Transcript
Topologies Bus Topology
Terminator
Terminator
A main “trunk” or “backbone” line using coaxial networking cable, with computers attached at intervals, terminators at each end. One of the simplest ways to connect a group of computers. How does it work? The sending workstation broadcasts to all the stations attached. Each computer sits and listens. When it “hears” (using NIC) a message directed to it, using its own unique address, it accepts the data. Ready to transmit it makes sure no one else is using the bus and then transmits packets of information. Advantages 1. single node failure does not disrupt the network 2. extending the network is simple, up to 1000 feet there is no need for a repeater, just plug in extra stations 3. it is reliable, using CSMA protocol to stop collisions Disadvantages 1. Prone to loose connections, cable breaks and cable shorts which are difficult to troubleshoot. Can actually bring down whole network.
Star Topology
Server
Each computer is connected to a device called a hub. It is connected with its own cable to a port in the hub. How does it work? It uses the same wait-and-listen strategy to access or send data as is used by the bus topology. Advantages 1. Easily expandable, run a cable from the computer to the hub. 2. Limited by number of ports in the hub, but hubs can be “daisy chained”. 3. Greatest benefit is in adding to the network without disrupting the service to those already on the network. 4. If one computer goes down, the other computers can still communicate with each other. Disadvantages 1. Cable costs can be high as each computer needs its own cable. 2. Purchasing hubs can add to costs when building a network.
Ring Topology
Computers linked as in a star topology with a Multistation Access Unit (MAU) providing the central connection instead of a hub. How does it work? The information moves in one direction only. Computers on the network actually retransmit messages (packets) they receive and send them onto the next computer on the ring. The computers in the ring pass a token around the circle. This token is a special packet of data and is passed round until a computer wanting to transmit data, takes possession of it. The computer holding the can send data onto the network. Ring topologies tend only to be used in large corporate networks due to disadvantages listed below. Disadvantages 1. 2. 3. 4. 5.
Difficult to troubleshoot. The failure of one computer can disrupt data flow. Adding, removing, computers disrupt the operation of the network. Token Ring hardware is expensive. Substantial knowledge is needed to administer this network.
Mesh Topology
All stations are connected to each other. Advantages 1. Ultimately reliable – no collisions, more than one way through the network. 2. Avoids bottlenecks – several routes through network. 3. Node failure does not disrupt network performance. Disadvantage 1. Cabling costs can be very high.
