R1+R2

z i.e. DS2, 6.312Mbps=4x1.544Mbps + 136 Kbpsz Pulse stuffing format

z Fixed-length master frames with each channel allowed to stuff or not to stuff a single bit in the master frame.

z Redundant stuffing specificationsz signaling or specification bits (other than data bits) are distributed

across a master frame.

Muxing of equal-rate signals Pulse stuffing

requires perfect synch


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Wavelength-Division Multiplexingz Optical fiber link carries several wavelengths

z From few (4-8) to many (64-160) wavelengths per fiber z Imagine prism combining different colors into single beamz Each wavelength carries a high-speed stream

z Each wavelength can carry different format signalz e.g. 1 Gbps, 2.5 Gbps, or 10 Gbps

1

2

m

OpticalMUX 1

2

m

OpticaldeMUX

1 2. m

Opticalfiber


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Example: WDM with 16

wavelengths

1 5 5 0 nm

1 5 6 0 nm

1 5 4

0 nm

30 dB


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Typical U.S. Optical Long-Haul

Network


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NetworksSONET


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SONET: Overviewz S ynchronous Optical NET workz North American TDM physical layer standard for

optical fiber communicationsz 8000 frames/sec. (T frame = 125 sec)

z compatible with North American digital hierarchyz SDH (Synchronous Digital Hierarchy) elsewhere

z Needs to carry E1 and E3 signalsz Compatible with SONET at higher speeds

z Greatly simplifies multiplexing in network backbonez OA&M support to facilitate network managementz Protection & restoration


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Pre-SONET multiplexing: Pulse stuffing required demultiplexingall channels

SONET Add-Drop Multiplexing: Allows taking individual channels inand out without full demultiplexing

Removetributary

Inserttributary

DEMUX MUXMUX DEMUX

ADM

Removetributary

Inserttributary

MUX DEMUX

SONET simplifies multiplexing


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SONET Specificationsz Defines electrical & optical signal interfacesz

Electricalz Multiplexing, Regeneration performed in electrical

domainz STS Synchronous Transport Signals definedz Very short range (e.g., within a switch)

z Opticalz Transmission carried out in optical domainz Optical transmitter & receiver z OC Optical Carrier


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SONET & SDH Hierarchy

STM: SynchronousTransfer Module

OC: Optical Channel STS: SynchronousTransport Signal

STM-649953.28OC-192STS-192

STM-162488.32OC-48STS-48

STM-121866.24OC-36STS-36

STM-81244.16OC-24STS-24STM-6933.12OC-18STS-18

STM-4622.08OC-12STS-12

STM-3466.56OC-9STS-9

STM-1155.52OC-3STS-3N/A51.84OC-1STS-1

SDHElectrical Signal

Bit Rate (Mbps)Optical SignalSONET Electr icalSignal


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SONET Equipmentz By Functionality

z ADMs: dropping & inserting tributariesz Regenerators: digital signal regenerationz Cross-Connects: interconnecting SONET streams

z By Signaling between elementsz

Section Terminating Equipment (STE): span of fiber between adjacent devices, e.g. regeneratorsz Line Terminating Equipment (LTE): span between adjacent

multiplexers, encompasses multiple sectionsz

Path Terminating Equipment (PTE): span between SONETterminals at end of network, encompasses multiple lines


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Section, Line, & Path in SONET

z Often, PTE and LTE equipment are the samez Difference is based on function and locationz PTE is at the ends, e.g., STS-1 multiplexer.z LTE in the middle, e.g., STS-3 to STS-1 multiplexer.

PTELTE

STE

STS-1 Path

STS Line

Section Section

STE = Section Terminating Equipment, e.g., a repeater/regenerator LTE = Line Terminating Equipment, e.g., a STS-1 to STS-3 multiplexer PTE = Path Terminating Equipment, e.g., an STS-1 multiplexer

MUX MUXReg Reg Reg

SONETterminal

STE STELTE

PTE

SONETterminal

Section Section


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Optical

Section

Optical

Section

Optical

Section

Optical

SectionLine

Optical

SectionLine

Optical

SectionLine

Path

Optical

SectionLine

Path

Section, Line, & Path Layers in

SONET

z SONET has four layersz Optical, section, line, pathz Each layer is concerned with the integrity of its own signals

z

Each layer has its own protocolsz SONET provides signaling channels for elements within a

layer


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SONET STS Framez SONET streams carry two types of overheadz

