Date: Fri, 21 Jun 1996 18:16:47 -0700 From: hendel@uask4it-223.Eng.Sun.COM ( Ariel Hendel) To: P8021@hepnrc.hep.net, Steve_Horowitz@prominet.com Subject: Re: Priority Service and 802.3 Flow Control Cc: Brian_Ramelson/ENG/WEBO/PROMDOM1%PROMDOM1@notes.worldcom.com > To: P8021 > From: Steve Horowitz > Date: 21 Jun 96 19:12:49 > Subject: Priority Service and 802.3 Flow Control > > Hi, > > 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. > The case was considered, but in my opinion it was not realistic to specify behavior for a hipotetical priority definition. > 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. > Don't think you can do this per the specification. If you support flow control you are expected to stop. People also view PAUSE as a useful mechanism for other functions that rely on the link stopping, but they will not keep the link blocked for a long period of time. > 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? > Not that I know of. Luca Cafiero made such a proposal but nothing in the spec. MAC Frames and PAUSE Frames are extensible (Rich Seifert dixis). In that sense you are allowed to invent these new PAUSE frames, but for interoperability the priority PAUSE behavior has to be part of the standard. > 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. > Agreed. > > -- Steve > Ariel Hendel Sun Microsystems