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[802.3_DMLT] Supporting TSSI with MAC Merge

Dear Colleagues,

The TSSI produces an indication from the generic Reconcilliation Sublayer (gRS) when a the SFD of a frame occurs.

When IET (preemption) is supported, then it is fairly obvious that the MAC Merge sublayer should provide the TSSI as it knows the frame starts (as opposed to start of continuation fragments). 

There might be an ambiguity of whether a TSSI indication came from an express or a premptable frame.  There are a few options for removing the potential ambiguity:
       1) two TSSIs, one for each MAC,
       2) an optional parameter indicating express or preemptable added to the TSSI primitives in Clause 90, or
       3) an additional value such as P_DETECTED should be added for the SFD parameter

Two TSSIs seems clumsy. 
Adding an optional parameter might be best as it avoids having to update references to the SFD parameter to allow for a new value.

Some joint time at the next meeting could discuss whether there really is an ambiguity and, if so, which approach should be used to resolve it.

Regards,
Pat