Editing Transmission Control Protocol (section)

===Out-of-band data===
It is possible to interrupt or abort the queued stream instead of waiting for the stream to finish. This is done by specifying the data as ''urgent''. This marks the transmission as [[out-of-band data]] (OOB) and tells the receiving program to process it immediately. When finished, TCP informs the application and resumes the stream queue. An example is when TCP is used for a remote login session where the user can send a keyboard sequence that interrupts or aborts the remotely running program without waiting for the program to finish its current transfer.<ref name=comer/>

The ''urgent'' pointer only alters the processing on the remote host and doesn't expedite any processing on the network itself. The capability is implemented differently or poorly on different systems or may not be supported. Where it is available, it is prudent to assume only single bytes of OOB data will be reliably handled.<ref>{{cite web |last= Gont |first= Fernando |title= On the implementation of TCP urgent data |publisher= 73rd IETF meeting |date= November 2008 |url= http://www.gont.com.ar/talks/IETF73/ietf73-tcpm-urgent-data.ppt |access-date= 2009-01-04 |archive-date= 2019-05-16 |archive-url= https://web.archive.org/web/20190516181338/https://www.gont.com.ar/talks/IETF73/ietf73-tcpm-urgent-data.ppt |url-status= live }}</ref><ref>{{cite book |last= Peterson |first= Larry |title= Computer Networks |url= https://archive.org/details/computernetworks00pete_974 |url-access= limited |publisher= Morgan Kaufmann |year= 2003 |page= [https://archive.org/details/computernetworks00pete_974/page/n419 401] |isbn= 978-1-55860-832-0}}</ref> Since the feature is not frequently used, it is not well tested on some platforms and has been associated with [[Vulnerability (computing)|vulnerabilities]], [[WinNuke]] for instance.