Network Topology
Network topology is the physical and the logical layout of the network. Physical layout is the actual layout of the computer cables and other network devices. Logical layout is the way in which the network appears to the devices that use it.



Bus / Line Topology

 
In a Bus topology, all devices attach to the same transmission medium. The medium has a physical beginning and end. All buses are implemented using electrical cable, usually coax, and the ends of the cable must be terminated with a terminating resistor that matches the impedance of the cable. The terminating resistor prevents data reflections from coming across as data corruption. The bus is considered a multi-point system because all devices tap into the same backbone cable.

Advantages
  • It is the easiest network topology for connecting peripherals or computers in a linear fashion.
  • It works very efficient well when there is a small network.
  • Length of cable required is less than a star topology.
  • It is easy to connect or remove devices in this network without affecting any other device.
  • Very cost-effective as compared to other network topology i.e. mesh and star
  • It is easy to understand topology.
  • Easy to expand by joining the two cables together.
Disadvantages
  • Bus topology is not great for large networks.
  • Identification of problem becomes difficult if whole network goes down.
  • Troubleshooting of individual device issues is very hard.
  • Need of terminators are required at both ends of main cable.
  • Additional devices slow network down.
  • If a main cable is damaged, whole network fails or splits into two.
  • Packet loss is high.
  • This network topology is very slow as compared to other topologies.


Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction. A failure in any cable or device breaks the loop and can take down the entire network. To implement a ring network it could use the Token Ring technology. A token, or small data packet, is continuously passed around the network. When a device needs to transmit, it reserves the token for the next trip around, then attaches its data packet to it.

Advantages
  • In this data flows in one direction which reduces the chance of packet collisions.
  • In this topology additional workstations can be added after without impacting performance of the network.
  • Equal access to the resources.
  • There is no need of server to control the connectivity among the nodes in the topology.
  • It is cheap to install and expand.
  • Minimum collision.
  • Speed to transfer the data is very high in this type of topology.
  • Due to the presence of token passing the performance of ring topology becomes better than bus topology under heavy traffic.
  • Easy to manage.
  • Ring network is extremely orderly organized where every device has access to the token and therefore the opportunity to transmit.
Disadvantages
  • Due to the Uni-directional Ring, a data packet (token) must have to pass through all the nodes.
  • If one workstation shuts down, it affects whole network or if a node goes down entire network goes down.
  • It is slower in performance as compared to the bus topology
  • It is Expensive.
  • Addition and removal of any node during a network is difficult and may cause issue in network activity.
  • Difficult to troubleshoot the ring.
  • In order for all the computer to communicate with each other, all computer must be turned on.
  • Total dependence in on one cable.
  • They were not Scalable.


Star Topology

 
In a star network, each node (file server, workstations, and peripherals) is connected to a central device called a hub. The hub takes a signal that comes from any node and passes it along to all the other nodes in the network. Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. The hub, switch, or concentrator manages and controls all functions of the network. The star topology reduces the chance of network failure by connecting all of the systems to a central node.

There is also an extended version of Star Topology called Extended Star. In this topology, there are end nodes and sub end nodes. All the sub end nodes are connected to end nodes. And they are conecteto the central node.

Advantages
  • It is very reliable – if one cable or device fails then all the others will still work
  • It is high-performing as no data collisions can occur
  • Less expensive because each device only need one I/O port and wishes to be connected with hub with one link.
  • Easier to put in
  • Robust in nature
  • Easy fault detection because the link are often easily identified.
  • No disruptions to the network when connecting or removing devices.
  • Each device requires just one port i.e. to attach to the hub.
  • If N devices are connected to every other in star, then the amount of cables required to attach them is N. So, it’s easy to line up.
Disadvantages
  • Requires more cable than a linear bus .
  • If the connecting network device (network switch) fails, nodes attached are disabled and can’t participate in network communication.
  • More expensive than linear bus topology due to the value of the connecting devices (network switches)
  • If hub goes down everything goes down, none of the devices can work without hub.
  • Hub requires more resources and regular maintenance because it’s the central system of star .
  • Extra hardware is required (hubs or switches) which adds to cost
  • Performance is predicated on the one concentrator i.e. hub.


