Length (5 bits) (Token-Ring)

Protocol: Token-Ring RIF / Source Routing RIF PCI (0-30 bytes) (Token-Ring)

Field: RIF / length

Length: 5 bits

Contents: RIF length indicator.

Depending on the number of current route designators the RIF may vary in length.

The maximum RIF length (18 bytes) is as follows:

[ 2 bytes routing control ] + [ {2 bytes routing designator } * 8 ]

If a frame is sent as all route broadcast or single route broadcast, its length is 2 bytes; the 'RIF length' field is set '2' indicating that the RIF only contains 2 bytes of the routing control parameter. Each bridge passed by the bradcast will add another 2 bytes (next ring segment number) excepted by the first bridge that adds another 4 bytes (two designators for source ring segment number and next ring segment number).

Because only 8 routing designators can be added, the transmission path is restricted to seven bridges between source and destination.

Non-broadcast frames already contain all routing information (set by the source station); their length won't be changed by bridges.

Frames are discarded (a) if the RIF is less than 2 bytes or more than 18 bates in length, (b) if there is an odd number of RIF bytes.