Asynchronous

1. In relation to ATM, asynchronous means that sources are not limited to sending data during a set time slot (as is the case with circuit switching). While ATM cells are transmitted synchronously to maintain clock between sender and receiver, the sender is not limited to sending data every, say, 24th cell. Rather, the sender transmits when it has something to send and, when idle, sends empty cells synchronously. So, in short, data is sent asynchronously, cells are sent synchronously.
2. Signals that are sourced from independent clocks. These signals generally have no relation to each other and so have different frequencies and phase relationships.

• Isochronous
• Plesiochronous
• Synchronous