From: Tony Li <[email-masked]>
Date: Sat, 8 Nov 1997 18:23:40 -0800 (PST)

Subject: Re: The problem with tagging packets
References: <[email-masked]> <[email-masked]>
From: Tony Li <[email-masked]>
Date: 08 Nov 1997 18:23:40 -0800
In-Reply-To: [email-masked]'s message of 8 Nov 97 22:52:20 GMT
Message-ID: <[email-masked]>
Lines: 39
X-Mailer: Gnus v5.3/Emacs 19.34

David,

> Even with high priority non-adaptive apps and catastrophic topology changes?

Yes.

> If the network topology is fixed and all the apps are perfectly behaved (like
> TCP), this might work, but in reality, we need more than two levels.

Why?

> John Curran of GTE is quoted in a recent issue of the Cook report as saying
> that GTE plans to <.... use SONET APS ...>
> There's an obvious
> opportunity to sell that bandwidth (as best effort with no reliability in the
> case of catastrophic failures) provided that a mechanism exists to dump that
> traffic into bitbuckets immediately upon catastrophic failure (and charge
> more to people who don't want their traffic treated that way).  The bit
> we use to avoid congestion in a normally functioning network will not
> help take advantage of this opportunity.

This seems like a fine argument for being able to distinguish best effort
from non-best effort traffic.  That requires 1 bit.

Given that the bulk of the traffic on the network is and, IMHO, will
continue to be best effort, and that we have to engineer for those traffic
levels anyway, what is the demand for multiple levels of 'better' traffic?
Certainly one can architect a great deal of granularity, but given the
law of large numbers, is there any pragmatic difference?  If your voice app
is prioritized higher than your video app, does it actually get better
service?  Do those high priority queues ever congest, anyway?

Further, just what is the correlation between priority and drop
preference?  If it is -1, then why do we need to differentiate?

In practical terms, can this problem be solved with only one bit?

Tony

---

From: David Black <[email-masked]>
Date: Sat, 08 Nov 1997 22:03:27 -0500

Tony,

> from non-best effort traffic.  That requires 1 bit.

At least one if not both of those classes of traffic need congestion control
for the ordinary case in which the ring is intact.  That's the second bit.
The use of "best effort" in this context is potentially confusing because
the traffic that runs over the bandwidth that is being used today is 
best effort (and "best effort with/without catastrophic failure immunity"
is one heck of a mouthful).

> levels anyway, what is the demand for multiple levels of 'better' traffic?

Start with the basic "best effort" service offered over the intact ring. I
suggest that the following three variations are commercially interesting:

(1) "best effort" plus some degree of immunity to congestion (e.g., drop pref.)
(2) "best effort" as is
(3) "best effort" minus catastrophic failure protection

There's the fourth possibility of minus catastrophic failure protection plus
congestion immunity, but I'm sceptical about that one for now.

In any case, 3 levels of service can't be distinguished with 1 bit.

--David

============================================================================
David L. Black            THE OPEN GROUP     Voice: +1 (617) 621-7347
The Open Group                                 Fax: +1 (617) 621-8696
Eleven Cambridge Center      RESEARCH       E-Mail: [email-masked]
Cambridge, MA  02142        INSTITUTE         http://www.opengroup.org/~dlb/
============================================================================

---

From: Jon Crowcroft <[email-masked]>
Date: Mon, 10 Nov 1997 08:48:38 +0000

>preference?  If it is -1, then why do we need to differentiate?
 
right....

i like a 1-bit priority
scheme where we dimension the net for X% priority, 100-X% 2nd level,
and then apply RED within both classes. The lower class gets a higher
drop probability, necessarily, under congestion, but gets a share of
the higher class when its underused (and the higher priority class
gets a share of the lower priority class, but gets dropped above its
share some percewnt, where i tend to think Van is right ,and 100% is
right, when the lower priority class is "full")

 >In practical terms, can this problem be solved with only one bit?

yes...(oh, wait, i don't do implementations that sell for money,
better ask someone who does....:-)

cheers

 jon