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Re: [802.3_MAINT] summary of MAC interface issues

> Is this behavior derived from Pascal?

No. TransmitFrame is a function and it does not
return instantaneously. The execution stalls until
the function returns.

The fundamental problem that we have here is a
contradiction between state machine conventions
that indicate that actions is a state are in
order but instantaneous, and the use of Pascal
as one of the actions that is not instantaneous.

Shimon.


Glen Kramer wrote:

Brad,

Since, according to your earlier post, the call to TransmitFrame returns instantaneously (i.e., it is "timeless") and MA_DATA.request takes no time as well, MAC Client can issue a large number of requests during transmission of a single frame.

What I understand you say is that some of those frames will find enough space in MAC buffer and will eventually be transmitted. Other frames, unlucky ones, will see a full buffer and will be dropped by the MAC.

Is this behavior derived from Pascal?

How would MAC Client know which frames got dropped?

Glen


-----Original Message-----
From: owner-stds-802-3-maint@xxxxxxxx [mailto:owner-stds-802-3-
maint@xxxxxxxx] On Behalf Of Brad Booth
Sent: Tuesday, August 12, 2008 9:27 PM
To: STDS-802-3-MAINT@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_MAINT] summary of MAC interface issues

Glen,

The latter.  It should buffer.  But it is out of buffer space, then the
frame would be dropped.

Cheers,
Brad


-----Original Message-----
From: owner-stds-802-3-maint@xxxxxxxx
[mailto:owner-stds-802-3-maint@xxxxxxxx] On Behalf Of Glen Kramer
Sent: Tuesday, August 12, 2008 5:49 PM
To: STDS-802-3-MAINT@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_MAINT] summary of MAC interface issues

Brad,



The MAC Client doesn't need to know when the TransmitFrame function
can perform the requested operation.

If MAC Client doesn't know when the TransmitFrame function can perform
the requested operation, the MAC Client may issue another
MA_DATA.request immediately after the previous MA_DATA.request.

I am trying to understand what would happen if (a) the state machine
works as you described (i.e., it comes back to waiting for .request
immediately) and (b) MAC Client sends the second MA_DATA.request while
the MAC is still sending the previous frame. Looking at the state
machine in Figure 4-6, it appears that the second call to TransmitFrame
function will be made before previous call has completed.

But the section 4.2.8 says: The TransmitFrame operation is synchronous.
Its duration is the entire attempt to transmit the frame; when the
operation completes, transmission has either succeeded or failed, as
indicated by the TransmitStatus status code.

What is the correct behavior when the TransmitFrame is called second
time before the previous call has completed? Should the TransmitFrame
function ignore all calls while it is busy, or should it buffer a new
frame with every call until it can send the frame?

Glen



-----Original Message-----
From: owner-stds-802-3-maint@xxxxxxxx [mailto:owner-stds-802-3-
maint@xxxxxxxx] On Behalf Of Brad Booth
Sent: Tuesday, August 12, 2008 11:03 AM
To: STDS-802-3-MAINT@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_MAINT] summary of MAC interface issues

Glen,

I am of the second opinion.  The TransmitFrame is a function call.
The function call is performed and the UCT transitions you out to the
WAIT_FOR_TRANSMIT.

The MAC Client can determine the speed of the link as management is
assumed to be pervasive and it's why we have all those nice MIBs. :-)

The MAC Client doesn't need to know when the TransmitFrame function
can perform the requested operation.  That's why the state machine was
written the way it is.  Once a MA_DATA.request is received, the state
machine enters GENERATE_TRANSMIT_FRAME, TransmitFrame function call is
made and then the state machine transitions back to WAIT_FOR_TRANSMIT.
There is no time variable associated with the state machine;
therefore, the transition through the GENERATE_TRANSMIT_FRAME is
timeless.  In other words, it happens immediately.

Cheers,
Brad

-----Original Message-----
From: Glen Kramer [mailto:glen.kramer@xxxxxxxxxxxx]
Sent: Tuesday, August 12, 2008 12:47 PM
To: Brad Booth; STDS-802-3-MAINT@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_MAINT] summary of MAC interface issues

Brad,

Thank you for the feedback.

From previous discussions, I heard two opinions on how the state
machine in Figure 4-6 actually works. One opinion was that the state
machine remains in GENERATE_TRANSMIT_FRAME state until function
TransmitFrame completes. The second opinion was that after calling the
TramsmitFrame function, the state machine immediately transits to
state WAIT_FOR_TRNSMIT and there it is ready to accept another
MA_DATA.request.

Which is your opinion?


If the upper layer protocol is
transmitting MA_DATA.requests faster than the frames are being
transmitted, then an implementer must be prepared to buffer those
frames until the TransmitFrame function can perform the requested

operation.

The TransmitFrame function is not an instantaneous action, but
rather a queued routine.

Generally, MAC client doesn't know the speed of the underlying MAC and
PHY. Also, MAC delay can be variable. Think auto-negotiation, CSMA/CD,
flow control.

How can MAC Client know when the TransmitFrame function can perform
the requested operation?


Thanks,
Glen



-----Original Message-----
From: owner-stds-802-3-maint@xxxxxxxx [mailto:owner-stds-802-3-
maint@xxxxxxxx] On Behalf Of Brad Booth
Sent: Tuesday, August 12, 2008 9:19 AM
To: STDS-802-3-MAINT@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_MAINT] summary of MAC interface issues

Glen,

Thanks for providing the slides.  I was unable to attend the meeting
in Denver, so the slides are helpful in getting up to speed on this.

Here's some feedback on the problems you highlight in slide 2:
1) I don't understand how this is a problem.  From what I can see,
the
existing state machine and function call look fine.  As a matter of
fact, I believe the changes being proposed would break the existing
standard.  The goal of the state machine is to queue up incoming
data for the TransmitFrame function.  Waiting for the TransmitFrame
function to complete before waiting for the next frame would be
assuming that no other MA_DATA.requests are received.  If the upper
layer protocol is transmitting MA_DATA.requests faster than the
frames
are being transmitted, then an implementer must be prepared to
buffer those frames until the TransmitFrame function can perform the

requested operation.

The TransmitFrame function is not an instantaneous action, but
rather a queued routine.
2) The MA_DATA.request can be generated instantaneously after the
current MA_DATA.request is completed.  You are correct that the MAC
Client is unaware of the status of the request.  If, and that's a
big if, the 802.3 WG felt that an indication of the status of the
request was required, then the MAC and the MAC Client would need to
exchange a
unique identify for each frame to track the status of that frame.
This would be required due to the fact that in problem #1, the
interaction between 4.2.8 and the TransmitFrame function results in
a queue; therefore, the status response to the MA_DATA.request may
be delayed relative to the original request.

Thoughts?

Thanks,
Brad


-----Original Message-----
From: owner-stds-802-3-maint@xxxxxxxx
[mailto:owner-stds-802-3-maint@xxxxxxxx] On Behalf Of Glen Kramer
Sent: Monday, August 11, 2008 5:56 PM
To: STDS-802-3-MAINT@xxxxxxxxxxxxxxxxx
Subject: [802.3_MAINT] summary of MAC interface issues

All,

In the attached slides, I tried to summarize the MAC interface
issues that were discussed in Denver and on the reflector, as well
as outline
various options to resolve them. I could not join the conference
call,
so if some other options were discussed, please let me know and I'll
add those.

I am looking forward to everyone's feedback.

Thanks,
Glen