RFC 205 (rfc205) - Page 2 of 13

NETCRT - a character display protocol

RFC 205          NETCRT - A CHARACTER DISPLAY PROTOCOL     6 August 1971


NETCRT PROTOCOL - VERSION 3

A. INTRODUCTION

   The UCLA Campus Computing Network (CCN) node intends to provide
   Network access to its conversational remote job entry system URSA.
   The URSA system is display-oriented, supporting only character
   displays with local buffers (originally IBM 2260 displays, now CCI
   301 TV display consoles).  This document defines a third-level
   protocol called NETCRT which allows a Network user in a remote Host
   to look like a CCI console to URSA.  NETCRT is defined in terms of a
   virtual character display ("VCD") terminal, simulated by a process in
   the user host.

   URSA, like many on-line console systems, attempts to provide a good
   man/machine interaction by keeping tight control over the state of
   the terminal.  On the other hand, the Network Working Group has
   deliberately built some "squishiness" into the standard Network
   protocols.  We believe this squishiness is a conceptual mistake when
   dealing with remote man/machine interaction, and we would support
   protocol revisions to allow control over the effective communication
   compliance between processes in different hosts.  However, this
   NETCRT protocol attempts to cope with the present squishiness, which
   is apparently built into a number of host's NCPs.  In fact, we have
   arranged things so a host can improve response time and reduce
   Network traffic with NETCRT by using the message buffering inherent
   in his NCP.

B. THE VIRTUAL CHARACTER DISPLAY

   A VCD consists of the following virtual hardware (see Figure 1):

   1. A rectangular _display screen_ capable of displaying N lines of M
      characters.

   2. A _local buffer_ of M x N characters used to refresh the display.

   3. A _cursor register_ which addresses the characters in the buffer
      (and hence on the screen).  This register controls the writing of
      text into the local buffer from either the keyboard or the server,
      and the reading of the local buffer by the server.

   4. A _keyboard_ containing text keys and control keys.  Each text key
      enters a character into local buffer at the current cursor address
      and steps the cursor register by 1.






Braden