> From: Fred Baker <fred@cisco.com>
>> Something that was useful in the circa late 80s DDN was the use of the
>> RFC-791 ToS bits to help in path selection. In particular, it was
>> helpful in sorting out delay-sensitive traffic (candidate for routing
>> via SATCOM vice cable). This capability would still be useful.
> the commercial importance was nil - Proteon and 3COM implemented the
> feature, Proteon found a few takers, but nobody else did that I ever
> heard of. Nowadays, the lowest delay route, the highest throughput
> route, the least cost, and the most reliable, are all the same path -
> the optical one.
I wouldn't be so quick to write off constraint-capable routing - which is
what you're really talking about here. TOS routing, QOS, various kinds of
policy - when you look at them, what they all really are is the ability to
select a path given a set of constraints.
It's hard to say what the network of the future will look like, if you go far
enough out - and so a system which is fine-tuned around what we do today,
instead of providing powerful, flexible, basic capabilities, is likely to be
one that disappoints. (The classic example is the Web, which wasn't even a
gleam in anyone's eye in the last 70's.)
So, it's hard to say we won't need constraint-capable routing in the future.
Here's a blue-sky example, which may not pan out - but it is an example of
the kind of thing that could happen. Let's say that 20 years out quantum
computing is starting to happen - and people, for whatever reason, want to be
able to ship qubits around. Not all paths may support qubit transmission -
presto, you need constraint-capable routing.
It seems that in each decade some people have a use for constraint based
routing, although the specific application has changed over time from policy,
to ToS, to QoS. We've generally been unable to meet that demand, and people
have bodged something together - which I suppose is an argument that "if we
really needed it, people would have done it". On the other hand, some pretty
ugly hacks are being put out there because we don't have it, and because it
would be so very painful (read: impossible) to add it to the current system.
Noel
This archive was generated by hypermail 2b29 : Mon Aug 04 2003 - 04:10:03 EDT