THD204 - TMA02 - Part 1
Star Network
Example of a Star Network[1]
Star topology: is a network topology in which peripheral nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. Protocols include Token polling for older networks and Token passing.
Advantages: The failure of a transmission line, i.e., channel, linking any peripheral node to the central node will result in the isolation of that peripheral node from all others, but the other nodes should continue to function normally
Disadvantages: Failure of the central node renders the network inoperable. On older systems the dumbness of the terminals affected the speed of operation.
Ring Network
Example of a Ring Network[1]
A ring network is a local area network (LAN) in which all computers are connected in a ring topology. Messages circulate in the form of frames around the network passing from one node to the next. The most common protocol on a ring network is a token passing scheme, which is used to prevent the collision of data between two computers that want to send messages at the same time. The Token Ring protocol is standard specified as IEEE 802.5. Briefly this is how it works: The sending node is able to send when it has the token all other nodes are now listeners. Once the destination node has received the message it acknowledges and the sending node sees the acknowledge and drops the token which now circulates once more.
Note: The token scheme can also be used with bus and star (ARCnet) topology LANs.
Advantages: Doesn't have the problems of collisions as does Ethernet with its CSMA/CD
Disadvantages: A single node failure will crash the network. Limited geographic area, such as a single building.
Bus Network
Example of a Bus Network[1]
Bus topology: In this type of network all devices are connected either side of a common single backbone (bus). Ethernet is the most widely installed LAN technology. Specified in a standard, IEEE 802.3, An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Devices connected to the cable compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.
Advantages: A node can be lost and the network will continue to operate normally. Expandability. Can be extended to suit a growing need easily.
Disadvantages: Failure of the single backbone will render the network either degraded or inoperable dependant on the failure.
On a congested network the amount of collisions detected by CSMA/CD can severely affect it efficiency, using a Token passing method can alleviate this.
[1] Diagrams from OU course material for T171 You, Your Computer and the Net. Labelling by me.