Wednesday, June 19, 2019

Network Topologies

Network topologies are the architecture of a network (= physical structure). the arrangement of the hardware (printers, servers, workplaces, etc.) There are three basic architectures that can be mixed without any problems:
  • Bus topology
  • Ring topology
  • Star topology

The bus topology was mainly installed earlier. Today it is actually uncommon, you can find it occasionally still in Altinstallationen. In this form of topology, multiple devices, one behind the other or side by side, are all connected to a cable. At the beginning and at the end of the cable there is a resistance, which serves to avoid reflections. Connecting a device to the cable or to the bus is done via a T-piece.

The collisions in this realization of a network are pre-programmed, can not be overlooked. Thus, special access methods such as e.g. CSMA / CD are used to prevent participants from interfering with each other. In bus topology, there is no "central brain" in the transmitted sense, much more, every station is a brain. All the intelligence of the topology comes from the stations.

The topology is usually realized by coaxial cable, resulting in a cost-effective implementation. So it makes sense to install the bus topology in smaller low-cost networks.

Bus topology representatives include Ethernet and the token bus.

  • Easy installation and extension economical
  • Failure of a computer has no effect on the network
  • Saving of cable
  • Easily audible
  • Failure of the main cable silences the entire network
  • Elaborate troubleshooting
  • Collisions slow down the network

In the ring topology, the devices are connected in the form of a circle. Two devices are connected to each other via two-point connection until a closed circuit is created. The data is transferred from one station to the next, so that every station that comes in front of the receiver gets to see the data. In this case, the stations are even considered as amplifiers, whereby a high transmission range can be achieved, of course with suitable cables (for example glass fiber).

But if one station fails, the circle is interrupted. The net collapses, nothing works. Remedying help stations that control a protection switching. In such networks, the data is always sent in a certain direction, e.g. clockwise. If a station now fails, the direction is simply changed, so that the data still arrive at the destination, just on a different path.

Again, it is, just like the bus topology, easy for eavesdroppers. You only need to have your station, e.g. a laptop, to include in the circle, so between two stations. Already, the eavesdropper can listen to virtually all traffic.

Application examples: Token Ring (logical) and FDDI (physical).

  • No collisions
  • Failure of a computer has no effect on the network
  • Saving of cable
  • Stations have a nice side effect and serve as amplifiers
  • Expensive
  • Easily audible
  • Failure of a station has fatal consequences

Unlike bus topology, where each station is a "brain," the star topology has "one central brain" about which everything goes. With this "brain" all participants are connected via two-point connection. This brain is usually a hub or switch, but of course it can also be a router or something similar. But here too, the central device fails, e.g. the router, forcibly also fails the entire network. In contrast, the network does not mind if a single non central station fails.

  • Simple troubleshooting
  • Easily expandable
  • High transmission rate possible
  • Failure of a station at the end has no further consequences
  • If the central device fails, the entire network inevitably fails
  • Elaborate wiring

The mesh topology or mangled topology is rarely used. The advantage of this topology is that if one computer should fail, it can be immediately replaced by another computer in the network. In mesh topology, each computer is directly connected to each other. This has the disadvantage that you need another network card per computer. So if 5 computers are to be connected as in the example picture, each computer must possess 4 network maps. It is therefore used in very small networks with few computers where 100% resilience is required.


Hierarchical topology is also called tree topology. It actually consists of several nets with a star topology. At the top is the most powerful device, after which distributors usually come, until finally the clients are connected to the distributors. The highest device in the hierarchy is usually connected via a very fast connection.

The term tree topology probably comes from the fact that the topology is comparable to a tree, more precisely with a tree top, because there is no strain in the true sense. Much more are branches that can be branched on and on, so some parts of the tree topology are also called branches.

  • Failure of terminal does not matter
  • If a device that is higher in the hierarchy fails, all devices fall below it.

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