Network topology refers to the physical layout of the network in which all the devices are connected. There are several types of topographical design and strategies used to implement LAN. Network designers consider several factors when determining which topology or combination of topologies to use: the type of computers installed, type of cabling, the cost of components, distance between each computer and the speed with which data must travel around the network. The commonly used physical network topologies are bus, star and ring.
Bus network is an arrangement in a local area network (LAN) in which each node is connected to a main cable or link called the bus. Transmission from any station travels the length of the bus. Transmission from any station travels the length of the bus, in both directions, and can be received by all other stations. The bus has terminators at either end which absorb the signal, removing it from the bus.
Data is transmitted into small groups called packets. A packet is a data segment that includes a header, payload and control elements that are transmitted together. The receiving computer reconstructs the packet into the original structure.
Advantages of bus topology are:
- Low traffic network, since only small amount of devices are allowed in the network.
- Inexpensive because it needs a server, workstation, an Ethernet, cable, and network interface cards.
- Bus topology use short length cable which decrease the installation cost. It is simple and easy to maintain.
Disadvantages of bus topology are:
- If problem occurs on the backbone “cable”, the entire network will go down.
- Troubleshooting could be difficult.
- Limited to future addition of other devices.
In the ring topology, nodes are connected to each in a closed loop by a single communication cable. Data transfers in one direction, from one node to another around the ring. Thus, the data packets circulate along the ring in either clockwise or anti-clockwise direction. As a packet circulates past each station, the destination station recognizes its address on the packet header, and copies the packet contents onto itself. After a packet travels a full circle, it is removed at the source station. A ring topology is also called loop network.
Advantages of Ring topology are:
- Transmission of data is fairly simple as it only travels in one direction.
- No data collisions.
- Extra computers can be added easily with little effect on performance although you have to shut down the network to be able to do this.
Disadvantages of Ring topology are:
- If one workstation or port goes down, the entire network gets affected.
- Network is highly dependent on the wire which connects different components.
- Data must pass through every computer until it reaches its destination. This can make it slower than other network layouts.
Star topology is the most common topology in use today. In a star topology, each device has a dedicated point to point link only to central controller “hub”. A hub is a rectangular box-shaped device with multiple plug-in points called ‘ports’. Groups of data are routed through the hub and sent to all the attached nodes, thus eventually reaching their destinations.
Advantages of Star topology are:
- Stations can be easily added to or removed from the LAN.
- All other links stay active even if one link fails to work.
- Easy to find the failure link.
- It is less expensive.
- Very few data collisions as each workstations has its own cable to the server.
- Good security – no workstation can interact with another without going through the server first.
Disadvantages of Star topology are:
- The entire network becomes inoperable, if the central hub fails to work.
- More cabling is needed as compared to bus or ring topologies.
- If traffic between the workstations is high, an undue burden is placed on the central hub.
- Difficult to expand.
Types of Network
Networks can be deployed to meet range of needs for a company. Their configuration reflects the way they service those needs. Different types of networks are distinguished based on their size, their data transfer speed, and their reach. Private networks are networks that belong to a single organization. There are three different types of networks. They are:
- Local Area Network (LAN)
- Metropolitan Area Network (MAN)
- Wide Area Network (WAN)
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