CSCI 1200 / ASSC 1000

Chapter 8

Telecommunications

• long distance, electronic communications.

• protocol : rules.

Network

• two or more computers linked together.

• why?– share hardware, software & data.– connect people, allowing collaboration.

Keep the Network Running

• network administrator (person).

• network management software.

• Network Operating System - NOS

Network Operating System

• functions for connecting computers & devices to a LAN.

• must deal with multiple computers & coordinate things throughout the network.

• today many operating systems have networking functions built in.

Intranet

• open standard protocols instead of a proprietary operating system.

• same technology as the Internet, but owned by an organization or individual.

Important Terms

• nodes – any point on a network (often a computer).

• servers - the computers & devices that allocate resources for the network.

• backbone - key connection, very high speed, heavy traffic.

Important Terms

Protocol :

In the case of a network, a set of agreed upon rules & signals defining how the computers and devices on the network will communicate.

Important Terms

• Bridges & Gateways - connect networks, may translate if the networks use different protocols or operating systems, may also handle security (like firewalls).

• Router - forwards network traffic, sending it to bridges & gateways.

• Switches & Hubs – forwards traffic between network nodes

Type of Networks

• LAN – Local Area Network– physically close, usually the same building.– may use cables or be wireless.– wireless is slower, but convenient and less

invasive.

• MAN - Metropolitan Area Network– city sized network.– typically links several LANs.

Type of Networks

WAN – Wide Area Network– geographically large.– each node is a site.– telephone lines, microwave towers,

satellite links make WANs possible.– corporate & government.

Special Networks

GPS – Global Positioning System – network of 24 satellites.– 4 above horizon at any time.– 3 to calculate position, may use up to 6.– land beacons may augment the network.– radio transmitters & atomic clocks, time for the signal

to travel from the satellite to you.– hand held devices, vehicle navigation, mobile phones,

outdoor enthusiasts.– more accurate for the military.

Special Networks

Financial Networks :–money represented digitally.– banking & financial industry operate on

a global scale.– access your bank account from almost

any country.

Building a Network

Connection Technology :

• Direct Connection – dedicated physical link.

• Remote Connection – phone lines, cable lines, satellites.

Building a Network

Traffic Issues :– devoted connection to each node.– or many computers must share the line.

Building A Network

Network Interface Card– special hardware.– inserted into a slot.– adds a network port for a direct connection.– controls data flow between network &

computer’s memory.– boosts the signal on it’s way out.– Ethernet port is often built in now.

Bandwidth

• amount of data that can be transmitted in a fixed amount of time.

• bps, kbps, mbps. • to increase speed:– widen the pipe.– increase the speed of traffic through the

pipe.– better protocols.

Connections

Modem– longer distances.– connect to a telephone line.– internal / external.– phone network – designed for sound.– convert stream of bits to a continuous sound

wave – digital to analogue.– generally slower than a direct connection.– speed measured in bps – 56k.

Connections

Broadband Technology – single medium (wire) can carry several

channels at once.• DSL – phone lines• Cable Modems – cable television lines• Wireless – radio or infrared waves• Satellite – satellites & dishes

Connections

Fiber Optic – use light instead of electricity.– replace 10,000 copper telephone lines.– 500 million bps – half a gigabit per

second.– “last mile”

Connections

Wireless :–may use a radio or infrared transmitter–mobility over speed

Infrared :– line of sight is needed.– short distances.– sunlight

Connections

Wi-Fi (wireless fidelity)– radio based LAN protocol.– describes any type of 802.11 network.– base station, devices may be a distance

of about 150 feet.

Connections

Bluetooth – short-range radio links – up to 30 feet.– lower energy than Wi-Fi - battery

operated devices. –mobile computers, mobile phones,

digital cameras, other portable devices.– not competing with Wi-Fi, replace

cables needed to plug stuff in.

Connections

3G• next generation of mobile communications

technology. • other countries more fully utilize mobile

phones.• increased bandwidth, up to 384 kbps when a

device is stationary or moving at pedestrian speed, 128 kbps in a car, and 2 mbps stationary.

• video, multimedia support.

Approaches to Networking

Client Server Model– server fulfils client requests– high speed, high capacity computer is

the server– hierarchical structure, server is

essential

Approaches to Networking

Peer 2 Peer Model– any computer can be a client or a

server.– often used on smaller networks (but not

necessarily, e.g. music sharing).–Windows & MacOS allow for P2P

networking.

Internet

• global network of networks.

• TCP / IP communication standard.

• to communicate, networks must speak the same language.

Internet Motivation

• Researchers : share computing resources, very few computers, expensive.

• Military : cold war, wanted a communication network.

Military Needs

• assume unreliability.

• decentralized : all connected computers are equal.

• most work when lines are broken, and nodes are down.

Network Must

• connect important government & research computers.

• resist point-of-failure attacks : continue to operate even if a city on the network was destroyed.

• be fault-tolerant : continue to operate even if something went wrong within the network – e.g., a computer crashed, or a transmission line was broken.

Solution

• designed to be a decentralized network of computers that could adapt the flow of traffic and to changes in the state of the overall system.

• the way that information travels on the Internet is similar to the way that traffic moves on an interconnected system of roads and highways.