kinds of Networks

We can classify networks in different ways

1. Based on transmission media: a. Wired (UTP, coaxial cables, fiber-optic cables)b. Wireless

2. Based on network size: a. LAN b. WAN c. MAN

3. Based on management method:a. Peer-to-peer b. Client/Server

4. Based on topology (connectivity): a. Bus, b. Star, c. Ring d. Mesh

Topologies

Topology is the physical layout of computers, cables, and other components on a network.

Many networks are a combination of the various topologies that we will look at:

· Bus· Star· Mesh· Ring

Bus Topologies A bus topology uses one cable to connect multiple computers. The cable is also called a trunk, a backbone, and a segment. T-connectors are used to connect to the cabled segment. They are called T-connectors because they are shaped like the letter T. Commonly coaxial cable is used in bus topologies.

Key component of a bus topology- All computers are connected on one linear cable.- There is the need for termination. To prevent packets from bouncing up and

down the cable, devices called terminators must be attached to both ends of the cable.

(A terminator absorbs an electronic signal and clears the cable so that other computers can send packets on the network. If there is no termination, the entire network fails.)

Only one computer at a time can transmit a packet on a bus topology. Computers in a bus topology listen to all traffic on the network but accept only

the packets that are addressed to them. Broadcast packets are an exception because all computers on the network

accept them. When a computer sends out a packet, it travels in both directions from the

computer. This means that the network is occupied until the destination computer accepts the packet.

The number of computers on a bus topology network has a major influence on the performance of the network.

A bus is a passive topology. The computers on a bus topology only listen or send data. They do not take data

and send it on or regenerate it. So if one computer on the network fails, the network is still up.

Advantages

a. One advantage of a bus topology is cost. The bus topology uses less cable than the star topology or the mesh topology.

b. The ease of installation. With the bus topology, you simply connect the workstation to the cable segment, or backbone.

c. If a computer fails, the network stays up.

Disadvantages

The main disadvantage of the bus topology is

a. The difficulty of troubleshooting. b. A cable break between computers on a bus topology would take the entire

network down. c. Only one computer at a time can transmit a packet on a bus topology.d. The heavier the traffic, the slower the network.e. The bus topology is not very scalable.

(Scalability is an important consideration with the dynamic world of networking. Being able to make changes easily within the size and layout of your network can be important in future productivity or downtime. )

Star Topologies

In a star topology, all computers are connected through one central hub or switch, as illustrated in Figure below.

Advantages

One advantage of a start topology is

a. the centralization of cabling. With a hub, if one link fails, the remaining workstations are not affected like they are with other topologies,

b. Centralizing network components can make an administrator’s life much easier in the long run.

c. it is also easy to add or change configurations with all the connections coming to a central point.

Disadvantages

On the flip side to this is the fact that

a. if the hub fails, the entire network, or a good portion of the network, comes down.

b. The more cost to connect each workstation to a centralized hub; you have to use much more cable than you do in a bus topology.

Mesh Topologies

A mesh topology is not very common in computer networking. The mesh topology is more commonly seen with something like the national

phone network. With the mesh topology, every workstation has a connection to every other

component of the network, as illustrated in Figure 1-4.

Computers in a mesh topology are all connected to every other component of the network

Advantages

The biggest advantage of a mesh topology is

a. Fault tolerance. If there is a break in a cable segment, traffic can be rerouted. This fault tolerance means that the network going down due to a cable fault is almost impossible

Disadvantages

A mesh topology is

a. very hard to administer and manage because of the numerous connections.b. High cost. With a large network, the amount of cable needed to connect and the

interfaces on the workstations would be very expensive.

Ring Topologies

In a ring topology, all computers are connected with a cable that loops around. As shown in Figure, the ring topology is a circle that has no start and no end. Terminators are not necessary in a ring topology. Signals travel in one direction on a ring while they are passed from one

computer to the next.

Each computer checks the packet for its destination and passes it on as a repeater would. If one of the computers fails, the entire ring network goes down.

Signals travel in one direction on a ring topology

Advantages

The nice thing about a ring topology is that

a. each computer has equal access to communicate on the network. (With bus and star topologies, only one workstation can communicate on the network at a time.)

b. The ring topology provides good performance for each workstation. This means that busier computers who send out a lot of information do not inhibit other computers from communicating.

Disadvantages

The biggest problem with a ring topology is that

a. if one computer fails or the cable link is broken the entire network could go down.

b. if you make a cabling change to the network or a workstation change, such as a move, the brief disconnection can interrupt or bring down the entire network.

