Re: [8023-CMSG] Proposed Upper Layer Compatibility Objective

[Hugh Barrass <hbarrass@xxxxxxxxx>]

Title:

David,

My example was considering frames that have the same priority. Adding priority to the mix simply multiplies the problem by the number of priority levels.

Hugh.

David Martin wrote:

Hugh,

For sake of discussion, if you take as a given that all bridges have 8 output queues per port, where frames are classified based on CoS (MEF terminology) aka user_priority (802.1 terminology), then if a downstream bridge could send a Pause_CoS_n (where n=0..7) backwards / upstream, wouldn't that alleviate the scalability issue you mentioned?

In arithmetic terms, Device 1 would need 8*P queues, where P is the number of ports it has.

Doesn't the scalability issue you mentioned only arise when different bridges use different output queue classification approaches? Then I could imagine a squared-type of relationship.

Just trying to follow the line of reasoning here.

Thanks.

...Dave

David W. Martin
Nortel Networks
dwmartin@ieee.org
+1 613 765-2901 (esn 395)
~~~~~~~~~~~~~~~~~~~~

-----Original Message-----
From: Hugh Barrass [mailto:hbarrass@CISCO.COM]
Sent: Thursday, May 20, 2004 9:23 AM
To: STDS-802-3-CM@listserv.ieee.org
Subject: Re: [8023-CMSG] Proposed Upper Layer Compatibility Objective

Brad,

I've answered below:

Booth, Bradley wrote:

>Hugh,
>
>I want to lock in on one paragraph you mentioned.  It is listed below:
>
>"The only use of PAUSE that would (might) work would be if device 2
>could
>signal to device 1 that only frames destined for port K should be
>paused. This would require that device 1 must understand how device 2 is
>going to classify and direct the traffic and device 1 must maintain
>separate queues on its output port corresponding to the output ports of
>device 2. This means that device 1 will wind up with a total number of
>queues equal to the sum of all the queues on all of the devices
>connected to it. Scaling for more than 2 devices is left as an exercise
>for the reader."
>
>You said that this would require device 1 to understand how device 2
>classify and directs traffic.  When you say that are you referring to
>the 802.3 portion of device 1?  If you are, then I would agree that we
>have an issue of adding "intelligence" to the 802.3 MAC.  If not, would
>not 802.1 know how to classify this traffic?  Maybe this has to do with
>the definition of port, priority and queue.  It might help if you could
>explain your use of the terminology to a layman.
>
>
>
If device 2 wants to send a message that says, "pause the traffic that
will be directed to my output queue K" then device 1 must understand the
criteria that device 2 will use to forward traffic to its output K. That
may be MAC address, that may be IP address, or something else entirely.

Note that the "output queues" of device 2 may be physical ports, virtual
ports or even s/w queues for an edge device.

Hugh.