Frame Status (1 byte) (Token-Ring)

Protocol: Token-Ring MAC Token-Ring PCI

Field: frame status

Length: 1 byte

Contents: address recognized / frame copied indicator.

a

The 'Frame Status' bits are used for MAC layer acknowledgement. These bits are set to all zero by the source station. These bits are set to AC=11 for frame acknowledgement.

The A/C bits are double because they are not covered by the MAC frame checksum.

These bit combinations may be detected by a source station:

AC=00

A. Destination ring unknown / frame not copied by bridge.

B. If RIF exists: bridge couldn't find "Route Designator" field.

C. Destination station isn't active.

AC=11

A. The destination station had received this frame.

B. A source routing bridge had received this frame.

AC=10

A. The destination station had recognized this frame but couldn't copy it into its buffers.

B. A source routing bridge had recognized this frame but couldn't copy it into its buffers.

AC=01

Invalid A/C comination (senseless).

Duplicate station addresses

The A/C bits are mainly used by the 'Duplicate Address Test': Any new ring station sends a MAC frame addressed to its own address. If a second station would have the same address, the new station will receive its own frame with the A bit set to 1.

Bridge operation

Source routing bridges that recognize that they have to route a frame will

... set A/C bits to "11" on the source ring,

... set A/C bits to "00" on the destination ring.