Based on network size it can be classify as:

Local Area Network

A Local Area Network (LAN) is a network that is confined to a relatively small area.

It is generally limited to a geographic area such as a writing lab, school, or building.

A group of computers that share a common connection and are usually in a small area or even in the same building. For example an office or home network.

They are usually connected by Ethernet cables and have high speed connections.

If it was a wireless setup it would be called a WLAN, which would have a lower connection speed.

On a single LAN, computers and servers may be connected by cables or wirelessly.

Wireless access to a wired network is made possible by wireless access points (WAPs).

These WAP devices provide a bridge between computers and networks. A typical WAP might have the theoretical capacity to connect hundreds or even

thousands of wireless users to a network, although practical capacity might be far less.(DELETE)

Advantages Of LANs

Advantages of connecting computers in a LAN:

i. Workstations can share peripheral devices like printers. This is cheaper than buying a printer for every workstation.

ii. Workstations do not necessarily need their own hard disk or CD-ROM drives which make them cheaper to buy than stand-alone PCs.

iii. Users can save their work centrally on the network file server. This means that they can retrieve their work from any workstation on the network. They do not need to go back to the same workstation all the time.

iv. Users can communicate with each other and transfer data between workstations very easily. One copy of each application package such as a word processor, spreadsheet etc, can be loaded onto the file and shared by all users.

v. When a new version comes out, it only has to be loaded onto the server instead of onto every workstation.

Disadvantages Of LANsDisadvantages of connecting computers in a LAN:

i. Special security measures are needed to stop users from using programs and data that they should not have access to.

ii. Networks are difficult to set up and need to be maintained by skilled technicians.

iii. If the file server develops a serious fault, all the users are affected, rather than just one user in the case of a stand-alone machine.

iv. Wired and therefore more difficult to setup.

v. Drilling holes in wall, running cables in lofts etc, fitting sockets and redecorating. More expensive to set up.

vi. More time consuming to set up. vii. Not as flexible, can only use where there is a socket .

viii. Wired systems cannot be used in listed buildings.

Metropolitan Area Network (MAN) A Metropolitan Area Network (MAN) is normally composed of a number of

smaller Local Area Networks (LANs), which will typically be linked together using high-bandwidth technology such as fiber-optic cable. 

MAN (Metropolitan Area Network) falls in between the LAN and WAN. It therefore increases the efficiency of handling data while at the same time

saves the cost attached to establish a wide area network. MAN (Metropolitan Area Network) offers centralized management of data. It enables you to connect many fast LANs together. Telephone companies worldwide have facilitated the transfer of data with the

help of an underground optical fiber network. These optical fibers increase the efficiency and speed of data transfer. The

optical fibers enable you to access a speed of almost 1000mbps. This is a larger network that connects computer users in a particular geographic

area or region. For example a large university may have a network so large that it may be

classified as a MAN. The MAN network usually exists to provide connectivity to local ISPs, cable tv,

or large corporations. It is far larger than a LAN and smaller than a WAN.

Advantages of MANs

i. The biggest advantage of MANs is the bandwidth (potential speed) of the connecting links. 

ii. This means that resources (such as databases and files) shared on the network can be accessed extremely quickly. 

iii. Some installations allow multiple users to share the same high-speed Internet connection, thereby sharing the cost of the service and securing a better quality of service through collective bargaining and economies of scale.

Disadvantages of MANs

i. The key disadvantage of MANs is the cost of the cutting-edge technology employed. Also, this equipment generally has to be installed for the first

time, as the copper traditionally used for the phone network is generally considered to be too slow to be annexed for this purpose. 

ii. The cost is what inhibits the geographical reach of MANs, which is also another drawback.

Wide Area Network

Wide Area Networks (WANs) connect networks in larger geographic areas. Satellite uplinks may be used to connect this type of global network. A Wide Area Network (WAN) is a network that covers a broad area (i.e.,

any telecommunications network that links across metropolitan, regional, or national boundaries) using private or public network transports.

Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations.

In essence, this mode of telecommunication allows a business to effectively carry out its daily function regardless of location.

The Internet can be considered a WAN as well, and is used by businesses, governments, organizations, and individuals for almost any purpose imaginable.

Advantages of WANi. Covers a large geographical area so long distance businesses can connect on the

one networkii. Shares software and resources with connecting workstations

iii. 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).

iv. 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.

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

vi. Share information/files over a larger area.vii. large network cover.

