memberfiles.freewebs.com · Web viewExplain communication protocols Understand what is internet and email and its uses in modern communication Appreciate the use of satellite communication

LECTURE TWO

OBJECTIVES

At the end of this lecture you should be in a position to:

Understand the use of computer network

Identify different components of computer network

Identify different types of network

Explain communication protocols

Understand what is internet and email and its uses in modern communication

Appreciate the use of satellite communication.

ANATOMY OF A NETWORK

TRANSMISSION LINKS

Convey bits, bytes, packets

Physical medium

Copper (or aluminum)

ADVANCED COMPUTER STUDIES & E-COMMERCE Page 1

Optical fibre

Glass, plastic

Free-space optical

Laser

Radio

Satellite, microwave link, mobile, wireless LAN, ‘Bluetooth’

Mode

Point-to-point

Shared medium (multicast)

Broadcast

REPRESENTING DATA: BITS & BYTES

Bits

Different codes used in different interface standards

Images, multi-media

Require special bit pattern as delimiter

Bytes

Text is usually ASCII or Unicode characters

Text files, documents

Character set includes special control characters

BITS BYTES

01100001011000111 01110101 00000010 10000000 10100001


DATA TRANSMISSION MODES

There are three ways for transmitting data from one point to another;

1. Simplex: In simplex mode the communication can take place in one direction. The receiver receives the signal from the transmitting device. In this mode the flow of information is Uni.-directional. Hence it is rarely used for data communication.

2. Half-duplex: In half-duplex mode the communication channel is used in both directions, but only in one direction at a time. Thus a half-duplex line can alternatively send and receive data.

3. Full-duplex: In full duplex the communication channel is used in both directions at the same time. Use of full-duplex line improves the efficiency as the line turn-around time required in half-duplex arrangement is eliminated. Example of this mode of transmission is the telephone line.

NETWORK TOPOLOGY


NETWORKS ARE BROKEN INTO 3 TOPOLOGIES.

THEY ARE:

BUS TOPOLOGY

STAR TOPOLOGY

RING TOPOLOGY

BASICS OF NETWORKING

BUS TOPOLOGY Allows information to be directed from one computer to the other. Lots of binary collision though.

ADVANTAGES OF BUS TOPOLOGY

i. It is quite easy to set up.

ii. If one station of the topology fails it does not affect the entire system.

iii. Requires less cable length than a star topology.

DISADVANTAGES OF BUS TOPOLOGY

i. Any break in the bus is difficult to identify.

ii. Entire network shuts down if there is a break in the main cable.

iii. Terminators are required at both ends of the backbone cable.

iv. Difficult to identify the problem if the entire network shuts down.


v. Not meant to be used as a stand-alone solution in a large building.

STAR TOPOLOGY is the most common type Used. A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator. All computers are attached to a hub.

There is bi-directional communication between various nodes.

The central node controls all the activities of the nodes.

ADVANTAGES OF STAR TOPOLOGY

i. Less collisions and most efficient.

ii. It offers flexibility of adding or deleting of workstations from the network.

iii. Breakdown of one station does not affect any other device on the network.

iv. Easy to install and wire.

DISADVANTAGES OF STAR TOPOLOGY

i. Failure of the central node disables communication throughout the whole network.

ii. Requires more cable length than a linear topology.

NB: The protocols used with star configurations are usually Ethernet or Local Talk. Token Ring uses a similar topology, called the star-wired ring.


RING TOPOLOGY

RING TOPOLOGY- Uses a token to pass Information from 1 computer to the other.

A token is attached to the message by the Sender to identify which computer should receive the message. As the message moves around the ring, each computer examines the token. If the computer identifies the token as its own, then it will process the Information.

A disadvantage of a token ring is if one Computer is broken or down, the message cannot be passed to the other computers.

CONSIDERATIONS WHEN CHOOSING A TOPOLOGY

1) Money. A linear bus network may be the least expensive way to install a network; you do not have to purchase concentrators.

2) Length of cable needed. The linear bus network uses shorter lengths of cable.

3) Future growth. With a star topology, expanding a network is easily done by adding another concentrator.

4) Cable type. The most common cable in schools is unshielded twisted pair, which is most often used with star topologies.

CLASSIFICATIONS OF NETWORKS

• Based on size:


– System/Storage area networks (SAN)

• within the same room

– Local area networks (LAN)

• in a close proximity

– Metropolitan area networks (MAN)

• span a city

– Wide area networks (WAN)

• connecting computers situated anywhere

• Connects many networks together

LOCAL AREA NETWORK (LAN)

Networks used to interconnect computers in a single room, rooms within a building or buildings on one site.

LAN links computers, i.e., software and hardware, in the same area for the purpose of sharing information.

MAJOR CHARACTERISTICS OF LAN

Every computer has the potential to communicate with any other computers of the network.

High degree of interconnection between computers.

Easy physical connection of computers in a network.

