CHAPTER 1 INTRODUCTION TO

NETWORKING

BASIC CONCEPTS OF COMPUTER NETWORKS

NETWORK

Computer and devices, connected by some type of media.

Two computers to thousands of computers connected across the world via the Internet.

Networks may link mainframe computers, desktop computers, printers, plotters, fax machines, and phone systems.

NETWORK (CONT.)

Manage and administer resources on multiple computer from one location.

Networks allow multiple users to share devices and resources such as:- printers- faxes- program and files

ADVANTAGES OF NETWORKING

• File Sharing : The major advantage of a computer network is that is allows file sharing and remote file access. A person sitting at one workstation of a network can easily see the files present on the other workstation.

• Resource Sharing : If there are four people in a family, each having their own computer, they will require four modems (for the Internet connection) and four printers, if they want to use the resources at the same time. A computer network, on the other hand, provides a cheaper alternative by the provision of resource sharing.

• Increased Storage Capacity : As there is more than one computer on a network which can easily share files, the issue of storage capacity gets resolved to a great extent. When many computers are on a network, memory of different computers can be used in such case. One can also design a storage server on the network in order to have a huge storage capacity.

• Increased Cost Efficiency : There are many software's available in the market which are costly and take time for installation. Computer networks resolve this issue as the software can be stored or installed on a system or a server and can be used by the different workstations.

TYPES OF NETWORK Peer-to-Peer

Client / Server

PEER-TO-PEER NETWORKS

Peer-to-peer networks : Resource sharing, processing, and

communication controls are fully decentralized often called a workgroup.

All clients are given equal importance in using the network resources and users are individually authenticated by workstations.

No fixed clients and servers. Common with up to 12 computers Disadvantage – slow transmission

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Peer-to-Peer Networks

CLIENT / SERVER NETWORKS

Client/server networks It is a network where the servers provide

services to different clients. A centralized server provides client

authentication services. Servers play a key role in managing several

applications like access to shared files, printers, and hardware.

CLIENT-SERVER

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Usually high-powered servers. The types of servers are: -

CLIENT-SERVER

Advantages Disadvantages

Security and data sources are controlled by the server

spending more costly for a server

All components (client / network /server) work simultaneously

need maintenance every time the rates are determined to ensure the effectiveness of the system.

Sharing data and software applications can be done

Networking does not work if something went wrong on the server.

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Client/Server Networks

LANS, MANS AND WANS

There are three main categories of networks:• Local Area Network (LAN) – is a relatively

small network of computers, printers, and other devices in single building or floor.

• Metropolitan Area Network (MAN) – is a high-speed internetwork of LANs across a metropolitan area.

• Wide Area Network (WAN) – traditionally connects LANs using the PSTN(Public Switched Telephone Network) or more commonly the Internet. To provide connectivity over a large geographic area.

LOCAL AREA NETWORK (LAN)

LAN characteristics: They are used within small areas ( such as in

an office building). They offer high-speed communication-typically

100Mbps or faster. They provide access for many devices. They use LAN- specific equipment such as hub

and NICs-usually no need router.

METROPOLITAN AREA NETWORK MAN characteristics: Sites are dispersed across a city/large campus and perhaps the surrounding area as well. With the advent of MANs, historically slow connection (56Kbps-1.5Mbps) have given way to communication at hundreds of megabits per second and even gigabit speeds. They use devices such as routers, telephone switches, and microwave antennas as part of

their communication infrastructure A MAN usually interconnects a number of (LANs) using a

high-capacity backbone technology, such as fiber-optical links.

WIDE AREA NETWORK

WAN characteristics : They can cover a very large geographic area even span the world. They usually communicate at slow speed

(compared to LANs). They use devices such as routers, modems, and

WAN switches, connectivity devices specific to LANs and used to connect to long-haul transmission media.

COMMON NETWORK ELEMENT

Client A computer on the network that requesting resources or services.

Server A computer on the network that manages

network access and shared resources. Network Interface Card (NIC) A device inside a computer that connects a computer to the network media. Network Operating System(NOS)

Server that enable a computer to control network access and manage resources. The most popular NOS are Microsoft Windows Server, Novell NetWare and UNIX.

