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Computer Communication

Networks

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Communications activity associated withdistributing or exchanging information

Telecommunications technology of communications at a distance that permitsinformation to be created any where and used

everywhere with little delay Today it, involves

Data: digital and analog (how analog data istransmitted?)

Voice: spoken word, music..

Video: telelcommunication imaging

Introduction

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Communication Services &Applications

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

everywhere .

E-mail

E-mailserver Exchange of text messages via servers

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Communication Services &Applications

Web Browsing

Web server

Retrieval of information from web servers

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Communication Services &Applications

Instant Messaging

Direct exchange of text messages

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Communication Services &Applications

Telephone

Real-time bidirectional voice exchange

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Communication Services &Applications

Cell phone

Real-time voice exchange with mobile users

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Communication Services &Applications

Short Message Service

Fast delivery of short text messages

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SummarizingSummarizing

Two or more than two computersystems connected by means of acommunication medium like cables is

termed as a Network. Computer Network is a

communication system, which linkscomputers and their resources.

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Why we need Networking? Sharing of data and resources Distributing computation

among nodes Remote I/O devices To share data/files access.

Personal Communication (Chat,E-mail, now VOIP)

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BENEFITS OF A NETWORK BENEFITS OF A NETWORK

Following are the benefits of networking. Information Sharing

Printer Sharing Hard Disk Sharing Modem Sharing

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Hardware Sharing Software Sharing Service Access

Easy Back-Up Management Security Centralized Administration and

SupportNetworking helps to increase

the productivity

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Many other examples!

Peer-to-peer applicationsFile exchangeSearching for Extraterrestrial

Intelligence (SETI) Audio & video streaming Network games On-line purchasing Text messaging in PDAs, cell phones

(SMS) Voice-over-Internet

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What is a communicationnetwork?

The equipment (hardware & software) and facilities that provide the basiccommunication service

Virtually invisible to the user; Usually represented by a cloud

CommunicationNetwork

EquipmentRouters, servers,

switches,multiplexers, hubs,modems,

FacilitiesCopper wires,

coaxial cables,optical fiber

Ducts, conduits,telephone poles

How are communication networks designed and operated?

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Communication NetworkArchitecture

Network architecture : the plan thatspecifies how the network is built andoperated

Architecture is driven by the network services

Overall communication process is complex Network architecture partitions overall

communication process into separatefunctional areas called layers

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Networking: Why do we neednetworks?

Direct point-to-point communication is notalways possible/practical/efficient: Communicating entities can be too far apart for a single

link A large set of communicating entities (e.g. telephones)

would need impractically large number of connections

(full connectivity for N nodes needs N (N 1) / 2 links) Not all links would be needed all the time!

Solution isa communication network: Wide Area Network (WAN) Metropolitan Area Network (MAN)

Local Area Network (LAN)

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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

Informationtransfer

persecond

NextGeneration

Internet

?

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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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A Communication Model

Sourcegenerates data to be transmitted

TransmitterConverts data into transmittable signals

Transmission SystemCarries data

ReceiverConverts received signal into data

DestinationTakes incoming data

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Communications Tasks

Transmission systemutilization

Addressing

Interfacing Routing

Signal generation Recovery

Synchronization Message formatting

Exchange management Security

Error detection andcorrection

Network management

Flow control

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Simplified CommunicationsModel - Diagram

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Data Communication System Components

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Network Transmission Medium

Open air

radio, microwaves, satellites, infrared

noise signals, collision

Optical fiber

clear signals, low power and high rate (Gbps)

Copper wire

Lower cost interfacesBi-directional

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Whats a protocol?

human protocols: whats the time? I have a question introductions

specific msgs sent specific actions

taken when msgsreceived, or otherevents

network protocols: machines rather than

humans all communication

activity in Internetgoverned by protocols

protocols define format,order of msgs sent and received among network

entities, and actions taken on msg

transmission, receipt

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Whats a protocol?a human protocol and a computer network protocol:

Hi

HiGot thetime?2:00

TCP connection

reqTCP connectionresponseGet http://www.awl.com/kurose-ross

time

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Key Elements of a Protocol

SyntaxData formatsSignal levels

SemanticsControl informationError handling

TimingSpeed matchingSequencing

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Basic Concepts

Line Configuration Topology

Transmission Mode Categories of Networks Internetworks

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Point-to-Point Line Configuration

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Point-to-Point Line Configuration

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Point-to-Point Line Configuration

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Multipoint Line Configuration

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Networking

Point to point communication notusually practicalDevices are too far apartLarge set of devices would need

impractical number of connections Solution is a communications network

Wide Area Network (WAN)

Local Area Network (LAN)

