Network Working Group J. Postel
Request for Comments: 864 ISI
May 1983 Character Generator Protocol
This RFC specifies a standard for the ARPA Internet community. Hosts on
the ARPA Internet that choose to implement a Character Generator
Protocol are expected to adopt and implement this standard.
A useful debugging and measurement tool is a character generator
service. A character generator service simply sends data without regard
to the input.
TCP Based Character Generator Service
One character generator service is defined as a connection based
application on TCP. A server listens for TCP connections on TCP port
19. Once a connection is established a stream of data is sent out
the connection (and any data received is thrown away). This
continues until the calling user terminates the connection.
It is fairly likely that users of this service will abruptly decide
that they have had enough and abort the TCP connection, instead of
carefully closing it. The service should be prepared for either the
carfull close or the rude abort.
The data flow over the connection is limited by the normal TCP flow
control mechanisms, so there is no concern about the service sending
data faster than the user can process it.
UDP Based Character Generator Service
Another character generator service is defined as a datagram based
application on UDP. A server listens for UDP datagrams on UDP port
19. When a datagram is received, an answering datagram is sent
containing a random number (between 0 and 512) of characters (the
data in the received datagram is ignored).
There is no history or state information associated with the UDP
version of this service, so there is no continuity of data from one
answering datagram to another.
The service only send one datagram in response to each received
datagram, so there is no concern about the service sending data
faster than the user can process it.
The data may be anything. It is recommended that a recognizable
pattern be used in tha data.
One popular pattern is 72 chraracter lines of the ASCII printing
characters. There are 95 printing characters in the ASCII
character set. Sort the characters into an ordered sequence and
number the characters from 0 through 94. Think of the sequence as
a ring so that character number 0 follows character number 94. On
the first line (line 0) put the characters numbered 0 through 71.
On the next line (line 1) put the characters numbered 1 through
72. And so on. On line N, put characters (0+N mod 95) through
(71+N mod 95). End each line with carriage return and line feed.