chapter 1 communication networks and servicesljilja/ensc427/spring15/news/leon-garcia_widjaja... ·...

Chapter 1 Communication

Networks and ServicesNetwork Architecture and Services

Telegraph Networks & Message SwitchingTelephone Networks and Circuit Switching

Computer Networks & Packet SwitchingFuture Network Architectures and Services

Key Factors in Network Evolution

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Chapter 1Communication

Networks and Services

Network Architecture and Services

2

Communication Services & Applications

A communication service enables the exchange of information between users at different locations.Communication services & applications are everywhere.

E-mail

E-mail server

Exchange of text messages via servers 3



Web Browsing

Web server

Retrieval of information from web servers 4


Instant Messaging

Direct exchange of text messages


5


Telephone

Real-time bidirectional voice exchange


6


Cell phone

Real-time voice exchange with mobile users


7


Short Message Service

Fast delivery of short text messages


8

Many other examples!

Peer-to-peer applicationsNapster, Gnutella, Kazaa file exchangeSearching for ExtraTerrestrial Intelligence (SETI)

Audio & video streamingNetwork gamesOn-line purchasingText messaging in PDAs, cell phones (SMS)Voice-over-Internet

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Services & Applications

Service: Basic information transfer capabilityInternet transfer of individual block of informationInternet reliable transfer of a stream of bytesReal-time transfer of a voice signal

Applications build on communication servicesE-mail & web build on reliable stream serviceFax and modems build on basic telephone service

New applications build on multiple networksSMS builds on Internet reliable stream service and cellular telephone text messaging

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What is a communication network?

The equipment (hardware & software) and facilities that provide the basic communication serviceVirtually invisible to the user; Usually represented by a cloud

CommunicationNetwork

EquipmentRouters, servers, switches, multiplexers, hubs, modems, …

FacilitiesCopper wires, coaxial cables, optical fiberDucts, conduits, telephone poles …

How are communication networks designed and operated?11

Communication Network Architecture

Network architecture: the plan that specifies how the network is built and operatedArchitecture is driven by the network servicesOverall communication process is complexNetwork architecture partitions overall communication process into separate functional areas called layers

Next we will trace evolution of three network architectures: telegraph, telephone, and computer networks 12

Network Architecture Evolution

1.0E+00

1.0E+02

1.0E+04

1.0E+06

1.0E+08

1.0E+10

1.0E+12

1.0E+14

1850 1875 1900 1925 1950 1975 2000

Telegraphnetworks

Telephonenetworks

Internet, Optical& Wireless networks

Info

rmat

ion

trans

fer

per s

econ

d

Next Generation

Internet

?

13

Network Architecture Evolution

Telegraph NetworksMessage switching & digital transmission

Telephone NetworksCircuit SwitchingAnalog transmission → digital transmissionMobile communications

InternetPacket switching & computer applications

Next-Generation InternetMultiservice packet switching network

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Networks and ServicesTelegraph Networks &

Message Switching

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Telegraphs & Long-Distance Communications

Approaches to long-distance communicationsCourier: physical transport of the message

Messenger pigeons, pony express, FedExTelegraph: message is transmitted across a network using signals

Drums, beacons, mirrors, smoke, flags, semaphores…Electricity, light

Telegraph delivers message much sooner16

Optical (Visual) TelegraphClaude Chappe invented optical telegraph in the 1790’sSemaphore mimicked a person with outstretched arms with flags in each handDifferent angle combinations of arms & hands generated hundreds of possible signalsCode for enciphering messages kept secretSignal could propagate 800 km in 3 minutes! 17

Message SwitchingNetwork nodes were created where several optical telegraph lines met (Paris and other sites)Store-and-Forward Operation:

Messages arriving on each line were decodedNext-hop in route determined by destination address of a messageEach message was carried by hand to next line, and stored until operator became available for next transmission

Northline

Southline

Westline

Eastline

NetworkNode

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Electric Telegraph

William Sturgeon Electro-magnet (1825)Electric current in a wire wrapped around a piece of iron generates a magnetic force

Joseph Henry (1830)Current over 1 mile of wire to ring a bell

Samuel Morse (1835)Pulses of current deflect electromagnet to generate dots & dashes Experimental telegraph line over 40 miles (1840)

Signal propagates at the speed of light!!!Approximately 2 x 108 meters/second in cable 19

Morse code converts text message into sequence of dots and dashesUse transmission system designed to convey dots and dashes

