Subject: diff-serv and MPLS

From: Jean-Yves Le Boudec <[email-masked]>
Date: Tue, 23 Dec 1997 20:28:55 +0200

If MPLS is going to become a reality, why not use tags for differentiating
packets. With Yoram's scenario, the ISP ingress router classifies packet
according to the flowspec carried in RSVP reservation messages and appends
to them a label which means "high priority". Deciding which label
corresponds to which priority is a matter of local implementation and can
be negotiated during with the label distribution protocol.

Advantage: no need to cast in stone the number of bits we need for which
service. All we need is appropriate attributes in the label distribution
protocol.

Drawback: requires MPLS

JY

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From: Tony Li <[email-masked]>
Date: 23 Dec 1997 16:59:04 -0800

> service. All we need is appropriate attributes in the label distribution

This is indeed the intent of some of us working on MPLS.  I should point
out that there are currently 3 bits in the label header for encoding QoS,
so that there are two alternatives:

1) The one described above, where a particular LSP is tied to a particular
   flowspec.

or

2) Tie an LSP and QoS value to a particular flowspec.  This has the
   advantage that it requires fewer LSPs and thus scales more nicely.

Tony

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From: Masataka Ohta <[email-masked]>
Date: Wed, 24 Dec 97 17:25:45 JST

JY;

> If MPLS is going to become a reality,

It is not. It simply does not scale.

Non-the-less,

> why not use tags for differentiating
> packets.

it's not a bad idea, as long as the link already has tags. But, as
L2 links support multiple L3 protocols, they always have tags to
distinguish L3 protocols.

That is, it's not a problem to have assigned one, three, seven or
fifteen more new Ethertypes or PPP types for differentiated IPv4
and IPv6 service.

The important difference from poor MPLS is that tags for the
differentiation are not destination specific.

> Drawback: requires MPLS

No, we don't need MP something.

We, at most, need IP specific services.

The question, of course, is, "do we need differentiated service at all?"
and I'm quite negative.

							Masataka Ohta