Networking Essentials Complete

8/6/2019 Networking Essentials Complete

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INTRODUCTION TO COMPUTERS NETWORKS

At its most elementary level, a network consists of two computers connected to each other by a

cable so that they can share data. All networking, no matter how sophisticated, stems from that

simple system. The idea of two computers getting connected by a cable was a major achievement

in communication that is a computer network can be simply defined as an inter connection ofcomputers with the view of sharing resources and for communication purpose. A network

enables distributed computers and users to communication and share resources.

REASONS FOR NETWORKING

1. Sharing of hardware (cpu, printers, scanners, etc) and software resources.2. For control purposes.3. For communication purpose .i.e. sending and receiving messages along the network.4. Sharing of information \5.

Cost reduction

TYPES OF NETWORKS

There are two approaches namely:-

1. Geographical coverage approach.2. Resource distribution approach.

GEOGRAPHICAL COVERAGE APPROACH

This approach classifies networks depending on their geographical extend.

Three types of networks can be indentified under this approach:-

Local Area Networks Wide area networks Metropolitan area networks

LOCAL AREA NETWORK

They are used to inter connect devices that are relatively in close proximity (limited geographical

area). Such a network might be a single floor of a building or with one small company. LANS

are restricted in size in that they only spar a limited geographical areas of radius


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WIDE AREA NETWORK

These are necessary and inter connect LANS across geographical distances. They are able and

spar buildings, states, countries and even continental boundaries. WANS are characterized by

high number of errors, low security due to external connections, costly to install and low

transmission speed.

WANs inter connect LANs with a device called a ROUTER. This enables each LANS to offer its

user access to resources stored on other inter connected LANS.Without compromising its own

identity. In other words, a router inter connects LANS without condensing them in to just one big

LANS.

METROPOLITAN AREA NETWORK

These are more closely related to WANS than LANS because they are used to interconnect

limited geographical areas. They remain relatively obsecure and they are really used.

RESOURCES DISTRIBUTION APPROACH

This describes the manner in which attached resources can be accessed. Resources can be

clients servers, files, data etc. that reside on a client or a server. These resources can be accessed

in one of the two ways.

Peer-To peer network Client/ server networks

PEER-TO-PEER NETWORKS

This supports unstructured access to networks attached to resources. Each device in a peer to

peer network can be clients and a server simultaneously while all devices in the network are

capable of accessing data, software and other networks resources.

BENEFITS

They are easy to implement and operate. They are not expensive.- they lack expensive sophist dedicated servers that require

special administrative care and climate condition

Can be established with familiar old systems such as windows They are more fault tolerant due to the absence of hierarchical dependence.


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LIMITATIONS OF PEER TO PEER

SECURITYLack of central repository of resources compromises the security of this type of network.

ADMINISRATIONThis is spread to the users and it creates:-

Co-ordinated and highly in consistence back ups of data and software. Decentralized responsibility enforcing file naming and storage location. PERFORMANCE

Machine are not meant for multi-user purpose thus anytime a remote client longs on,

performance goes down. Resources are only available when a particular machine is on otherwise

there is number access whatsoever.

SCALABILITYMore peer s make the network unmanageable.

CLIENT/ SERVER NETWORK

In this network, frequently shared resources are consolidated in a separate group of computers

known as servers. These do not have primary users rather they are multi-users machines that

regulate the sharing of their resources across a base of clients. This way, clients are relieved off

the burden of functioning as servers to other clients.

BENEFITS OF A CLIENT

SECURITY- This is managed centrally to peer to peer networks. ADMISTRATIVE TASKS- Tasks like backups can be done consistently and

reliable.

Each client only needs to keep up with the requests generated by its primary andonly user but not for other clients.

Since all processing is off-loaded to the server, (more processing power andmemory) thus client computers can better satisfy their own requests for

centralized resources much more effectively.

Users are spared the effort required to learn which resources are stored in anetwork.

Scalability does not compromise the performance of a network.


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LIMITATIONS

Cost limitation to implement and operate: - Hardware and software costespecially for the server is usually high.

Operation cost- trained personnel are necessary for administrative work. Risk server failure which can virtually affect the entire network.

TYPES OF SERVERS

1. FILE SERVERS: - This is a central storage for files.2. PRINT SERVER: - Used for sharing printers among LAN users.3. Application server: - this is a central storage for application software.4. Mail servers: - manage electronic messaging between network users.5. Fax servers- They manage fax traffic in and out of the network users.6. Communication servers-they handle data flow and email messages between servers on

network and other networks.

NETWORK TOPOLOGY

The term network topology refers to the arrangements or physical layout of computers,

cables and other components on the network. It can also refer to the basic design of a

network. A network topology affects its capabilities choosing one topology over another can

impact on the :-

Type of equipment the network needs. The capabilities of the equipment. Networks growth. The way a network is managed.

STANDARD TOPOLOGIES

All network design stems from 3 basic topologies:-

Bus topology Star topology Ring topology

If computers are connected in a row along a single cable, the topology is referred to as a bus.

