Via Net Loss (VNL) is a network architecture of telephone systems using circuit switching technologies deployed in the 1950s with Direct Distance Dialing and used until the late 1980s.
The five levels of PSTN switching systems used with VNL were: Class 5 end-office switches provide local telephone service and dialtone to residential, business, and government subscribers, as well as telephone company payphones.
Intrastate calls are generally more expensive than inter-state calls due to favorable tariffs with price plans approved by the Public Utilities Commission or Public Service Commission for each state.
Class 4 switches provide access to long-distance service in rural areas.
Class 3 switches also act as Service Switching Points or SSP's that provide access to Intelligent Network services such as Toll-Free, Virtual Private Network, Calling Card, and Credit Card calls.
Analog trunk connections between Class 1 switches were required to have a loss of zero decibels.