Physical Topologies

All physical topologies are variations of two fundamental methods of connecting devices. They are:

• Point-to-point
• Multipoint

1. Point-to-point Topology -

Point-to-point (PTP) topology connects two nodes directly together.

The following examples are pure point-to-point links:

• Two computers communicating via modems
• A mainframe terminal communicating with a front-end processor
• A workstation communicating along a parallel cable to a printer.

In a point-to-point link, two devices monopolize a communication medium. Because the medium is not shared, a mechanism is not needed to identify the computers. Therefore, a simple, two device point-to-point network has no need for addressing.

Point-to-point links can be simplex, half-duplex or full-duplex. When devices must engage in bi-directional communication on a half-duplex link, some turnaround mechanisms must be in place to switch the roles of the sending and receiving devices.

2. Multipoint Topology -

Multipoint topologies link three or more devices together through a single communication medium. Multipoint topologies work much like a party-line telephone service where several subscribers are connected to the same telephone line.

Because multipoint topologies share a common channel, each device needs a way to identify itself and the device to which it wants to send information. The method used to identify senders and receivers is called addressing.

The following are different types of physical topologies are frequently used in computer networking:

• Bus
• Star
• Ring
• Tree
• Hybrid.