/ɜːr-dʒ/

n. “A TCP control flag indicating that certain data should be treated as urgent.”

In the context of the Transmission Control Protocol (TCP), URG (short for urgent) is a flag used to indicate that some of the transmitted data in a segment is urgent and should be prioritized by the receiving application. The flag works alongside the Urgent Pointer field in the TCP header to specify the position in the data stream where the urgent data ends.

Key characteristics of URG include:

  • Marks Urgent Data: Signals that part of the segment requires immediate attention.
  • Works with Urgent Pointer: Defines the end of the urgent data in the byte stream.
  • Application-Level Handling: The receiving application decides how to process the urgent data.
  • Optional Use: Rarely used in modern applications but still supported for legacy protocols.

Conceptual example of URG usage:

// TCP segment with URG flag
Client sends segment with URG flag set
Urgent Pointer indicates urgent data boundary
Server prioritizes delivery of urgent data to application
Remaining data continues normal processing

Conceptually, URG is like flagging a portion of a message with “handle this immediately,” ensuring the recipient pays attention to critical information before other routine data.

Network
Protocol
Communication