MTN 2013 Computer Network Technology

Chapter 2 Computer Network

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Outline

1. Introduction to Networking2. Network Configuration3. Network Criteria4. Transmission Mode5. Network Topology

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1. Introduction to Networking

• What is network?• A network consists of 2 or more computers

connected together, and they can communicate and share resources (i.e. information)

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Why Networking?

• Sharing information — i.e. data communicationDo you prefer these?

Or this?

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Networking• Sharing hardware or software

• Centralize administration and support

• E.g. print document

• E.g. Internet-based, so everyone can access the same administrative or support application from their PCs

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How many kinds of Networks?

• Depending on one’s perspective, we can classify networks in different ways

• Based on transmission media: Wired (UTP, coaxial cables, fiber-optic cables) and Wireless

• Based on network size: LAN and WAN (and MAN)• Based on management method: Peer-to-peer and

Client/Server• Based on topology (connectivity): Bus, Star, Ring …

::

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2. Network Configuration

• Form/arrangement/setup of network parts/elements.

• Ways that computers can be connected together to form networks.

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3. Network Criteria• To be considered effective and efficient, a network must meet a number of

criteria. The most important of these are performance, reliability, and security.

Performance

Number of user

Type of transmission

Type of connection Hardware Software

Reliability Frequency of failure

Catastrophe

Security

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Performance

• Performance can be measured in many ways, including transit time and response time.

• Transit time is the amount of time required for a message to travel from one device to another.

• Response time is the elapsed time between an enquiry and a response.

• The performance of a network depends on a number of factors, including the number of users, the type of transmission medium, the capabilities of the connected hardware, and the efficiency of the software.

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Number of User

• Having a large number of concurrent users can slow response time in a network not designed to coordinate heavy traffic loads.

• The design of a given network is based on an assessment of the average number of users that will be communicating at any one time.

• In peak load periods, however, the actual number of users can exceed the average and thereby decrease performance.

• How a network responds to loading is measure of its performance.

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Type of Connection

– Point to Point - single transmitter and receiver

– Multipoint - multiple recipients of single transmission

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Type of Transmission

• Unicast, multicast, broadcast• Transmission medium

– The medium defines the speed at which data can travel through a connection. Today’s networks are moving to faster and faster transmission media, such as fiber-optic cabling, a medium that can carry data at only 10 megabits per second. However, the speed of light imposes an upper bound on the data rate.

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Hardware

• The types of hardware included in a network affect both the speed and capacity of transmission. A higher-speed computer with greater storage capacity provides better performance.

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Software• The software used to process data at the sender,

receiver, and intermediate nodes also affects network performance.

• Moving a message from node to node through a network requires processing to transform the raw data into transmittable signals, to route these signals to the proper destination, to ensure error-free delivery, and to recast the signals into a form the receiver can use.

• The software that provides these services affects both the speed and the reliability of a network link.

• Well-designed software can speed the process and make transmission more effective and efficient.

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Reliability

• In addition to accuracy of delivery, network reliability is measured frequency of failure, the time it takes a link to recover from a failure, and the network’s robustness in a catastrophe.

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Frequency of Failure

• All networks fail occasionally. • A network that fails often, however, is of little

value to a user.• Recovery time of a network after a failure:

How long does it take to restore service? A network that recovers quickly is more useful than one that does not.

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Catastrophe

• Networks must be protected from catastrophic events such as fire, earthquake, or theft.

• One protection against unforeseen damage is a reliable system to back up network software.

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Security • Network security issues include protecting data from unauthorized access and

viruses.

Unauthorized access:

For a network to be useful, sensitive data must be protected from unauthorized access. Protection can be accomplished at a number of levels. At the lowest level are user identification codes and passwords. At a higher level are encryption techniques. In these mechanisms, data are systematically altered in such a way that if an unauthorized user intercepts them, they will be unintelligible.

Viruses:

Because a network is accessible from many points, it can be susceptible to computer viruses. A virus is an illicitly introduced code that damages the system. A good network is protected from viruses by hardware and software designed specifically for that purpose.

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4. Transmission Mode• Defines the direction of data flow between two

linked devices. • The manner or way in which data is transmitted

from one place to another is called data transmission mode.

