Different types of Networks

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 systmes. 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 fibre 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.