Subject: problem descrition (was Re: Mod: TOS bit semantics )

From: Scott Bradner <[email-masked]>
Date: Sat, 8 Nov 1997 21:21:09 -0500 (EST)

Tony sez:
--
The problem, as I see it, is that we would like to provide differentiated
services over the Internet.  The whole Internet.  We would like to do this
in a practical, scalable, well-defined, interoperable way. 
--

focus on delay, reliability, or bandwidth, all or ??

Scott

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From: Paul Ferguson <[email-masked]>
Date: Sun, 09 Nov 1997 00:14:32 -0500

Delay, sure. Reliability? I can't see how we could factor
reliability into the equation and avoid getting sucked into
a signaling protocol black hole.

The problem thus far has been trying to solve all possible
problems. I think we need to step back and take a hard look
at what we are trying to accomplish, for sure. Coming up
with reasonable diff-serv mechanics is going to involve
making a few compromises.

I think that some reasonable selection criteria for
delay (transmission servicing) and drop preference
is easy enough. Trying to factor in other criteria,
such as available local & aggregate path bandwidth,
gets us back into a reliance on an signaling protocol.

I suppose the question that needs to be answered is
whether we are trying to come up with a 'light-weight
RSVP', or a mechanism by which use of a couple of simple
bit flags set in packets can be used to trigger some sort
of calculated action on traffic under certain conditions?

- paul

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From: Zheng Wang <[email-masked]>
Date: Sun, 09 Nov 1997 22:52:48 -0500

>focus on delay, reliability, or bandwidth, all or ??

Yes, we need discuss the problems we try to solve
in diff-serv. 

It seems to me that the current simple FIFO model creates two problems:

1) it encourages greedy behaviors (the bad guy gets more - people 
use multiple tcp connections to get more bandwidth)

2) it makes it difficult to quantify the service. For example, if
a customer is not satisfied with the bandwidth he is getting
and tells his ISP that he wants to pay twice of the basic fee and get
twice the bandwidth he is getting now (or he wants to pay for two
accounts and use them as a single super account). It is very difficult
for an ISP to implement now which is very unsatisfactory both for the
customer and the ISP.

Multiple delay classes do not solve those problems. Users in the upper
class do not have to worry about those in the lower class, but within
a single class, the problems remain the same. The only difference is that
the upper class gets more bandwidth by eliminating users in lower
classes. However, it is known that simple priority queuing can cause users
in lower classes to be completely starved.

What I proposed in the User-Share scheme is to use a resource sharing
approach. We define a basic service unit as a "share" so that a
user's right in sharing the network resource can be quantified 
with the number of shares the user has. This allows, for example,
an ISP to create a Silver account that is equivalent to 3 basic
accounts. Such differentiation does not have the starvation problem
that occurs in single priority-based scheme. The traffic isolation 
also eliminates the incentive for greedy behavior.

As an abstract concept, the "share" here is not that dissimilar to the
shares in a company. A share is the basic unit of owership and
it quantifies exactly how much one owns a company (rather than just
saying that one is an owner of the company), and one's relative rights
to the company's profits (or losses).

Cheers
Zheng

Cheers
Zheng

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From: Paul Ferguson <[email-masked]>
Date: Mon, 10 Nov 1997 07:11:12 -0500

>in lower classes to be completely starved.

Zheng,

Fairness is all well and good, but you can't provide differential services
with fairness, as you already well know.

I don't believe anyone is necessarily meaning to imply that a FIFO
scheme is needed here. A variable depth, multi queue scheme with
WFQ might do the trick.

- paul