Disadvantages of WAN

i. Are expensive and generally slow.ii. Need a good firewall to restrict outsiders from entering and disrupting the

network.

iii. Setting up a network can be an expensive and complicated experience. The bigger the network the more expensive it is.

iv. 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.

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

vi. Vulnerable to hackers or other outside threats.

Based on transmission media

Organizations rely heavily on the ability to share information throughout the

organization in an efficient and productive manner.

Computer networks have allowed for this technology and are now apart of

almost every business.

An organization has two options when it comes to setting up a network.

They can use a completely wired network, which uses networking cable to

connect computers, or they can use a wireless network, which uses radio

frequencies to connect computer.

Wireless networks have allowed organizations to become more mobile;

therefore, organizations are now using a combination of both wired and

wireless networks.

Wired Networks

Wired networks, also called Ethernet networks, are the most common type of

local area network (LAN) technology.

A wired network is simply a collection of two or more computers, printers,

and other devices linked by Ethernet cables.

Ethernet is the fastest wired network protocol, with connection speeds of 10

megabits per second (Mbps) to 100 Mbps or higher.

Wired networks can also be used as part of other wired and wireless

networks.

To connect a computer to a network with an Ethernet cable, the computer

must have an Ethernet adapter (sometimes called a network interface card, or

NIC).

Ethernet adapters can be internal (installed in a computer) or external

(housed in a separate case).

Some computers include a built-in Ethernet adapter port, which eliminates

the need for a separate adapter.

Advantages

I. Wired networks have existed for a long times, therefore have developed

exponentially over the recent years.

II. Improvements have been made in the fields of speed, security and reliability.

III. Wired networks offer the fastest transfer speed of all the networks.

IV. Gigabit Ethernet is currently the best choice for wired networks and provides

speeds of up to one gigabit per second. This is almost three times faster than

the best wireless connection available and almost ninety times faster than a

regular connection.

V. Wired networks consist of physical, fixed connects which are not prone to

interference and fluctuations in available bandwidth caused by factors such

as walls. Features such as shielding (adding an aluminium foil around the

wires) and twisting at different strengths help reduce interference.

VI. Wired networks also have a better security system than wireless networks.

The network itself is harder to connect to since it has to be physically

connected to through wires which can become a hassle when trying to hack

into it.

VII. It cannot be accessed from anywhere since the signals are not broadcasted.

Disadvantages

Wired networks mainly suffer the inverse of the advantages of a wireless network

system such as lack of mobility and greater cost.

Wireless network require greater resources such as cabling, switch/hub and

network cards to install and to maintain therefore the initial and long term costs

are much higher. It can also be a large loss when it has to be disassembled and

reinstalled since they wiring has to be completely overhauled and is normally

unusable after because of damage.

Wired networks can also be a hassle to install new components into because of all

the hardware required to do this. Cables and network cards are required to install

new computers to the system and wires need to be drawn from the switch to the

computers. The wiring can become messy and indistinguishable very quickly and

can become a potential safety hazard due to the risk of triping.

Wireless Networks

A wireless network, which uses high-frequency radio waves rather than wires

to communicate between nodes, is another option for home or business

networking. Individuals and organizations can use this option to expand their

existing wired network or to go completely wireless. Wireless allows for devices

to be shared without networking cable which increases mobility but decreases

range.

A major cause of interference with any radio signals are the materials in your

surroundings, especially metallic substances, which have a tendency to reflect

radio signals. Needless to say, the potential sources of metal around a home are

numerous things like metal studs, nails, building insulation with a foil backing and

even lead paint can all possibly reduce the quality of the wireless radio signal.

Materials with a high density, like concrete, tend to be harder for radio signals to

penetrate, absorbing more of the energy. Other devices utilizing the same

frequency can also result in interference with your wireless

On the other hand, many wireless networks can increase the range of the signal

by using many different types of hardware devices. A wireless extender can be

used to relay the radio frequency from one point to another without losing signal

strength. Even though this device extends the range of a wireless signal it has

some drawbacks. One drawback is that it extends the signal, but the transmission

speed will be slowed.

There are many benefits to a wireless network. The most important one is the

option to expand your current wired network to other areas of your organization

where it would otherwise not be cost effective or practical to do so. An

organization can also install a wireless network without physically disrupting the

current workplace or wired network. Wireless networks are far easier to move than

a wired network and adding users to an existing wireless network is easy.

Organizations opt for a wireless network in conference rooms, lobbies and offices

where adding to the existing wired network may be too expensive to do so.

Advantages

There are many advantages associated with installing a wireless network

compared to a wired network such as mobility, cost-effectiveness and adaptability.