Host A device that provides resource sharing for other computers on the same network.

COMMON NETWORK ELEMENTS (CONT.)

• Node A device such as, client, server, or other network equipment that is identified by a unique network address.

• Topology The physical layout of a computer network. Network topology can be a ring, bus or star formation, or hybrid combinations.

• Backbone The backbone of a network (Cable) that combines smaller network into a large network.

• Transmission Media Media that carrying the network signal (cable/channel)

• Connectivity Devices Modems, repeaters, bridges, routers, switch, hub and etc.

• Segment It is a physical partitioning of network.

NETWORK TOPOLOGIES

Network topology is the layout pattern of interconnections of the various elements (cable, nodes, etc.) of a computer network. Bus Ring Star Hybrid Mesh

Group Activities…

Bus???Ring???

Star??? Mesh???

Hybrid???

BUS Connect two or more computer using coaxial cable and

BNC connector. Terminator are installed on both ends of the cable. Without the terminator, the electrical signal that

represent the data would reached the end of cooper wire and bounce back, causing errors on the network.

Advantages : inexpensive to install, can easily add more workstation.

Disadvantages : If the cable break down, the network is down, access time and network performance degrade as devices are added to the network.

Bayonet Neill–Concelman(BNC connector)

Bus Topology

RING

Computer are connected in a ring (circle). It has no beginning or end, so there is no need to

terminate the cable. Every device have an equal advantage in accessing

the media. Advantages : There are no collisions , no terminators

are needed, easy to locate and correct problems with devices and cable.

Disadvantages : requires more cable than a bus network, a break in the cable brings the entire network down.

Ring Topology

STAR

All computer are connected to a central point such as hub or switch

The most common topology used today Data on a star topology passes through the hub or

switch before continuing to its destination. Advantages : Cable failure will not disrupt the

network. Disadvantages : Single point of failure.

Star Topology

HYBRID

• Combination of any two or more different topologies.• The most commonly used topologies are Star-Bus or

Star-Ring.• Advantages : If a computer fails, it will not affect the

rest of the network• Disadvantages : If the central component, or hub, that

attaches all computers in a star, fails, no computer will be able to communicate.

• Combination of any two or more different topologies.• The most commonly used topologies are Star-Bus or

Star-Ring.• Advantages : If a computer fails, it will not affect the

rest of the network• Disadvantages : If the central component, or hub, that

attaches all computers in a star, fails, no computer will be able to communicate.

MESH

All computer are connected to every other computer on the network

Rarely used on a Local Area Network (LAN) The topology of the Internet. Advantages : Very redundant. No disruption when

expanded. Disadvantages : Expensive. Requires a lot of cable and

network interface cards.

ADVANTAGES & DISADVANTAGES OF

TOPOLOGIESTopology Advantages Disadvantages

BusBus Less cableEasy to installNetwork not working even with 1 PC failed

Cable faulty, entire system downDifficult to troubleshootLeast fault tolerance

StarStar InexpensiveEasy to troubleshootEasy to reconfigure

Low data rateModerately difficult to installRequire more cables

RingRing Almost no loss in signal quality over networkNot that easy to install & troubleshoot

Failure of single connection can take down entire network

MeshMesh Every PC connected to each otherMost fault tolerance

Large amount of cablesVery expensive & difficult to manage

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NETWORKING STANDARDS ORGANIZATIONS

Organizations that set standards for networking: American National Standards Institute (ANSI) Electronic Industries Alliance (EIA) and

Telecommunication Industry Association (TIA) Institute of Electrical and Electronics Engineers (IEEE) International Organization for Standardization (ISO) International Telecommunication Union (ITU) Internet Society (ISOC) Internet Assigned Numbers Authority (IANA) and

Internet Corporation for Assigned Names and Numbers (ICANN)

ORGANIZATIONS AND ASSOCIATIONS

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SAFETY STANDARDS

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PRINCIPLES OF NETWORKING

Sender• The first of these elements is the message source, or sender. It is the device which sends the data messages. • Message sources are people, or electronic devices, that need to communicate a message to other individuals or devices.

