Networks & Telecommunication

At the end of this class, you will be able to:

• List the basic components of a network

• Diagram how ADSL and cable modems work

• Analyze the advantages that networks can provide

• Understand in a general way how networks work

“Any sufficiently advanced technology is indistinguishable from magic.”

Arthur C. Clarke

Learning Objectives

A computer network is anycomputer system that linkstwo or more computers

There are three essentialcomponents in a network: Hardware Software People

Basic Network Anatomy

Costallows people to share hardware

Efficiency & Productivityallows people to share data and software

Opportunityallows people to work together in ways that are otherwise difficult or impossible

Why is networking important?

Linking Up: Network Basics

Visualization of a Network A computer network can be pictured or modeled

as a graph where each “node” in the graph represents a device on the network Means we can use concepts from graph theory when

designing networks

A LAN is a network in which the computers are physically close to each other (ex: same building)

– They typically share peripherals (printers)

– Each computer and shared peripheral is a node on the LAN

LAN (Local Area Network)

Cover a long geographic distance. WANs are often made up of LANs

WAN (Wide Area Network)

Physical Media for NetworksNetworks are built on physical media.

Plain Old Telephone Service (POTS) Twisted pair (Category 5) Coaxial Cable (TV) Fiber optic Wireless/infrared

Line of sight Wireless/radio

All have various characteristics, but all can send a signal from one point to another point

“Never in history has

distance meant less.”

Alvin Toffler

Fiber Optic Cables

Fiber optic cables are replacing aging copper lines They use light waves to carry information They provide data rates over one billion bits per

second (high bandwidth) They offer extremely low error rates Signals travel extremely fast across them (low

delay)

a

Terminal

Modem

Modem

Analogsignals

Phone line

Digitalsignals

Digitalsignals

Computer

The word modem comes from theterms modulation and demodulation

ModulationDemodulation

How a Modem Works

Modems Computers understand digital signals Telephone lines use analog signals Modem converts the digital signal from computer to

analog and vice-versa

The Network Interface A Network Interface Card

(NIC): Is needed to connect directly

to a network Can add an additional port to

the computer Controls the flow of data

between the RAM and the network cable

Converts the computer’s digital signals into the type required for the particular network

Most common today is ETHERNET

ADSL: How it Works

Copper wirePOTSDigital data

To work properly the ADSL modem must be located within a certain distance from the phone company’s answering ADSL modem.

Cable Modem:How it WorksEtherNet Card

Network Performance How “fast” a network performs is classified in

two ways: Bandwidth – how much information can be sent

(usually measured in bits per second, or bps) Bandwidth is affected by the amount of network traffic,

software protocols, and type of network connection

Propagation delay – how long it takes for data to physically travel across a connection

Delay is affected by the amount of network traffic, software protocols, and type of network connection

Client

ServerClient software sends requests from the user to the server

Server software responds to client requests by providing data

Client/Server Model

The peer-to-peer model allows every computer on the network to be both client and server

Many networks use a hybrid of client/server and peer-to-peer

Examples of P2P: BitTorrent, Gnutella, Kazaa, etc

Advantages? Disadvantages?

Peer-to-Peer Model

Packets and Routing Messages sent across a computer network are

often broken into small pieces called packets Each packet is then routed from point to point

by devices called routers The receiver then reassembles the original

message from the individual packets. Animation from CD (Chapter 9, TCP/IP)

We need to be able to… agree on how messages will be sent and

received divide the message into manageable pieces

(packets) find the “address” of a computer reassemble the message at the receiver resend pieces if they are lost

All of these details are handled by a protocol

Protocols A network protocol is a set of rules which govern

how computers “talk” to each other Covers details such as:

How big should each packet be? How do we determine if a packet is lost? How do we reassemble messages? How do we route a packet across the network? How do we identify a particular computer on the

network? A collection of protocols is called a protocol

suite