Network Types
LAN
A local area network (LAN) is two or more computers directly linked within a small well defined area such as a room, building, or group of closely placed buildings. A LAN may be made up of only microcomputers or any combination of microcomputers and large systems. A LAN usually consists of the following :
- Two or more computers
- Peripheral devices such as printers and hard disk drivers
- Software to control the operation of he computers or other devices connected to the LAN
- Special cables, usually coaxial or fiber optic, to connect computers and other devices.
- A plug in board to handle the data transmissions.
The number of computers in a LAN varies from smaller LANs that typically connect 2 to 25 computers, to large LANs that can connect as many as 10,000 computers. The length of the cable connecting a computer to a LAN also varies depending on the LAN. Most LANs allow cables of about 1,000 feet, but allow cables of several miles to be used. The data transfer speeds range from several thousand bits per second to around 10 million bits per second. The programs that control LANs also vary in the features they offer.
Ethernet is the most widely used LAN technology because it is relatively fast and economical. It was introduced by DEC (Digital Equipment Corporation), Intel and Xerox in 1980. Subsequently, a slightly modified version of it was adopted by the IEEE as a standard LAN technology. The network topology used for Ethernet is, multi- access bus topology. Communication medium used is low-loss coaxial cable having a data transfer rate of 10 Mbps. A message is transmitted from one node to another by breaking it up into packets (called frames in Ethernet), and then broadcasting packets to the bus. An address designator is associated with each packet. As a packet travels on the bus, each node checks whether the packet is addressed to it, and the addressee node picks up the message.
WAN
A wide area network is two or more computers that are geographically dispersed, linked by communication facilities such as telephone system on microwave relays,. This type of network is usually limited to use by large corporations and government agencies because of the high cost involved in building mmaintainingthem. A wAN is a network that links separate geographical locations and this network can be a public system or any of the various packet services provides by the public telecommuncaiton agencies.
The main differentce between a WAN and LAN is under the complete control of the owner, whereas the WAN needs the involvement of another authority like telecom department. LANs are successful and capable of handling very high data transfer rates at low cost because of the small area covered. Besides LANs have a lower rate than WANs.
The ARPANET of the Advanced Research Projects Agency of the U.S. Department of Defense was the first WAN.
It connected about 40 universities and research institutions throughout the United States and Europe with about 50 computers, ranging in size from mini-computers to supercomputers. ERNET (Education and Research Network) is a WAN linking several education and research institutions in India. NICNET (National Informatics Centre’s Network) is a WAN linking several offices of NIC (National Informatics Centre) of India up to district headquarters. Indian Railways also has its own WAN linking its booking offices across the nation, facilitating passengers to book tickets on most major trains from anywhere in India. Similarly,. international airlines worldwide also link their computers to form a WAN facilitating booking of flight tickets on international flights. SWIFT is a WAN interconnecting computers of International banks to reconcile their accounts and for electronic funds transfer. The Internet (described in next chapter) is a W AN encompassing many LAN s and computers across the world.
MAN
A metropolitan area network (MAN) is a computer network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network.Most widely used technologies to develop a MAN (Metropolitan Area Network) network are FDDI (fiber distribution data interface), ATM (Asynchronous Transfer Mode) and SMDS (switched multi megabit data service).ATM (Asynchronous Transfer Mode) is a digital data transfer technology. It was developed in 1980 to improve the transportation of real time data over a single network. ATM (Asynchronous Transfer Mode) works just like cell relay system, where data is separated in the form of fixed equal sized packets and is transferred overtime. The purpose of ATM (Asynchronous Transfer Mode) was to access clear audio and video results during a video conferencing. The attributes of ATM has enabled it to become a base of wide area data networking.FDDI is a standard for data transfer over LAN, which can be extended to the range of approximately 200kms. FDDI can help support the data transmission of many thousand users. FDDI uses optical fiber for its basic infrastructure that is why it is referred to as fiber distribution data interface. When data is transferred through a connectionless service we use the technology named as SMDS. Connectionless service implies that data is transferred by storing the information in the header and it reaches its destination independently through any network. When the data is transferred using the technology of SMDS, it also forms small data packets just like in ATM. However SMDS allows the transmission of data over large geographical areas in the form of datagrams (the data packets of an unreliable data service provider). Nowadays MAN (Metropolitan Area Network) links are established using infrared and microwave signals.
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.
Campus Area Network
This is a network which is larger than a LAN, but smaller than an MAN. This is typical in areas such as a university, large school or small business. It is typically spread over a collection of buildings which are reasonably local to each other. It may have an internal Ethernet as well as capability of connecting to the internet.
Wireless Local Area Network
This is a LAN which works using wireless network technology such as Wi-Fi. This type of network is becoming more popular as wireless technology is further developed and is used more in the home and by small businesses. It means devices do not need to rely on physical cables and wires as much and can organise their spaces more effectively.
System Area Network This network connects computers together on an especially high-speed connection, in a configuration known as a cluster. This means computers which are connected together so as to work as a single system, and can be done as a result of very high speed computers and new low cost microprocessors. They are usually used to improve performance and for cost effectiveness.
Storage Area Network This network connects servers directly to devices which store amounts of data without relying on a LAN or WAN network to do so. This can involve another type of connection known as Fibre Channel, a system similar to Ethernet which handles high-performance disk storage for applications on a number of professional networks.
