Physical Topology :
- It refers to the way in which a network is laid out physically or physical representation of the computer network is known as topology in networking.
Every device has a dedicated point-to-point link to every other device.
In mesh topology, we need (n*(n -1)) /2 duplex-mode links.
- Dedicated links guarantees that each connection can carry its own data load, thus eliminating the traffic problems.
- A mesh topology is robust.
- Privacy or security
- Amount of cabling.
- Number of I/O ports required
2.Star Topology :-
- Each device has a dedicated point-to-point link only to a central controller, usually called a hub.
- The devices are not directly linked to one another.
- The controller acts as an exchange:
- i.e if one device wants to send data to another, it sends the data to the controller, which then relays the data to the other connected device.
- A star topology is less expensive than a mesh topology. i.e each device needs only one link and one I/O port to connect it to any number of others.
- It easy to install and reconfigure.
- Far less cabling needs to be housed, and additions, moves, and deletions involve only one connection: between that device and the hub.
- It is robustness. If one link fails, only that link is affected. All other links remain active.
- Dependency of the whole topology on one single point, the hub. If the hub goes down, the whole system is dead.
- Each node must be linked to a central hub. For this reason, often more cabling is required in a star than in some other topologies (such as ring or bus).
- The star topology is used in local-area networks (LANs)
- High-speed LANs often use a star topology with a central hub.
- It is multipoint. One long cable acts as a backbone to link all the devices in a network.
- Nodes are connected to the bus cable by drop lines and taps.
- A drop line is a connection running between the device and the main cable.
- A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core.
- A bus uses less cabling than mesh or star topologies. Only the backbone cable stretches through the entire facility. Each drop line has to reach only as far as the nearest point on the backbone.
- Difficult reconnection and fault isolation.
- Signal reflection at the taps can cause degradation in quality.
- A fault or break in the bus cable stops all transmission, even between devices on the same side of the problem. The damaged area reflects signals back in the direction of origin, creating noise in both directions.
- Each device has a dedicated point-to-point connection with only the two devices on either side of it.
- A signal is passed along the ring in one direction, from device to device, until it reaches its destination.
- Each device in the ring incorporates a repeater. When a device receives a signal intended for another device, its repeater regenerates the bits and passes them along
- Easy to install and reconfigure. Each device is linked to only its immediate neighbours (either physically or logically). To add or delete a device requires changing only two connections. The only constraints are media and traffic considerations (maximum ring length and number of devices).
- Fault isolation is simplified. Generally, in a ring, a signal is circulating at all times. If one device does not receive a signal within a specified period, it can issue an alarm. The alarm alerts the network operator to the problem and its location.
- Unidirectional traffic can be a disadvantage. In a simple ring, a break in the ring (such as a disabled station) can disable the entire network.
- A network can be hybrid.
- For example, we can have a main star topology with each branch connecting several stations in a bus topology as shown below figure.