Path overhead (POH) :z inserted & removed at the endsz Synchronous Payload Envelope (SPE) consisting

of Data + POH traverses network as a single unitz Transport Overhead (TOH):

z processed at every SONET nodez TOH occupies a portion of each SONET framez TOH carries management & link integrity

information


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Special OH octets :

A1, A2 Frame Synch

B1 Parity on Previous Frame(BER monitoring)J0 Section trace

(Connection Alive?)H1, H2, H3 Pointer Action

K1, K2 Automatic ProtectionSwitching

810 Octets per frame @ 8000 frames/sec

9 rows

90 columns

1

2Order of transmission

A1 A2 J0 J1

B1 E1 F1 B3D1 D2 D3 C2

H1 H2 H3 G1

B2 K1 K2 F2

D4 D5 D6 H4D7 D8 D9 Z3

D10 D11 D12 Z4

S1 M0/1 E2 N1

3 Columns of Transport OH

Section Overhead

Line Overhead

Synchronous Payload Envelope (SPE)1 column of Path OH + 8 data columns

Path Overhead

Data

STS-1 Framez 810x64kbps=51.84 Mbps


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SPE Can Span Consecutive Frames

z Pointer indicates where SPE begins within a framez Pointer enables add/drop capability

Pointer 87 Columns

9 Rows

First column is path overhead

Synchronouspayload

envelope

Frame

k

Framek +1

Pointer

First octet

Last octet


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Stuffing in SONETz Consider system with different clocks (faster out than in)z Use buffer (e.g., 8 bit FIFO) to manage differencez Buffer empties eventuallyz One solution: send stuffz Problem:

z Need to signal stuff to receiver

FIFO1,000,000 bps 1,000,001 bps


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STS-1

STS-1 STS-1

STS-1

STS-1 STS-1

Map

Map

Map

STS-1 STS-1

STS-1 STS-1

STS-1 STS-1

ByteInterleave

STS-3

IncomingSTS-1 frames

Synchronized new

STS-1 frames

Synchronous Multiplexingz Synchronize each incoming STS-1 to local clock

z Terminate section & line OH and map incoming SPE into a new STS-1 synchronized to the local clock

z This can be done on-the-fly by adjusting the pointer z All STS-1s are synched to local clock so bytes can be

interleaved to produce STS-n


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Concatenated Payloadsz Needed if payloads of interleaved

frames are locked into a bigger unit

z Data systems send big blocks of information grouped together, e.g.,a router operating at 622 Mbps

z SONET/SDH needs to handlethese as a single unit

z H1,H2,H3 tell us if there isconcatenation

z STS-3c has more payload than 3STS-1s

z STS-Nc payload = Nx780 bytesz OC-3c = 149.760 Mb/sz OC-12c = 599.040 Mb/sz OC-48c = 2.3961 Gb/sz OC-192c = 9.5846 Gb/s

Concatenated Payload OC-Nc

J1B3C2G1

F2H4Z3Z4N1

(N /3) 1columns of

fixed stuff

z N x 87 columns

87N - ( N /3)columns of

payload


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NetworksTransport Networks


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TelephoneSwitch

Transport Network

Router Router

Router

TelephoneSwitch

TelephoneSwitch

Transport Networksz Backbone of modern networksz Provide high-speed connections: Typically STS-1 up to OC-192z Clients: large routers, telephone switches, regional networksz Very high reliability required because of consequences of failure

z 1 STS-1 = 783 voice calls; 1 OC-48 = 32000 voice calls;


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ADM

Removetributary

Inserttributary

MUX DEMUX

SONET ADM Networks

z SONET ADMs: the heart of existingtransport networks

z ADMs interconnected in linear and ring

topologiesz SONET signaling enables fast restoration

(within 50 ms) of transport connections


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1 2 43

1

2

3

4

Linear ADM Topologyz ADMs connected in linear fashionz Tributaries inserted and dropped to connect clients

z Tributaries traverse ADMs transparentlyz Connections create a logical topology seen by clientsz Tributaries from right to left are not shown

1+1 Li A i P i


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T = Transmitter W = Working lineR = Receiver P = Protection line

