Topology
A network can be arranged or configured in several different ways. Two types of topology is recognized:
Physical Topology
The physical topology of a network refers to configuration of cables, computers, and other peripherals.
Logical Topology
The logical topology is concerned with data transmission on the network,that is the methods used to pass information between workstations. Thus, the logical topology refers to data transmission protocols.
The following are the four basic types of physical topology used in networks:
Linear Bus
Star
Star-Wired Ring
Tree
Linear Bus
All the communications travel along a common cable called a bus.A linear bus topology consists of a main run of a cable with a terminator at each end of the line. All nodes (file server, workstations, and peripherals) are connected to the linear cable. As the information passes along the bus, it is examined by each device to see if the information is intended for it.
The bus network is typically used when only a few microcomputers are to be linked together. A twisted pair, coaxial or fiber optic cable can be used in this configuration. The protocols used with Linear Bus topology are Ethernet or LocalTalk.
Advantages of a Linear Bus Topology:
- Easy to connect a computer or peripheral to a linear bus.
- Requires less cable length than a star topology.
Disadvantages of a Linear Bus Topology:
- Entire network shuts down if there is a break in the main cable.
- Terminators are required at both ends of the backbone cable.
- Difficult to identify the problem if the entire network shuts down.
- Not meant to be used as a stand-alone solution in a large building.
Star
A Star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central unit, the network hub or switch. The data on this type of network passes through the hub or the switch before getting to its destination. The hub or the switch controls and mangages all the functions of the network. It may also have a function of a repeater for the data transmitted.
This set-up is common with the use of twisted pair cable, however, coaxial cable or fiber optic cable could also be used. The protocols used with Star configurations are Ethernet or LocalTalk.
Advantages of Star Topology:
- Easy to install and wire.
- No disruption to the network when connecting or removing devices, or if there is a break in one of the cables.
- Easy to detect faults on the nodes and make repairs without disruption.
Disadvantages of a Star Topology:
- Requires more cable length than a linear bus topology.
- If the hub or switch fails, nodes attached are disabled.
- More expensive to set up because of the cost of the hub or the swich.
Star-Wired Ring
A Star-Wired topology is similar to a star topology. Internally, MAU (multistation access unit) of a Star-Wired Ring contains wiring that allows information to pass from one device to another in a circle or ring.
The Token Ring protocol is used in a Star-Wired Ring topology. A twisted pair cable is required for this configuration.
Tree
A Tree topology combines characteristics of Linear Bus and Star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable.
Tree topologies allow the expansion of an already existing network, and permit configuring a network to meet the needs. A twisted pair, coaxial or fiber optic cable can be used in a Tree configuration. Ethernet is the protocol used with a Tree topology.
Advantages of a Tree Topology:
- Point-to-point wiring for individual segments.
- Supported by several hardware and software venders.
Disadvantages of a Tree Topology:
- The length of each segment is limited by the type of cabling used.
- If the backbone line breaks, the entire segment goes down (similar to Linear Bus).
- More difficult to configure and wire than other topologies due to its complexity.
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