Subject: RE: [Ieprep] Re: ToS bits in STD-3

From: "King, Kimberly S." <[email-masked]>
Date: Sat, 30 Nov 2002 15:44:23 -0500

> On Tuesday, Nov 26, 2002, at 20:04 America/Montreal, [email-masked] 
> wrote:
> > Perhaps you could comment on the applicability/correctness of the 
> > following requirement out of the DoD Joint Technical Architecture 
> > document:
> >
> > "In addition, all implementations of IP must pass the 8-bit 
> > Type-of-Service
> > (TOS) byte transparently up and down through the transport layer
> > as defined in IETF Standard 3, Host Requirements."

This thread is an example of people talking about different things.  We
began with a discussion about what happens to "DiffServ" marked packets when
they traverse an ISP boundary.  The above was then offered about what a host
should do when it gets/sends a "DiffServ" marked packet. These are different
things. 

Here is an example of the first ... ISP A labels some packets blue, perhaps
it does this for local reasons (e.g., preferential treatment for internal
routing).  Now, ISP B gets some traffic from ISP A.  ISP B has a decision to
make...it can keep blue ones blue or it can relabel them a default color.  

If ISP B gives some special treatment to blue packets and it doesn't choose
to relabel those coming from ISP A then it has just created a vulnerability
for itself. It now has to trust ISP A will not overwhelm it or break ISP B's
handling of blue packets.  Unfortunately, it's also a hard problem to figure
out how to charge ISP A for blue packets over regular ones sent to ISP B
(note this is very different than the Telco model and there are some
fundamental problems in this area).  Hence, without remarking, ISP B would
open itself up to vulnerability without any financial incentives for it.
Therefore, many ISPs choose to remark (this includes the largest ISPs).  

Here is an example of the host topic ... Joe's machine receives some blue
packets for some application it is running.  The application should be
informed this stuff came in as blue.  In addition, the application might
want to send information that packets associated with this application to be
sent over the network should also be colored blue.  

I hope this is more clear now.

Kimberly

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