Bridge

T

T R

RW

P

Selector

1+1 Linear Automatic Protection

Switching

Simultaneous transmission over diverse routes Monitoring of signal quality Fast switching in response to signal degradation

100% redundant bandwidth


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Switch

T

T R

RW

P

Switch

APS signaling

1:1 Linear APS

Transmission on working fiber Signal for switch to protection route in response to

signal degradation

Can carry extra (preemptible traffic) on protection line


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Switch

T RW

T RP

Switch

T RW

1

T RW n

APS signaling

1:N Linear APS

Transmission on diverse routes; protect for 1 fault Reverts to original working channel after repair More bandwidth efficient


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a

b

c

OC-3 nOC-3 n

OC-3 n

(a) (b)

Three ADMs connected in

physical ring topology

Logical fully connected

topology

a

b c

SONET Ringsz ADMs can be connected in ring topologyz Clients see logical topology created by tributaries


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SONET Ring Optionsz 2 vs. 4 Fiber Ring Networkz

Unidirectional vs. bidirectional transmissionz Path vs. Link protection

z Spatial capacity re-use & bandwidthefficiency

z

Signalling requirements


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W = Working Paths

W

P

1

2

3

4

UPSR

P = Protection Pathsz No spatial re-useEach path uses 2x bw


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UPSR Propertiesz Low complexityz

Fast path protectionz 2 TX, 2 RXz No spatial re-use; ok for hub traffic patternz Suitable for lower-speed access networksz Different delay between W and P path

Four-Fiber Bidirectional Line


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Four Fiber Bidirectional Line

Switched Ringz 1 working fiber pair; 1 protection fiber pair z Bidirectional

z Working traffic & protection traffic use same routein working pair

z 1:N likez Line restoration provided by either:

z Restoring a failed spanz Switching the line around the ring


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P

WEqualdelay

SpatialReuse

1

2

3

4

4-BLSR

Standby

bandwidthis shared


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P

WEqualdelay

1

2

3

4

Fault onworking

links

BLSR Span Switching

z SpanSwitchingrestores

failed line


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P

WEqualdelay

1

2

3

4

Fault onworking and

protectionlinks

BLSR Span Switching

z LineSwitchingrestores

failed lines


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4-BLSR Propertiesz High complexity: signalling requiredz Fast line protection for restricted distance

(1200 km) and number of nodes (16)z 4 TX, 4 RXz Spatial re-use; higher bandwidth efficiencyz Good for uniform traffic patternz Suitable for high-speed backbone networksz Multiple simultaneous faults can be handled

Backbone Networks consist of


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Interofficerings

Metroring

Regionalring

Interconnected Rings

UPSR

OC-12

BLSR

OC-48,OC-192

UPSR or BLSR

OC-12,OC-48


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Mesh Topology Networks using


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BC

DF

A

G E

Router

Router

Router

Router

p gy g

SONET Cross-Connectsz Cross-Connects are nxn switchesz Interconnects SONET streamsz More flexible and efficient than ringsz Need mesh protection & restoration


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From SONET to WDMSONETz combines multiple SPEs

into high speed digitalstream

z ADMs andcrossconnectsinterconnected to form

networksz SPE paths between

clients from logicaltopology

z

High reliability throughprotection switching

WDMz combines multiple wavelengths into a

common fiber z Optical ADMs can be built to insert and

drop wavelengths in same manner asin SONET ADMS

z Optical crossconnects can also be builtz All-optical backbone networks will

provide end-to-end wavelengthconnections

z Protection schemes for recovering

from failures are being developed toprovide high reliability in all-opticalnetworks


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Opticalfiber switch

Wavelengthcross-connect

W D M

W D M W

D M

Output Input M U X

D

e M U X

Addedwavelengths

Droppedwavelengths

W D M

Optical Switching


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NetworksCircuit Switches


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User 1

SwitchLink

User n

User n 1

Control

123

N

123

N

Connectionof inputsto outputs

Network: Links & switchesz Circuit consists of dedicated resources in sequence

of links & switches across networkz Circuit switch connects input links to output links

z Network

z Switch


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Circuit Switch Typesz Space-Division switches

z Provide separate physical connection betweeninputs and outputs

z Crossbar switchesz Multistage switches

z Time-Division switchesz Time-slot interchange techniquez Time-space-time switches

z Hybrids combine Time & Space switching


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N

1 2

1

N

2

N 1

Crossbar Space Switch

z N x N array of crosspoints

z Connect an input toan output by closinga crosspoint

z Nonblocking: Anyinput can connect toidle output

z Complexity: N 2

crosspoints


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Clos Non-Blocking Condition:


