Trailing-Edge - PDP-10 Archives - cust_sup_cusp_bb-x130c-sb - 10,7/unscsp/nrt/nrt.rnm
There are no other files named nrt.rnm in the archive.
.rm 75
.fig 20
.center 80;NRT - TOPS-10 Network Virtual Terminal Program

Digital Equipment Corporation, Maynard, Massachusetts, U.S.A.

This software is furnished under a license and may be used and copied only
in accordance with the terms of such license and with the inclusion of the
above copyright notice.  This software or any other copies thereof may not
be provided or otherwise made available to any other person.   No title to
and ownership of the software is hereby transferred.

The information in this software is subject to change  without  notice and
should not be construed as a commitment by Digital Equipment Corporation.

Digital  assumes  no  responsibility  for  the  use  or reliability of its
software on equipment which is not supplied by Digital.
.title NRT
.chapter Introduction
.subtitle Introduction
.lm 5
.hl 1
	NRT is a user program which allows a TOPS-10 system to access
the remote terminal handler on another system connected via DECnet.
NRT is expressly supported only for homogeneous connections (i.e.,
connections where the remote operating system is either TOPS-10 or
TOPS-20), however, it knows a limited amount about talking to VMS,
RSX, or RSTS operating systems as well.
	NRT runs as user mode program and is normally run automatically by the
monitor command:
.bl 1
.indent 20
SET HOST remote
.bl 1
where "remote" is the node to which the virtual terminal connection is
to be initiated.  Under these conditions, NRT will be run automatically by the monitor if the
specified node name ("remote") is undefined in the ANF network (if any)
on which the user job currently resides and is "known" to DECnet.
	Note that the beginning sections of this document describes NRT
as assembled with the default feature tests enabled/disabled.  The behaviour
of and messages output by NRT can appear different if other feature tests
are implemented.  The function of each feature test and the change it
makes upon messages output is described in Chapter 3.
	Throughout this document, the node on which NRT is originally
run (i.e. the node where the user types "SET HOST") will be referred to
as the "local host" and the target node (specified as "remote" in the
above "SET HOST" command) will be designated as the "remote host."
	In the examples in this document, user input is usually
underscored; output from the monitor or NRT is not.
	NRT may also be run via the "R" or "RUN" monitor commands, or the
RUN UUO from within a program.  NRT has no CCL entry.
	In the case in which NRT is run by the SET HOST monitor command, then
it will certain command defaults (see user interface below).  If NRT is
started via "R", "RUN", or a RUN UUO it will enter a dialogue which will ask
the user the values which he wishes for the above mentioned defaults.
.chapter User Interface
.subtitle User Interface:  Exit Dialogue
.lm 5
.hl 1 Exit Dialogue
	Unlike ANF, DECnet supports network virtual terminals as a user
program.  Because of this, setting host to a DECnet node ^&does not\& detach
the current job from the user's terminal, but ^&does\& destroy the user's
core image.
	Also, in order to return to the original host node, one ^&does not\&
issue another "SET HOST" command on the remote node, but merely types a
pre-defined "escape character."  Typing this "escape character" at any time
in the dialogue with the remote system enters the user into a dialogue
whereby his characters are interpreted by the NRT program as commands rather
than being sent to the remote host.  This fact is flagged by the output of the message (1):
.fn 4
.bl 1
(1) The type of dialogue described here is known as the ^&NOVICE\&
exit dialogue.  Please see the section on SWITCH.INI for a
description of other exit dialogue formats.
.end foot
.bl 1
.indent 5
[Connection broken, back to node xxxxxx::]
.indent 5
.bl 1
where "xxxxxx" is the name of the local host.
This message, however, can be altered.  Please see the section on SWITCH.INI
support for further details on this.
	Upon entering the dialogue via typing the "escape character", the
user has the following options:
.bl 1
.lm 40
.ts 10,20,40
.indent -30
^&\Command	Mnemonic	Meaning\&
.bl 1
.indent -30
E	E[xit]	Abort the terminal session on the remote node.  The
effect on the job (if any) at the remote node
is determined by the remote operating system.
.bl 1
M	M[onitor]	Return to monitor, but leave the connection
to the remote system open.  If the user does not destroy
his core image before typeing "CONTINue" or "REENTEr", then
the connection to the remote system will be re-established.
If his core image is destroyed, the link to the remote
system will be aborted as if the user had used the "E[xit]" command.
Using "CONTINue" is equivalent to the "R[econnect]" command to NRT;
using "REENTEr" is equivalent to using the "C[hange]" command to NRT.
.bl 1
.indent -30
R	R[econnect]	Reconnect to the remote system (as if the
"escape character" had not been typed).
.bl 1.indent-30
P	P[ass]	Reconnect to the remote system, but pass the "escape
character" through to the remote system.
.bl 1.indent-30
