+.PP
+TCP supports one socket option which is set with
+.IR setsockopt (2)
+and tested with
+.IR getsockopt (2).
+Under most circumstances, TCP sends data when it is presented;
+when outstanding data has not yet been acknowledged, it gathers
+small amounts of output to be sent in a single packet once
+an acknowledgement is received.
+For a small number of clients, such as window systems
+that send a stream of mouse events which receive no replies,
+this packetization may cause significant delays.
+Therefore, TCP provides a boolean option, TCP_NODELAY (from
+.IR <netinet/tcp.h> ,
+to defeat this algorithm.
+The option level for the
+.I setsockopt
+call is the protocol number for TCP,
+available from
+.IR getprotobyname (3N).
+.PP
+Options at the IP transport level may be used with TCP; see
+.IR ip (4P).
+Incoming connection requests that are source-routed are noted,
+and the reverse source route is used in responding.