Physical Structure of Network:
Because network is interconnection of devices capable to communication connected via link or channel so physical structure of network refer to way of links used to connected devices and this is called networking. Usually there are two techniques in networking use to connect devices: point-to-point and multi point connections.
In point-to-point connection networking a link is dedicated between to communication devices. In this technique mostly cable is use to connect host but other options such as microwave and satellite link are also possible between ends. The entire capacity of link is reserved for transmission of data between end devices. Example of point-to-point connection is remote control system, i.e. when we change channel of TV, point-to-point connection is establish.
Multi point Connection:
In multi point connection networking more than two devices use same link for transmission of data with each other. In multi point technique capacity of link is shared between devices usually which are spatially shared and time shared connection technique. If multiple devices are capable to share link simultaneously that is called spatially shared connection while users take turns, it is a time shared connection.
In Mesh Topology, point-to-point technique is used and every device has a dedicated link to every other device. In mesh topology every device is connected with n-1 devices because a link is dedicated possible pair of devices. In mesh topology every host need (n-1) I/O ports to make connection with (n-1) devices.
Mesh topology providing several advantages on other network topologies.
- Mesh topology provide strong privacy and security of data due to dedicated connection.
- Second because every link carry just its own data between two communicating devices so it eliminate the traffic problem.
- Entire system is not go down if one link become unusable.
- Fault identification and fault isolation in mesh topology is easy due to point-to-point connection.
Major disadvantage of mesh topology is cost, because it consist on dedicated link between devices so large amount of cable and I/O ports are require.
Telephone regional offices are the example of mesh topology where each regional office must be connected with other regional offices.
In Star Topology all devices has a dedicated point-to-point connection via central controller called Hub. In star topology devices are not directly connected so if one device send to another it must pass from hub so hub act as control exchange. In star topology cabling expenses are much less than mesh topology and beside this only single I/O port is require for connection with network. One major drawback of star topology is if hub goes down than whole network become unusable.
LAN is example of Star Topology.
Unlike mesh and star topology, bus topology not provide point-to-point connection to devices in network. In Bus Topology a main cable which act as back bone of network provide link to all devices. Drop line and Taps are used between a host and main cable. A tap is connector which use to puncture sheath of main cable and create contact with metal core while drop line act as link.
Advantages of bus topology is easy installation. Less cable is require than star and mesh topology due to main cable technique.
Disadvantages of bus topology is fault identification and isolation. A limit number of taps bus can b support because when a signal move in main cable some of its energy convert in heat and signal become weak. Installation of new devices is also difficult. Signal reflection at the taps can cause degradation in quality. Major drawback is if main cable goes down than transmission of all network fail.
In Ring Topology every device has a dedicated point-to-point connection just with only two devices on either side of it, so transmission of data in ring topology occur device to device and each device act as repeater. When a device receive signal intended for other device, its repeater regenerate the bits and pass it to next device until it reaches on its target.
Ring topology is easy to install and reconfigure because each device is connected with its neighbors. Further fault identification and isolation is very ease.
Disadvantage of ring topology is unidirectional traffic and if fault occur in ring than entire network goes down however this drawback can be removed by using dual ring.
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