3.5 Describe different network topologies.
A topology is physical and logical network layout. Physical layout include actual layout of cables and other network devices where as Logical layout include the way in which the network appears to the devices that use it.
Mesh : In this topology each computer is connected to every other. This topology is rarely used.
Advantages
1. It provide multiple paths between two devices so if one path fails other can be used
2. Network can be expanded without disruption to current uses
Disadvantages
1. It has high level of redundancy
2. wiring is very complicated
3. Cabling cost is very high
4. Finding fault in cabling is very tricky
Ring : In this topology each network computer and device are connected to each other forming a large circle (or similar shape). Each packet is sent around the ring until it reaches its final destination. Typically FDDI, SONET or Token Ring technology are used to implement a ring network.
Advantages
1. Any fault in cable can be found easily.
2. These networks are comparatively easy to install.
Disadvantages
1. Expansion will cause disruption in current network
2. Single fault in cable will disrupt entire network.
BUS : Bus networks use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.
Advantages
1. Easy to implement
2. Less cable is used
3. No specialized network equipment is needed.
Disadvantages
1. Single fault in cable will disrupt entire network.
2. Expansion will cause disruption in current network
3. Troubleshooting is difficult.
Star: In Star topology, all the components of network are connected to the central device called "hub" which may be a hub, a router or a switch. All the data on the star topology passes through the central device before reaching the intended destination. Hub acts as a junction to connect different nodes present in Star Network, and at the same time it manages and controls whole of the network. Depending on which central device is used, "hub" can act as repeater or signal booster. Central device can also communicate with other hubs of different network. Unshielded Twisted Pair (UTP) Ethernet cable is used to connect workstations to central node.
Advantages
1. Gives better performance compared to BUS
2. New devices can be added easily.
3. Centralized management makes monitoring the network is easier.
4. Single node failure will not affect entire network.
Disadvantages
1. If central device (Hub) fails whole network goes down.
2. Use of central device increase overall cost.
3. Performance of network depends on capacity of central device.
Hybrid: It is an integration of two or more different topologies to form a resultant topology. This combination of topologies is done according to the requirement of the organization. For example an office can use a star topology in each of its department and ring topology to connect these departments.
Advantages
1. Fault detection is easier.
2. Size of the network can be increased easily without distruption to current network.
3. It is very flexible as network can be designed according to requirements and available resources.
Disadvantages
1. Overall cost of network is high as it requires lot of cables, many network devices like HUB to connect various networks.
2. Design becomes more and more complex as number of networks increase
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