Inexpensive medium of data transmission

High data transmission rate.

ADVANTAGES OF LAN

The reliability of network is high because the failure of one computer in the network does not affect the functioning for other computers.

Addition of new computer to network is easy.

High rate of data transmission is possible.


Peripheral devices like magnetic disk and printer can be shared by other computers.

DISADVANTAGE

If the communication line fails, the entire network system breaks down.

USES OF LAN

Followings are the major areas where LAN is normally used

File transfers and Access

Word and text processing

Electronic message handling

Remote database access

Personal computing

Digital voice transmission and storage

INTERCONNECTING LANs & WANs

WIDE AREA NETWORK (WAN)

The term Wide Area Network (WAN) is used to describe a computer network spanning a regional, national or global area.


Therefore the transmission mediums used are normally telephone lines, microwaves and satellite links.

CHARACTERISTICS OF WAN

Followings are the major characteristics of WAN.

1. Communication Facility

2. Remote Data Entry

3. Centralized Information

COMMUNICATION FACILITY

Computer conferencing is another use of WAN where users communicate with each other through their computer system.

REMOTE DATA ENTRY

Remote data entry is possible in WAN.

CENTRALISED INFORMATION

In modern computerized environment big organizations go for centralized data storage.

As the data are generated at different sites, WAN permits collection of this data from different sites and save it at a single site.

DIFFERENCES BETWEEN LAN & WAN

a. LAN is restricted to limited geographical area of few kilometers. But WAN covers great distance and operate nationwide or even worldwide.

b. In LAN, the computer terminals and peripheral devices are connected with wires and coaxial cables. In WAN there is no physical connection. Communication is done through telephone lines and satellite links.

c. Cost of data transmission in LAN is less because the transmission medium is owned by a single organization. In case of WAN the cost of data transmission is very high because the transmission mediums used are hired either telephone lines or satellite links.

d. The speed of data transmission is much higher in LAN than in WAN. The transmission speed in LAN varies from 0.1 to 100 megabits per second. In case of WAN the speed ranges from 1800 to 9600 bits per second (bps).

e. Few data transmission errors occur in LAN compared to WAN. It is because in LAN the distance covered is negligible.


BASIC TERMINOLOGIES

Web Client

Machine that initiates internet request

Web Server

Machine that services internet request

Browser

Software at the client side to interact with data

Intranet

An internal network of computer confined to a simple place.

Extranet

When two or more intranets are connected with each other, they form an Extranet eg. Virtual Private Network (VPN)

Internet

Global network of networks

World Wide Web (WWW)

It is a protocol that uses the internet as the communication structure.

Protocol

TCP-IP

FTP

SMTP

Hypertext Transfer Protocol (HTTP)

Native protocol of WWW designed for making web page requests

WHAT IS THE INTERNET

• The Internet is a collection of networks connected by interconnecting devices.


• The connecting devices

– are specialized computing devices, e.g. routers

– forward data from one network to another.

INTERNET

A collection of networks

THE INTERNET TOPOLOGY


COMMUNICATING OVER THE INTERNET

• To communicate over the Internet, the computers must:

– use a common language or a protocol to govern the exchange of messages.

– have a way to address one another.

• Protocol:

– specifies exact format, order of messages sent and received among network entities, and actions taken on message transmission and receipt.

• Addressing:

– defines where to deliver the messages.

PROTOCOL LAYERING

• Internet has a large collections of protocols organized in a layering model.

– Application: enables the user, whether human or software, to access the network.

– Transport: responsible for reliable source-to-destination (end-to-end) delivery of the entire message.


– Network: responsible for routing a packet (also called datagram) from source-to-dest (possibly) across multiple (different) networks.

– Data link (also called network interface): specify how to organize data into frames and how to deliver a frame over a network.

– Physical: coordinates the functions required to transmit a bit stream over a physical medium.

– Two key protocols are:

• IP (Internet Protocol)

– Oversee end-to-end delivery of individual packets

– Does not recognize relationships among packets

– Treats each packet independently, as if they belong to different message

• TCP (Transport Control Protocol)

– Ensure whole message arrive intact and in order

– (eg, check if packets are missing or arrive out of order)

INTERNET ADDRESSES

• Every Computer Is Assigned A Unique Address

– Each computer attached to the Internet must be assigned a unique address.

• IP Addresses Are Not Random

– Computers on the same network have the same prefix (Netid).


INTERNET ADDRESSING

• IP or Internet address is a 32-bit (4 byte) address that uniquely defines every computing device on the Internet.

• Decimal notation to make it easier to read.

CLASSES OF IP ADDRESSES

• Designers chose a compromise - multiple address formats that allow both large and small prefixes

• Each format is called an address class

• Class of an address is identified by first four bits


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memberfiles.freewebs.com · Web viewExplain communication protocols Understand what is internet and email and its uses in modern communication Appreciate the use of satellite communication