GENWiki

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]