A network topology refers to the physical layout in which all the devices are interconnected and it defines the manner in which the cables are arranged. There are many types of topological design used to implement LAN. The major types of topology are as follows:
There are also two basic categories of network topologies:
Classification of Physical Topologies
Bus Topology:
A bus topology, all stations are connected to single communication lines. A station which wants to communicate with another station on the network sends a broadcast message into the wire. Each station checks the destination address field in the information frame for its own address. If the address does not match then the station discards the information back on the bus. If the destination address matches with its address, then it accepts the information and process it. Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable breaks, the entire network will be down.
Star Topology
A star topology, consists no. of stations connected directly to a central station or server. Communications between stations ans central point in a star topology can be bi-directional and use point-to-point. A station in this type of network transfer information to the central point (like hubs, switches) which then forwards to its destination. The central point manages and controls all communication between stations in a network.
Failure of one station can be easily detected and can be removed without affecting the network. But failure of the central point disables entire networks.
Note : The points where the stations are connected to the networks are known as Nodes.
It is LAN, in which all the station are connected to one another to form a closed loop. In this, each packet of information will be transmitted around the ring until it reaches its final destination. Failure of a station in a ring topology disturbs the ring because the information is not regenerated.
Tree Topology (hierarchical network)
Tree Topology extends the branches of the bus topology and allows mote stations to access the bus. In a bus or tree topology, there is no central point of management and control and these functions are handled by every station on the bus.
Mesh Topology
Mesh topology is a type of wireless network setup where each of the systems and network devices are interconnected with one another in a network for the data transmission. Mesh topology provides increased network stability and connectivity, as it is relatively flexible. It is independent of any central device and this ensures high reliability of the network. the network can still operate even if one of the connections breakup. It is also highly suitable for the large network connections as it allows multiple sites on the network to connect with each other. This network is fast network as high speed exchange of information is possible between the source and the destination device. But this topology is also costly to install and is unsuitable for smaller organisation. It involves high maintenance and is not easily managed because of the latge number of cables and connections required. This is mesh topology has a complex physical layout as well.
Note: In most practical networks that are based upon the physical partially connected mesh topology, all of the data that is transmitted between nodes in the network takes the shortest path (or an approximation of the shortest path) between nodes, except in the case of a failure or break in one of the links, in which case the data takes an alternative path to the destination. This requires that the nodes of the network possess some type of logical 'routing' algorithm to determine the correct path to use at any particular time.
Hybrid Topology
The hybrid topology combines multiple topology into one large topology. It is common in large wide are networks.
Advantages:
The logical classification of network topologies, generally follows the same classifications as those in the physical classifications of network topologies. The path that the data takes between nodes being used to determine the topology as opposed to the actual physical connections being used to determine the topology
Advantages and Disadvantages of LAN Topologies
Source : en.Wikipedia.org
- Star Topology
- Bus (point-to-multipoint) Topology
- Ring Topology
- Tree Topology
- Mesh Topology
- Hybrid Topology
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| Network Topologies |
Classification of Network Topologies
There are also two basic categories of network topologies:
- Physical topologies
- Logical topologies
- Office Layout
- Troubleshooting Techniques
- Cost of Installation
- Type of cable used
Classification of Physical Topologies
Bus Topology:
A bus topology, all stations are connected to single communication lines. A station which wants to communicate with another station on the network sends a broadcast message into the wire. Each station checks the destination address field in the information frame for its own address. If the address does not match then the station discards the information back on the bus. If the destination address matches with its address, then it accepts the information and process it. Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable breaks, the entire network will be down.
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| Bus Topology |
- Linear bus : In this, All of the nodes of the network are connected to a common transmission medium which has exactly two endpoints – all data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all nodes in the network virtually simultaneously.
- Distributed bus : In this, All of the nodes of the network are connected to a common transmission medium which has more than two endpoints that are created by adding branches to the main section of the transmission medium.
Star Topology
A star topology, consists no. of stations connected directly to a central station or server. Communications between stations ans central point in a star topology can be bi-directional and use point-to-point. A station in this type of network transfer information to the central point (like hubs, switches) which then forwards to its destination. The central point manages and controls all communication between stations in a network.
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| Star Topology |
Failure of one station can be easily detected and can be removed without affecting the network. But failure of the central point disables entire networks.
Note : The points where the stations are connected to the networks are known as Nodes.
