Interface to 802.3 MAC:Followup

Jeff MandinPMC-Sierra

Maintenance Adhoc – August 2008

Aug 2008 802.3 Maintenance Adhoc 2

Discussions since the first telecon

Many perspectives on how to understand the interaction between the MAC client and the MAC via MA_DATA.Request():

a) “There is implicit interaction between the MAC and the MA_DATA.Request primitive, so that the packet is not presented to the MAC until the MAC is ready for it”

- In one understanding this results in implicit queueing of the packet and increased latency

- In another understanding, MA_DATA.Request might block in some cases

b) “Client is responsible for ensuring that it doesn’t have multiple MA_DATA.Request() outstanding, but client state diagrams do not include this explicitly”

c) “MAC interface should be modified”

d) Also some variations on the above

Aug 2008 802.3 Maintenance Adhoc 3

On what issues is there some consensus?

a) Each of the descriptions of the Client/MAC interaction on the previous slide has issues - none is wholly satisfactory

b) To make a conclusive statement and to avoid future problems, there should be some discussions with experts in 802.1

c) The 802.3 MAC only processes one transmit request at a time

- To the eyes of many readers, the current MAC Control diagrams (ie. PAUSE and MPCP) appear to flout this and transmit multiple requests

Aug 2008 802.3 Maintenance Adhoc 4

Clarifying the MAC Control Diagrams

Approaches:

a) Add exit condition to the transmission states, so that the control flow does not advance until the MAC is ready

- ie. make the “magic step” explicit- Does it lead to missed requests in the state diagram? Is it consistent

with other MAC Clients?

b) Add text to indicate that the state diagram describes transmission logic for a packet, and that the client is responsible for ensuring that it does not invoke MA_DATA.Request when the MAC is not ready

- Work out the precise text after the 802.1 discussion

Aug 2008 802.3 Maintenance Adhoc 5

PAUSE State Diagram + exit condition

Aug 2008 802.3 Maintenance Adhoc 6

MPCP Control Multiplexer