Morse Code

Morse Code

Morse Code

Morse Code

A · — J · — — — S · · · 2 · · — — —

B — · · · K — · — T — 3 · · · — —

C — · — · L · — · · U · · — 4 · · · · —

D — · · M — — V · · · — 5 · · · · ·

E · N — · W · — — 6 — · · · ·

F · · — · O — — — X — · · — 7 — — · · ·

G — — · P · — — · Y — · — — 8 — — — · ·

H · · · · Q — — · — Z — — · · 9 — — — — ·

I · · R · — · 1 · — — — — 0 — — — — —

Digital Communications

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Switches

Message

Destination

SourceMessage

Message

Message

Electric telegraph networks explodedMessage switching & Store-and-Forward operationKey elements: Addressing, Routing, Forwarding

Optical telegraph networks disappeared

Electric Telegraph Networks

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Operator 25-30 words/minutebut a wire can carry much more

Baudot multiplexer: Combine 4 signals in 1 wireBinary block code (ancestor of ASCII code)

A character represented by 5 bitsTime division multiplexing

Binary codes for characters are interleavedFraming is required to recover characters from the binary sequence in the multiplexed signal Keyboard converts characters to bits

Baudot Telegraph Multiplexer

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Baudot Telegraph Multiplexer

…A2D1C1B1A1

PaperTape

Printer

PaperTape

Printer

PaperTape

Printer

PaperTape

Printer

BaudotDemultiplexer

Keyboard

BaudotMultiplexer

5 bits / character

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Elements of Telegraph Network Architecture

Digital transmissionText messages converted into symbols (dots/dashes, zeros/ones)Transmission system designed to convey symbols

MultiplexingFraming needed to recover text characters

Message SwitchingMessages contain source & destination addressesStore-and-Forward: Messages forwarded hop-by-hop across networkRouting according to destination address

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Networks and ServicesTelephone Networks and

Circuit Switching

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Bell’s TelephoneAlexander Graham Bell (1875) working on harmonic telegraph to multiplex telegraph signalsDiscovered voice signals can be transmitted directly

Microphone converts voice pressure variation (sound) into analogous electrical signalLoudspeaker converts electrical signal back into sound

Telephone patent granted in 1876Bell Telephone Company founded in 1877

Signal for “ae” as in cat

Microphone Loudspeakeranalog

electricalsignalsound sound

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Bell’s Sketch of Telephone

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Signaling

Signaling required to establish a callFlashing light and ringing devices to alert the called party of incoming callCalled party information to operator to establish calls

Signaling + voice signal transfer

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The N2 Problem

For N users to be fully connected directlyRequires N(N – 1)/2 connections Requires too much space for cablesInefficient & costly since connections not always on

N = 1000N(N – 1)/2 = 499500

1

2

34

N

29

Telephone Pole Congestion

30

Circuit Switching

Patchcord panel switch invented in 1877Operators connect users on demand

Establish circuit to allow electrical current to flow from inlet to outlet

Only N connections required to central office1

23

N – 1

N

31

Manual Switching

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Strowger SwitchHuman operators intelligent & flexible

But expensive and not always discreetStrowger invented automated switch in 1888

Each current pulse advances wiper by 1 positionUser dialing controls connection setup

Decimal telephone numbering systemHierarchical network structure simplifies routing

Area code, exchange (CO), station number

...

0

9

0

9...

0

9

0

9

...

1st digit 2nd digit . . .

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Strowger Switch

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Telephone subscribers connected to local CO (central office)

Tandem & Toll switches connect CO’s

Hierarchical Network Structure

TandemCO

Toll

CO COCO

CO

TandemCO = central office

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Network selects route;

Sets up connection;

Called party alerted

Telephonenetwork

Pick up phone

Dial tone.

Dial number

Exchange voice signals

1.

2.

3.

4.

5.

Telephonenetwork

Telephonenetwork

Telephonenetwork

Telephonenetwork

Telephonenetwork

Hang up.6.

Connection set up

Information transfer

Connection release

Three Phases of a Connection

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Computer Connection ControlA computer controls connection in telephone switchComputers exchange signaling messages to:

Coordinate set up of telephone connectionsTo implement new services such as caller ID, voice mail, . . .To enable mobility and roaming in cellular networks

“Intelligence” inside the networkA separate signaling network is required

SignalingComputer

Switch connectsInlets to Outlets. .

.

