From: "Norman W. Finn" Subject: Re: Priority, 8 levels or 2 To: mjs@NSD.3Com.COM (Mick Seaman) Date: Wed, 17 Apr 1996 02:05:14 -0700 (PDT) Cc: p8021@nic.hep.net (Sorry for the slow reply, Mick -- I'm in Anchorage at the ATM Forum.) Mick Seaman writes: > > Norm, > In response to your request: > > >> Can you comment on the relationship between the 8 levels of destination > >> MAC priority in 802.1p and the two levels of priority suggested by 802.3 > >> in the source I/G bit? This seems like one priority mechanism too many. > > >> -- Norm > > I have set down a number of thoughts. Some at least, I hope, will prove > pertinent to your concern. Much is background and I have included it > since we have such a wide cc: list on this discussion. > > 1. This is the first I have heard that 802.3 is specifying the source > I/G bit as priority. I'll refrain from saying more until I know > more about the proposal. This was cleared up by earlier E-mail. Sorry, but I evidently started a rumor based on the question to 802.1 posed by 802.3 at La Jolla asking how many levels of priority we might want them to provide. Asking others what he meant, I was told "the I/G bit." Rumors, rumors. Sorry! > 2. In the superset MAC Service (ISO/IEC 10039) and in .1D a > distinction is made between the user priority of a frame and the > access priority. The user priority is (ideally) communicated end to > end (at least at the MAC layer - see further on). The access > priority is a hop-by-hop or segment by segment concept. The access > priority reflects what the frame needs to compete with other frames > on a particular segment... I agree, that's a difference. > 3. Personally I believe that 8 levels of priority far exceeds the > requirements at the MAC layer and that 2 should be quite > sufficient. ... > > 4. However there are a number of powerful arguments, technical, > pragmatic, and human, for keeping the number of priority levels > at 8 in the production of .1p as a standard. > > We have managed to reach consensus, at least in task group > discussion, as of a couple of meetings ago, that we could all > live with 8 priorities and an option to have upto 8 traffic > classes. If two is sufficient, 8 should certainly leave no one wanting more. I haven't objected to 8 levels. > [... cutting down to 2 priority levels would] > cause the number of classes to be reduced, it would also cause > the number of people who are happy with .1p to be reduced. ... [Much text deleted in an argument over 8 vs. 2 levels of prority.] 8 vs. 2 is a side-bar to the real issue, Mick, which I would summarize as: 1. tieing priority to destination MAC address is a mechanism that cannot be used without altering the operation of existing protocols; and 2. distributing that priority information around a large VLAN-bridged installation. I would claim that 802.1p, by allowing unicast registration with priorities, introduces a mechanism that will have difficulty scaling along with 802.1q, and cannot be used by existing protocols. I do not want to standardize something that may well go into hardware unless there is some standards-based use for it. Note that I am not talking about such ongoing work as RSVP. The I/G bit is perfectly compatible with RSVP. I have seen no indication that anyone has suggested a mechanism for IPv4 or IPX to make use of a destination MAC based priority mechanism. If this is due to my lack of knowledge of proposals, I apologize for wasting time, and would greatly appreciate pointers to such proposals. > Having reached consensus I believe (as task group chair) that it is > important to move on to more important issues. The points I have > made above have been aired and heard, other points have been aired > and heard. The time has come to enforce the rule that we will > give agenda time only to new data, not to new opinions (and > certainly not to restating old opinions). The exception to this > rule would be if there was a significant change of opinion > and a request by those who'd changed to revisit the issue and > make a decision against their former stated position. It is tough for a chair to balance suppression of debate against rehashing old issues. The constant turnover in standards groups is always a problem. I have no desire to de-rail the train. (Of course, I also don't want to get railroaded. ;-) Your summary of the issues said nothing about my main points, but talked only of the 8 vs. 2 debate. I was hoping for some reassurance that the issues I raised were groundless. On the other hand, you're not obligated to educate the ignorant. The burden is on me, the newcomer, to at least check the mail archives of p802.1 and the meeting minutes, contributions, etc., and look up the old debate to see whether these points have been raised. Again, I would be grateful for any hints or pointers to summaries of issues, etc. In the meantime, this electronic forum seems to me to be an ideal place for this discussion. (: E-mail always has a low signal-to-noise ratio. :) I intend to use this forum to solicit comments from others to see whether these considerations, which may not have been thoroughly discussed, before, merit the change of opinion you need to reopen debate at the meetings. Thaks for the update. I *very* much appreciate the time you took to summarize the 8-vs.-2 and link-vs.-queue questions. -- Norm From: "Norman W. Finn" Subject: Re: Priority, 8 levels or 2 To: mjs@NSD.3Com.COM (Mick Seaman) Date: Wed, 17 Apr 1996 02:14:57 -0700 (PDT) Cc: nfinn@cisco.com, P8021@nic.hep.net Mick Seaman writes: > > Norm, > In response to your request: RE: MY IMMEDIATELY PRECEEDING MESSAGE. My apologies to Mick for suggesting he answered the wrong question! I got my mail messages confused. His very long answer on 8 vs. 2 priority levels was precisely to the point I raised. In my reply, I'm the one who talked about the other issues, not Mick. I notice what I'd done immediately after sending the message in question, as I continued looking through my mail. Sorry, Mick! My questions about 802.1p remain, and feel my issues are valid, but *please* disregard those parts that accuse Mick of missing my point. (I hate answering e-mail after 1:00 AM. I should know better.) -- Norm