CHAPTER 3 COMPUTER NETWORKING

COMPUTER NETWORKING

Definition of computer network:

A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users. Networks are commonly categorized based on their characteristics.

There are so many different types of computer networks in existence, it can be hard to understand the differences between them, particularly the ones with very similar-sounding names. This lesson explains the structures and functions of some of the most popular computer networks.

Types of Networks

There are several different types of computer networks. Computer networks can be characterized by their size as well as their purpose.

The size of a network can be expressed by the geographic area they occupy and the number of computers that are part of the network. Networks can cover anything from a handful of devices within a single room to millions of devices spread across the entire globe.

Some of the different networks based on size are:

1.      Personal area network, or PAN

2.      Local area network, or LAN

3.      Metropolitan area network, or MAN

4.      Wide area network, or WAN

In terms of purpose, many networks can be considered general purpose, which means they are used for everything from sending files to a printer to accessing the Internet. Some types of networks, however, serve a very particular purpose. Some of the different networks based on their main purpose are:

1.      Storage area network, or SAN

2.      Enterprise private network, or EPN

3.      Virtual private network, or VPN

Let's look at each of these in a bit more detail.

Personal Area Network

A personal area network, or PAN, is a computer network organized around an individual person within a single building. This could be inside a small office or residence. A typical PAN would include one or more computers, telephones, peripheral devices, video game consoles and other personal entertainment devices.

If multiple individuals use the same network within a residence, the network is sometimes referred to as a home area network, or HAN. In a very typical setup, a residence will have a single wired Internet connection connected to a modem. This modem then provides both wired and wireless connections for multiple devices. The network is typically managed from a single computer but can be accessed from any device.

This type of network provides great flexibility. For example, it allows you to:

·         Send a document to the printer in the office upstairs while you are sitting on the couch with your laptop.

·         Upload the photo from your cell phone to your desktop computer.

·         Watch movies from an online streaming service to your TV.

·         If this sounds familiar to you, you likely have a PAN in your house without having called it by its name.

Local Area Network

A local area network, or LAN, consists of a computer network at a single site, typically an individual office building. A LAN is very useful for sharing resources, such as data storage and printers. LANs can be built with relatively inexpensive hardware, such as hubs, network adapters and Ethernet cables.

The smallest LAN may only use two computers, while larger LANs can accommodate thousands of computers. A LAN typically relies mostly on wired connections for increased speed and security, but wireless connections can also be part of a LAN. High speed and relatively low cost are the defining characteristics of LANs.

LANs are typically used for single sites where people need to share resources among themselves but not with the rest of the outside world. Think of an office building where everybody should be able to access files on a central server or be able to print a document to one or more central printers. Those tasks should be easy for everybody working in the same office, but you would not want somebody just walking outside to be able to send a document to the printer from their cell phone! If a local area network, or LAN, is entirely wireless, it is referred to as a wireless local area network, or WLAN.

Metropolitan Area Network

A metropolitan area network, or MAN, consists of a computer network across an entire city, college campus or small region. A MAN is larger than a LAN, which is typically limited to a single building or site. Depending on the configuration, this type of network can cover an area from several miles to tens of miles. A MAN is often used to connect several LANs together to form a bigger network. When this type of network is specifically designed for a college campus, it is sometimes referred to as a campus area network, or CAN.

Wide Area Network

A wide area network, or WAN, occupies a very large area, such as an entire country or the entire world. A WAN can contain multiple smaller networks, such as LANs or MANs. The Internet is the best-known example of a public WAN.

Network Components

1. Hots/End Nodes

·         refers to the data source and the data destination

·         exp: personal computer, terminals, workstation, automatic teller machine.

    2. Transmission Media

·         for transmitting data and control signal.

·         responsible for sending electric or signal through specific media.

                                         

Bounded (Wired)	Unbounded(Wireless)
Twisted pair wire	Radio Signals
Coaxial cable	Satellite Transmission
Fiber optic cable	Infrared transmission

  3. Network Electronic Device

·         responsible to control data from source to destination.

·         to connect multiple network together or to connect computer or network to the internet

·         exp: bridges, routers, multiplexers, switches, hubs, gateways, front end processors.

