RFC 768                                                        J. Postel
                                                                     ISI
                                                          28 August 1980



                         User Datagram Protocol
                         ----------------------

Introduction
------------

This User Datagram  Protocol  (UDP)  is  defined  to  make  available  a
datagram   mode  of  packet-switched   computer   communication  in  the
environment  of  an  interconnected  set  of  computer  networks.   This
protocol  assumes  that the Internet  Protocol  (IP)  [1] is used as the
underlying protocol.

This protocol  provides  a procedure  for application  programs  to send
messages  to other programs  with a minimum  of protocol mechanism.  The
protocol  is transaction oriented, and delivery and duplicate protection
are not guaranteed.  Applications requiring ordered reliable delivery of
streams of data should use the Transmission Control Protocol (TCP) [2].

Format
------

                                    
                  0      7 8     15 16    23 24    31  
                 +--------+--------+--------+--------+ 
                 |     Source      |   Destination   | 
                 |      Port       |      Port       | 
                 +--------+--------+--------+--------+ 
                 |                 |                 | 
                 |     Length      |    Checksum     | 
                 +--------+--------+--------+--------+ 
                 |                                     
                 |          data octets ...            
                 +---------------- ...                 

                      User Datagram Header Format

Fields
------

Source Port is an optional field, when meaningful, it indicates the port
of the sending  process,  and may be assumed  to be the port  to which a
reply should  be addressed  in the absence of any other information.  If
not used, a value of zero is inserted.

Destination  Port has a meaning  within  the  context  of  a  particular
internet destination address.

Length  is the length  in octets  of this user datagram  including  this
header  and the data.   (This  means  the minimum value of the length is
eight.)

Checksum is the 16-bit one's complement of the one's complement sum of a
pseudo header of information from the IP header, the UDP header, and the
data,  padded  with zero octets  at the end (if  necessary)  to  make  a
multiple of two octets.

(以下，略)

References
----------

[1]     Postel,   J.,   "Internet  Protocol,"  RFC 760,  USC/Information
        Sciences Institute, January 1980.

[2]     Postel,    J.,   "Transmission   Control   Protocol,"   RFC 761,
        USC/Information Sciences Institute, January 1980.