COMPUTER NETWORK: A computer network is 1. a group of 2 or more computer systems 2. with other computing hardware devices 3. that are linked together through a communication medium 4. to facilitate communication between connected systems 5. and information and resource-sharing among a wide range of users.

Networks are used for the following key reasons: To facilitate communication via email, video conferencing, instant messaging, etc. To enable multiple users to share a single hardware device like a printer or scanner To enable file sharing across the network To allow for the sharing of software or operating programs on remote systems To make information easier to access and maintain among network users

There are many types of networks, including:

Local Area Networks (LAN) Personal Area Networks (PAN) Home Area Networks (HAN) Wide Area Networks (WAN) Campus Area Networks (CAN) Metropolitan Area Networks (MAN) Enterprise Private Networks Internetworks The Internet

Models of Network Computing: After we have all the required things for a network, a structure must be made in order to organize the way in which communication and sharing will occur. This structure is known as Model of Network Computing.

There are basically 3 models.1. Centralized computing model2. Distributed computing model3. Collaborative computing model

Centralized Computing Model:

The centralized computing model involves the following:

1. All processing takes place in the central, mainframe computer.2. Terminals are connected to the central computer and function only as input / output devices.3. Networks may be employed to interconnect two or more mainframe computers. 4. Terminals connect only to the mainframe, never to each other.

Distributed Computing Model:

Distributed computing involves the following:

1. Multiple computers are capable of operating independently.2. Tasks are completed locally on various computers.3. Networks enable the computers to exchange data and services but do not provide processing assistance.

Collaborative Computing Model

Collaborative computing involves the following:

1. Multiple computers cooperating to perform a task2. A network that enables the computers to exchange data and services3. Software designed to take advantage of the collaborative environment.

Computer Networking Models:

Computer network model defines the category in which a computer network can be grouped into.

Networks are divided into two broad categories:1. Peer to Peer Network model2. Client- Server Network Model

1. PEER TO PEER NETWORK MODEL

When nodes or workstations perform the same communication functions, they are referred to as peers.

In this network model, both server and client operations are performed by the same computer.

Each user administers his/her workstation and the resources in it.

In a peer-to-peer network, there are no dedicated servers, and there is no hierarchy among the computers.

All the computers are equal and therefore are known as peers.

Each computer functions as both a client and a server.

There is no administrator responsible for the entire network.

The user on each computer determines which data on that computer is shared on the network.

Security is also managed by the user of the devices. This model is not quite secure and is suited for a

small computer networks (with 10 computers or less) where users do not want to share files.

User’s files are decentralized – they are not stored in a single location.

Criteria for selecting PEER TO PEER NETWORK MODEL

Where ten or fewer users will be sharing resources. No server is available. Nobody has the time or knowledge to act as a network administrator. There is little or no concerns about security The organization and the network will experience only limited growth within the foreseeable future.

Advantages of using peer to peer network model They are easy to configure Computers communicate easily. They don’t require additional server hardware or software Users can manage their own resources. They don’t require a network administrator They reduce total cost of network setup.

Disadvantages of using peer to peer network model They provide a limited number of connections for shared resources. Computers with shared resources suffer from sluggish performance. They don’t allow for central management Users are responsible for managing resources. These resources include data in shared directories, printers, fax cards, and so on. They offer very poor security.

CLIENT SERVER NETWORK MODEL

This is a network model that offers centralized access to services and devices.

One computer plays the role of a server. It is the most common type of network architecture

today that provides centralized data storage, security, manning of applications and network administration.

Most servers operating system are Novel Netware, Windows NT, Apple talk, Linux, Banyan VINES etc...

Disadvantages of Client-Server modelCost: - More expensive in terms of hardware and network operating system. Complexity: - Experienced system administrators are required to manage the systems.

Dependence: - When server goes down, operations will cease across the network.

Advantages of Client-Server model1. Security: - All major server based systems

provides sophisticated security. 2. Administration: - Servers are centralized

making them easier to manage. 3. Stability: - Server based systems are designed

to support a wide range of organization sizes. Additional servers are added to increase capacity.

4. Flexibility - New technology can be easily integrated into the system.

5. Accessibility - Server can be accessed remotely and across multiple platforms.

6. Client server networks offer centralized backup where data can be stored in one server.

7. They are best suited for 10 or more users.

Network topology: It is the arrangement of the various elements (links,

nodes, etc.) of a computer. Essentially, it is the structure of a network, and may

be physical or logical. Physical topology refers to the placement of various

components of a network, including device location and cable installation.

Logical topology shows how data flows within a network, regardless of its physical design.

Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ between two networks, yet their topologies may be identical.

