Network Working Group                                         E. Harslem
Request for Comments: 39                                      J. Heafner
                                                                    RAND
                                                           25 March 1970


                  COMMENTS ON PROTOCOL RE: NWG/RFC #36

   We offer the following suggestions to be considered as additions to
   the April 28th 1970 protocol grammar specifications.

   ERROR MESSAGES

        <ERR> <Code> <Command in error>

   It is desirable to include debugging aids in the initial protocol for
   checking out Network Control Programs, etc.

   There are three classes of errors--content errors, status errors, and
   resource allocation or exhaustion. <Code> specifies the class and the
   offending member of the class.  The command is returned to the
   sending NCP for identification and analysis.

   Examples of status errors are: messages sent over blocked links and
   attempts to unblock an unblocked link.  Examples of content errors
   are: an invalid RFC complete; a message sent on a link not connected;
   closing of an unconnected link; and an attempt to unblock an
   unconnected link.  Examples of resource errors are:  a request for a
   non-existent program and connection table overflow, etc.  Resource
   errors should be followed by a <CLS> in response to the <RFC>.

   QUERIES

        <QRY> <My   Socket>  < >

   or   <QRY> <Your Socket>  <Text>

   Queries provide an extension to the <ERR> facility as well as limited
   error recovery, thus avoiding re-initialization of an NCP.

   The first command requests the remote NCP to supply the status of all
   connections to the user specified by the user number in <My socket>.
   The second is the reply; <Text> contains the connection status
   information.  If an NCP wants the status of all connections to a
   remote HOST, the <My Socket> is zero.






Harlsem & Heafner                                               [Page 1]

RFC 39            COMMENTS ON PROTOCOL RE: NWG/RFC #36        March 1970


   PROGRAM TERMINATION NOTIFICATION

        <TER> <My Socket>

   This command supplements rather than replaces <CLS>.  It severs all
   communication between a program and those programs in a given HOST to
   which it is connected.  This command performs what would otherwise be
   handled by multiple <CLS> commands. <My Socket> contains the sender's
   user number.

   HOST STATUS

        <HCU>
        <HGD>

   These messages (HOST coming up and HOST voluntarily going down) are
   compatible with asynchronous, interrupt-driven programs, as opposed
   to the more conventional post/poll method.

   TRANSMIT AND BROADCAST

        <TRN> <Body>
        <BDC> <Body>

   Unlike the previous commands, these are not sent over the control
   link, but rather over links assigned to user programs.  The prefix of
   <TRN> or <BDC> indicates, to the receiving NCP, the disposition of
   the message body. <TRN> indicates a message to be passed to a single
   process. <BDC> specifies to the destination NCP that the message is
   to be distributed over all receiving connections linked to the
   sender.  In response to a system call by the user to an NCP
   requesting <BDC>, the NCP generates one <BDC> to each HOST to which
   the sender is connected.

   RFC AND DYNAMIC RECONNECTION

   This protocol is complex; it proliferates control messages; it causes
   queues (to become associated with re-entrant procedures) that are
   artificially imposed via the protocol (remote AEN assignment); and
   discounts the situation where only controlling process "A" has
   knowledge that slave process "B" should be "rung out" in a dynamic
   reconnection.

   The <ERR>, etc., are suggestions for inclusion as additions in the
   April 28th protocol specifications.  The above criticism is, of
   course, not intended to affect modification of the RFC structure by
   April 28th, nor to reflect on those who planned it.  We have not
   studied the problem.  It is meant, however, to voice our concern



Harlsem & Heafner                                               [Page 2]

RFC 39            COMMENTS ON PROTOCOL RE: NWG/RFC #36        March 1970


   about complexity and resulting response times.  This is a difficult
   problem and it deserves more study after we have exercised the
   current RFC specifications.  We hope to offer constructive
   suggestions with respect to the RFC in the future.



   JFH:hs


         [ This RFC was put into machine readable form for entry ]
          [ into the online RFC archives by Mario Vitale 08/99 ]







































Harlsem & Heafner                                               [Page 3]