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nxk

nxk

nxk

N/n x N/n

N/n x N/n

N/n x N/n

k xn1

N/n

Desiredinput

1

j m

N/n

Desiredoutput

1

2n -1

k xn

k xn

n-1

N/n x N/nn+1

N/n x N/n2n-2

Free path Free path

n-1busy

n-1busy

k=2n-1z Request connection from last input to input switch j to last output in output switch m

z Worst Case: All other inputs have seized top n-1 middle switches AND all other outputs have seized next n-1 middle switches

z If k=2n-1 , there is another path left to connect desired input to desired output

# internal links =2x # external links

l l h


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C(n) = number of crosspoints in Clos switch

= 2Nk + k ( )2 = 2 N (2n 1)+(2 n 1)( ) 2

Differentiate with respect to n:

0 = = 4 N + 4N ==> n

The minimized number of crosspoints is then:

C* = (2N + )(2( )1/2

1) 4N 2N = 4 2N 1.5

This is lower than N 2 for large N

Minimum Complexity Clos Switch

N 2

N /2

2N 2

n2

2N 2

n3

2N 2

n2

N 2

C

n

N

n

N

n

N

2


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Time-Slot Interchange (TSI)S i hi


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1

2

3

22

zzz

23

24

Writeslots inorder of arrival

Read slots

according toconnectionpermutation

24 23 12

Time-slot interchange

24 23 12abcd b a d c

a

b

c

d

Switchingz Write bytes from arriving TDM stream into memoryz Read bytes in permuted order into outgoing TDM streamz Max # slots = 125 sec / (2 x memory cycle time)

z Incoming TDM

stream

z Outgoing TDM

stream

Ti S Ti H b id S it h


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nxk

nxk

nxk

nxk

N/n x N/n k xn1

2

N/n

N inputs

1

3

1

12

zzz

n

Time-slot interchange

Input TDMframe withn slots

Output TDMframe with k slots

n 2 1 k 2 1

Time-Space-Time Hybrid Switchz Use TSI in first & third stage; Use crossbar in middle

z Replace n input x k output space switch by TSI switch that takes n-slotinput frame and switches it to k-slot output frame

Flow of time slots betweenit h


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n k N/n N/n

N/n N/n

N/n N/n

k n1 1

2

N/n

1

2

k

k n

k n

n k 2

n k N/n

First slot

k th slot

First slot

k th slot

switches

z Only one space switch active in each time slot

Time Share the Crossbar Switch


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nxk

nxk

nxk

nxk

N/n x N/nTime-sharedspace switch

k xn

1

2

N/n

N inputs

1

2

3 3

N/n

N outputs

TDM

n slots

n slots

n slots

n slots

k xn

k xn

k xn

TDM

k slots

TDM

k slots

TSI stage TSI stageSpace stage

Time-Share the Crossbar Switch

z Interconnection pattern of space switch isreconfigured every time slot

z Very compact design: fewer lines because of TDM& less space because of time-shared crossbar

Example: A 3 B 4 C 1 D 3


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2x3

2x3

3x21

2

1

2

3x2D1

B1 A1B2 A2

C1D2 C2

B1 A1

C1D1

A1

B1

C 1

D1

A1 C1

B1 D1

(b)

AB

CD

(a)C

A

D

B

Example: A 3, B 4, C 1, D 3

z 3-stageSpaceSwitch

z Equivalent TST Switch

Example: T S T Switch Design


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Example: T-S-T Switch Design

For N = 960z Single stage space switch ~ 1 million crosspointsz T-S-T

z Let n = 120 N/n = 8 TSIsz k = 2 n 1 = 239 for non-blockingz Pick k = 240 time slotsz Need 8x8 time-multiplexed space switch

For N = 96,000z T-S-T

z Let n = 120 k = 239z N / n = 800z Need 800x800 space switch

Available TSI Chips circa 2002


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Available TSI Chips circa 2002

z OC-192 SONET Framer Chipsz Decompose 192 STS1s and perform (restricted)

