[e2e] Question the other way round:

Ted Faber faber at isi.edu
Wed Nov 20 11:13:40 PST 2013

On 11/20/2013 10:23, Joe Touch wrote:
> On 11/19/2013 7:14 PM, Ted Faber wrote:
>> Unless someone's edited it, you should read the first sentence again.  I
>> see:
>>> Congestion control concerns controlling traffic entry into a
>>> telecommunications network, so as to avoid congestive collapse by
>>> attempting to avoid oversubscription of any of the processing or link
>>> capabilities of the intermediate nodes and networks and taking resource
>>> reducing steps, such as reducing the rate of sending packets.
>> I read the reference to packets as an example.
> Me too.
> But circuits don't have a collapse or oversubscription. They simply
> reject calls that aren't compatible with available capacity.
> I'm not disagreeing with the definition; I'm disagreeing with the
> assumption that having a network implies congestion and thus the need
> for congestion control.
> There are a variety of mechanisms that avoid congestion, typically by
> a-priori reservation (circuits), or by limiting resource use implicitly
> (e.g., ischemic control). These are a kind of proactive control that
> avoid congestion in the first place.

A agree with those facts.  A purist that wants to assert that all
networks have congestion control would say that your admission control
or ischemic control is a proactive centralized congestion control.  I'm
not of a purist to have that fight.

I do think that it's worth noting that even the admission control
problem gets difficult with scale quickly.  An admission control that
beings calls in slowly enough looks a lot like congestion collapse to
the person trying to make a call.

And there are very few pure reservation systems of any scale in the
world.  As you know, phone system circuits are heavily multiplexed and
violating the assumptions that underlie those systems can congest them,
circuits or no.

> That's not to say whether these mechanisms are scalable or efficient
> compared to the resource sharing afforded by packet multiplexing.

It's the same old thing.  Pre-book your resources and underuse them or
overbook and deal with contention.

What makes congestion control an interesting endeavour from my
perspective is doing that job in the presence of large scale and
imperfect information.

Economists will say that I've made the problem too easy by only dealing
with info transfer which allows some simplifying assumptions.

Ted Faber
http://www.isi.edu/~faber           PGP:
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