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Network Working Group                                          R. NelsonRequest for Comments: 1159                           Clarkson University                                                               June 1990Message Send ProtocolStatus 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.Discussion   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   "SEND".   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 datagramNelson                                                          [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   console.   If this protocol is changed, the revision number will be changed.  In   no case will any of the four parts be removed.Advisories   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   used.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   EMail:  nelson@sun.soe.clarkson.eduNelson                                                          [Page 2]