Network Working Group                                          R. Nelson
Request for Comments: 1159                           Clarkson University
                                                               June 1990

                         Message Send Protocol

Status of this Memo

   This RFC suggests an Experimental Protocol for the Internet
   community.  Hosts on the Internet that choose to implement a Message
   Send Protocol may experiment with this protocol.  Please refer to the
   current edition of the "IAB Official Protocol Standards" for the
   standardization state and status of this protocol.  Distribution of
   this memo is unlimited.


   The Message Send Protocol is used to send a short message to a given
   user on a given terminal on a given host.  This is similar to the
   service provided by Unix's write command, which is limited to the
   users on that host.  This service is also known on some hosts as

   As the Internet grows, more and more people are using hosts that do
   not run TCP/IP at all times.  These hosts may be able to use a simple
   protocol that can be implemented in a subset of TCP/IP.  The Message
   Send Protocol is one such protocol.

   Note that a message sending protocol is already defined using TCP.
   The SMTP protocol includes a "SEND" command that will direct mail to
   a user's terminal.  SMTP's SEND is not useful in this instance
   because TCP requires quite a bit of code.  For the purposes of
   standardization, we will include a TCP based Message Send Service.

TCP Based Message Send Service

   One message send service is defined as a connection based application
   on TCP.  A server listens for TCP connections on TCP port 18.  Once a
   connection is established a short message is sent by the client out
   the connection (and any data received by the client is thrown away).
   The client closes the connection after sending the message.

UDP Based Message Send Service

   Another message send service is defined as a datagram based
   application on UDP.  A server listens for UDP datagrams on UDP port
   18.  When a datagram is received by the server, an answering datagram

Nelson                                                          [Page 1]

RFC 1159                 Message Send Protocol                 June 1990

   is sent back to the client containing exactly the same data.

Message Syntax

   The message should consist of several parts.  The first part is a
   single octet indicating the protocol revision, currently decimal 65,
   'A'.  The second part is the name of the user that the message is
   directed to.  This and the remaining parts are null-terminated, and
   consist of eight-bit characters.  Do not strip the eighth bit of the
   characters.  The third part is the name of the terminal.  The fourth
   part is the actual message.

   The total length of the message shall be less than 512 octets.  This
   includes all four parts, and any terminating nulls.

   If the terminal part is empty, then "the right" terminal is chosen.
   If the user part is empty, then the message is written on the

   If this protocol is changed, the revision number will be changed.  In
   no case will any of the four parts be removed.


   It is advisable for servers to strip escape sequences before sending
   them to actual terminals.  Some terminals can do nasty things when
   you send them certain escape sequence.

   In both the TCP and UDP versions of the service, checksums are always

Security Considerations

   Security issues are not addressed in this memo.

Author's Address

   Russell Nelson
   Educational Computing System
   Clarkson University
   Potsdam, NY 13699-5730

   Phone:  (315) 268-6455


Nelson                                                          [Page 2]