Bus network

From Academic Kids

A bus network is a network architecture in which a set of clients are connected via a shared communications line, called a bus. There are several common instances of the bus architecture, including one in the motherboard of most computers, and those in some versions of Ethernet networks.

Bus networks are the simplest way to connect multiple clients, but often have problems when two clients want to communicate at the same time on the same bus. Thus systems which use bus network architectures normally have some scheme of collision handing or collision avoidance for communication on the bus, quite often using Carrier Sense Multiple Access or the presence of a bus master which controls access to the shared bus resource.

A true bus network is passive – the computers on the bus simply listen for a signal; they are not responsible for moving the signal along. However, many active architectures can also be described as a "bus" if they provide the same logical functions as a passive bus; for example, switched Ethernet is can still be regarded as a logical bus network, if not a physical one. Indeed, the hardware may be abstracted away completely in the case of a software bus.

With the dominance of switched Ethernet over passive Ethernet, passive bus networks are uncommon in wired networks. However, almost all current wireless networks can be viewed as examples of passive bus networks, with radio propagation serving as the shared passive medium.

Contents

More About Bus Topology

    central cable, which is known as the bus or backbone.  Bus networks are the simplest ways to connect together and create a network, but when two of the clients on the network want to communicate at the same time, problems can often occur.  As a result of these problems, a bus network have some kind of collision handling and collision avoidance protocols for communication across the bus.

All the computers that are connected to the bus donít actually physically do something; they listen for a signal but they are not responsible for transmitting it. Within a bus there is a protocol known as a scheduler Ė when a computer wishes to transmit some data it must first send a message to the scheduler. The scheduler is then responsible for taking the message and placing it into a queue along with all other requests from other devices on the network, sorting them out into order of highest priority.

Each message that is sent to the scheduler contains a unique identification code, which is sent to all the other devices on the network. As soon as the bus (the actual physical wire that connects the network) isnít busy, the scheduler is able to transmit the next message in the queue to the correct computer.

Despite the fact that bus networks are relatively cheap networks to set up on a small scale compared to other topologies, as well as being easy to set up and efficient, there are also several disadvantages. The main one being that it can be slower than other networks (due to the scheduler system) and also it can be unreliable because if a cable were to break in any place then it could disable the entire network.

Comparing bus networks to other types of network

Advantages

  • Easy to implement and extend
  • Well suited for temporary networks (quick setup)
  • Typically the cheapest topology to implement
  • Failure of one station does not affect others

Disadvantages

  • Difficult to administer/troubleshoot
  • Limited cable length and number of stations
  • A cable break can disable the entire network
  • Maintenance costs may be higher in the long run
  • Performance degrades as additional computers are added

See also

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