Subject: Re: Number of drop classes

From: [email-masked]
Date: Thu, 20 Nov 1997 09:48:23 -0600

>Comments follow

______________________________ Reply Separator _________________________________
Subject: Number of drop classes
Author:  Rickard Janson <[email-masked]> at Internet
Date:    11/20/97 11:05 AM

Definition of only two drop classes (IN&OUT) will make the 
network planning more difficult than if more drop classes
are defined. The reason is that it is economically impossible 
to allocate enough bandwidth in a complex network topology
so that all IN traffic can be carried unrestricted (without 
drops) on all links - in a worst case (still realistic) traffic 
scenario.
The same statement is valid even if more than two drop classes are 
defined (i.e. no hard garanties for a specific drop class). However, 
the difference is that the network behavior will be more elastic and 
smooth.
> assuming an even distribution of users in services
For example (>2 DC); a premium user might loose a few packets,
at the same time a casual user (low subscription charge)  experience 
a severe drop and the bulk file transfer halts for the time of the 
congestion.
The same example with IN/OUT DC: all users experience same 
drop rate (on the jammed link) if they are sending IN profile.

> I understand your motivation, but what happens if you achieve
> success in your marketing and everyone wants to buy premium service?      
> Market forces will eventually cause competing ISP's to drop pricing on   
> the premium service anyway. "You can get premium service with us for the 
> same amount that our competitor sells you normal service..." Use diff     
>services and monitor the traffic passed/dropped/marked. This will let you  
>provision in a more intelligent manner(read not have to buy excess  
>capacity). IMHO overselling of capacity is a fact of life at many ISP's -  
> diff sevices lets them better balance capacity and demand. 

Ken Peirce 

All opinions expressed herein are mine and not those of my employer, 3COM.

I.e. little correlation exists between the aggregate of users 
IN profiles bandwidth and the actual bandwidth on a specific 
link in a large network.

Cheers/ Rick

------------------------------------------------ 
Rickard Janson                     Ericsson Telecom 
[email-masked]            +46 8 7190486 
------------------------------------------------

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From: [email-masked] (Kilkki Kalevi NRC/Hki)
Date: Fri, 21 Nov 1997 11:08:46 +0200

On 20. Nov. Wu-chang Feng wrote:

>> If one adopts a reactive definition of the congestion
>
>Agreed.  However, this is not a general weakness of single-bit schemes.   
 You
>can be more proactive with single-bit schemes by marking every packet   
within your
>profile / TSpec (as previous work has shown).
>
>When considering adaptive marking, I'm not sure multiple bits   
necessarily
>help. Determining the bit settings for a multiple-bit scheme is akin to   
determining
>a marking rate/fraction with a single bit.  It's only over time that you   
can
>detect the appropriate value(s) for either.
>
>Wu

As it still seems to be difficult for many of you to perceive the   
fundamental meaning and advantage of several drop preference bits, we   
have prepared a short report "Why three bits?" in our web pages   
http://www-nrc.nokia.com/sima/. We hope that the report may somewhat   
clarify the situation.

In this mail I only tell that with 3 DP bits there is no need to keep   
track of every individual flow in every network node, and it makes   
possible to efficiently integrate real-time services with non-real-time   
services.

I guess that some of you will not agree with us on certain statements in   
the report. I cannot, however, understand if someone after carefully   
reading the pages says that there is absolutely no reason to use more   
than 1 DP bit.

.. Kalevi