Source routing optimally uses parallel and redundant paths, so links are not left idle. It also allows IBM controller timing to be properly set for extended LANs. Source routing has its disadvantages. The route discovery process requires more overhead than transparent bridging. If many devices are simultaneously performing route discovery, the network slows down considerably.
Transparent bridges choose a new path per frame.
Source-routing functionality must be engineered into the bridges, making them more expensive and complex than transparent bridges. An ARB frame traverses all possible routes between end stations, while an SRB takes only one route between end stations. Multiple copies of the ARB travel over all possible routes back to the originating station. Note that an ARB can never travel the same ring twice nor exceed the hop count limit - source routing uses the spanning tree structure, which can be configured so only one copy of the frame reaches each ring. As the frame passes through a bridge, the bridge inserts its own bridge number and the numbers of its attached LAN segments into the frame's Routing Information Field.