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-----Original Message-----
From: Shao, Winnie [mailto:winnie.shao@xxxxxxxxx]
Sent: Monday, April 28, 2003 8:48 AM
To: Castellano, Robert; Anoop Ghanwani
Cc: RPR (E-mail)
Subject: RE: [RPRWG] How to process ClassB frames requested to be marked f airness eligible and with no shaperC credits if client does not support VDQ
-----Original Message-----
From: Castellano, Robert [mailto:RCastellano@xxxxxxxxx]
Sent: 2003Äê4ÔÂ26ÈÕ 6:44
To: Anoop Ghanwani; Shao, Winnie
Cc: RPR (E-mail)
Subject: RE: [RPRWG] How to process ClassB frames requested to be marked f airness eligible and with no shaperC credits if client does not support VDQ
Hi,
The classB HOL blocking is a pretty common question that
comes up.
The MAC stage queue is designed that there
will be no HOL blocking.
It is important to
understand how the stage queue processes classB
and
classC frames in both the cases where the client does the MarkFE
marking
or the MAC does the marking.
The first is to understand the purpose of the MarkFE for
classB frames.
ClassB traffic class is provisioned
for a CIR and EIR. The sendB signal
from the
MAC indicates when the client can send classB traffic that is within
CIR.
Whenever there is no sendB signal, it means
there is no more CIR credit available.
Likewise the
sendC signal indicates when the client can send classC
or classB EIR frames. If the MAC transmits a classB frame when
there
is a sendC signal and noSendB, the classB EIR
is deducted from the classC
credit pool.
Meaning the client can transmit classB
whenever
there is a sendB or sendC signal from the MAC. When
a classB frame is transmitted, the appropriate classB or
classC
credits are deducted depending on whether the
sendB or sendC
signals are active. If there is
a sendB, the classB is sent with
MarkFE=false, and
if there is sendC and no sendB, the classB
frame is transmitted MarkFE=true. (My assumption here is
that the sendA, sendB,
and sendC signals are all
independent, and can be active simultaneously.
The
client then chooses which service class to transmit based on
its own queue and scheduling states and the state of the
sendX signals.)
The advantage of transmitting a classB frame with
MarkFE=true is when there
are no classB credits,
however there are class C credits and the client
decides to transmit a class B frame ahead of any pending class C
frames.
In this case there is no HOL blocking for
class B traffic. If there are no
classB or
classC credits, classB is blocked any way.
If the client has classB credits it makes much more sense to
transmit
with MarkFE=false (if client is
marking). The scenario you bring up is a case where there
are classB credits but no classC credits, and the client is
blocked
from transmitting classB because of one
classB at the front of the
classB queue marked
MarkFE=true. The better approach is
to
transmit the classB frames with MarkFE=false when there is a
sendB signal avoiding a classB HOL blocking issue.
If the MAC is doing the MarkFE marking, this is pretty
transparent
to the client and there are no HOL
blocking issues. The client
is allowed to send
classB whenever the MAC provides a sendB or sendC
signal. In the case where a classB frame is sent with
sendB,
the MAC sets MarkFE=false. If the
client sends a classB when
there is no sendB but
there is a sendC, the MAC will mark the
frame as
MarkFE.
As Anoop points out the client has to be able to manage
separate
classB and classC traffic queues and do the
appropriate scheduling
based on the sendB/sendC
signals from the MAC. The client needs
to be
intelligent enough to determine when it sees a sendC that it can transmit
either
a classB or classC frame. The client
must also be careful
not to starve classC frames if
classB always has precedence
over classC.
These are all client design issues.
thanks,
robert
> -----Original Message-----
>
From: Anoop Ghanwani [mailto:anoop@xxxxxxxxxxxxxx]
> Sent: Friday, April 25, 2003 10:04 AM
> To: 'Shao, Winnie '; 'RPRWG (E-mail) '
> Subject: RE: [RPRWG] How to process ClassB frames requested
> to be marked f airness eligible and with no
shaperC credits
> if client does not support
VDQ
>
>
>
>
> If the client does not have some kind of
intelligent queueing,
> then what you say about
HOL blocking will be true. However, if
>
the client doesn't do some form of intelligent queueing, one
> would have to question the need for it to set
the markFE
> parameter.
>
> Further, the client can take
advantage of the sendC signal
> being deasserted
when there are no shaperC credits. If it
>
does that, it should never request a classB frame for
> transmission with markFE set when there are no classC
> credits.
>
> -Anoop
>
> -----Original Message-----
> From: Shao, Winnie
> To: RPRWG
(E-mail)
> Sent: 4/25/03 12:08 AM
> Subject: [RPRWG] How to process ClassB frames
requested to be marked
> fairness eligible and
with no shaperC credits if client does
>
not support
> VDQ
>
>
> In
draft2.2, ClassB frames requested to be marked fairness
eligible
> and with no shaperC credits are not
accepted for transmission.
> But this classB
frame will be HOL of other classB frames including CIR
> traffic.
>
> Thanks,
> Winnie Shao
> Senior Software Engineer
>
IXA Development Center, Shenzhen Branch, PRC
>
I-net: 8-754-1008
>