- Extended Star : A type of network topology, is same as star topology but this topology has one or more repeaters between the central node and the peripheral or 'spoke' nodes, the repeaters are being used to extend the maximum transmission distance of the point-to-point links between the central node and the peripheral nodes beyond that which is supported by the transmitter power of the central node or beyond that which is supported by the standard upon which the physical layer of the physical star network is based. If the repeaters in a network that is based upon the physical extended star topology are replaced with hubs or switches, then a hybrid network topology is created that is referred to as a physical hierarchical star topology, although some texts make no distinction between the two topologies.
- Distributed Star : in this topology, is composed of individual networks that are based upon the physical star topology connected together in a linear fashion
It is LAN, in which all the station are connected to one another to form a closed loop. In this, each packet of information will be transmitted around the ring until it reaches its final destination. Failure of a station in a ring topology disturbs the ring because the information is not regenerated.
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| Ring Topology |
Tree Topology (hierarchical network)
Tree Topology extends the branches of the bus topology and allows mote stations to access the bus. In a bus or tree topology, there is no central point of management and control and these functions are handled by every station on the bus.
- 1.) A network that is based upon the physical hierarchical topology must have at least three levels in the hierarchy of the tree, since a network with a central 'root' node and only one hierarchical level below it would exhibit the physical topology of a star.
- 2.) A network that is based upon the physical hierarchical topology and with a branching factor of 1 would be classified as a physical linear topology.
- 3.) The branching factor, f, is independent of the total number of nodes in the network and, therefore, if the nodes in the network require ports for connection to other nodes the total number of ports per node may be kept low even though the total number of nodes is large – this makes the effect of the cost of adding ports to each node totally dependent upon the branching factor and may therefore be kept as low as required without any effect upon the total number of nodes that are possible.
- 4.) The total number of point-to-point links in a network that is based upon the physical hierarchical topology will be one less than the total number of nodes in the network.
- 5.) If the nodes in a network that is based upon the physical hierarchical topology are required to perform any processing upon the data that is transmitted between nodes in the network, the nodes that are at higher levels in the hierarchy will be required to perform more processing operations on behalf of other nodes than the nodes that are lower in the hierarchy. Such a type of network topology is very useful and highly recommended.
Mesh Topology
Mesh topology is a type of wireless network setup where each of the systems and network devices are interconnected with one another in a network for the data transmission. Mesh topology provides increased network stability and connectivity, as it is relatively flexible. It is independent of any central device and this ensures high reliability of the network. the network can still operate even if one of the connections breakup. It is also highly suitable for the large network connections as it allows multiple sites on the network to connect with each other. This network is fast network as high speed exchange of information is possible between the source and the destination device. But this topology is also costly to install and is unsuitable for smaller organisation. It involves high maintenance and is not easily managed because of the latge number of cables and connections required. This is mesh topology has a complex physical layout as well.
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| Mesh Topology |
Note: In most practical networks that are based upon the physical partially connected mesh topology, all of the data that is transmitted between nodes in the network takes the shortest path (or an approximation of the shortest path) between nodes, except in the case of a failure or break in one of the links, in which case the data takes an alternative path to the destination. This requires that the nodes of the network possess some type of logical 'routing' algorithm to determine the correct path to use at any particular time.
Hybrid Topology
The hybrid topology combines multiple topology into one large topology. It is common in large wide are networks.
Advantages:
- One company can combine the benefits of several different types of topologies
- Work-group efficiency and traffic can be customized
- The devices on topology cannot be placed into another topology without some hardware issues.
The logical classification of network topologies, generally follows the same classifications as those in the physical classifications of network topologies. The path that the data takes between nodes being used to determine the topology as opposed to the actual physical connections being used to determine the topology
- Notes:
- 1.) Logical topologies are often closely associated with media access control (MAC) methods and protocols.
- 2.) The logical topologies are generally determined by network protocols as opposed to being determined by the physical layout of cables, wires, and network devices or by the flow of the electrical signals, although in many cases the paths that the electrical signals take between nodes may closely match the logical flow of data, hence the convention of using the terms 'logical topology' and 'signal topology' interchangeably.
- 3.) Logical topologies are able to be dynamically reconfigured by special types of equipment such as routers and switches.
Advantages and Disadvantages of LAN Topologies
Topology | Advantages | Disadvantages |
BUS Topology |
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RING Topology |
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STAR Topology |
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