There are seven basic topologies

Point-to-point Bus Star Ring or circular Mesh Tree Hybrid

1. Point-to-Point Topology: The simplest topology is a permanent link between two endpoints.

2. Bus: Bus Topology is the simplest of network topologies.

In this type of topology, all the nodes (computers as well as servers) are connected to the single cable (called bus), by the help of interface (T) connectors.

This central cable is the backbone of the network and is known as Bus (thus the name).

Every workstation communicates with the other device through this Bus.

A signal from the source is broadcasted and it travels to all workstations connected to bus cable.

Although the message is broadcasted but only the intended recipient, whose IP address matches, accepts it.

If the IP address of machine doesn’t match with the intended address, machine discards the signal.

A terminator is added at ends of the central cable, to prevent bouncing of signals.

Advantages (benefits) of Bus Topology

1. It is easy to set-up and extend bus network.2. Cable length required for this topology is the least compared to other networks.3. Bus topology costs very less. Bus network is mostly used in small networks. Good for LAN.

Disadvantages (Drawbacks) of Linear Bus Topology

1)   There is a limit on central cable length and numberof nodes that can be connected.

2)   Dependency on central cable in this topology has itsdisadvantages. If the main cable (i.e. bus) encounterssome problem, whole network breaks down.

3)   Proper termination is required to dump signals. Useof terminators is must.

4)   It is difficult to detect and troubleshoot fault atindividual station.

5)   Maintenance costs can go higher with time.6)   Efficiency of Bus network reduces as the number of

devices connected to it increases.7)   It is not suitable for networks with heavy traffic. 8)   Security is very low because all the computers

receive the sent signal from the source.

3. Star Topology

In Star topology, all the components of network are connected to the central device called “hub” which may be a hub, a router or a switch.

Unlike Bus topology, where nodes were connected to central cable, here all the workstations are connected to central device with a point-to-point connection.

So it can be said that every computer is indirectly connected to every other node by the help of “hub”.

All the data on the star topology passes through the central device (hub) before reaching the intended destination.

Hub acts as a junction to connect different nodes present in Star Network, and at the same time it manages and controls whole of the network.

Depending on which central device is used, “hub” can act as repeater or signal booster.

Central device can also communicate with other hubs of different network.

Unshielded Twisted Pair (UTP) cable is used to connect workstations to central node.

Advantages of Star Topology

1. As compared to Bus topology it gives far much better performance, signals don’t necessarily get transmitted to all the workstations. A sent signal reaches the intended destination after passing through no more than 3-4 devices and 2-3 links. Performance of the network is dependent on the capacity of central hub.

2. Easy to connect new nodes or devices. In star topology new nodes can be added easily without affecting rest of the network. Similarly components can also be removed easily.

3. Centralized management. It helps in monitoring the network.

4. Failure of one node or link doesn’t affect the rest of network. At the same time it’s easy to detect the failure and troubleshoot it.

Disadvantages of Star Topology

1. Too much dependency on central device has its own drawbacks. If it fails whole network goes down.

2. The use of hub, a router or a switch as central device increases the overall cost of the network.

3. Performance and as well number of nodes which can be added in such topology is depended on capacity of central device.

4. Ring Topology

In Ring Topology, all the nodes are connected to each-other in such a way that they make a closed loop.

Each workstation is connected to two other components on either side, and it communicates with these two adjacent neighbors.

Data travels around the network, in one direction. Sending and receiving of data takes place by the help of TOKEN.

Advantages of Ring Topology

1. This type of network topology is very organized.

2. Each node gets to send the data when it receives an   empty token. This helps to reduces chances of collision.

3. In ring topology all the traffic flows in only one direction at very high speed.

4. Even when the load on the network increases, its performance is better than that of Bus topology.

5. There is no need for network server to control the connectivity between workstations.

6. Additional components do not affect the performance of network.

7. Each computer has equal access to resources.

Disadvantages of Ring Topology

1. Each packet of data must pass through all the computers between source and destination.

2. This makes it slower than Star topology. 3. If one workstation or port goes down,

the entire network gets affected. 4. Network is highly dependent on the wire

which connects different components. 5. Network cards are expensive as

compared to Ethernet cards and hubs.

5. Mesh Topology

In a mesh network topology, each of the network node, computer and other devices, are interconnected with one another.

Every node not only sends its own signals but also relays data from other nodes.

A true mesh topology is the one where every node is connected to every other node in the network.

This type of topology is very expensive as there are many redundant

connections, thus it is not mostly used in computer networks.

It is commonly used in wireless networks.

Flooding or routing technique is used in mesh topology.

Types of Mesh Network topologies:-

1) Full Mesh Topology: - In this, like a true mesh, each component is

connected to every other component. Even after considering the redundancy factor

and cost of this network, its main advantage is that the network traffic can be redirected to other nodes if one of the nodes goes down.