If the computers are connected to a cable segment that branch out from a single point or hub the

topology is called a star.


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If the computers are connected to a cable that forms a loop the topology is called a ring.

1. BUS TOPOPLOGY|LINEAR BUS.This is the simplest and most common method of networking computers.

It consists of a single cable called a trunk (segment backbone) that connects all of the computers

in a network in a single line.

COMMUNICATION ON THE BUS.

Computers on a bus topology network communicate by addressing data to a particular computer

and putting that data on the cable in form of electronic signals.

Sending the signal

Network data in form of electronic signals is send to all of the computers on the network.

However, the information is accepted only by the computer whose address and coded in the

original signal/message. Only one computer at a time can send a message. Since only one

computer at a time can send data on a bus network, network performance is affected by the

number of computers attached to the bus.

The more computers on a bus, the more computers there will be waiting to put data on the bus,

and the slower the network. However, the amount the network slows down is not only related to

the number of computers on the network. It depends on numerous factors:-

Hardware capabilities of computer on the network. The number of times computer on a network transmit data. Types of application being run on the network. Types of cables used on the network. Distance between the computers on the network.

..

The bus topology is a passive topology. Computers on a bus only listen for data being send on

the network. They are not responsible for moving data from one computer to next. If one

computer fails that is it does not affect the rest of the network. In an active topology, computers

regenerate signals and move data across the network.

SIGNAL BOUNCE

Since the data is send and the entire network, it will travel from one end of the cable to the other.

If the signal were allowed to continue uninterrupted, it would keep bouncing back and forth


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around the cable and prevent other computers from sending signals that is the signals must be

stopped after it has had a chance to reach the proper destination address.

THE TERMINATOR

It stop the signal from bouncing, a component called the terminator is placed at each end of thecable to absorb free signal. Absorbing the signal clears the cable so that other coups can send

date.

2. STAR TOPOLOGYIn this topology computer are connected to a centralized component called a hub .Signals are

transmitted from the transmitted from the sending computer through the hub to all the computers

on the network. This topology offers centralized resources and management. However because

each computer is connected to a central point, this topology requires a great deal of cable in a

large network installation. Also if the central point fails the entire network goes down. If one

computer is the cable that connects to the hub fails. In a star topology the failed computer will

not be able to received or send network data. The rest of the network continues to function

normally.

3. RING TOPOLOGYThe ring topology connects computer on a single circle of cable. There are no terminated

ends. The signals travels in a round the loop in one direction and pass through each

computer. Unlike the passive bus topology, each computers acts as a repeater to boost

the signal and send it onto the next computers. Because the signal passes through each

computer the failure of one computer can impact the entire network.

4. MESH TOPOLOGYThis is the simplest logical topology in terms of data flow and most complete in terms of

physical design. In this topology, every device is connected to every other device. Its not

commonly found in LANS due to cabling complexity. Because of its design, its very

expensive to install and maintain. However, it has an advantage of its high fault

tolerance.

5. HYBRID TOPOLOGYLarger, more complex networks can combine different physical topologies such as star-bus topology and a star-ring topology.

TRANSMISSION MEDIA

(NETWORK CABLING)

Important terms.

1. Shielding (iron box cable)


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This refers to the woven/stranded metal mesh that surrounds some type of cabling. It protects

transmitted data from absorbing stray electronic signals referred to as noise.

2. Cross-talk.This refers to signals over-flow from adjacent cables.

3. Attenuation.This is decrease in strength of a signal as it travels along a transmission media. This is due to

impedance (resistance offered by the cable)

4. Distortion.Unwanted modification of the signal on transit.

PRIMARY CABLE TYPES.

1. The vast major of networks today are connected by some sort of wire or cabling whichacts as the network transmission media carrying signals between computers. There is a

variety of cables that can meet varying needs & sizes of network from small to large.

There are three major groups of cabling that connects majority of the network;

a). coaxial cable

- Thinnet coaxial.

- Thicknet coaxial.

b). Twisted pair cable.- Shielded twisted pair. (S.T.P)

- Unshielded twisted pair. (U.T.P)

c). Fibre optic cable.

a) COAXIAL CABLE.At one time the coaxial cable was one of the most used networking cables. This is because it was

inexpensive; it was light, flexible and easy to work with.

It was so popular that it became a safe easily supported installation. In its simplest form, coaxial cable consists of a single core with an outer conductor that

acts as a shield. The signal is transmitted in the inner core.

The inner core and the outer shield are separated by an insulator either plastic or mica.The cable is then enclosed in a p.v.c. (polyvinyl chloride) to protect it and give it some

strength.


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TYPES OF COAXIAL CABLE.

They are two types of coaxial cable;

1. Thin (thinnet)2. Thick (thicknet)1. THINNET

This is a coaxial cable about 0.25 thick. Networks that use thinnet have the cable

connected directly to a computer network adapter cable.

2. THCKNET-This is relatively rigid coaxial cable about 0.5 in diameter.

-Its copper core is thicker than thinnet core.

-The copper core the further the cable can carry signals.

