XOFF (Transmission Off) is a control character used in telecommunications and computer networking to signal the temporary stoppage or pause in the transmission of data. It operates in tandem with XON in the XON/XOFF software flow control method, which is especially utilized in serial communications.

Here’s a brief overview of XOFF:

Control Character: XOFF is represented by the control character with the ASCII value of 19 (or 0x13 in hexadecimal). In ASCII representation, it’s denoted as ^S or Ctrl-S.

Function: The primary role of the XOFF character is to tell the transmitting device to halt or pause its data transmission. When the receiving device’s buffer (temporary storage) nears its capacity and can’t handle more incoming data promptly, it sends an XOFF character to the transmitting device.

Usage: XOFF is used in conjunction with the XON character in the XON/XOFF flow control scheme.

  • When the receiving device is nearing its buffer capacity, it sends an XOFF signal to the transmitting device to indicate, “Pause your transmission; I can’t handle more data right now.”
  • Once the receiving device has processed enough data from its buffer and is ready for more, it sends an XON signal to signal the transmitting device to resume sending data.

Software Flow Control: XON/XOFF is a software-based flow control mechanism. This means that rather than relying on separate hardware signals or lines, it uses these control characters embedded within the data stream itself to manage data transmission.

Advantages: The primary benefit of XON/XOFF is that it doesn’t need extra hardware or dedicated signal lines, making it ideal for straightforward serial connections.

Drawbacks: A potential challenge with XON/XOFF is the possibility of data confusion if the actual transmitted data accidentally includes XON or XOFF characters. Various techniques, like data escaping or byte stuffing, can manage this potential issue.

In a nutshell, XOFF is a control signal indicating, “Stop sending data for now,” and is an essential part of the software-based flow control method called XON/XOFF.