Definition
A physical topology is the physical layout of a network design. There are three basic types, bus, ring, star or it can be a mix of all these to create the hybrid topology. The physical topologies affect the logical topologies, the cabling structure and what kind of media is used.
Physical Topologies
Bus
Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium, that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. Bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. Bus networks work best with a limited number of devices. If more computers are added to a bus, performance problems will result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
Ring
A ring topology consists of computers connected together in a circular mode where data travels in one direction (i.e. clockwise) around the ring. Data is transmitted via token passing whereby packet called a token is transmitted around the ring. If a node is to transmit data, it must wait for the token to arrive and adds its data to the token. The token is then transformed into a frame and is moved on around the ring until the intended destination is located. When the recipient receives the frame it returns an acknowledgment to the sender who then releases a new free token. This method ensures that only the computer with the token is able to communicate and send data at any given time and that prevents conflicts. As each computer is involved in this it can be called an active topology. These networks do not require terminators. The main disadvantage is that one single computer can disable the network. Other disadvantage is when more computers are added it slows down the whole network.
Star
Coming soon...