Full mesh topology is used only for backbone networks.

2) Partial Mesh Topology:- This is far more practical as compared to full

mesh topology. Here, some of the systems are connected in

similar fashion as in mesh topology while rests of the systems are only connected to 1 or 2 devices.

In partial mesh, the workstations are ‘indirectly’ connected to other devices.

This one is less costly and also reduces redundancy.

Advantages of Mesh topology

1. Data can be transmitted from different devices simultaneously. This topology can withstand high traffic.

2. Even if one of the components fails there is always an alternative present. So data transfer doesn’t get affected.

3. Expansion and modification in topology can be done without disrupting other nodes.

Disadvantages of Mesh topology

1. There are high chances of redundancy in many of the network connections.

2. Overall cost of this network is way too high as compared to other network topologies.

3. Set-up and maintenance of this topology is very difficult.

4. Administration of the network is tough.

6. Tree Topology

Tree Topology integrates the characteristics of Star and Bus Topology.

In Tree Topology, the number of Star networks is connected using Bus.

The main cable seems like a main stem of a tree, and other star networks as the branches.

It is also called Expanded Star Topology.

Ethernet protocol is commonly used in this type of topology.

Advantages of Tree Topology

1. It is an extension of Star and bus Topologies, so in networks where these topologies can't be implemented individually for reasons related to scalability, tree topology is the best alternative.

2. Expansion of Network is possible and easy.

3. Here, we divide the whole network into segments (star networks), which can be easily managed and maintained.

4. Error detection and correction is easy.5. Each segment is provided with dedicated

point-to-point wiring to the central hub.6. If one segment is damaged, other

segments are not affected.

Disadvantages of Tree Topology

1. Because of its basic structure, tree topology, relies heavily on the main bus

cable, if it breaks whole network is crippled.

2. As more and more nodes and segments are added, the maintenance becomes difficult.

3. Scalability of the network depends on the type of cable used.

7. Hybrid Topology

In this type of topology we integrate two or more different topologies to form a new topology which has good points, as well as weaknesses, of all the constituent basic topologies rather than having characteristics of one specific topology.

This combination of topologies is done according to the requirements of the organization.

Advantages of Hybrid Network Topology1. Reliable: Unlike other networks, fault detection

and troubleshooting is easy in this type of topology. The part in which fault is detected can be isolated from the rest of network and required corrective measures can be taken, without affecting the functioning of rest of the network.

2. Scalable: It’s easy to increase the size of network by adding new components, without disturbing existing architecture.

3. Flexible: Hybrid Network can be designed according to the requirements of the organization and by optimizing the available resources. Special care can be given to nodes where traffic is high as well as where chances of fault are high.

4. Effective: Hybrid topology is the combination of two or more topologies, so we can design it in such a way that strengths of constituent topologies are maximized while there weaknesses are neutralized. For example we saw Ring Topology has good data reliability (achieved by use of tokens) and Star topology has high tolerance capability (as each node is not directly connected to other but through central device), so these two can be used effectively in hybrid star-ring topology.

Disadvantages of Hybrid Topology

1. Complexity of Design: One of the biggest drawbacks of hybrid topology is its design. It’s not easy to design this type of architecture and it’s a tough job for designers. Configuration and installation process needs to be very efficient.

2. Costly Hub: The hubs used to connect two distinct networks, are very expensive. These hubs are different from usual hubs as they need to be intelligent enough to work with different architectures and should be function even if a part of network is down.

3. Costly Infrastructure: As hybrid architectures are usually larger in scale, they require a lot of cables; cooling systems, sophisticate network devices, etc.

Token Ring Network A Token Ring network is a local area

network (LAN) in which all computers are connected in a ring or star topology

A bit- or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time.

How it works?1. Empty information frames are

continuously circulated on the ring.2. When a computer has a message to

send, it inserts a token in an empty frame (this may consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame.

3. The frame is then examined by each successive workstation. If the workstation sees that it is the destination for the message, it copies the message from the frame and changes the token back to 0.

4. When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame.

5. The frame continues to circulate as an "empty" frame, ready to be taken by a workstation when it has a message to send.

Data Frame Format in Token Ring Network

Frame field Description

Start delimiter Indicates start of the frame

Access control indicates the frame's priority and whether it is a token or a data frame

Frame control Contains either Media Access Control information for all computers or "end station" information for only one computer

Frame field Description

Destination indicates the address of the address computer to receive the frame

Source address indicates the computer that sent the frame

Data Contains the data being sent

Frame check Contains CRC error-checking sequence information

End delimiter indicates the end of the frame

Frame status tells whether the frame was recognized, copied, or whether the destination address was available

In a Token Ring network, the hub is known by several names as follows:

MAU (Multistation Access Unit). MSAU (MultiStation Access Unit). SMAU (Smart Multistation Access Unit).

