A network is a set of devices often referred to as nodes connected by media links. A node can be as computer, printer or any other device capable of sending and receiving data guaranteed by other nodes on the network. The links connecting the devices are often called communication channels.
- Distributed Processing: –
Network uses distributed processing in which a task is divided among multiple computers instead of a single large machine being responsible for all aspects of a process, each separate computer called work station handles a subset.
Following are the advantages of distributed processing.
1. Security / Encapsulation: –
A system designer can limit kind of interactions that a given used can have with the entire system.
A bank can allow users to access their own accounts through an Automated Teller Machine (ATM) without allowing then to access the bank’s entire database.
2. Distributed Database: –
No one needs to provide storage capacity for the entire database.
WWW gives users access to information that may be actually stored & maintained & manipulated anywhere on the internet.
3. Faster Problem Solving: –
Multiple computers working on parts of a problem concurrently often can solve the problem faster then a single machine working alone.
4. Security Through Redundancy: –
Multiple computers running the same program at the same time can provide security through redundancy.
5. Collaborative Processing: –
Both multiple computers & multiple users may interact on a task, this is called collaborative processing.
Network Criteria: –
To be considered effective & efficient, a network must meet a number of criteria. The most important of those are performance, reliability and security.
- Performance: –
Performance can be measured in many ways, including transmit time & response time. Transmit time is the amount of time required for a message to travel from one device to another response time is the clasped time between on inquiry & a response.
The performance of a network depends on a number of factors.
- Number of Users: –
Having a large number of concurrent users can slow response time in a network that is not designed to co – ordinate heavy traffic loads. The designed of such network is based on an assessment of the average number of users that will be communicating at any one time. However, the number of users can exceed the average & there by decrease performance.
- Type of Transmission Medium: –
The medium defines data rate that is the speed at which data can travel through a connection. A medium that can carry data at 100 MB per seconds is 10 times more powerful than a medium that can carry data at only 10 MBPS.
- Hardware: –
The types of hardware included in a network affect both the speed & capacity of transmission. A higher speed computer with grater storage capacity provides better performance.
- Software: –
The software used to process data at the sender, receiver & intermediate nodes also affects network performance. Well designed software can speed the process & make transmission more effective & efficient.
- Reliability: –
In addition to accuracy of delivery, network reliability is measured by frequency of failure, the time it takes a link to recover from a failure & the networks robustness in a catastrophe.
- Frequency of Failure: –
All network fail occasionally, a network that fails often however, is of little value to a user.
- Recovery Time of Failure After Failure: –
How long does it take to restore service decides how useful the network is!
- Catastrophe: –
Network must be protected from catastrophic events, such as fire, earthquake or one protection against unforeseen damage is a reliable system to back up network software.
- Security: –
Network security issue includes protecting data from unauthorized access & viruses.
A protocol is a set of rules that given data communication. A protocol defines what is communicated, how it is communicated & when it is communicated.
In computer networks communication occur between entities and different systems. An entity is anything capable of sending or receiving information. A system is physical object that contains one or more entities, but two entities can not just send bit streams to each other & expect to be understood, for communication to occur the entities must agree on a protocol. The key elements of a protocol are.
- Syntax: –
It refers to the structure or format of the data meaning the order in which they are presented.
- Semantics: –
It refers to the meaning of each section of bits that is how a particular pattern is to be interpreted & what action is to be taken based on that interpretation.
- Timing: –
It refers to two characteristics.
- When data should be sent.
- How fast they can be sent.
Line Configuration: –
Line configuration refers to the way two or more communication devices are attached to a link. A link is the physical communication pathway that transfers data from one device to another for the purpose of visualization; it is simplest to imagine any link as a line drawn between two points. For communication to occur, two devices must be connected in some way to same link at the same time. There are two possible line configurations.
- Point-to-Point: –
A point-to-point line configuration provides a dedicated link between two devices. The entire capacity of the channel is reserved for transmission between those two devices. Most point-to-points line configurations use an actual length of wire or cable to connect the two ends, but other options such as microwaves or satellite links are also possible. When you change television channels by infrared remote control, you are establishing a point-to-point line configuration between remote control and television control system.
- Multipoint: –
A multipoint also called multi drop line configuration is one which more than two specific devices share a single link. In a multipoint environment, the capacity of a channel is shared, either specially or temporarily. If several devices can use the link simultaneously, it is a specially shared line configuration. If users must take turn, it is a time shared line configuration.
Categories of Network: –
There are generally three primary categories of network. Into which category a network falls is determined by its size, ownership, distance it covers and its physical architecture.
Following are the categories of network.
- Local Area Network (LAN): –
A local area network is usually privately owned & links the devices in a single office, building or campus. Depending on the needs of an organization & the type of technology used a local area network can be as simple as for pc and printer, or it can extend throughout a company & include voice, sound & video to a few kilometers.
Local area networks are designed to allow resources to be shared between pc and workstations. One of the computers may be given a large capacity disk drive & become a server to the other clients. Software can be stored on this central server & based as needed by the whole group.
In addition to size, local area networks are distinguished from other network by their transmission media & topology. In general, local area network will use only one type off transmission medium. The most common local area network topologies are bus, ring and star.
Traditionally, local area networks have data rates in the 4 to 16 MBPS range. Today, however speeds are increasing and can reach 100 MBPS with gigabit systems in developments.
Local area network can be defined as a network which does not exceed a distance of more than 1.25 mile from one end to other end.
Uses & Benefits of Local Area Network: –
- Local area network connects users to a set of common resources.
- Sharing & accessing of information in this way is easier & economical. To access to files in a central storage area, a pointer is shared among a group of users or e-mail access is provided. In this way, local area networks can improve productivity in an organization.
- If a department has 10 users each requiring 25 GB of storage space. It would be better for users to share a single 250 GB hard disk instead of providing each user with their own dedicated 25 GB hard disk.
- Cost per unit of storage is significantly reduced.
- In local area networks the distance is limited.
- Because of distance is limited, the number of computers are limited.
- Metropolitan Area Network (MAN): –
A metropolitan area network is designed to extend over an entire city. It may be single network such as a cable network or it may be a means of connecting a number of local area network into a larger network so that resources may be shared local area network to local area network as well as device to device.
A company can use a metropolitan area network to connect the local area networks in all of its offices through out the city.
A metropolitan area network may be wholly owned & operated by a private company or it may be a service provided by a public company, such as a local telephone company. Many telephone companies provide a popular metropolitan area network service called Switched Multi Data Service (SMDS).
- Wide Area Network (WAN): –
A wide area network provides long distance transmission of data, voice, image and video information over large geographical areas that may comprise a country, a continent or even the whole world.
In contrast to local area networks which depend on their own hardware for transmission, wide area network may utilize public, leased or private communication devices usually in combinations and can therefore span on unlimited number of miles.
A wide area network that is wholly owned & used by a single company is often referred to as an enterprise network. It is often made up of multiple local area networks joined together.
Wide area network actually consist of two or more different networks. The most commonly known wide area network is internet.
Wide area network uses satellites & wireless communications, therefore the information can be shared faster.
- Campus Area Network (CAN): –
campus area network be defined as a network which is limited in scope to a single geographical location while the size may exceed the size defined for local area network.
When two or more networks are connected, they become an internetwork or internet. Individual networks are joined into internetworks by the use of internetworking devices. These devices include routers & gateways. The term internet should not be confused with the internet. The first is a generic term used to mean an interconnecting of networks. The second is the name of a specific world wide network thus the internet is the network of networks.