Point-to-Point Topology

Point-to-point (PTP) topology connects two nodes directly together. Often, the receiving end of one host is connected to sending end of the other end and vice-versa. If the hosts are connected point-to-point logically, then may have multiple intermediate devices. But the end hosts are unaware of underlying network and see each other as if they are connected directly

Advantages
  • Highest Bandwidth because there is only two nodes having entire bandwidth of a link
  • Very fast compared to other network topologies because it can access only two nodes.
  • Very simple connectivity
  • It provides low Latency
  • Easy to handle and maintain
  • Node Can be Replaced in few seconds
Disadvantages
  • This topology is only used for small areas where nodes are closely located.
  • The entire network depends on the common channel in case of link broken entire network will become dead.
  • There is another major drawback of this topology there are only two nodes if any of the node stops working, data cannot be transfer across the network.


Partial / Full Mesh Topology

 
In this topology, each node is connected to every other node in the network. Implementing the mesh topology is expensive and difficult. In this type of network, each node may send message to destination through multiple paths. While the data is travelling on the Mesh Network it is automatically configured to reach the destination by taking the shortest route which means the least number of hops

Advantages
  • Failure during a single device won’t break the network.
  • There is no traffic problem as there is a dedicated point to point links for every computer.
  • Fault identification is straightforward.
  • This topology provides multiple paths to succeed in the destination and tons of redundancy.
  • It provides high privacy and security.
  • Data transmission is more consistent because failure doesn’t disrupt its processes.
  • Adding new devices won’t disrupt data transmissions.
  • This topology has robust features to beat any situation.
  • A mesh doesn\’t have a centralized authority.
Disadvantages
  • It\’s costly as compared to the opposite network topologies i.e. star, bus, point to point topology.
  • Installation is extremely difficult in the mesh.
  • Power requirement is higher as all the nodes will need to remain active all the time and share the load.
  • Complex process.
  • The cost to implement mesh is above other selections.
  • There is a high risk of redundant connections.
  • Each node requires a further utility cost to think about.
  • Maintenance needs are challenging with a mesh.


Tree Topology

Tree Topology is a topology which is having a tree structure in which all the computer are connected like the branches which are connected with the tree. In Computer Network, tree topology is called as a combination of a Bus and Start network topology. The main advantages of this topology are these are very flexible and also have better scalability.

Advantages
  • This topology is the combination of bus and star topology.
  • This topology provides a hierarchical as well as central data arrangement of the nodes.
  • As the leaf nodes can add one or more nodes in the hierarchical chain, this topology provides high scalability.
  • The other nodes in a network are not affected, if one of their nodes get damaged or not working.
  • Tree topology provides easy maintenance and easy fault identification can be done.
  • A callable topology. Leaf nodes can hold more nodes.
  • Supported by several hardware and software vendors.
  • Point-to-point wiring for individual segments.
Disadvantages
  • This network is very difficult to configure as compared to the other network topologies.
  • Length of a segment is limited & the limit of the segment depends on the type of cabling used.
  • Due to the presence of large number of nodes, the network performance of tree topology becomes a bit slowly.
  • If the computer in first level is erroneous, next level computer will also go under problems.
  • Requires large number of cables compared to star and ring topology.
  • As the data needs to travel from the central cable this creates dense network traffic.
  • The Backbone appears as the failure point of the entire segment of the network.
  • Treatment of the topology is pretty complex.
  • The establishment cost increases as well.
  • If the bulk of nodes are added in this network, then the maintenance will become complicated.


Hybrid Topology

A hybrid topology is a type of network topology that uses two or more differing network topologies. These topologies can include a mix of bus topology, mesh topology, ring topology, star topology, and tree topology.

Advantages
  • This type of topology combines the benefits of different types of topologies in one topology.
  • Can be modified as per requirement.
  • It is extremely flexible.
  • It is very reliable.
  • It is easily scalable as Hybrid networks are built in a fashion which enables for easy integration of new hardware components.
  • Error detecting and trouble shooting is easy.
  • Handles large volume of traffic.
  • It is used for create large network.
Disadvantages
  • It is a type of network expensive.
  • Design of a hybrid network is very complex.
  • There is change hardware in order to connect topology with another topology.
  • Usually hybrid architectures are usually larger in scales so they requires a lot of cables in installation process.
  • Hubs which are used to connect two distinct networks, are very costly. And hubs are different from usual hubs as they need to be intelligent enough to work with different architectures.
  • Installation is a difficult process.

 
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