Date: Fri, 21 Jun 1996 17:19:22 -0700 To: Steve Horowitz From: seifert@netcom.netcom.com (Rich Seifert) Subject: Re: Priority Service and 802.3 Flow Control Cc: P8021 , Brian Ramelson/ENG/WEBO/PROMDOM1 At 7:12 PM 6/21/96, Steve Horowitz wrote: > >I am raising this issue without having read the 802.3 flow control >specification .... > >That said, what happens if we have multiple levels of queueing service for the >multiple levels of priority, and one of the queues fills up? As I understand >it today, if you send an 802.3 pause frame, all traffic is paused. This, of >course, has the unintended effect of also pausing the frames of the other >priorities that may actually have queue space available. > >I would recommend one of two approaches to fix this problem. > >1. The pause frame only applies to normal priority queues and their associated >traffic. The thinking behind this is that the higher priority traffic is >likely to be time sensitive and pausing that traffic, well you might as well >drop it anyway. > >2. Allow the pause frame to have priority intelligence. I believe that >this is >allowed in the spec that I did not read, but is it described anywhere? > The currently-defined PAUSE function is not "priority-aware" (since there currently IS NO PRIORITY in Ethernet). We fully expect to either extend the PAUSE function to support priorities, or to create a new opcode for a prioritized PAUSE function, once the priority mechanisms are defined. >Anyway, I think that as part of our work with priorities, we need to liason >with 802.3 to make sure that this works on Ethernet networks that have flow >control. > Part of any effort to add priorities to Ethernet will likely deal with the extension of the flow control mechanism for those priorities. There is currently NO official activity within 802.3 to add priorities to Ethernet. -- Rich Seifert Networks and Communications Consulting seifert@netcom.com 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95030 (408) 395-1966 FAX "... specialists in Local Area Networks and Data Communications systems"