What are the uses of the star topology

Network (topology)

In a computer network, the topology describes the structure of the connections between several devices in order to ensure a common exchange of data.

The topology of a network is decisive for its reliability: only if there are alternative paths between the nodes, the functionality is maintained in the event of failure of individual connections. There are then one or more alternative routes (or diversions) in addition to the commute to work.

A distinction is made between physical and logical topology. The physical topology describes the structure of the network cabling; the logical topology the flow of data between the end devices.

Knowledge of the topology of a network is also useful for evaluating its performance, as well as the investment costs and for selecting suitable hardware.


Ring topology

When networking in ring topology, 2 participants are connected to each other via two-point connections, so that a closed ring is created. The information to be transmitted is forwarded from subscriber to subscriber until it reaches its destination.

In order to avoid overlaps, this type of networking requires special addressing methods. Since each participant can act as a repeater at the same time (if no splitters are used), large distances can be bridged in this way (when using fiber optic cables in the kilometer range).

If one of the participants fails, the entire network collapses, unless the participants have mastered protection switching. In a ring with protection, the work path is often guided around the ring in a certain direction of rotation, the substitute path in the other direction of rotation. This method is also used, among other things, in fieldbus systems based on fiber optics.

advantages
  • Deterministic network communication - predecessor and successor are defined
  • All stations work as amplifiers
  • No collisions
  • All computers have the same access options

disadvantage
  • The failure of a terminal device leads to the entire network communication being interrupted


Star topology

In networks with a star topology, all other participants are connected to a central participant with a two-point connection. The central participant does not necessarily have to have special control intelligence.

This is generally not the case in transport networks. In computer networks it can be a specialized device, for example a hub or switch. A private branch exchange is also usually set up as a star network: The switching system is the central node to which the subscriber sets are connected in a star configuration.

In any case, a central component in a network causes a higher probability of failure for the individual connections: a failure of the central participant inevitably results in the failure of all connection options at the same time. A common protective measure in star networks is to duplicate the central component (redundancy).

advantages
  • The failure of a terminal has no effect on the rest of the network.
  • This network offers high transmission rates.
  • Easily expandable
  • easily understandable

disadvantage
  • Elaborate cabling
  • Network traffic becomes impossible if the distributor fails.


Bus topology

A bus topology consists of a main cable, the bus, to which all devices are connected, and two terminating resistors. The connection between the devices (i.e. network cards) and the main cable is made via T-pieces.

Access procedures prevent the participants from interfering with one another. They regulate which subscriber has the common line - the bus - available at what time.

Problems with this method include the following
  • During the data traffic, each participant must listen to every broadcast. As a result, the load (current) on the transmitter's output modules increases with the number of participants on the bus.

  • Field bus systems can extend over an area of ​​several hundred meters. Here the line length is no longer negligibly small in comparison with the wavelength of the transmission. In order to avoid disturbing reflections, bus terminating resistors are required, which also load the transmitter outputs with higher currents. Smaller field bus systems can still be networked very well according to the bus principle.
The data can be transmitted in both directions. The advantages of a bus network are the low cable requirement and independence from the function of individual stations: if a node or station fails, the entire system remains intact. The greatest danger, however, is a cable break in the main cable, which can cause the entire bus to fail.

The bus topology is a passive topology, which means that the connected stations do not process the signal. They pick up the signals from the cable or send them to the cable where the signal then spreads in both directions. A diffusion network is used here.

advantages
  • Only low costs, as only small amounts of cables are required.
  • Simple cabling and network expansion

disadvantage
  • All data is transmitted over a single cable.
  • Data transmissions can easily be intercepted (keyword: sniffers).
  • A fault in the transmission medium at a single point in the bus (defective cable, loose plug connection, defective network card) blocks the entire network line.
  • The search for the source of the error is then often very time-consuming.
  • Only one station can send data at a time. All others are blocked during the transmission (data congestion).
  • Due to the possibility of collisions, the medium should only be used to approx. 30%


Mesh network (Safest topology)

In a meshed network, each terminal is connected to one or more other terminals. When every node is connected to every other node, it is called a fully meshed network.

If a terminal or a line fails, it is usually possible to continue communicating by rerouting (routing) the data. In large networks one often finds a structure that is composed of several different topologies. The Internet is largely a meshed network, but there are "main traffic arteries" (the backbone lines) that are similar to a bus.

advantages
  • Safest variant of a network
  • If a terminal device fails, data communication is redirected
    still possible

disadvantage
  • A lot of cable is necessary
  • Complex cabling for a fully meshed network
  • Very high energy consumption


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