A method of creating physical links between the enichiting and receiving points.
Public switch telephone network offerces two types of services.
1. DILT-UP SERVICES: The customer pays on per-use bases.
2. LEASED DETECATED SERVICES: The customer is geranted exclusive access.
The PSTN maintains large numbers of path but not nearly enough to service all customers simultaneously. When a customer request, a path is switch in to the service which customers need. When the customer hangs up, the path is reused by another customer for other customers.