-It can thus be used to connect several smaller thinnet based network.

COAXIAL CABLE CONNECTION HARDWARE.

Both thinnet and thicknet use connection components known as British Naval connectors

(B.N.C.), to make the connection between the cable and the computers. There are

important components in the BNC family including;

a) The BNC cable connector; this is either soldered or crimped to the end of the cable.b) The BNC-T cable; this joins the network interface card in the computer to the

network cable.

c) The BNC barrel connector; this connector is used to join to lengths of thinnet cable tomake one longer length.

d) The BNC terminator; it closes each end of a bus cable to absorb stray signals.Without BNC terminator a bus network will not function.

COAXIAL CABLE CONSIDERATIONS

Use coaxial if you need:-

a) A transmission medium which will transmit voice, data and video.


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b) Want to transmit data longer distances than less expensive cabling cantransmit.

c) A familiar technology that offers reasonable data security.TWISTED PAIR CABLE

In its simplest form, twisted pair consists of two insulated strands of copper wire twisted around

each other.

These are two types of twisted pair cable:-

Unshielded twisted pair (UTP) Shielded twisted pair (STP)

A number of twisted pair wires are often grouped together and enclosed in a protective sheath t

for a cable. The actual number of pairs in cable varies. The twisting cancels out electrical noise

from adjacent pairs and from other sources such as motors, relays and transformers. Thethroughput (reliability/ performance) of twisted pair cable s can be improved by:-

a) Increasing the number of twists.b) Applying a protective layerc) Increasing the length of the twisted pair cable.UNSHIELDED TWISTED PAIR

UTP comes in five categories:-

1) Category 1This refers to the traditional UTP transfer telephone cable which can carry voice but notdata.

2) Category 2This supports data transmission up to four mbps (megabits per second) and consists of

four twisted pairs.

3) Category 3This supports data transmission up to 100mbps. It consists of four twisted pairs with 3

twists per foot.

4) Category 4This supports data transmission up to 16 mps. It consists of 4 twisted pairs.

5) Category 5This supports data transmission up to 100 mbps. It consists of 4 twisted pairs of copper

wires.

SHIELDED TWISTED PAIR (STP)


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STP uses woven copper braided jacket which is a higher quality, more protective jacket than

UTP has. STP also uses a fail wrap between and around the wire pairs, and the internal twisting

of the pairs.

This gives STP excellence shielding to protect the transmitted data from outside interferences.

TWISTED PAIR CONNECTION HARDWARE

Twisted pair uses RJ45 telephone connectors to connect to a computer. This is similar to RJ 11

telephone connecters. Although they look a like at first glance, there crucial differences between

them. The RJ45 is slightly larger and will not fit into the RJ 11telephone jack. The RJ 45 house

eight (8) cable connection while RJ 11 house 4 cable connections.

TWISTED PAIR CONSIDERATION

Use twisted pair:-

If your LAN is under budget constraints. When you want a relatively easy installation where computers connection are simple.

Do not use twisted pair:-

Unless you are absolutely sure of data integrity transmitted over great distances at highspeed.

FIBRE OPTICS CABLE

In this cable optical fibres carry digital data in form of modulated pulses of light. This is a

relatively safe way to send data because no electrical impulses are carried over the fibre optic

cable. This means that the fibre optic cable cannot be trapped and data storing which is possible

with any copper based cable caring data in form of electronic signals. Fiber optic cable is that is

good for:-

High speed High capacity data because of lack of attenuation of purity of the signal.FIBRE OPTIC COMPOSITION

It consists of a surrounded by a concentric layer of glass known as cladding. The fiber is

sometimes made of plastic which is easier to store but cannot carry light pulses as far the


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glass. Each glass strand only passes signal in one direction, so the cable, consists of two

strands in separate jackets. One strand transmits and one receives. a reinforcing layer of

plastic surrounds each glass strands in separate jackets. One strand transmits and one

receives. A reinforcing layer of plastic surrounds each glass strand while Kevlar fiber

provides strength.

Use fiber optics if you need to transmit data at very high speed over long distances in a very

secure media. Do not use fiber optic if:-

You are under tight budget You do not have the expertise to properly install and connect devices to it.

NETWORK INTERFACE CARDS (NIC)

(NETWORK ADAPTER CARDS)

NICS acts as the physical interface or connection between the computer and the network cable.

the cards are installed in an expansion slot in each computer and server on the network. After the

card has been installed, the network cable is attached to the cards port to make the actual

physical connection and the rest of the network. The role of NIC is:-

1. Properly format data (prepare) so that it can be accepted in the network.2. Placing data onto the network.3. Accepting transmitted data that is addressed to it.

NIC is common in LANs and its a circuit board installed in a computer and occupies theinput/output slot on its motherboard. The network is then cabled to the port provided by this

board.

NIC INSTALLING, configuring and troubleshooting

The successful operation of the NIC card requires that two things be done correctly:-

The adapter card must be firmly steed in a slot on the PCs motherboard. The proper drivers must be installed and configured to match the networks architecture.

