Bus topology is the physical and logical design of a bus network. All the nodes (devices) on a bus network have to share access to the network to communicate. The nodes can only transmit data one device at a time. A bus is the central cable, the main wire that connects all devices on a LAN (Local Area Network). Bus topology is known as the simplest network topology, and also known as a linear bus (Oliviero and Woodward, 2009, p. 104). Bus topology is the choice in most LAN topologies.
A bus topology is a type of network setup where each computer and network device is connected to a single cable or backbone that typically uses coaxial cabling. The signal travels both ways from one end of the bus to the other. A terminator is needed at both ends of the bus so the signal does not reflect back across the bus or so it does not bounce back and forth across the cable.
When data is sent by a device on a bus, the data packet is sent to all the devices on the bus. All the devices examine the packets to see if it is addressed to them or not. The devices ignore the packets that are not addressed to them and respond to those that are addressed to them.
A media access method called CSMA/MA is used to handle the collision that occur when two signals are placed on the bus at the same time, that is when two or more devices try to transmit data at the same time. IEEE, Ethernet 802.3 is the protocol most associated with bus topology. CSMA/MA, carrier sense multiple access with collision detection is Ethernet contention-based MAC protocol. It is referred to as contention because the devices on the bus contend for the use of the wire to communicate, and transmit data. Carrier sense is when the devices listen to see if the bus is free, or if there is no voltage detected. If the line is free that device can use the line to transmit data. If two devices detect the bus to be free, and they both attempt to transmit data, collision
References: Dooley, A. (2005). Business data communications: introduction to networking. Upper Saddle River, NJ: Pearson. Oliviero, A / Woodward, B. (2011). Cabling: The complete guide to copper and fiber-optic networking. 111 River ST. Hoboken, NJ: John Wiley and Sons.