TSI

z Single-chip TSTz 64 inputs x 64 outputsz Each line @ STS-12 (622 Mbps)z

Equivalent to 768x768 STS-1 switch

Pure Optical Switching


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Pure Optical Switching

z Pure Optical switching: light-in, light-out,without optical-to-electronic conversion

z Space switching theory can be used todesign optical switchesz Multistage designs using small optical switchesz Typically 2x2 or 4x4z MEMs and Electro-optic switching devices

z Wavelength switchesz Very interesting designs when space switching is

combined with wavelength conversion devices


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NetworksThe Telephone Network

Telephone Call


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Telephone Call

z User requests connectionz Network signaling

establishes connectionz Speakers conversez User(s) hang upz Network releases

connection resources

Signal

Source

Signal

Release

Signal

Destination

Goahead Message

Call Routing


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(b)

LATA 1 LATA 2

Net 1

Net 2

(a)

1

2 3

4

5

A B

C D

Call Routingz Local calls routed

through local network(In U.S. Local Access &Transport Area)

z Long distance calls

routed to long distanceservice provider


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Fiber-to-the-Home or Fiber-to-the-Curve?


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Fiber to the Curve?

z Fiber connection to thehome provides huge

amount of bandwidth,but cost of opticalmodems still high

z

Fiber to the curve(pedestal) with shorter distance from pedestalto home can providehigh speeds over copper pairs

Table 3.5 Data rates of 24-gauge twisted pair

1000 feet, 300 m51.840Mbps

STS-1

3000 feet, 0.9 km25.920Mbps

1/2 STS-1

4500 feet, 1.4 km12.960Mbps1/4 STS-1

12,000 feet, 3.7 km6.312 MbpsDS2

18,000 feet, 5.5 km1.544 MbpsT-1

DistanceData RateStandard

Two- & Four-wire connections


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Originalsignal

Hybridtransformer

Received signal

Echoedsignal

Receive pair

Transmit pair

z From telephone to CO, two wires carry signals in both directionsz Inside network, 1 wire pair per directionz Conversion from 2-wire to 4-wire occurs at hybrid transformer in

the COz Signal reflections can occur causing speech echoz Echo cancellers used to subtract the echo from the voice signals

z Two Wires

z Four Wires


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Setting Up Connections


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g p

Manuallyz Human Interventionz Telephone

z Voice commands &switchboard operators

z Transport Networksz Order forms &

dispatching of craftpersons

Automaticallyz Management Interface

z Operator at console setsup connections atvarious switches

z Automatic signalingz Request for connection

generates signalingmessages that control

connection setup inswitches

Stored-Program Control Switches


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SPC

ControlSignaling Message

z SPC switches (1960s)z Crossbar switches with crossbars built from relays

that open/close mechanically through electrical controlz Computer program controls set up opening/closing of crosspoints to establish connections between switchinputs and outputs

z Signaling required to coordinate path set up acrossnetwork

Message Signaling


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Switch

Processor

Office B

Switch

Office A

Processor Signaling

ModemModem

Trunks

z Processors that control switches exchange signalingmessages

z Protocols defining messages & actions definedz Modems developed to communicate digitally over

converted voice trunks

Signaling Network


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Access SignalingDial tone

Internodal SignalingSignaling System 7

STP

STP

STP

STP

SSP SSP

Transport Network

Signaling Network

SSP = service switching point (signal to message)STP = signal transfer point (packet switch)

SCP = service control point (processing)

SCP

z Common Channel Signaling (CCS) #7 deployed in 1970s to control call setupz Protocol stack developed to support signalingz Signaling network based on highly reliable packet switching networkz

Processors & databases attached to signaling network enabled many newservices: caller id, call forwarding, call waiting, user mobility

Signaling System Protocol Stack


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Application layer

Transport layer

Network layer

Data link layer

Physical layer

Presentation layer

Session layer

SCCP

MTP level 3

MTP level 2

MTP level 1

ISUPTCAPTUP

ISUP = ISDN user part MTP = message transfer partSSCP = signaling connection control part TCAP = transaction capabilities part

