Why SVCs are useful

Basically SVCs are easier to support and more robust than PVCs, even if all
you do is nail them up like PVCs.

As an example, say an ATM service provider sets up a L2 service and a bunch
of ISPs come and begin to interconnect bi-laterally. Each PVC has to be
among three parties -- two ISPs and the ATM service provider. This is time
and error prone, but workable. Now, suppose after all this has been set up,
happens to the ATM switch and it forgets about a PVC. (Of course this would
happen, just like no router would ever get in a strange state and forget a
There is nothing on the endpoints able to re-establish the circuit, even
though it is
obvious that it is down or missing. No one on the endpoints can change the
QoS or
reconfigure their circuits and no one can set up their connection to accept
connection requests on demand, etc.

In short, even without thinking about futuristic bandwidth on demand, SVCs
would make
the current classical paradigm easier to manage and more robust. Your first
is your current service delivery department and NOC.