Sometimes, network cards just stop functioning due to age, environmental agents, quality or

amount of continued use. Often however, if may fail to work due to configuration errors or

compatibility problems with the PC or its operating system. Thus one can investigate on:-

1. Lights of the back. they are usually two:- Link light (red) - shows that the card has established connectivity with the

network.


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Transmission light (green) - which blinks as the card receives /transmitsinformation across the network. (No light, No connection)

2. Check the dates of the existing network drivers installed- could be there are new driversthat will help resolve the problem.

NETWORK SOFTWARE

(NETWORK OPERATING SYSTEM)

With the growth in the networking, there has been the need by the users to access the

information and share it among the other users. At this end, a number of software venders

have developed what I would call network operating system, first to bring about the

sharing this needs of additional services for both end users and on network operating

systems that is provides a platform on which networks operates.

ROLE OF A NETWORK O/S

a) A network o/s ties together all of the computers and peripherals in the network.b) It co-ordinates the functions of all computers and peripherals in network.c) It provides security for and access to data and peripherals in a network.

There are two major components of network software:-

i. The network software thats installed on clients.ii. The network software that installed on the servers.

EXAMPLES OF NETWORK OPERATING SYSTEM

Novell Netware-novel- early 1980s. Vines (virtual network software) - banyan system. inc-1980-extinct UNIX -1980s / Linux (Unix like o/s ) Windows o/s (NT, 2000, up, 2003 server)- Microsoft inc.

MODEMS

This is a device that makes it possible for computers to communicate over a telephone line. A

modem at the sending, end convert the computer digital signal into Analog signal and transmit

the analog signals onto the telephone line. A modem at the receiving end coverts the incoming

analog signal back to the digital signal for receiving computer. In other words-A sending modem


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modulates digital signal into Analog signal and the receiving modem demodulates analog signal

back to the digital signals.

MODEM HARDWARE

Modems are known as data communication equipments (DCE) and share the followingcharacterists:-

i. A serial (RS-232) communication interface.ii. An RJ 11 telephone line interface (A four wire telephone plug) modems are available as

both internal and external modem. The internal modem is stored in an expansion slot just

likely any other circuit board. An external modem is a small box thats connected to the

computer serial (RS-232) cable running from the computer serial port to the modems

computer cable connection. The modem uses a cable with an RJ-11 connector to connect

to the wall.

NETWORK PROTOCOLS

Protocols are rules and procedures for communicating e.g. diplomat from one country adhere to

protocol to guide them in interacting with diplomats from other countries. The use of

communication rules apply in the same way in a computer environment. When several

computers are networked, the rules and technical procedures governing their communication and

interaction are called protocols.

NB

a. There are many protocols which lack protocols allows basic communication, they havedifferent purposes and accomplish difference tasks. Each protocol has its own advantages

and restrictions.

b. Some protocols work at the various OSI layers (open system interconnection). The OSIlayer at which a protocol works describes its function.

c. Several protocols may work together in what is known as protocol stack/suite (groups ofprotocols working together. Just as the network incorporates functions in every layer of

the OSI model, different protocols also work together at different levels in a single

protocol stack. The levels in the protocol stack mark or correspond to the layer of the OSI

model. Taken together, the protocol describes the entire stacks functions and capabilities.

HOW PROTOCOLS WORK

The entire technical operation of transmitting data over the network has to be broken down

into discrete systematic steps at each step certain actions take place which cannot take place

at any other step. Each step has its own rules and procedures, or protocols. The steps must be


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carried out in a consistent order so that its the same way on every computer in the network.

In the sending computer, these steps must be carried out from top to down. In the receiving

machine, these steps must be carried out from the bottom up.

THE SENDING COMPUTER

At the sending computers the protocol:-

Breaks the data into smaller sections called packets that the protocol can handle. Protocols add addressing all to the packets so the destination computer on the

network will know that data belongs to it.

Prepares the data for actual transmission through the network adapter card and outonto the network cable.

THE RECEIVING COMPUTER

At the receiving computer protocols carry out the same series of steps in reverse order. At the

receiving end.

a. Takes the data packets off the cable.b. Brings the data packets into the computer through the network adopter card.c. It strips the data packets off all the transmitting all added by the sending.d. Copies the data from the packet to a buffer (temperature storage) for reassembly.e. It passes the reassembled data to the application in a usable form.

NB

Both the sending and the receiving computer need to perform each step the same way so that

data will look the same when received as it did when it was send.

PROTOCALS IN LAYERDED ARCHITECTURE

OSI SUITE

OSI LAYERS FUNCTION

Application layer Initiate / Accept a request


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Presentation layer Add formatting, display, and encrypting all the

packets.

Session layer Add traffic flow all to determine when the

packet gets sent.

Transport layer Add error handling information

Network layer Add sequencing and addressing all to the

packets

Data link layer Adds error checking all and prepares data for

going onto the physical medium

Physical layer Packet is sent a bit stream

In a network, several protocols have to work together to ensure that data is:

Prepared Transferred Received Acted upon

The work of various protocols must be coordinated so that there are no conflicts or incompleteoperations. The answer to this coordination effort is called Layering.