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Mesh Network Topology

Type I - Nodes are arranged in gridseach node can talk to its neighbors directlynon-neighbor nodes needs store-and-forward

for communication

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Type II - Mesh Topology

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Star Network TopologyOne node at the center acts as the master nodeOther nodes linked to the master function as slaves

slaves communicate via master

easy to arbitrate among slaves (master decides)

not scalable (the master is the bottleneck)

normally for small networks or that requirespredictable performance

master failure shutdowns the whole net

Example: Ethernet, DSLMaster

slave

slave

slave

slave slave

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Star Topology

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Tree Topology

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Bus Network TopologyEvery node taps into a common mediumSignals may collide with each other

need to arbitrate who will get the bus

capable of broadcasting message (one send & many listen)

the common medium is the bottleneck

single node failure causes no network failure

the medium failure brings down the network

Example: (10BASE2, 10BASE5) Ethernet

common medium

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Bus Topology

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Ring Network Topology

Nodes are arranged in a ring One node receives from its predecessor & sends

to its successor arbitrate who can access the ring messages forwarded by each node sender deletes its messages from the ring the common ring is the single point of failure (complicated

connectors needed)

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Ring Topology

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Hybrid Network Topology

No restrictions on how to link the nodes Topology can adapt to individual organization

needs

Master

slave

slave

slave

slave slave

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Hybrid Topology

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Simplex

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Half-Duplex

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Full-Duplex

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Network Classification

Classification of interconnectedprocessors by scale.

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Network Types by Scope

WAN - wide area network cross large span of space (continental)

typically heterogeneous and low speed

example: Internet

MAN - metro-area network regional scope (city-wide)

LAN - local area network

limited scope (a couple of buildings)

typically homogeneous & high speed

example: Ethernet & Token ring

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Local Area Networks

Local area networks (LANs) areprivately-owned networks within asingle building or campus of up to afew kilometers in size.

LANs are distinguished by threecharacteristics: (Restricted in) Size Transmission technology: 10 Mbps to 10

Gbps (1 Mbps = 1,000,000 bits/sec, 1Gbps = 1,000,000,000 bits/sec).

Topology: bus and ring

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Local Area Networks

Two broadcast networks (a) Bus: Ethernet IEEE 802.3 (b) Ring: IEEE 802.5, FDDI

Local Area Network

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Local Area Network

Local Area Network

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Local Area Network

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LAN Configurations

SwitchedSwitched Ethernet

May be single or multiple switches

ATM LAN

Fibre Channel Wireless

MobilityEase of installation

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Metropolitan Area Networks

A metropolitan Area Networks (MAN)is a network that interconnects userswith computer resources in ageographic area or region such as acity.

Deployment Cable television Wireless: IEEE 802.16

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Metropolitan Area Networks

MAN Middle ground between LAN and

WAN

Private or public network High speed data transmission Large area coverage

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Metropolitan Area Networks

A metropolitan area network based oncable TV.

Metropolitan Area Network

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Metropolitan Area Network

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Wide Area Networks

A wide area network (WAN ) spans alarge geographical area, often a countryand continent.

It contains a collection of machines(hosts ).

The hosts are connected by acommunication subnet .

The subnet consists of two components: Transmission lines Switching elements: router

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Wide Area Networks

Relation between hosts on LANs and thesubnet.

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Wide Area Networks

Large geographical area Crossing public rights of way Rely in part on common carrier circuits

Alternative technologiesCircuit switchingPacket switchingFrame relay

Asynchronous Transfer Mode (ATM)

Wide Area Network

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Internetworks

Different networks are connected bymeans of machines called gateways .

A collection of interconnected networks

is called an internetwork or internet . A common form of internet is acollection of LANs connected by a WAN.

Internetwork

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Internetwork (Internet)

Networking

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NetworkingConfiguration

Wh t th I t t t d b lt

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Whats the Internet: nuts and boltsview

millions of connectedcomputing devices: hosts,end-systems PCs workstations, servers PDAs phones, toasters

running network apps

communication links fiber, copper, radio, satellite transmission rate bandwidth

routers: forward packets(chunks of data)

local ISP

companynetwork

regional ISP

router workstationserver

mobile

C l i t t li

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Cool internet appliances

Worlds smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html

IP picture frame

http://www.ceiva.com/

Web-enabled toaster + weather forecaster

Wh t th I t t t d b lt

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Whats the Internet: nuts and boltsview protocols control sending,

receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP

Internet: network of networks loosely hierarchical public Internet versus private

intranet

Internet standards RFC: Request for comments IETF: Internet Engineering Task

Force

local ISP

companynetwork

regional ISP

router workstationserver

mobile

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Whats the Internet: a service view communication

infrastructure enablesdistributed applications: Web, email, games, e-

commerce, database.,

voting, file (MP3) sharing communication servicesprovided to apps: connectionless connection-oriented

cyberspace [Gibson]:a consensual hallucination experienced daily by

billions of operators, in every nation, ...."

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Frame Relay

Packet switching systems have largeoverheads to compensate for errors Modern systems are more reliable

Errors can be caught in end system Most overhead for error control is stripped

out

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Asynchronous Transfer Mode

ATM Evolution of frame relay Little overhead for error control

Fixed packet (called cell) length Anything from 10Mbps to Gbps Constant data rate using packet switching

technique

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Wireless Communication

Wireless communication is not anew idea.Native American smoke signal

Chinese Beacon fireWireless telegraph using Morse Code

Modern digital wireless systems

have better performance, but thebasic idea is the same.