• There are three ways for transmitting data from one location to another. These are: – Simplex– Half duplex– Full duplex

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Simplex Mode• The communication can take place in only one direction. • A terminal can only send data and cannot receive it or it can only

receive data but cannot send it.• It means that in this mode communication is uni-directional. • Today, this mode of data communication is not popular, because most

of the modem communications require two-way exchange of data. • However, this mode of communication is used in business field at

certain point-of-sale terminals in which sales data is entered without a corresponding reply.

• The other examples of simplex communication modes are radio and TV transmissions.

• Computer system, the keyboard, monitor and printer are examples of simplex devices.

• The keyboard can only be used to enter data into computer, while monitor and printer can only accept (display/print) output.

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Half/Semi Duplex Mode• The communication can take place in both directions, but only

in one direction at a time. • In this mode, data is sent and received alternatively. It is like a

one-lane bridge where two-way traffic must give way in order to cross the other.

• In half-duplex mode, at a time only one end transmits data while other end receives.

• In addition, it is possible to perform error detection and request the sender to re-transmit information.

• The Internet browsing is an example of half duplex. When we issue a request to download a web document, then that document is downloaded and displayed before we issue another request.

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Full Duplex Mode

• The communication can take place in both directions simultaneously, i.e. at the same time on the same channel.

• It is the fastest directional mode of communication. • Example of this mode is conversation of the persons

through telephone. • This type of communication is similar to automobile

traffic on a two-lane road.• The telephone communication system is an example

of full duplex communication mode.

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5. Network Topology

• The network topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions.

Bus Topology

Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable.

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Bus Topology

• Advantages– It is easy to handle

and implement. – It is best suited for

small networks.

• Disadvantages– The cable length is

limited. This limits the number of stations that can be connected.

– This network topology can perform well only for a limited number of nodes.

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Star & Tree Topology

The star topology is the most commonly used architecture in Ethernet LANs. When installed, the star topology resembles spokes in a bicycle wheel.Larger networks use the extended star topology also called tree topology. When used with network devices that filter frames or packets, like bridges, switches, and routers, this topology significantly reduces the traffic on the wires by sending packets only to the wires of the destination host.

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Star Topology

• Advantages– Due to its centralized

nature, the topology offers simplicity of operation.

– It also achieves an isolation of each device in the network.

• Disadvantages– The network operation

depends on the functioning of the central hub.

– Hence, the failure of the central hub leads to the failure of the entire network.

Hub

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Tree Topology

• A tree topology is a hierarchical computer network that is a combination of star and bus topologies.

• Allows for multiple hubs to exist on a network which act as roots for terminals connected to them.

• This tree like branched structure of networks provides high scalability.

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Tree Topology• Advantages

– It is the best topology for a large computer network for which a star topology or ring topology are unsuitable due to the sheer scale of the entire network.

– Tree topology divides the whole network into parts that are more easily manageable. Tree topology makes it possible to have a point to point network.

– All computers have access to their immediate neighbors in the network and also the central hub. This kind of network makes it possible for multiple network devices to be connected with the central hub.

– It overcomes the limitation of star network topology, which has a limitation of hub connection points and the broadcast traffic induced limitation of a bus network topology. A tree network provides enough room for future expansion of a network.

• Disadvantages- Dependence of the entire network on one central hub is a point of vulnerability for this topology. A failure of the central hub or failure of the main data trunk cable, can cripple the whole network.- With increase in size beyond a point, the management becomes difficult.

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Ring Topology

A frame travels around the ring, stopping at each node. If a node wants to transmit data, it adds the data as well as the destination address to the frame.

The frame then continues around the ring until it finds the destination node, which takes the data out of the frame.

Single ring – All the devices on the network share a single cable

Dual ring – The dual ring topology allows data to be sent in both directions.

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Ring Topology

• Advantages– The data being

transmitted between two nodes passes through all the intermediate nodes.

– A central server is not required for the management of this topology.

• Disadvantages– The failure of a single

node of the network can cause the entire network to fail.

– The movement or changes made to network nodes affects the performance of the entire network.

Mesh Topology

The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions. Implementing the mesh topology is expensive and difficult.

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Mesh Topology

• Advantages– The arrangement of

the network nodes is such that it is possible to transmit data from one node to many other nodes at the same time.

• Disadvantages– The arrangement

wherein every network node is connected to every other node of the network, many of the connections serve no major purpose.

– This leads to the redundancy of many of the network connections.

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Q&A

END