STP operates at the Data Link layer of the OSI model which prevents traffic loops. STP chooses only one root switch/bridge, out of which all data paths span out logically getting the data to the target the quickest and detect and correct link failures when a switch/bridge fails...STP stands for Spanning Tree Protocol. The root is chosen based on its BID( Bridge ID) which is the combination of a 2 byte priority field and the bridge/switch MAC address....Since all switch/bridges on the network start out with the same priority, the one with the lowest MAC address becomes the root bridge.

STP is basically used for loop prevention and to prodive redundancy. Devices participating in STP perform a root bridge election process. Device having the lowest priority will be choosen as the root bridge. If every device participating in STP have the same priority value, device with the lowest mac-address becomes the root bridge. The root bridge will be responsible to make th overall traffic flow decision on the LAN. Non-root bridges use a lowest cost path to reach the root bridge. This cost is dependent on the interface speed. Topological changes downstream from the root bridge is communicated to the root bridge.

s

I dunno.