TUP = telephone user part

z Lower 3 layers ensuredelivery of messages tosignaling nodes

z SCCP allowsmessages to bedirected to applications

z TCAP defines

messages & protocolsbetween applications

z ISUP performs basiccall setup & release

z TUP instead of ISUP insome countries

Future Signaling: Calls, Sessions,& Connections


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Call/Sessionz An agreement by two end

parties to communicatez Answering a ringing

phone (after looking atcaller ID)

z TCP three-wayhandshake

z Applies in connection-less &connection-oriented

networksz Session Initiation Protocol

(SIP) provides for establishment of sessions inmany Internet applications

Connectionz Allocation of resources to

enable information transfer between communicatingpartiesz Path establishment in

telephone callz Does not apply in

connectionless networksz ReSerVation Protocol

(RSVP) provides for resourcereservation along paths inInternet

Network Intelligence


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SSPSSP

Transport Network

Signaling

Network

Intelligent

Peripheral

ExternalDatabase

z Intelligent Peripherals provide additional service capabilitiesz Voice Recognition & Voice Synthesis systems allow users to access

applications via speech commandsz Voice browsers currently under development (See: www.voicexml.org)z Long-term trend is for IP network to replace signaling system and provideequivalent servicesz Services can then be provided by telephone companies as well as new

types of service companies


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Traffic Management & OverloadControl


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z Telephone calls come and goz People activity follow patterns

z Mid-morning & mid-afternoon at officez Evening at homez Summer vacation

z Outlier Days are extra busyz Mothers Day, Christmas,

z Disasters & other events cause surges in trafficz Need traffic management & overload control

Traffic concentration


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z Traffic fluctuates as calls initiated & terminatedz Driven by human activity

z Providing resources soz Call requests always met is too expensivez Call requests met most of the time cost-effective

z Switches concentrate traffic onto shared trunksz Blocking of requests will occur from time to time

z Traffic engineering provisions resources to meet blockingperformance targets

Fewer

trunks

Manylines

Fluctuation in Trunk Occupancy


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1

2

3

45

6

7

T r u n k n u m

b e r

N(t)

t

All trunks busy, new call requests blocked

z Number of busy trunks

z activez active

z active

z activez active

z active

z activez active

z active

z active

Modeling Traffic Processes


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z Find the statistics of N(t) the number of calls in the system

Modelz Call request arrival rate : requests per secondz In a very small time interval ,

z Prob[ new request ] = z Prob[no new request] = 1 -

z

The resulting random process is a Poisson arrival process:

z Holding time : Time a user maintains a connectionz X a random variable with mean E(X)

z Offered load : rate at which work is offered by users:z a = calls/sec * E( X ) seconds/call (Erlangs)

( T)k e T k!

Prob( k arrivals in time T ) =

Blocking Probability & Utilization


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z c = Number of Trunksz Blocking occurs if all trunks are busy, i.e. N(t)=c z If call requests are Poisson, then blocking probability

P b is given by Erlang B Formula

z The utilization is the average # of trunks in use

P b =

a c

c!

k !a k

k =0

c

Utilization = (1 P b) E [ X ]/c = (1 P b ) a /c

Blocking Performance


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z a

To achieve 1% blocking probability:a = 5 Erlangs requires 11 trunksa = 10 Erlangs requires 18 trunks

Multiplexing Gain


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0.85117100

0.8510690

0.8075600.786450

0.714230

0.561810

0.53179

0.53158

0.50147

0.46136

0.45115

0.401040.3883

0.2972

0.2051

UtilizationTrunks@1%Loadz At a given P b, the

system becomes more

efficient in utilizingtrunks with increasingsystem size

z Aggregating trafficflows to share centrallyallocated resources ismore efficient

z This effect is calledMultiplexing Gain


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Alternative Routing


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z Deploy trunks between switches with significant traffic volumez Allocate trunks with high blocking, say 10%, so utilization is highz Meet 1% end-to-end blocking requirement by overflowing to

longer paths over tandem switchz Tandem switch handles overflow traffic from other switches so it

can operate efficientlyz Typical scenario shown in next slide

Switch SwitchHigh-usage route

Tandemswitch

Alternative route

Typical Routing Scenario


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High-usage route B-E

Tandemswitch 1

Alternative routesfor B-E, C-F

High-usage route C-F

Switch B

Switch C

Switch E

Switch D

Switch F

Tandem

switch 2

Switch A

Dynamic Routing


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High-usage route

Alternative routes

Switch A Switch B

Tandemswitch 3

Tandemswitch 1

Tandemswitch 2

z Traffic varies according to time of day, day of weekz East coast of North America busy while West coast idle

z Network can use idle resources by adapting route selectiondynamicallyz Route some intra-East-coast calls through West-coast switches

z Try high-usage route and overflow to alternative routes

Overload Control


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C a r r

i e d l o a

d

Offered load

Network capacity

Overload Situationsz Mothers Day, Xmasz Catastrophesz Network Faults

Strategiesz Direct routes firstz Outbound firstz Code blockingz Call request pacing