PROTOCOL STACKS

A protocol stack is a combination of protocols. Each layer specifies a different protocol for

handling a function or sub-system of the communication processor. Each layer has its own set of

rules.

STANDARD STACKS (SUITES)

The computer industry has designated several stacks as standard protocol models. The most

important ones include:

The ISO / OSI protocol suite. The IBM system network Architecture ( SNA)


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The Digital Decnet Novel Network AppleTalk Internet protocol suite (TCP / IP)

Protocols exist at each level of these stacks doing the job specified at that level, however, the

communication tasks networks need to perform are assigned to protocols working as one of the

three protocol types. These protocol types map roughly to the OSI model. They are:

Application layer Presentation layer Session layer Transport layer Network layer Data link layer Physical layer

1) APPLICATION PROTOCALSApplication protocols work at the upper layers of the OSI model. They provide application to

application interaction and data exchange. Most popular Application protocols include:

FTAM ( File Transfer Access and Management )OSI file access protocol

SMTP ( Simple Mail Transfer Protocol )An internet protocol for transferring email

FTP ( File Transfer Protocol )An internet protocol for transferring files

TelnetAn internet protocol for logging onto remote host and processing data locally


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AppleTalk and AppleShareThis is Apples protocol suite

AFP ( AppleTalk File Protocol )Apples protocol for remote file access

DAP ( Data Access Protocol )Its a Decnet file access protocol

2) TRANSPORT PROTOCOLSThese provide for communication sessions between computers and ensure that data is able to

move reliably between computers. Popular Transport Protocols include:

TCP (Transmission Control Protocol)This is a TCP / IP protocol for guaranteed delivery of sequenced data.

SPX (Sequential Packet Exchange)This is part of Novells IPX / SPX protocol suite for quarantined delivery of sequenced

data.

NW LinkThis is the Microsoft implementation of the INX / SPX protocol

NETBEUI (Network BIOS) Basic I/O system) Extended user Interface)This establishes communication between computers (NETBIOS) and provides

underlying data and transport services.

ATP (AppleTalk Transaction Protocol)This is the Apples communication session and Data Transport Protocols.

3) NETWORK PROTOCOLSThese provide link services. These handle addressing and routing all error checking and

transmission request. Network protocols also define rules for communicating in a particular

network environment. Popular Network Protocols include:

IP (Internet Protocol)


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This is the TCP /IP protocol for the packet forwarding and routing.

IPX (Internet Packet Exchange)This is part of the IPX/SPX suite for packet forwarding and routing.

NW LinkThis is the Microsoft implementation of the IPX/SPX protocol.

NETBEUIThis is a transport protocol that provides data transport services for NETBIOS

Sessions and Applications.

DDP (Datagram Delivery Protocol) (AppleTalk Protocol)This is an AppleTalk Data Transport Protocol.

COMMON PROTOCOLS

Some of the most commonly protocols include:

a) TCP/IP (Transmission Control Protocol / Internet Protocol)This is an industry standard suite of protocols providing communication in a

heterogeneous environment (Contains variety of different computer systems). In addition

TCP/IP provides routable, enterprise networking protocol and access to world wide

internet and its resources. It has become the standard protocol used for interoperability

(Ability to work together) among many different types of computers. This

interoperability is one of the primary advantages of the TCP/IP. Almost all networks

support TCP/IP as a protocol hence it is commonly known as an Inter-networking

Protocol. Because of its popularity, TCP/IP has become the default standard for

networking. Other protocols written specifically for the TCP/IP suite include:

a) SMTP (Simple Mail Transfer Protocol)Used for sending email.

b) FTP (File Transfer Protocol)Used for exchanging files among computers running TCP/IP.

c) SNMP (Simple Network Management Protocol)


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Used for network management.

b) NETBEUI (NetBIOS Extended User Interface)This is a small, fast, and efficient transport layer protocol that is supplied with all

Microsoft network products.

Advantages:

Small stack size High speed of data transfer on the network medium Its compatibility with all Microsoft based networks

However, it does not support routing and it is limited to Microsoft based networks.

c) IPX/SPX and NW LinkThis is a protocol stack that is used in Novell networks. It is relatively a small and fast

protocol and supports routing. Microsoft provides NW Link as its version of IPX/SPX

which is a transport protocol that is routable.

d) AppleTalk ProtocolAppleTalk is a part of Apple proprietary designed to enable Apple Macintosh computers

to share files and printers in a network environment.

e) OSI Protocol SuiteThis is a complete protocol stack. Each protocol maps directly to a single layer of the

OSI model. The OSI protocol suite include routing and Transport protocols, Session

layer, Presentation layer, and several Application layer protocols designed to provide full

networking functionality including file access, printing, and terminal emulations.

f) DECNET ( Digital Equipment Corporation Proprietary ProtocolStack/Suite)

This is a set of hardware and software that implement the digital network architecture

(DNA). It defines communication networks over Local Area Network and Wide Area

Network that use private or public data transmission facilities. It is a routable protocol.

