Asynchronous start-stop is the lower data-link layer used to connect computers to modems for many dial-up Internet access applications, using a second (encapsulating) data link framing protocol such as PPP to create packets made up out of asynchronous serial characters. The most common physical layer interface used is RS-232D. The performance loss relative to synchronous access is negligible, as most modern modems will use a private synchronous protocol to send the data between themselves, and the asynchronous links at each end are operated faster than this data link, with flow control being used to throttle the data rate to prevent overrun.