Request For Comments - RFC1159
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Network Working Group R. Nelson
Request for Comments: 1159 Clarkson University
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
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RFC 1159 Message Send Protocol June 1990
is sent back to the client containing exactly the same data.
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 issues are not addressed in this memo.
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