Chi-Cheng Lin, Winona State University

CS 313 Introduction to Computer Networking &

Telecommunication

Introduction

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Topics

Introduction Metric Units Network Hardware Network Software Reference Models Example Networks Standards and Standards

Organizations

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Introduction

First two decades of computingHighly centralized computer systems

NowA large number of SEPARATE but

INTERCONNECTED computers Computer networks

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What is Computer Network?

An INTERCONNECTED collection of AUTONOMOUS computersInterconnected: Able to EXCHANGE

INFORMATION via transmission mediaMedia: copper wire, fiber optics,

microwaves, communication satellites

Autonomous: no master/slave relationNOT autonomous:

One computer can control another one e.g., a large computer with remote printers

and terminals

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What is Telecommunication?

What is data communication?Exchange of data between two

devices via some form of transmission media

Data are represented by bits – 0s and 1s

What is telecommunication?Exchange of information over

distance using electronic equipment

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What is Telecommunication? Components of data communication

Sender, receiver, medium, message, and

Protocol: set of rules governing data communication

Key elements of a protocolSyntax

Structure/formatSemantics

MeaningTiming

When and how fast

Data Communication

Components of data communication

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Sender ReceiverMedium

Message

Step 1: …Step 2: … :

ProtocolStep 1: …Step 2: … :

Protocol

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Distributed System vs. Computer Network Distributed system

TRANSPARENCYA collection of independent computers

appear as a single coherent system

Single model/paradigm to usersMiddleware on top of OSExample?

Computer networkNo such coherence, model, middlewareMachines visible to users

Users log onto remote machines

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Distributed System vs. Computer Network

A distributed system is a SOFTWARE system built on top of a network

Distinction between network and distributed systemSoftware (especially OS) rather than

hardware However, considerable overlap

between the two subjects

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Uses of Computer Networks

Business applicationsResource sharingCommunication mediumE-commerce

Client-server modelClient requests, server performs & then

replies E.g., one or more file servers, many

clients

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Business Applications of Networks

A network with two clients and one server.

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Client-Server Model

1

2

3

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Uses of Computer Networks Home applications

Access to remote informationOn-line publishing, digital library, WWW

Person-to-person communicationEmail, instant messaging, peer-to-peer

communication, videoconferencing, Internet phone, E-learning

Interactive entertainment Video on demand (VOD), games

E-commerceHome shopping, electronic banking and

investment, on-line auction

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Home Network Applications (2)

In peer-to-peer system there are no fixed clients and servers.

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Mobile Users

Notebook, PDA, cellular phone M-commerce Wireless networking and mobile

computing

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Metric Units

The principal metric prefixes.

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Network Hardware By transmission technology

Broadcast links smaller, geographically localized

networksPoint-to-point links

larger networks By scale

PANLANMANWAN

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Classification by Scale

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Broadcast Network

A single communication channel shared by all machines on the network

Packets (short messages) sent by any machine are “received” by all the othersAddress field of packet: whom it is intended

Message transmissionUnicast: one sends, one receivesBroadcasting: one sends, all receiveMulticasting: one sends, a group receives

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Point-to-Point Networks

Many connections between pairs of machines

Intermediate machines (called routers) might have to be visited by a packet from source to destination – more than one path is possible

Routing algorithms are importantRouting: process of finding a path

from a source to the destination(s) in the network

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Local Area Network (LAN)

Private-owned Networks Within a single building/campus Size: up to a few kilometers Characteristics

SizeRestricted by size worst-case transmission time bounded

and known in advance network management simplified

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LAN Characteristics

Transmission technologyMachines attached to a single cableSpeed/capacity (High): 10 - 100 Mbps,

Gbps Mbps/Gbps: Megabit/Gigabit per second 1 megabit=1,000,000 (not 220=1,048,576) bits

Delay (low): microseconds, nanosecondsErrors: very few

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LAN

Characteristics Topology – the way in which a

network is laid outExamples: bus, ring, tree, star, fully-

connected

Bus Ring

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LAN - Topology Bus (linear cable)

Only one machine can transmit at a timeArbitration mechanism needed to resolve

conflicts when two or more computers want to transmit simultaneouslyCentralized or Distributed

Example: IEEE 802.3 (Ethernet):Bus-based broadcast network with

decentralized control operating at 10 Mbps to 10Gbps.

If two or more packets collide, each computer just waits a random time and tries again later.

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LAN - Topology

TreeCentralized deviceExample: Ethernet w/ hubs/swtches

RingBits propagate around the ringArbitration mechanism is needed, tooExample: IEEE 802.5 (IBM Token Ring)

Ring-based LAN operating at 4 and 16 Mbps

Arbitration is based on “token” Only token holder can transmit

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LAN - Channel Allocation

Needed as all computers share one communication pathway

Static channel allocationDivide up time into discrete intervalsRun a round robin algorithmAllow each machine to broadcast only

when its time slot comes upProblem: Wasting channel capacity

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LAN - Channel Allocation

Dynamic channel allocationCentralized

A central entity determines who goes next

DecentralizeNo central entityEach machine decides for itself to

transmit or notAlgorithms needed to resolve potential

chaos

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Metropolitan Area Network (MAN)

Covers city Examples

Cable TV networkIEEE 802.16 high-speed wireless

Internet access

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Metropolitan Area Networks

A metropolitan area network based on cable TV.

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Wide Area Network (WAN)

Country or continent Components

Host (end system) Machine running user (application)

programs

Communication subnet (subnet) Connecting hostsCarrying messages from host to host

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WAN - Subnet Components

Transmission linesMove bits between machines

Switching elementsSpecialized computers that connect

two or more transmission linesDetermine out going line for incoming

dataROUTER

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WAN - Hosts and Subnet

: Host

: Router

H1

H2

R1 R2

R3 R4

R5 R6

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WAN - Architecture

Contains numerous cables or telephone lines

Each cable connects a pair of routers Two routers must communicate

indirectly if they are not connected by a cable

There might be more than one route between two hosts and it might change from time to timeE.g., Route from H1 to H2

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WAN - Architecture

An intermediate router in a WANReceives a packet in its entiretyQueues the packet until required

output line is freeForwards the packet

Subnet using the principle above is calledStore-and-forward or packet-switched

subnet

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Wide Area Networks

A stream of packets from sender to receiver.

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Topology – LANs vs WANs Local networks

Bus, Ring, StarTree

WANs typically irregular

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WAN - Broadcast Systems Satellite system

Each router has an antennaSometimes routers are connected to

a substantial point-to-point subnet, with some of them having a satellite antenna

Inherently broadcast

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Wireless Network

System interconnectionExample: Bluetooth

Wireless LANsEasy to install IEEE Standard 802.11

Wireless WANsIEEE Standard 802.16

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Wireless Networks

Bluetooth configuration Wireless LAN

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Wireless Network

Combinations of wired and wireless networking (e.g., flying LAN)

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Home Network Categories Computers

Desktop PC, PDA, shared peripherals Entertainment

TV, DVD, VCR, camera, stereo, MP3 Telecomm

Telephone, cell phone, intercom, fax Appliances

Microwave, fridge, clock, furnace, aircon Telemetry

Utility meter, burglar alarm, babycam

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Internetwork What is internetwork?

A collection of interconnected networks "Internet" and "internet"

internet: internetworkInternet: the worldwide internetwork using

TCP/IP protocol suiteThe “Big Picture”

http://navigators.com/internet_architecture.html

Problem: Communication between networks with different SW/HWSolution: Gateways

Machines connect different, incompatible networks

Connection and translation