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