Subject: Re: Don't let Delay eat up all TOS bits.

From: Ed Ellesson <[email-masked]>
Date: Wed, 03 Dec 1997 14:30:11 -0500

Alessio, 

At 06:21 PM 12/3/97 +0100, Alessio Casati wrote:
>
>You say there are many thousands of SNA networks out there working fine using
>queueing priority. I assume every single organisation has its own network
operation center
>deciding which kind of traffic to place in which class. Let's suppose
every sender in the SNA
>net decides autonomously in which class to place its own current traffic
(much resembling what is 
>likely to happen in the internet). What do you expect to happen?

On an SNA network, an application can indicate the Class of Service
directly, or it can use a default setting by indicating a mode name.  On
VTAM, this is under the control of the system administrator for the
mainframe, so it is not likely to be set frivolously.  On PC workstations,
it is possible for an end user to access a configuration file and change
the setting of the Class of Service, if they know exactly what to look for,
but this is not likely, since most end users have bosses that they have to
worry about.    

On the public internet, you don't have to necessarily worry about what your
boss thinks, but if you want premium service, you will have to contract for
it from your ISP.  In the public internet today, if a sender starts sending
TOS bits today, they will be ignored or reset...at least, that is my
understanding...somebody correct me if I am wrong.  

Once an ISP configures their routers to begin looking at and honoring these
bits for the purposes of determining drop or delay preference, I expect
they will also configure them to reset them if the sender has not
contracted with the ISP for the privilege of using the service indicated by
the TOS settings.  

I think that has to be the case for any use of TOS byte, otherwise, an ISP
cannot protect the service level agreements which they enter into for
priority service to specific customers and specific kinds of traffic.  (If
someone wants disagree with me for their specific proposal, please do so.)  

This calls into question the whole business of how to distribute service
class policy to all the devices that are playing with these bits in a large
network, so that they get set properly to begin with, and so that people
are not allowed to steal service for which they have not contracted.  That
work is being done outside this working group, but it is being done,
nevertheless.  

>
>I would also know if there exist statistics about the distribution of
traffic over 
>the different delay classes
>
>-network control
>-high priority
>-medium priority
>-low priority 
>-routine
>
>As far as I could understand from your message, there seems to be
clustering in the
>high priority and low priority classes.
>
> > As I mentioned in earlier postings, SNA uses four priority levels. By
> > default, the network control flows run at the highest priority.  Most SNA
> > networks use at least two additional priorities: "high", for interactive
> > traffic, and "low", for batch traffic, like print jobs, for example.  I am
> > told that the majority of users run their SNA networks with these three
> > priorities, but that maybe 25% use all four priorities (this is an
educated
> > guess, based on experience with customers' networks, but not a hard
number).  
>TIA
>alessio

Regards, 

Ed Ellesson
Sr. Engineer, TCP/IP Technology Management
IBM Networking Software Products
Research Triangle Park, NC 
[email-masked]
919-254-4115