1. A method for processing cells at a user-network interface with automatic identification of virtual circuit identifiers and a testing function, the method comprising: distinguishing the source of the cell; when the cell is from a first source, testing the cell against at least one selected criteria; when at least one test determines the cell is invalid, marking the cell; when the tests determine the cell is valid, translating a virtual circuit identifier to a default setting; and forwarding the cell to a queue for further processing.