. . . Voice

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Digitization of Telephone Network

Pulse Code Modulation digital voice signalVoice gives 8 bits/sample x 8000 samples/sec = 64x103 bps

Time Division Multiplexing for digital voiceT-1 multiplexing (1961): 24 voice signals = 1.544x106 bps

Digital Switching (1980s)Switch TDM signals without conversion to analog form

Digital Cellular Telephony (1990s)Optical Digital Transmission (1990s)

One OC-192 optical signal = 10x109 bpsOne optical fiber carries 160 OC-192 signals = 1.6x1012 bps!

All digital transmission, switching, and control38

Digital Transmission Evolution

1.0E+00

1.0E+02

1.0E+04

1.0E+06

1.0E+08

1.0E+10

1.0E+12

1.0E+14

1850 1875 1900 1925 1950 1975 2000

Morse

T-1 CarrierSONETOpticalCarrier

Info

rmat

ion

trans

fer

per s

econ

d

WavelengthDivision

Multiplexing ?

Baudot

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Elements of Telephone Network Architecture

Digital transmission & switchingDigital voice; Time Division Multiplexing

Circuit switchingUser signals for call setup and tear-downRoute selected during connection setupEnd-to-end connection across networkSignaling coordinates connection setup

Hierarchical Network Decimal numbering systemHierarchical structure; simplified routing; scalability

Signaling NetworkIntelligence inside the network

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Networks and Services

Computer Networks & Packet Switching

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Computer Network Evolution Overview

1950s: Telegraph technology adapted to computers 1960s: Dumb terminals access shared host computer

SABRE airline reservation system1970s: Computers connect directly to each other

ARPANET packet switching networkTCP/IP internet protocolsEthernet local area network

1980s & 1990s: New applications and Internet growthCommercialization of InternetE-mail, file transfer, web, P2P, . . .Internet traffic surpasses voice traffic

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What is a protocol?

Communications between computers requires very specific unambiguous rulesA protocol is a set of rules that governs how two or more communicating parties are to interact

Internet Protocol (IP)Transmission Control Protocol (TCP)HyperText Transfer Protocol (HTTP)Simple Mail Transfer Protocol (SMTP)

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A familiar protocol

“Do you have a first name or street?”

Caller

“What name?”“Simpson”

Caller replies

System replies with number

System replies

System replies

System replies

Operator replies

“Thank you, please hold”

“Evergreen Terrace”

Caller replies

“Springfield”

Dials 411

“What city”?

Caller replies

Operator replies

Caller waits

“Thank you, please hold”Caller waitsCaller dials

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Terminal-Oriented Networks

Early computer systems very expensiveTime-sharing methods allowed multiple terminals to share local computerRemote access via telephone modems

Host computer

Terminal

Terminal. .

.

TerminalModem ModemTelephoneNetwork

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Dedicated communication lines were expensiveTerminals generated messages sporadicallyFrames carried messages to/from attached terminalsAddress in frame header identified terminalMedium Access Controls for sharing a line were developedExample: Polling protocol on a multidrop line

Medium Access Control

Host computer

TerminalTerminal . . . Terminal

Terminals at different locations in a cityMust avoid collisions on inbound line

Polling frames & output frames

input frames

46

Statistical MultiplexingStatistical multiplexer allows a line to carry frames that contain messages to/from multiple terminalsFrames are buffered at multiplexer until line becomes available, i.e. store-and-forwardAddress in frame header identifies terminalHeader carries other control information

CRC Information Header

Header Information CRC

Host computer

Terminal

Terminal

. . .

Terminal

Multiplexer

Frame

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Error Control ProtocolCommunication lines introduced errorsError checking codes used on frames

“Cyclic Redundancy Check” (CRC) calculated based on frame header and information payload, and appended Header also carries ACK/NAK control information

Retransmission requested when errors detected

Header Information CRC

CRC Information Header

Terminal

48

Tree Topology NetworksNational & international terminal-oriented networks Routing was very simple (to/from host)Each network typically handled a single application

New York City

San Francisco

Chicago AtlantaT

TT

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Computer-to-Computer Networks

As cost of computing dropped, terminal-oriented networks viewed as too inflexible and costlyNeed to develop flexible computer networks

Interconnect computers as requiredSupport many applications

Application ExamplesFile transfer between arbitrary computersExecution of a program on another computerMultiprocess operation over multiple computers