ROUTING PROTOCOLS


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Used to exchange information about reachability and traffic delays, allowing each router

to construct a next-hop routing table for paths through the internet. Relatively, simple

routing protocols are used between autonomous systems within a layer internet and more

complex routing protocols are used within each autonomous system.

E.g. RIP (Routing Information Protocol) Suitable for smaller internet.

OSPF (Open Shortest Path First Protocol) This is a transport protocol

CONNECTION LESS PROTOCOL

This is a protocol for exchanging data in an unplanned fashion and without prior

coordination e.g. datagram (i.e. UDP)

IP works at the network layer and handles the following functions and the methods it

uses are as follows:

For addressing; IOP uses the logical network address. For switching purposes; it uses the dynamic method. For route selection; it uses the dynamic method. For communication serves; IP provides error control.

CONNECTION ORIENTED TRANSPORT PROTOCOLS

These are transport protocols that use acknowledgments and responses to establish a

virtual connection between sending and receiving stations e.g. Tep


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In this mode, it is possible to send a group of bits at the same time but the

amount varies from device to device. However, the longer the parallel link, the

worst the degradation of the electronic signals from the nodes furthest away. His

is the most common networking and data communication systems. Parallel

communications are limited to peripherals directly connected to the system and

communication between systems that are physically close to each other.

Synchronous and Asynchronous CommunicationSynchronous means that communications between two nodes are closely watched by

each other. All actions resulting in data transmission and general link conditions are

closely synchronized between two nodes. If data is to be transmitted or received, the

nodes are aware of it at most immediately and exchange based on ordered data rates.

Asynchronous communication means that the nodes dont necessarily know when

data is communicating to them nor how long the data message will be. A goodexample is a terminal on a system. The system does not know when the system

user will walk up to the terminal and start typing so it has to be ready all the time.


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TRANSMISSION MODES

There are three modes of data transmission namely:

1. Simplex2. Half duplex3. Full duplex

1. SIMPLEXThis is a simple method of communication as it sounds. In simplex communication, there is only

one way of communication eg A TV transmission. The main transmitter sends out the signal

(broad costs) but does not expect a reply as the receiving units cannot issue a reply back into the

transmitter.

2. HALF DUPLEXIn this mode, both the units communicate over the same medium but only one unit can send data

a time. When one is in the send mode, the other unit is in receiving mode.

3. FULL DUPLEXIn this mode, both the ends can send and receive a message at the same time e.g. Two people

talking at the same time and they are actually communicating achieves full duplex.

FUNCTIONS OF PACKETS IN DATA COMMUNICATION


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Data tends to exist as rather large files, however, networks cannot operate if computer put large

amount of data on the cable at one time.

WHY?

Large amount of data send as one large unit up the network and makes timelyinteractions and communication impossible because the computer is flooding the

cable with data.

Network reformat large chunks of data into smaller packets so that incase there isan error in transmission, only a small section of data could be affected, so only a

small amount of data must be resent making it relatively easy to recover from

errors.

In order for many users to transmit data quickly and easily across the network, data must be

broken into small manageable chunks calledpackets orframes.

Packets are basic units of network communication with data divided into packets. Individual

transmission is speeded up so that every computer on the network will have more opportunities

to transmit and receive data.

At the target (Receiving computer), packets are collected and reassembled in the proper order to

form the original data.

When network O/S at the sending computer breaks the data into packets, it adds specific control

to each frame. This makes it possible to:

Send the original deassembled data in small chunks. Reassemble the data in the proper order at its destination. Check the data for errors after it has been reassembled.

PACKET STRUCTURE

Packets may contain several types of data including:

1. Information i.e. Messages or files2. Certain types of computer control data and command such as service request.


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3. Session control codes such as error correction that indicates need for a retransmission.PACKET COMPONENT

All packets have certain components in common. This includes:

1. A source address _ identifying the sending computer.2. Data that is intended for transmission.3. Destinations address _ identifying the recipient.4. Instructions that tell the network components how to pass the data along.5. Information that tell the receiving computer how to connect the packet to other packets in

order to reassemble the complete data package.

6. Error checking roe all to ensure that data arrives intact.The components are grouped in three sections:


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b) HubThis is a connectivity component that provides a common connection among the computers in a

star configured network. During communication between the connected computers, a hub makesavailable the data message to all the ports and only the port connected to the destination

computer takes up the message.

Types of Hubs

There are two types of Hubs, namely:

Passive HubThis just provides common connectivity ie it simply organizes wiring and does not require

electric power.

Active/ Repeating Hub

Require electric power and are able to regenerate and retransmit network data.

c) SwitchesA switch is an efficient kind of hub that sends packets of data only to the port that is connected to

the packet recipient rather than sending the packets to all the ports like a simple hub does. It

creates a temperature dedicated path for data messages between the communicating nodes. This

is what is called Circuit Switching.

d) BridgeUnlike a repeater which passes all data between cable segments, a bridge links cable systemswhile passing only certain specified traffic between them. The bridge functions as a filter

separating traffic that can be isolated on either side of a LAN and only allows data to pass

through which ought to be seen on the other side.


