The most widely used standard for defining digital certificates. For example, both Netscape and Microsoft use X.509 certificates to implement SSL in their Web servers and browsers.

One of the most common flow control protocols for asynchronous communication is called xon-xoff. In this case, the receiving device sends a an xoff message to the sending device when its buffer is full. The sending device then stops sending data. When the receiving device is ready to receive more data, it sends an xon signal.