Wireless Networking is relatively cheaper than wired Networks since they require

no cables between the computers as well as lower long term costs due to less

maintenance since there is less equipment. The reduction of cables also reduces

the trip hazard caused by cables running along the floor in most homes. Most

wireless network equipment is plug-and-play, which helps reduce the total cost

such as vendor installation and eliminates redundancy is case of a system crash.

Wireless Networking is also very mobile and versatile; it is adaptable to most

situations and requirements. Wireless networks can easily be set up and

dissembled, which is perfect for many people who are on temporary

worksites/homes or leased space. It can also provide networking in places where

regular wire cannot reach such as the backyard in a home situation. Access points

can be used to boost the wireless signal range if required. Since portable

workstations such as laptops have become popular, wireless networks can provide

quick and easy access to the internet and workspaces for students and teachers in

universities etc. It is also extremely easy to add other components onto this type of

network.

Disadvantages

Since wireless networking is a relatively new and contingent form of networking,

it is filled with it own hazards and problems such as unreliability and security.

Wireless networks have limited bandwidth, hence they cannot support Video

Teleconferencing(VTC). It is also limited in its expandability due to the lack of

available wireless spectrum for it to occupy.

Wireless Network can also be a security risk if not installed and maintained

properly. Wireless networks don’t require any physical components to connect up

to it such as wires, only a wireless adapter is required which significantly

increases the accessibility of the network to potential hackers. This scenario is

worsened if the network doesn’t contain a password since it can then be accessed

by anyone with ease.

Wireless networks also have an increased chance of jamming and interference due

to external factors such as fog and dust storms or when a flying object such as an

aeroplane passes over the field. When too many people in the same area use

wireless networks, the band of air that they transmit signals on can become

overloaded.

Based on management method

Local area networks can come in two forms (or architectures), peer-to-peer networking and server-based networking. Each have their advantages and disadvantages and may be used in different situations.Client-server arhitectureDevices on a server-based network are referred to as either clients or servers (the client-server arghitecture). Clients, such as computers, make requests for services like the use of a printer and servers handle the client requests. This is in contrast to a peer-to-peer network where the workstations act as both clients and servers. For example one computer in a peer-to-peer network may act as client and send a request for a text document stored on another computer whilst at the same time acting as a server by handling a request to print a document from a third computer.Peer-to-peer networkingIn peer-to-peer networking each computer has an equal status, each can use resources such as printers and scanners from other workstations and can commuicate with the other workstations without going through a server. Peer-to-peer networking is best used when there are only a small group of computers which do not require regular access to the data stored on the other work stations.The Advantages And Disadvantages of Peer-to-peer Network and client /server netwroksHere are some advantages and disadvantages of Peer-to-Peer NetworksAdvantages (Why) Disadvantages (Why)

Peer to Peer Networks are easy and simple to set up and only require a Hub or a Switch to connect all the computers together.

If you have not connected the computers together properly then there can be problems accessing certain files.

You can access any file on the computer as long as it is set to shared folder.

It doesn’t always work if you have many computers and works better with 2 – 8 computers.

The requirements for a Peer to Peer Network are that you have a 10 Base T Ethernet cable and an Ethernet hub/ switch. This is rather cheap than having a server.

Security is not good and you can set passwords for files that you don’t want people to access but apart from that the security is pretty poor.

The architecture of the lay out (How It Connects) is simple.

If one computer fails to work all the other computers connected to it continue to work.

Here are some advantages and disadvantages of Client/Server NetworksAdvantages (Why) Disadvantages (Why)

A Client Sever Can Be scaled up to many services that can also be used by multiple users.

A client server enables the roles and responsibilities of a computing system. This means that it can update all the computers connected to it. An example of this would be software updates or hardware updates.

When the server goes down or crashes. All the computers connected to it become unavailable to use.

All the data is stored on the servers, which generally have far greater security controls than most clients. Servers can better control access and resources, to guarantee that only those clients with the appropriate permissions may access and change data.

When everyone tries to do the same thing it takes a little while for the server to do certain tasks. An example of this would be everyone logging into there profile in an organisation or a college at the same time.

The security is a lot more advanced than a peer to peer network. You can have passwords to your won profile so that no one can access everything when they want. And the level off access range in different organisations

More expensive than a peer to peer network. You have to pay for start up cost.

Many mature client-server technologies are already available which were designed to ensure security, 'friendliness' of the user interface, and ease of use.

When you expand the server it starts to slow down due to the Bit rate per second.