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e) RoutersThese are devices to inter connect two or more separate network. Each LAN can be set without

the knowledge of the other and maintained and operated OS separate entities. Thus the primary

use of a router is to connect the LAN with the networks beyond the LANS domain.

Routers are intelligent devices. They can be programmed to allow data from particular users or

data of a particular nature to pass or not to pass through. Thus, they act as an effective Firewall

around LAN installation providing isolations for administrative purposes.

They are two types of Routers:

Static RoutersThis require an administrator to manually set up and configure the routing table and to specify

each route.

Dynamic RoutersThis do automatic discovery of routes and therefore they have a minimal amount of setup and

configuration. They are more sophisticated in that they examine information from other routers

and make packet by packet decision about how to send data across the network.

f) GatewaysThese are devices used to connect two dissimilar networks. Thus translation between two

networks takes place, making the gateway a slower and more expensive device than other

interconnecting relay devices. Gateway programs often do change the format of the message tomake it conform to the application program at the receiving end.

They are used to provide interface between IPX based LANS and the IP protocols of the internet

.

g) Brouter

These are capable of working as both router and bridges. They examine the packet type and route

those packets when they recognize the internal protocol, otherwise they act as bridges. Hence, a

brouter routes whenever it can and bridges whenever it cannot route.

NETWORK STANDARD


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These are rules of specification that vendors follow when manufacturing their equipment. The

standards guide each activity to the successful completion.

There are two primary set of standards used in network communication namely;

OSI Model(Open System Interconnection) IEEE Project 802 Model(Institute of Electrical and Electronic Engineers)

The OSI Model was developed by theInternational Standard Organitation (ISO) in the 1970s

to standard data communication. The OSI Model consisting of seven layers describe what

happens when a terminal talks to a computer or when a computer talks to another. This model

was designed to facilitate creating a system in which equipment from different vendors can

communicate. The IEE Project 802 Model was developed by the institute of Electrical and

Electronic engineers in 1980s

. It is a set of standards describing the cabling topology, electricaltopology, and access-scheme of network product.

1. OSI MODELThis model has a layered architecture which divides network communication into seven layers:

lication

Presentation

SessionTransport

Network

DataLinkPhysicalLayer


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LAYER 1/ PHYSICAL LAYER

This is responsible for the actual transmission of bit streams across a physical circuit. It allows

signals such as electrical, optical and radio signals to be exchanged among the communication

machines. The physical layer typically consists of hardware permanently installed in

communication devices. It also addresses the cables connectors, modems, NICs, repeaters etc all

used to permit machines to physically communicate. The physical layer has no mechanism for

determining the number of bit it transmits or receives. It is solely concerned with the physical

characteristics of electrical and optical signaling techniques.

LAYER 2/ DATA LINK LAYER

This is responsible for providing end to end integrity/ validity of data being transmitted. On the

transmit side, it is responsible for packing instructions and data into packets (A structure that

ensures that data can be successfully send across a LAN to its destination). The frame must

contain a mechanism to verify integrity of its contents upon delivery (Error checking

mechanism).

For guaranteed delivery, then:

The originating node must receive an acknowledgement for each frame received intact bythe destination node.

The destination node, prior to acknowledging receipt of a frame, must verify the integrityof that frames content.

Since anything can happen to frames transits, then the data link layer is responsible for detecting

and correcting such errors.

Devices found at the data link layer are:

Bridges NIC

LAYER 3/ NETWORK LAYER

This is responsible for establishing a route to be used between the originating and the destination

computer. This layers lacks any native transmission, error detection/ correction mechanism and

consequently. It is forced to rely upon end to end reliable transmission service of the data link


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layer. This is used to establish communication with the computer system that lie beyond the

LAN segment. It does so coz it has its own routing, addressing architecture which is separate and

distinct from layer two machine addressing. Thus, the use of network layer is optional for its

only required if computer systems reside on a different segment separately by a router.

LAYER 4/ TRANSPORT LAYER

This provides a similar service to the data link layer but it is capable of providing this service

beyond a LAN. It can detect packets that are discarded by routers and automatically generate a

retransmission request. This layer is also responsible for requesting packets that may have

arrived out of order. It is capable of identifying the original sequence of packets and must put

them back into that sequence before passing their contents to the session layer.

LAYER 5/ SESSION LAYER

This is responsible for the management of flow of communication during a connection between

two computer systems. It handles password recognition or verification, log on and log off

procedures, network monitoring and system usage. To accomplish the data flow management

task, the session layer defines three types of dialogs namely:

1. Two way simultaneous interaction where both systems can send and receive dataconcurrently (Full duplex)

2. Two way alternate interaction where systems take turns in sending and receiving data(Half duplex)

3. One way interaction where one system sends and receives the other one only receives(Simplex)

LAYER 6/ PRESENTATION LAYER

The 5 layer below this layer are all concerned with the orderly movement of strings of bits from

one system to another. It is the lowest layer interested in the meaning of those beats and deals

with the preservation of all contents of the data packets transmitted over the network. It is simply

responsible for transmission of data from the internal machine format of one processor into that

of another one.

