Type of Network topologies: Point-to-point, Bus and Star

 

Topologies:

The structure or arrangement of how all the computer networks are inter-connected to each other is called topology.  Topology defines the physical and logical aspects of the network. There is different type of network topology such as point-to-point, bus, ring, tree or mesh topology.

Point-to-point topology:

Point-to-point networks contains exactly two hosts such as computer, switches or routers, servers connected back-to-back using a single piece of cable. Often, the receiving end of one host is connected to sending end of the other and vice-versa. If the hosts are connected point-to-point logically, then may have multiple intermediate devices.

 

                  Fig. 1: Point-to-point topology.

 

Bus topology:

In bus topology, all devices share single communication line or cable. Bus topology may have problem while multiple hosts sending data at the same time. Therefore, Bus topology either uses CSMA/CD technology or recognizes one host as master to solve the issue. It is one of the simple forms of networking where a failure of a device does not affect the other devices. But failure of the shared communication line can make all other devices stop functioning.

 

                  

                                                     Fig. 2: Bus topology.

CSMA: It is a media access control used to control the data flow so that data integrity is maintained, i.e., the packets do not get lost. There are two alternative ways of handling the problems that occur when two nodes send the messages simultaneously.

CSMA/CD: CSMA/CD (Collision detection) is an access method used to detect the collision. Once the collision is detected, the sender will stop transmitting the data. Therefore, it works on "recovery after the collision".

CSMA/CA: CSMA/CA(Collision avoidance) is an access method used to avoid the collision by checking whether the transmission media is busy or not. If busy, then the sender waits until the media becomes idle. This technique effectively reduces the possibility of the collision. It does not work on "recovery after the collision".

Advantages of Bus topology:

·       Low-cost: In bus topology, nodes are directly connected to the cable without passing through a hub. Therefore, the initial cost of installation is low.

·       Speed: Coaxial or twisted pair cables are mainly used in bus-based networks that support up-to 10 Mbps.

·       Familiar technology: Bus topology is a familiar technology as the installation and troubleshooting techniques are well known, and hardware components are easily available.

·       Failure: A failure in one node will not have any effect on other nodes.

Disadvantages of Bus Topology:

·       Extensive cabling: A bus topology is quite simpler but still, it requires a lot of cabling.

·       Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes.

·       Signal interference: If two nodes send the messages simultaneously, then the signals of both the nodes collide with each other.

·       Reconfiguration difficult: Adding new devices to the network would slow down the network.

·       Attenuation: Attenuation is a loss of signal leads to communication issues. Repeaters are used to regenerate the signal.

 

 Star topology:

In star topology, all the devices are connected to a single hub through a cable. This hub is the central node and all other nodes are connected to the central node. The hub can be passive in nature i.e., not intelligent hub such as broadcasting devices, at the same time the hub can be intelligent known as active hubs. Active hubs have repeaters in them. Coaxial cable or RJ-45 cables are used to connect the computers.

                       Fig. 3: Star topology.

Advantages of Star topology:

·       Efficient troubleshooting: Troubleshooting is quite efficient in a star topology as compared to bus topology. In a bus topology, the manager has to inspect the kilometre of cable. In a star topology, all the stations are connected to the centralized network. Therefore, the network administrator has to go to the single station to troubleshoot the problem.

·       Network Control: Complex network control features can be easily implemented in the star topology. Any changes made in the star topology are automatically accommodated.

·       Failure: As each station is connected to the central hub with its own cable, therefore failure in one cable will not affect the entire network.

·       Familiar technology: Star topology is a familiar technology as its tools are cost-effective.

·       Expandable: It is easily expandable as new stations can be added to the open ports on the hub.

·       Cost Effective: Star topology networks are cost-effective as it uses inexpensive coaxial cable.

·       High data speeds: It supports a bandwidth of approximate 100 Mbps. Ethernet 100-Base-T is one of the most popular Star topology networks.

Disadvantages of Star topology:

Central Point of failure: If the central hub or switch goes down, then all the connected nodes will not be able to communicate with each other.

Cable: Sometimes cable routing becomes difficult when a significant amount of routing is required.

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