LOCAL AREA NETWORK (LAN)A local area network (LAN) is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building using any communication medium.

FEATURES OF LAN 1. Limited Geographic Limits:- A LAN is designed

for a small area. Generally it spans a single office, work group floor in a building, or in a campus etc. LAN uses different protocols or rules for information transmission.

2. Limited No. of Users: - Most LAN supports I number of users usually around five or ten. More users can be supported by connecting different

Start Delimiter

Access Control

Destination Address

Source Address

Data

Frame check

SequenceEnd

Delimiter

Frame Status

Frame Control

LANs together, which gives better results than making one; by network of the nature of MAN.

3. Reliability & Stability: - LANS tend to be very reliable failures on a LAN are mostly due to wrong or improper installation and monitoring. Software that comes along with a LAN provides a number of useful programs like error-detection, prevention of transmission loss and excellent security features.

4. Flexibility: - Major development in LANs today is flexibility they offer. Earlier versions would support only one type of desktop computers. Today's advanced LANs however can support different types of computers. The flexibility also extends to operating systems & storage media.

5. Expandable: - Most LANs can be expanded easily. More nodes (Terminal) can be added. Although, this depends on design of cabling plan (Topology) also. Also LANs can have more servers oil same network and a user at a terminal can connect to one or many servers and work comfortably.

6. Security & Administration:- A LAN administrator is one who supervises the operation of a LAN. He takes care of tasks like adding or deleting users, creating passwords providing authorizations and other resources like printers and backing up data. All these tasks can be performed without much difficulty since both hardware and software are quite easy to manage.

Advantages of LAN1. Easy to share devices (printers, scanners,

external drives)2. Easy to share data (homework, pictures.)3. Build a complex enough one and you may get

enough experience to get a new job.4. Cost of LAN Setup is low.Disadvantages of LAN1. Power - a good LAN is required to be on all

the times.2. Security - each computer and device become

another point of entry for undesirables.3. Upkeep - when things go wrong or the

software gets updated.4. Frustration if having a problem setting up.5. A lot of times a network shares one Internet

connection - if all computers running at once, can reduce speed for each.

6. Area covered is limited.Metropolitan Area Network (MAN)

1. A metropolitan area network (MAN) is a computer network that usually connects a city or a large campus.

2. A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links

3. It provides up-link services to wide area networks (or WAN) and the Internet.

4. Its geographic scope falls between a WAN and LAN.

FEATURES OF MANThe network size falls intermediate between

LANs and WANs. A MAN typically covers an area of between 5 and 50 km diameter. Many MANs cover an area the size of a city.

The MAN, its communications links and equipment are generally owned by either a group of users or by a single network provider who sells the service to the users.

A MAN often acts as a high speed network to allow sharing of regional resources (similar to a large LAN).

It is also frequently used to provide a shared connection to other networks using a link to a WAN.

Advantages of MAN1. It provides a good back bone for a large network and provides greater access to WAN. 2. A Man usually encompasses several blocks of a city or an entire city.3. Covers more area than a LAN.

Disadvantages of MAN1) More cable required for a MAN connection from one place to another

2) the large the network becomes difficult to mange3) it is difficult to make the system secure from hackers and industrial geographical regions.

WIDE AREA NETWORK (WAN)Wide Area Network (WAN) is a telecommunication

network that covers a broad area i.e., any network that links across metropolitan, regional, or national boundaries.

FEATURES OF WAN

1. WAN may use a similar topology as a LAN, but it uses different protocols to send packets over a wide distance. 2. A WAN is much more spanned in the distance it can send information to.3. A WAN uses point-to-point connections over a wide

distance. Advantages Of WAN Covers a large geographical area so long distance

businesses can connect on the one network Shares software and resources with connecting

workstations Messages can be sent very quickly to anyone else

on the network. These messages can have pictures, sounds, or data included with them (called attachments).

Expensive things (such as printers or phone lines to the internet) can be shared by all the computers on the network without having to buy a different peripheral for each computer.

Everyone on the network can use the same data. This avoids problems where some users may have older information than others.

Share information/files over a larger area large network cover

Disadvantages Of WAN Are expensive and generally slow Need a good firewall to restrict outsiders from

entering and disrupting the network Setting up a network can be an expensive and

complicated experience. The bigger the network the more expensive it is.

Security is a real issue when many different people

have the ability to use information from other computers. Protection against hackers and viruses adds more complexity and expense.

Once set up, maintaining a network is a full-time job which requires network supervisors and technicians to be employed.

Information may not meet local needs or interests Vulnerable to hackers or other outside threats.