Lewis and I attacked the puzzle of trying to figure out how SAS worked from a number of different angles. The system gave a technician the ability to connect to any phone line, so he could run tests to find out why a customer was hearing noise on his line or whatever the problem was. The tech would instruct SAS to dial in to the particular CO that handled the telephone line to be tested. It would initiate a call to a part of the SAS infrastructure at the CO known as a "remote access test point," or RATP.