APPLICATION LAYER


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This is the top most layer but despite its name, this layer doe not include user application, instead

it provides an interface between those application and the network services i.e. It is concerned

with all interchange between two application processes.

2. THE PROJECT 802 MODEL

In the late1970s, when LANs first began to emerge as potential tools, the IEEE realized there was

need to define certain LAN standards. To accomplish this task, the IEEE launched what came to

be known as project 802 named after the year and the month it began (1980 February). Project

802 defined network standards for the physical components of a network (NIC and cabling)

which are accounted form in the physical and data link layer of the OSI Model.

The 802 specifications defined the way the NIC accesses and transfers data over physical media.

This includes connecting, maintaining and disconnecting network devices.

IEE 802 CATEGORIES

The LAN standards 802 committees defined fall into 12 categories; this can be identified by

their 802 numbers as follows:

a) 802.1This specified standards for internetworking between WANs and MANs.

b) 802.2This defined the data link layer standard for telecommunication and all exchange between

systems.

It also divided the layer into two sub layers (Logical link control and Media Access Control

layer)

c) 802.3This established a standard for LANs that feature CSMA/ CD (Carrier Sense Multiple Access

Collision Detection) A.K.A Standard Ethernet Access Methodology.

d) 802.4


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Divide a physical layer standard for bus topology LAN with a Token passing media access

method.

e) 802.5Establish standard for token ring media access method (Token Ring LAN)

f) 802.6It Establishes standards for MANs.

g) 802.7Sets standards for broadband technical advisory group.

h) 802.8Sets standards for fibre optic technical advisory group.

i) 802.9Sets standards for integrated voice / data networks.

j) 802.10Sets standards for network security.

k) 802.11Sets standards for wireless networks.

l) 802.12Sets standards for demand priority access LANs.

FUNCTION OF ACCESS METHODS

The set of rules defining how a computer puts data onto the cable and how it takes data from the

cable is called anAccess Method.

TRAFFIC CONTROL ON THE CABLE

Multiple computers must share access to the cable. However, if two computers were to put data

onto the cable at the same time, the data packets from one computer will collide with data

packets from the other one and both sets of data packets will be destroyed. If data is to be


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sending over the network from one user to another or accessed from a server, there must be some

way for the data:

To access the cable without running into another data. To be accessed by the receiving computer with reasonable assurance that it has not been

destroyed in a data collision during transmission.

Access methods need to be consistent in the way they handle data. If different computers used

different access methods, the network would fail because some methods would dominate the

cable.

Access methods prevent simultaneous access to the cable by assuring that only one computer at a

time can put data on the network cable. Access methods keep the sending and the receiving of

network data an orderly process.

MAJOR ACCESS METHODS

There are three major ways of preventing simultaneous access of the cable:

1) Carrier Sense Multiple Access Method. With Collision Detection (CSMA/ CD) With Collision Avoidance (CSMA/CA)2) Token Passing Method.3) Demand Priority Method.

CSMA/ CD

With this method, each computer in the network including client and server check the cable for

network traffic.

A computer senses if the cable is free, there is no traffic on the cable, and then thecomputer can send data.

If there is data on the cable, no other computer may transmit until the data has reached itsdestination and the cable is free again.

CSMA/ CD therefore make some sense or listen to the cable (Carrier sense). There are usually

many computers on the network accepting to transmit data (Multiple Access) while at the same

time listening to see if any collisions occur that will make them wait before retransmitting

(Collision detection)

The collision detection capability is the parameter that imposes a distance limitation to CSMA/

CD. Dye to attenuation, the CD mechanism is not effective beyond 2500m. Segments cannot

sense signal beyond that distance, therefore may not be aware that the computer at the far end of


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the large network is transmitting. If more than one computer transmits data on the network, a

data collision will take place that will corrupt the data.

CMSA/ CD is also known as Contention Methodbecause computers on the network contend/

compete for opportunity to send data.

CSMA/ CA

In this method, each computer signals is intended to transmit before it actually transmits data. In

this way, computers sense when a collision may occur and may avoid transmission collision.

However, broadcasting the intend to transmit data increases the amount of traffic on the cable

and slows down network performance. Since CSMA/CA is a slower access method, its less

popular than CSMA/ CD.

TOKEN PASSING METHOD

A token is a predefined formation of bits that enable computers to place data onto the cable.

In token passing, a special type of a packet called a token circulates around a cable ring from

computer to computer. When any computer on the ring wants to send data across the network, it

must wait for a free token. When a free token is detected, the computer may take control of it.

The computer can now transmit data. While the token is in use by one computer, other computers

cannot transmit data because only one computer at a time can use the token. There is noconnection, no collision and no time spend while waiting for computer to resend token due to

network traffic on the cable. This method is also calledDeterministic Access Method.

DEMAND PRIORITY MEDIA ACCESS METHOD

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