Re: int-serv over e.g. ATM

[Andrew Smith <[e-mail]>]

> Date: Sat, 11 Nov 95 12:14:32 -0500
> From: [e-mail] (Noel Chiappa)
> To: [e-mail], [e-mail], [e-mail], [e-mail]
> Subject: Re: int-serv over e.g. ATM
> Cc: [e-mail]

Noel,

>     From: Curtis Villamizar <[e-mail]>
> 
>     On the other hand, SVCs may cost money. ... If you can often use either a
>     shared VC to the router (shared with other traffic from the same router) or
>     use a VC to that router rather than a direct VC all the way, you might
>     still get the QoS you want and reduce your costs when the router is lightly
>     loaded, and get the QoS you want when rejected using a direct VC.
> 
> This sounds to me like a pricing anomaly, i.e. an artifact of prices that
> don't correspond to the actual resources used. Carrying the packets around
> should cost the same in terms of resources consumed, no matter how many layers
> of mechanism you use to do it. So, I'm not sure how imporant this case is; it
> might go away since the market tends to drive prices toward "real" prices.

Unfortunately, reality intervenes in the short term :-( 

> About the only reason I can think of where it might be genuinely cheaper is if
> you have saved the overhead of state/setup required for a separate VC all
> through the net. If this is that big a deal, how come ATM isn't trying to
> aggregate VC's? 

The state overhead of VCs is considerable and relatively badly understood. The 
state involved for connectionless (best-effort) forwarding in a router is minimal 
and is well understood. The state for QoS-based forwarding in a router is significantly
less than that for VCs. ATM is trying to crawl before it tries running or even 
walking. VC aggregation into VPs will come later.

> But the "do we have to aggregate flows" is a whole separate
> can of worms.

It is not yet clear whether explicit-QoS flows need to be aggregated (the answer
is probably: "yes, but not urgently right now"). It is clear that best-effort flows 
do need to be, just in order to be able to build ATM-based networks as large as 
existing LAN-based ones are are now, let alone allowing for growth.

> 	Noel
> 

Andrew


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