  4. Software/Application

·         the application at the end nodes normally involve technique and protocols.

·         protocol determines the rule and procedure to send data, terminate data, interpret data, present data and control mistakes.

·         software in the network functions to ensure data is delivered at perspective destination.

·         to control data transmission.

    5. Network Architecture Standards & Protocols

Blueprint of standard that define:

·         How devices in a network typically connect.

·         How the devices can communicate?

·         to ensure interoperability between various devices and equipment made by different                            vendors.

·         to enable devices made by different companies to work or communicate with each other.

·         exp: TCP/IP, Ethernet (802.3), Wi-Fi (802.11), WiMAX etc.

Network Topology

Computers in a network have to be connected in some logical manner. The layout pattern of the interconnections between computers in a network is called network topology. You can think of topology as the virtual shape or structure of the network. Network topology is also referred to as 'network architecture.'

Devices on the network are referred to as 'nodes.' The most common nodes are computers and peripheral devices. Network topology is illustrated by showing these nodes and their connections using cables. There are a number of different types of network topologies, including point-to-point, bus, star, ring, mesh, tree and hybrid. Let's review these main types.

Bus

Bus topology uses one main cable to which all nodes are directly connected. The main cable acts as a backbone for the network. One of the computers in the network typically acts as the computer server. The first advantage of bus topology is that it is easy to connect a computer or peripheral device. The second advantage is that the cable requirements are relatively small, resulting in lower cost.

One of the disadvantages is that if the main cable breaks, the entire network goes down. This type of network is also difficult to troubleshoot. For these reasons, this type of topology is not used for large networks, such as those covering an entire building.

Star

In star topology, each computer is connected to a central hub using a point-to-point connection. The central hub can be a computer server that manages the network, or it can be a much simpler device that only makes the connections between computers over the network possible.

Star topology is very popular because the startup costs are low. It is also easy to add new nodes to the network. The network is robust in the sense that if one connection between a computer and the hub fails, the other connections remain intact. If the central hub fails, however, the entire network goes down. It also requires more cable than bus topology and is, therefore, more expensive.

Ring

In ring topology, the computers in the network are connected in a circular fashion, and the data travels in one direction. Each computer is directly connected to the next computer, forming a single pathway for signals through the network. This type of network is easy to install and manage.

If there's a problem in the network, it is easy to pinpoint which connection is defective. It is also good for handling high-volume traffic over long distances since every computer can act as a booster of the signal. On the downside, adding computers to this type of network is more cumbersome, and if one single computer fails, the entire network goes down.

Logical Topology

Logical topology (or signal topology) describes the access of devices to transmission medium. We have two kinds of logical topologies:

·         Shared media topology.

·         Token-based topology.

CSMA/CD

In case of Ethernet network CSMA/CD (Carrier Sense Multiple Access/Collision Detection) is the most popular protocol. It detects if the connection is able to send a signal and reacts on possible collisions.

Before the signal is sent, devices check if the transmission medium is busy or not. If it is busy, the device will wait for a randomly selected time and try again. When the device knows that the medium is not busy, it sends the signal. However, sometimes two devices start transmission, exactly,  at the same time. Then the whole transmission is stopped. Again, nodes select random amount of time and try to send the signal again.

This logical topology method is used in Ethernet networks using bus, star, three or mesh topology.

Token

Access to the transmission medium is provided by passing the token. Token is a bunch of data which contains the control information. If the device recognises the data, the transmission is allowed. Each network has only one access token passed between nodes. Data travels between nodes until it finds the receiver. Receiver sends information about receiving data to the broadcaster.

This logical topology is used in Token Ring network and FDDI.

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This week I learned about a computer network . there are a variety of computer network WAN, MAN, LAN, PAN. Other than that I can distinguish each of these networks. In summary WAN are commonly used in a country and the distance is greater. MAN is also used often in the city and is smaller, LAN is used in the building and the PAN in the smallest area. After that, I have studied the network topology, in the title of this new I know the various topologies used in networks such as BUS, STAR, and many others . For a better understanding please see video above.