50

Packet Switching

Network should support multiple applicationsTransfer arbitrary message sizeLow delay for interactive applicationsBut in store-and-forward operation, long messages induce high delay on interactive messages

Packet switching introducedNetwork transfers packets using store-and-forwardPackets have maximum lengthBreak long messages into multiple packets

ARPANET testbed led to many innovations51

ARPANET Packet Switching

Packet Switch

Packet Switch Packet

Switch

Packet Switch

Packet Switch

Message

Packet 1

Packet 2

Packet 1Packet 1

Packet 2 Message

Host generates messageSource packet switch converts message to packet(s)Packets transferred independently across network

Destination packet switch delivers messageDestination packet switch reasembles message

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ARPANET Routing

Packet Switch


Switch

Packet Switch

Packet Switch

Packets header includes source & destination addressesPacket switches have table with next hop per destination

No connection setup prior to packet transmission

Routing tables calculated by packet switches using distributed algorithm

PacketHdr

Dest: Next Hop:

xyz abc

wvr edf

Routing is highly nontrivial in mesh networks

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Other ARPANET Protocols

Packet Switch


Switch

Packet Switch

Packet Switch

Congestion control between source & destination packet switches limit number of packets in transit

Error control between adjacent packet switches

Flow control between host computers prevents buffer overflow

Error Control

Congestion Control

Flow Control

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ARPANET ApplicationsARPANET introduced many new applicationsEmail, remote login, file transfer, …Intelligence at the edge

UCLA RAND TINKER

USC

NBS

UCSB

HARV

SCD

BBN

STAN

AMES

AMES McCLELLAN UTAH BOULDER GWC CASE

CARN

MITRE

ETAC

MIT

ILLLINC

RADC

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Ethernet Local Area Network

In 1980s, affordable workstations availableNeed for low-cost, high-speed networks

To interconnect local workstationsTo access local shared resources (printers, storage, servers)

Low cost, high-speed communications with low error rate possible using coaxial cableEthernet is the standard for high-speed wired access to computer networks

56

Ethernet Medium Access ControlNetwork interface card (NIC) connects workstation to LANEach NIC has globally unique addressFrames are broadcast into coaxial cableNICs listen to medium for frames with their addressTransmitting NICs listen for collisions with other stations, and abort and reschedule retransmissions

Transceivers

57

The InternetDifferent network types emerged for data transfer between computersARPA also explored packet switching using satellite and packet radio networksEach network has its protocols and is possibly built on different technologiesInternetworking protocols required to enable communications between computers attached to different networksInternet: a network of networks

58

Internet Protocol (IP)Routers (gateways) interconnect different networks Host computers prepare IP packets and transmit them over their attached networkRouters forward IP packets across networks Best-effort IP transfer service, no retransmission

Net 1 Net 2

Router 59

Addressing & RoutingHierarchical address: Net ID + Host IDIP packets routed according to Net IDRouters compute routing tables using distributed algorithm

GG

G

GG

G

Net 1

Net 5

Net 3

Net 4Net 2

H

H H

H

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Transport ProtocolsHost computers run two transport protocols on top of IP to enable process-to-process communicationsUser Datagram Protocol (UDP) enables best-effort transfer of individual block of information Transmission Control Protocol (TCP) enables reliable transfer of a stream of bytes

Internet

Transport

Protocol

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Names and IP Addresses

Routing is done based on 32-bit IP addressesDotted-decimal notation

128.100.11.1Hosts are also identified by name

Easier to rememberHierarchical name structuretesla.comm.utoronto.edu

Domain Name System (DNS) provided conversion between names and addresses

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Internet Applications

All Internet applications run on TCP or UDPTCP: HTTP (web); SMTP (e-mail); FTP (file transfer; telnet (remote terminal)UDP: DNS, RTP (voice & multimedia)TCP & UDP incorporated into computer operating systemsAny application designed to operate over TCP or UDP will run over the Internet!!!

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Elements of Computer Network Architecture

Digital transmissionExchange of frames between adjacent equipment

Framing and error controlMedium access control regulates sharing of broadcast medium.Addresses identify attachment to network or internet. Transfer of packets across a packet networkDistributed calculation of routing tables

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Elements of Computer Network Architecture

Congestion control inside the network Internetworking across multiple networks using routersSegmentation and reassembly of messages into packets at the ingress to and egress from a network or internetwork End-to-end transport protocols for process-to-process communicationsApplications that build on the transfer of messages between computers.Intelligence is at the edge of the network.

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