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\subsection{UDP}
\index{udp}

\topic{NAME}
UDP (User Datagram Protocol)

\topic{SPECIFICATION}

\noindent J. Postel. {\it User Datagram Protocol}. Request for Comments 
768, USC Information Sciences Institute, Marina del Ray, Calif., Aug. 1980.

\topic{SYNOPSIS}

\noindent UDP is a trivial protocol that dispatches messages that arrive 
at the host to a process running on the host.

\topic{REALM}

\noindent 
UDP is in the ASYNC realm.

\topic{PARTICIPANTS}

\noindent 
UDP removes a pointer to a long (the UDP port number) from the
participant stack.  UDP ports must be less than 0x10000.  
If the local participant is missing, or if the
local protocol number is ANY\_PORT, UDP will select an unused local
port. 


\topic{CONTROL OPERATIONS}

\begin{description}

\item[{\tt UDP\_ENABLE\_CHECKSUM:}]
Cause the session to use checksums on its outgoing packets.  
(session only)
\begin{description}
\item[{\rm Input:}] none
\item[{\rm Output:}] none
\end{description}

\item[{\tt UDP\_DISABLE\_CHECKSUM:}]
Cause the session to not use checksums on its outgoing packets.
(session only) 
\begin{description}
\item[{\rm Input:}] none
\item[{\rm Output:}] none
\end{description}


\item[{\tt UDP\_GETFREEPORTNUM:}]
Returns an unused UDP port number.  This port number will not be given
out to subsequent UDP\_GETFREEPORTNUM calls until it is released with
UDP\_RELEASEPORTNUM.  This allows an opener to separate reservation of
free ports from the actual open operation, if desired.
(protocol only) 
\begin{description}
\item[{\rm Input:}] none
\item[{\rm Output:}] long
\end{description}


\item[{\tt UDP\_RELEASEPORTNUM:}]
Releases a UDP portnumber previously acquired with UDP\_GETFREEPORTNUM.
(protocol only)
\begin{description}
\item[{\rm Input:}] long
\item[{\rm Output:}] none
\end{description}

\end{description}

\topic{CONFIGURATION}

\noindent {\tt name=udp protocols=ip;}

\topic{AUTHORS}

\noindent Larry Peterson and Sean O'Malley