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Data is passed between the MDI driver and the MDI user in M_DATA(D7str) STREAMS messages. The format of the MDI data is different for each MAC type.
The format of the MAC data has been designed
such that MDI drivers
should not need to manipulate or interpret it.
MAC data may be passed down
from the MAC user
in multiple STREAMS messages
that are linked together using the b_cont member.
The following topics describe the format of the data within an MDI M_DATA message:
The data is likely to be distributed among several linked messages, but it is guaranteed that all the shaded fields in the diagrams supplied in these topics will be in the data pointed to by the first STREAMS message of the chain.
How MDI data is contained within STREAMS messages
Both Ethernet-II and IEEE 802.3 MAC frames may be used on Ethernet media. Therefore, MDI drivers for these types of adapters must be able to send and receive both frame types.
Format of MDI data for Ethernet
Token ring adapters generally perform LLC processing on the adapter. However, to provide a general solution for all media and to simplify MDI drivers, LLC processing is performed in a module above the MAC Driver Interface.
Format of MDI data for Token-Ring
The following MAC frame format will be used on FDDI networks:
Format of MDI data for FDDI