A Made IT project
Circuit switched, or digital dial-up (switched 56, ISDN) links form on demand. For the duration of a dial-up session, they behave as open pipes. Within the region of a service, the cloud that defines the boundary of that service in principle includes all end points. Establishing a link requires only a few seconds. Redundant paths exist among end points. Peer interaction among end points requires that the number of links grows beyond the number of end points.
Links from end points to the 'cloud' (boundary of the packet-switching service) (X.25, frame relay) are usually open pipes.Within the cloud, connections among end points are usually PVCs. Configuring a new PVC, which requires no
equipment changes, can take as little as a few hours.
Redundant paths can exist among end points. For every-to-every connectivity, the number of links into the cloud does exceed the number of end points (however, the number of PVCs must grow).