Urgent data

TCP's urgent data mechanism provides an application-to-application notification mechanism, which can be used by an application to mark parts of the data stream as being more urgent than the normal stream. It is up to the receiving application to interpret the meaning of the urgent data.

In many TCP implementations, including the BSD implementation, the urgent data feature increases the complexity of the implementation because it requires an asynchronous notification mechanism in an otherwise synchronous API. As our implementations already use an asynchronous event based API, the implementation of the urgent data feature does not lead to increased complexity.