Subject: RE: The problem with tagging packets

From: [email-masked] (Kilkki Kalevi NRC/Hki)
Date: Mon, 10 Nov 1997 11:37:03 +0200

On 7 Nov 97 at 11:11 Wu-chang Feng wrote:

> I believe the burden is on you to actually show that one bit isn't   
enough.
> There's been several pieces of work which have shown that one bit is   
enough
> to dynamically adapt to what's going on in the network.

> I think the majority of people agree on one-bit DP but definitely not
> multi-bit DP.  It seems to me that the best approach would be to only
> allocate one bit for now, see how well/poorly it provides service
> differentiation, and then look at allocating the additional bits.

> Wu

I try to clarify my reasoning by three questions:

What do you actually mean by "dynamically adapt to what is going on in   
the network"? It looks like an ABR-service.

Have you any feasible one-bit approach without any reservation mechanism   
for the higher priority part of the flow? There is already a reservation   
mechanism, RSVP.

What is the essential difference between one-bit approach and VBR with   
tagging in ATM-networks?

I hope that this differentiated service effort will not try to re-invent   
ABR, RSVP or VBR with tagging. They are already invented and they are not   
too simple.

If someone can present a simple one-bit approach (without any RSVP or ABR   
type of mechanism) that works smoothly with current TCP/IP applications   
under highly dynamic conditions, I will be very interested to analyze it.

... Kalevi

---

From: Wu-chang Feng <[email-masked]>
Date: Mon, 10 Nov 1997 09:21:45 -0500 (EST)

>> If someone can present a simple one-bit approach (without any RSVP 
  >> or ABR type of mechanism) that works smoothly with current TCP/IP 
  >> applications under highly dynamic conditions, I will be very 
  >> interested to analyze it.

Using a single bit, it provides soft bandwidth guarantees and weighted 
bandwidth sharing without an explicit signalling mechanism in a manner that 
can avoid congestion collapse.  http://www.eecs.umich.edu/~wuchang/pmg/
You certainly can provide multiple levels of service differentiation using 
a single bit.  If someone can present a convincing technical argument that
you need multiple-bits, I would be interested in analzying it.  Are there 
scenarios ISPs are thinking of which cannot be addressed using a single bit?  
If so, what are they?  I'm not against using multiple DP bits if it can be 
shown that multiple bits are absolutely necessary in order to address a 
particular problem which cannot be solved using a single bit.

To address Paul's concern about reliance on the end-host, adaptive marking
at the end-host does not preclude unmarking/dropping at the first hop 
router or anywhere else to enforce network level sevice agreements.  
Poor implementations of the marking at the end-host can be treated in 
the same manner as non-responsive best-effort flows are (through something 
like FRED or FBA).

Wu