Method and apparatus for source routing bridging

To improve the throughput of bridges in a multiple ring token ring network, External Copy Hardware (ECH) is provided for each source routing bridge to determine when a frame is to be copied as a candidate for forwarding to another ring by a given bridge. Each frame may contain a Routing Information Field (RIF), which the ECH searches for Segment Numbers in the RIF that are compared with host processor developed Primary Segment Numbers (each representing a primary ring number and a bridge number) and Secondary Segment Numbers (each representing an alternate ring number and a bridge number). The ECH uses the results of the comparisons along with a look-up table and a Routing Control Word (also present in the RIF) to determine if the frame under consideration is to be copied by a Protocol Handler (which interfaces with the ECH) and forwarded by the corresponding bridge to another ring. During the process of making a copy or non-copy decision, the frames are scanned unidirectionally, and the decision is made "on the fly", thereby increasing operation speed.