Re: [8023-CMSG] Questions
Brad,
The way you choose to ask the question sends the response in a particular
direction that you may, or may not be intending.
If I were to ask you if 10GBASE-T knows how to forward packets from the
MAC-Client interface one could respond in two different ways where both,
depending on perspective, are technically correct:
1. 10GBASE-T does not know anything about the MAC-Client interface as that
is exposed only in layers above 10GBASE-T.
2. Of course it does. By definition, 10GBASE-T references the upper layers.
These are, therefore, explicitly included in the 10GBASE-T specification.
Now someone might argue with each of these. For instance, the argument to
the second might be, "you don't understand, the MAC is common across
multiple port types." This argument is true, but misses the point. The fact
is, that is the beauty of the layered architecture.
Ethernet is not just the PMD. Ethernet is the PMD and all layers above the
PMD that provide a complete solution, whether those layers are shared or
not.
Just because 802.1 is shared with other 802 "dots" does not mean that when
it is integrated with Ethernet that it isn't part of Ethernet.
Some in 802.1 would argue that all of 802.1 is part of the MAC. 802.1 is
part of Layer 2. 802.1 is part of an Ethernet solution.
There are any number of ways that you could modify your question to get
opposite responses.
Example: Is it understood or implied that 802.3 knows how to direct to and
from multiple queues? Answer: Absolutely. See EPON. But, even without EPON,
MAC-Control knows how to deal with packets to/from control and data queues.
Etc.
My response to 1) would therefore be: 802.1 knows. Therefore, by definition
Ethernet knows.**
jonathan
** Exception: if there is no 802.1, then there are no queues and Ethernet
doesn't know because there is nothing to know. In this case, the question is
moot. :-)
> -----Original Message-----
> From: owner-stds-802-3-cm@LISTSERV.IEEE.ORG
> [mailto:owner-stds-802-3-cm@LISTSERV.IEEE.ORG]On Behalf Of Booth,
> Bradley
> Sent: Sunday, May 16, 2004 6:50 PM
> To: STDS-802-3-CM@LISTSERV.IEEE.ORG
> Subject: Re: [8023-CMSG] Questions
>
>
> Norm,
>
> Thanks for the response. Two follow-up questions:
> 1) Is it understood or implied that Ethernet knows how to
> direct frames
> to and from these 8 queues?
> 2) What if the device does not use a bridge as in an adapter?
>
> Thanks,
> Brad
>
> -----Original Message-----
> From: owner-stds-802-3-cm@LISTSERV.IEEE.ORG
> [mailto:owner-stds-802-3-cm@LISTSERV.IEEE.ORG] On Behalf Of
> Norman Finn
> Sent: Sunday, May 16, 2004 11:11 AM
> To: STDS-802-3-CM@LISTSERV.IEEE.ORG
> Subject: Re: [8023-CMSG] Questions
>
>
> Brad,
>
> I think you did miss the mark, particularly with:
>
> "Considering that Ethernet doesn't know in advance about the
> provisioning
> of the network and does not care about which packets it delays or
> drops,
> then it is likely that 802.1 and the upper layers can do all the
> priorities or differentiated services that they want but will see
> diminishing returns as the load on the network increases."
>
> I would agree with, "Ethernet doesn't know in advance about the
> provisioning
> of the network", but 802.1D bridges certainly do care about
> which frames
> are
> delayed or dropped. Bridges define the use of 8 queues per
> output port,
> and
> frames are marked with 8 levels of priority. Although strict priority
> scheduling is the only queue draining algorithm specified in the
> standard,
> others are explicitly allowed, and most vendors implement
> varieties that
> provide very good latency and bandwidth guarantees. Furthermore, a
> great
> many bridges are able to assign priorities to 802.3 frames based on
> criteria
> such as IP DSCP code points.
>
> In short, ethernet is *far* from "best effort".
>
> -- Norm
>
> Booth, Bradley wrote:
> > My apologies in advanced if the answers are obvious, but
> I've been so
> > focused on cabling and physical layer the last couple of
> weeks, so I'm
> a
> > bit brain dead to upper layer stuff.
> >
> > There has been some talk about differentiated services and
> priorities
> > associated with 802.1 and the upper layers. Here are my questions:
> > 1) If the network is overprovisioned (available bandwidth >= maximum
> instantaneous throughput), then am I correct in assuming that
> > these differentiated services and priorities operate just
> fine because
> > the upper layer protocols within the switches have sufficient
> > bandwidth? Should I also assume that the available
> bandwidth is based
> > upon what the end stations (adapters, servers, etc.) can handle?
> > 2) If the network is not overprovisioned (either in the switches or
> > adapters), then is it fair to assume that these differentiated
> services
> > and priorities will provide diminishing returns as throughput
> increases
> > over the available bandwidth?
> >
> > I keep coming back to the statement others have made that
> 802.1 or the
> > upper layers can handle this, but I cannot help think that
> would only
> be
> > true for an overprovisioned network. Considering that Ethernet
> doesn't
> > know in advance about the provisioning of the network and does not
> care
> > about which packets it delays or drops, then it is likely that 802.1
> and
> > the upper layers can do all the priorities or
> differentiated services
> > that they want but will see diminishing returns as the load on the
> > network increases.
> >
> > This would seem to me like going out and buying a Formula 1 race car
> to
> > use to drive to work in Silicon Valley. A lot of money in fuel and
> > equipment only to sit on 101 during rush hour(s).
> >
> > Am I off the mark here?
> >
> > Thanks,
> > Brad
> >
>