Chapter 4Ci i S i hi


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Circuit-SwitchingNetworks

Cellular Telephone Networks


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Cellular Communications


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Two basic concepts:z Frequency Reuse

z A region is partitioned into cellsz Each cell is covered by base stationz Power transmission levels controlled to minimize inter-cell

interferencez Spectrum can be reused in other cells

z Handoff z Procedures to ensure continuity of call as user moves from

cell to another z Involves setting up call in new cell and tearing down old one


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Signaling & Connection Control


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z Setup channels set aside for call setup & handoff z Mobile unit selects setup channel with strongest signal &

monitors this channelz Incoming call to mobile unit

z MSC sends call request to all BSSsz BSSs broadcast request on all setup channelsz Mobile unit replies on reverse setup channelz BSS forwards reply to MSCz BSS assigns forward & reverse voice channelsz BSS informs mobile to use thesez Mobile phone rings

Mobile Originated Call


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z Mobile sends request in reverse setup channelz Message from mobile includes serial # and possibly

authentication informationz BSS forwards message to MSCz MSC consults Home Location Register for

information about the subscriber z MSC may consult Authentication center z MSC establishes call to PSTNz BSS assigns forward & reverse channel


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Roaming

U b ib i i i


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z Users subscribe to roaming service to use serviceoutside their home region

z Signaling network used for message exchangebetween home & visited network

z Roamer uses setup channels to register in new area

z MSC in visited areas requests authorization fromusers Home Location Register z Visitor Location Register informed of new user z

User can now receive & place calls

GSM Signaling Standardz Base station


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z Base stationz Base Transceiver Station (BTS)

z Antenna + Transceiver to mobilez Monitoring signal strength

z Base Station Controller z Manages radio resources or 1 or more BTSsz Set up of channels & handoff z Interposed between BTS & MSC

z Mobile & MSC Applicationsz Call Management (CM)z Mobility Management (MM)

z Radio Resources Management (RRM) concernsmobile, BTS, BSC, and MSC


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CM Um

Cellular Network Protocol Stack

R di Ai I t f (U )


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LAPD m

Radio Radio

LAPD m

RRM

MM

C

RRM

LAPD

64kbps

m

Mobile station Basetransceiver

station

Radio Air Interface (U m)z LAPD m is data link control

adapted to mobilez RRM deals with setting up of

radio channels & handover

Abis


A I t f


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Radio

LAPD m

64kbps

LAPD

RRMRRM

LAPD

64kbps

64kbps

MTPLevel 3

MTPLevel 2

SCCP

Basetransceiver

station

Basestation

controller

Abis Interfacez 64 kbps link physical layer z LAPD mz BSC RRM can handle

handover for cells within its

control

CM A


Signaling Network (A)CM


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SCCP

MTPLevel 3

MTPLevel 2

64kbps

LAPD

MM

RRMRRM

64kbps

64kbps

MTPLevel 3

MTPLevel 2

SCCP

Basestation

controller

MSC

Signaling Network (A)Interface

z RRM deals handover involving cells withdifferent BSCs

z

MM deals withmobile user location,authentication

z CM deals with callsetup & releaseusing modified ISUP

LAPD m

Radio

RRM

MM

Mobile station

Whats Next for Cellular Networks?

z Mobility makes cellular phone compelling


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z Mobility makes cellular phone compellingz Cell phone use increasing at expense of telephone

z Short Message Service (SMS) transfers text usingsignaling infrastructurez Growing very rapidly

z

Multimedia cell phonesz Digital camera to stimulate more usagez Higher speed data capabilities

z GPRS & EDGE for data transfer from laptops & PDAsz WiFi (802.11 wireless LAN) a major competitor

Documents

Lgw 2 e Chapter 4 Presentation