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 RFCcomplete; 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 over- flow, 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.
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.
RFCAND 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 RFCstrUCture 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
about complexity and resulting response times. This is a difficult
problem and it deserves more study after we have exercised the
current RFCspecifications. We hope to offer constructive
suggestions with respect to the RFCin the future.
JFH:hs
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