Destination•The second element of communication is the destination, or receiver, of the message.•The destination receives the message and interprets it.

Source•A third element, called a channel, provides the pathway over which the message can travel from source to destination.

RULES OF COMMUNICATION IN NETWORKING

Identification of sender and receiver (establish a link)

Agreed-upon medium or channel (face-to-face, telephone, letter, photograph)-issue a command and command qualifier

Appropriate communication mode (spoken, written, illustrated, interactive or one-way)-acknowledgement of command

Common language

Grammar and sentence structure - dissection message

Error Control and correction Error detecting and recovering is one of the main functions of communication protocol. It ensures that data is transmitted without any error. It also solves the problem if an error is detected.

Speed and timing of delivery-termination and transmission

Ex:RS232 –handshaking concept

Protocols define the details of how the message is transmitted, and delivered. This includes issues of: Message format Message size Timing Encapsulation Encoding Standard message pattern

MESSAGE ENCODING

•Encoding is the process of converting thoughts into the language, symbols, or sounds, for transmission. Decoding reverses this process in order to interpret the thought.

In computer communication

Messages sent across the network are first converted into bits by the sending host.

Each bit is encoded into a pattern of sounds, light waves, or electrical impulses depending on the network media over which the bits are transmitted.

The destination host receives and decodes the signals in order to interpret the message.

Message formats depend on the type of message and the channel that is used to deliver the message.

Ex: The process of placing one message format (the letter) inside another message format (the envelope) is called encapsulation. De-encapsulation occurs when the process is reversed by the recipient and the letter is removed from the envelope.

Message formatting

MESSAGE FORMATTING(CONT.)

Each computer message is encapsulated in a specific format, called a frame before it is send to network.

A frame acts like an envelope; it provides the address of the intended destination and the address of the source host.

The format and contents of a frame are determined by the type of message being sent and the channel over which it is communicated.

MESSAGE SIZE When long message is sent from one host to

another over a network, it is necessary to break the message into smaller pieces.

Each piece is encapsulated in a separate frame with the address information, and is sent over the network.

At the receiving host, the messages are de-encapsulated and put back together to be processed and interpreted.

MESSAGE TIMING

People use timing to determine when to speak, how fast or slow to talk, and how long to wait for a response.

Rules: a) Access Method

Access Method determines when someone is able to send a message.

If two people talk at the same time, a collision of information occurs.

Hosts on a network need an access method to know when to begin sending messages and how to respond when errors occur.

MESSAGE TIMING (CONT.) b) Flow Control

Timing also effects how much information can be sent and the speed that it can be delivered.

In network communication, a sending host can transmit messages at a faster rate than the destination host can receive and process.

Source and destination hosts use flow control to negotiate correct timing for successful communication.

c) Response Timeout Hosts on the network also have rules that specify how

long to wait for responses and what action to take if a response timeout occurs.

MESSAGE PATTERN

Unicast A one-to-one message pattern Only a single destination for the message.

Multicast One-to-many pattern Multicasting is the delivery of the same message to a

group of host destinations simultaneously. The most complex type of message because they require a

means of identifying a set of specific devices to receive a message.

Broadcast If all hosts on the network need to receive the

message at the same time, a broadcast is used. One-to-all message pattern.

Networking fundamentals48

MESSAGE PATTERN(CONT.)

Unicast: 1-to-1

Multicast: 1-to-many

Broadcast: 1 to all

LETS TRY

NETWORK INTERFACE CARDS

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51Ethernet card.From top to bottom:RJ-45, AUI (Attachment Unit

Interface) , and BNC connectors

LOCALTALKEthernet Cards LocalTalk

Fast data transfer (10 to 100 Mbps)

Slow data transfer (23 Mbps)

Expensive - purchased separately

Built into Macintosh computers

Requires computer slot No computer slot necessary

Available for most computers

Works only on Macintosh computers

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TOKEN RING CARDS53

HARDWARE54

WORKSTATIONS

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SWITCH56

REPEATERS57

BRIDGES58

ROUTERS59

GATEWAYS60