Logical topology

Logical topology, or signal topology, is the arrangement of devices on a computer network and how they communicate with one another. How devices are connected to the network through the actual cables that transmit data, or the physical structure of the network, is called the physical topology. Physical topology defines how the systems are physically connected. It represents the physical layout of the devices on the network. The logical topology defines how the systems communicate across the physical topologies.

Logical topologies are bound to network protocols and describe how data is moved across the network. There are attempts to study the logical topology of the Internet by network scientists such as Albert-László Barabási. EXAMPLE : twisted pair Ethernet is a logical bus topology in a physical star topology layout. while IBM's token ring is a logical ring topology, it is physically set up in star topology.

Logical topologies

Shared media

In a shared media topology, all the systems have the ability to access the physical layout whenever they need it. The main advantage in a shared media topology is that the systems have unrestricted access to the physical media. Of course, the main disadvantage to this topology is collisions. If two systems send information out on the wire at the same time, the packets collide and kill both packets. Ethernet is an example of a shared media topology. To help avoid the collision problem, Ethernet uses a protocol called Carrier Sense Multiple Access/Collision Detection (CSMA/CD). In this protocol, each system monitors the wire, listening for traffic. If traffic is detected, the system waits until it hears no traffic before it sends.