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Wireless Networks

Categories of wireless networks:System interconnectionWireless LANsWireless WANs

System Interconnection

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System Interconnection

System interconnection is all aboutinterconnecting the components of acomputer using short-range radio.

Some companies got together to design ashort-range wireless network calledBluetooth to these components.

Bluetooth allows digital cameras, headsets,

scanners, and other devices to connect to acomputer is a short range.

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Bluetooth Standard

The Bluetooth document is adopted byIEEE (Institute of Electrical and ElectronicsEngineers) 802.15 as a basis for wirelesspersonal area networks.Work at 2.4 GHz Transfer up to 2 Mbps10 meters range

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Wireless Networks

(a) Bluetooth configuration (b) Wireless LAN

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Wireless LANS

The wireless local area networks (LANs)are systems in which every computer hasa radio modem and antenna with which itcan communicate with other systems.

Wireless LANs are common in small officesand homes.

There is a standard for wireless LANs,called IEEE 802.11 .

Wi l WANS

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Wireless WANS

The wireless wide area networks (WANs) aresystems used in the wide area. The radio network used for cellular

telephones is an example of a low-bandwidth (low transfer rate) wirelesssystem.First generation: analog for voice

Second generation: digital for voice Third generation: digital for voice and

data

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Wireless WANS

High-bandwidth wide area wirelessnetworks are also being developed. A standard for metropolitan area networks

(MANs), called IEEE 802.16 , has alsobeen developed .Work at 10-to-66 GHz Transfer up to 155 Mbps30 miles range

Wi l N k

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Wireless Networks

(a) Individual mobile computers (b) A flying LAN

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Wireless WANS

High-bandwidth wide area wirelessnetworks are also being developed. A standard for it, called IEEE 802.16 , has

also been developed.Work at 10-to-66 GHz Transfer up to 155 Mbps30 miles range

H N t k C t i

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Home Network Categories

Computers (desktop PC, PDA, sharedperipherals)

Entertainment (TV, DVD, VCR, camera,stereo, MP3)

Telecomm (telephone, cell phone,intercom, fax)

Appliances (microwave, fridge, clock,

furnace, airco) Telemetry (utility meter, burglar alarm,

babycam).

Home Network Properties

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Home Network Properties

The network and devices have to be easy to install. The network and devices have to be foolproof in operation. Low price is essential for success. The main application is likely to involve multimedia.

It must be possible to start out with one or two devices andexpand the reach of the network gradually.

Security and reliability will be very important .

A closer look at network

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structure:

network edge: applicationsand hosts

network core: routers

network of networks

access networks, physicalmedia: communication links

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Circuit Switching

Dedicated communications pathestablished for the duration of theconversation

e.g. telephone network

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Packet Switching

Data sent out of sequence Small chunks (packets) of data at a time Packets passed from node to node

between source and destination Used for terminal to computer and

computer to computer communications

Data Communication

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Frameworks

Two major data communicationframeworks have been developed to helpensure that networks meet business andcommunication requirements:Open Systems Interconnection (OSI) reference

model developed by the InternationalStandards Organization (ISO)

Transmission Control Protocol/Internet Protocol(TCP/IP) suite

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Transmission Speeds

Medium Speed CostTwistedWire 300bps-10Mbps LowMicrowave 256Kbps-100Mbps

Satellite 256Kbps-100MbpsCoaxial Cable 56Kbps-200MbpsFiber-Optic Cable 500Kbps-10Gbps High

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Important Standard-Setting

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Organizations

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Online System Requirements

Response Time Throughput Consistency Flexibility

Online Systems Requirements

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Continued

Availability ReliabilityMean time between failure (MTBF)Mean time to repair (MTTR)Fault Tolerance

Recovery Security

Business Data Communication

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Applications

Major data communication applicationsinclude:E-mailGroupware

Knowledge management systemsE-commerce and e-business applicationsWireless applications

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Groupware Applications

Group calendarsystems Electronic filing

cabinets Project

managementsoftware

Group supportsystems

Electronic meetingandvideoconferencingsystems

Documentmanagementsystems (imageprocessingsystems)

Other Data Communication

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Applications

Batch applications Data entryapplications

Distributedapplications

Inquiry/responseapplications

Interactiveapplications Sensor-based

applications Combined

applications

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Application Service Providers

Many businesses have turned to third-party services for some or all of theirbusiness and data communicationsapplications

Application service providers (ASPs) arethird-party organizations that manage anddistribute software and services to othercompanies over the Web

Many ASPs specialize in integrated e-commerce and e-business applications

Business Data Communications

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Issues Major data communications issues

include:Cost-effectiveness The InternetBandwidthEvolving technologiesConvergenceStandards

Privacy and security

Services versus Throughput Rates

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