Posted by: wasaa | June 22, 2008

Types of Network

Local Area Network (LAN)    LANs are networks usually confined to a geographic area, such as a single building or a college campus. LANs can be small, linking as few as three computers, but often link hundreds of computers. 

 

Metropolitan Area Network (MAN) – MAN is basically a bigger version of a LAN and normally uses similar technology. It might cover a group of near by corporate offices or a city and might be either private or public.

 

Wide Area Network (WAN) Often a network is located in multiple physical places. Wide area networking combines multiple LANs that are geographically separate. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links, and data packet carrier services.  

 

Local Area Network (LAN)

 Star topology 

 Ring topology 

 Mesh topology

Bus topology

Pear to Pear

 

Wide Area Network (WAN)

WAN interconnects computers (hosts), which are located geographically at long distances. The hosts are connected by communication subnet. The job of the subnet is to carry messages from host to host.

 

The routers are specialized computers. When data arrive on incoming line, the router chooses an outgoing line to forward them on. The collection of communication lines and routers (but not hosts) forms the subnet.

 

Many different networks, including LANs, MANs and WANs are together form an Internet.  

 

Transmission Media

 

Shielded twisted pair

Shielded twisted-pair cabling consists of one or more twisted pairs of cables enclosed in a foil wrap and woven copper shielding. The shield further reduces the tendency of the cable to radiate EMI and thus reduces the cable’s sensitivity to outside interference.

 

Twisted pair

A basic twisted-pair cable consists of two strands of copper wire twisted together. This twisting reduces the sensitivity of the cable to electro magnetic interference.

 

Unshielded twisted pair

Unshielded twisted-pair cable doesn’t incorporate a braided shield into its structure.

 

Coaxial Cable

Coaxial cables were the first cable types used in LANs. Gets its name because two conductors share a common axis; the cable is most frequently referred to as coax.

 

Fiber Optics

The centre conductor of a fiber-optic cable is a fiber that consists of highly refined glass or plastic designed to transmit light signals with little loss. A glass core supports a longer cabling distance, but a plastic core is typically easier to work with. The fiber is coated with a cladding that reflects signals back into the fiber to reduce signal loss. A plastic sheath protects the fiber.

 

Connectivity Devices

 

Hubs

The hub’s major function is to replicate data it receives from one device attached to it to all others

 

Repeaters

Any electrical signal reaching the repeater from one segment, will be amplified and retransmitted to the other segment. Using repeaters slows the signal’s propagation, and thus the amount of repeaters should be limited. 

 

Bridges

Bridges are used to increase the number of addressable nodes on a network or to link two geographically distant but similar networks.

 

Routers

A major feature of a router is that it chooses the best route between networks that may have multiple paths between them. IP addressing and subnet masking are used to route packets

 

Modems

A modem is a device that converts digital data originating from a computer to analog signals used by voice communication networks, such as the telephone system. A modem may also convert analogue data originating from a (say, a telephone line) to digital data for use by a computer.

 

Server –            Computer that provide shared resources to networks

Client –             Computer that access shared networks resources provided by server

 

Gateways

Gateways interface two dissimilar networks. Gateways translate one network protocol into another, thus overcoming both hardware and software incompatibilities.

Advantages of Computer Networks

          Sharing of expensive resources (e.g. A Laser printer, HDD, Internet)

          Sharing of databases and  other software

          Communication among different computer systems

          Transfer of multimedia files

          Entertainment – (Eg. Play multiple-player computer games from different locations)

          Faster transfer of data

          Back-up your files on multiple computers

Disadvantages of Computer Networks

          Initial cost

          Security of information (viruses, hackers, ..)

          System failures

 

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