C	C[hange]	Change the break character and then reconnect
to the remote system.  The same effect can be obtained
by using the "M[onitor]" to NRT command followed by a "REENTEr" monitor
command.  If the NRT is assembled with the performance analysis feature
enabled, then this is also the method to enter performance analysis
.bl 1
.indent -30
H	H[elp]	Print a short text describing each of the command options.
This is the command which is executed if an unrecognizable command is typed.
.indent -30
O	O[bscure]	Flush all network messages until one second
(real time) elapses with no messages, or until a character is typed.
This command works for TOPS-10/TOPS-20 remote hosts only and is used in
conjunction with _^O or _^C which cancels the source of messages at the remote
hosts.  the O[bscure] command is used to flush those messages in the
pipe or any more which may come if _^O or _^C was not typed.  _^O or
_^C should be typed ^&BEFORE\& the O[bscure] command.
.lm 5
.bl 1
	The default mode in which NRT runs requires that the above
commands be typed in followed by a carriage return in order for
the command to take effect.  Commands may be abbreviated to uniqueness;
this is currently deliberately set to one character.  This may not
always be the case in future versions, however.  The
carriage-return requirement may also be changed
by an appropriate option in SWITCH.INI.
.bl 1
.subtitle User Interface:  Initialization Dialogue
.hl 1 Initialization Dialogue
	If run via a "RUN" or "R" command or a RUN UUO, NRT enters the
^&long initialization dialogue\&.  If STARTed or REENTEred after any form
of exit (other than following the "M[onitor]" command to the exit dialogue)
or CONTINued from a non-continuable state (any exit other than the "M[onitor]"
command to the exit dialogue),
NRT enters the ^&short initialization dialogue\&.
	The first question of the long dialogue is:
.bl 1
.indent 5
DECnet Intersystem Remote Terminal Service
.indent 5
Escape character (c):
.bl 1
where "c" is the default "escape character."  This is normally _^P (control-P)
but may be changed with an option in SWITCH.INI (it may also
be changed when NRT is assembled).  At this point the
user should enter the desired character he wishes to use as the "escape
character", that is, the character which will initiate the NRT exit dialogue.
The character should ^&NOT\& be followed by a carriage return.  If the default
character is satisfactory, only a carriage return need be entered.
.note ***NOTE***
It is not recommended that any printing character be used for the escape
character, nor the character <ESC>.  NRT will parse some types of ANSI
or DEC terminal escape sequences should the need arise (this is primarily
of interest to VMS users), but if the escape character appears in the
escape sequence, the function of the escape character causing the user
to enter the exit dialogue will take precedence over the parsing of the
ANSI or DEC terminal escape sequence, with resultant confusion to both
NRT and the user.
.end note
	The second question of the long dialogue, and the only question
in the short dialogue is:
.bl 1
.indent 5
Node Name:
.bl 1
At this point the user should enter the name of the desired remote host.
	Note that if this is the short dialogue, the "escape character"
may not be the default character if it was changed through a previous
long dialogue question.
	Upon successfully connecting to the remote system, NRT will
inform the user of the type of operating system to which he is connected
(TOPS-10, TOPS-20, VMS, RSTS, or RSX), its name, and the escape character.
.lm 10
.bl 1
.bl 1
_.^&R NRT\&
.bl 1
DECnet Intersystem Remote Terminal service
Escape character (_^P): ^&_^_\\&
Node Name: ^&MARKET\&
.bl 1
[Connected to TOPS20 system MARKET::] 
[Type Control-_\ to return]
.bl 1
 Market - LCG's Timesharing System , TOPS-20 Monitor 5.3(1600)
.bl 1
[Connection broken, Back at node KL1026::]
.bl 2
.lm 5
.subtitle User Interface:  SWITCH.INI support
.hl 1 SWITCH.INI support
	NRT supports a limited number of switches which modify its
behaviour.  Switches may be abbreviated to uniqueness.  Switches are
^&not\& read from the command line.
	Whenever NRT is run it will look up SWITCH.INI on the UFD
specified by the user's current PPN.  If it is not found, NRT will
assume defaults for all switches (see table below).  SWITCH.INI is
searched for a line beginning with "NRT".  Switches on that line
are used to set the switch values if present.  If the line is not
found, default values are used for all switches; if a switch is not
found in a line then the default value is used for the switch.
	The form of the NRT line in SWITCH.INI is:
.bl 1
.indent 5
.bl 1
.lm 40
.ts 10,20,30,40
.indent -30
.bl 1
^&Switch	Arguments	Default	Meaning\&
.bl 1
.indent -30
/ESCAPE	c	_^P	The default "escape character".
This is the character "c".  The character is expected to be
in SWITCH.INI exactly as it is to be used.  This can be overriden
in the long dialogue.
.bl 1
.indent -30
/MODE	EXPERT	NOVICE	The##type##of##exit##dialogue which
NOVICE		will be initiated (see below).
.bl 1
.lm 5
	The /MODE switch modifies the exit dialogue format.  In the
case of /MODE:NOVICE, the exit dialogue proceeds as described in the
preceding section.  If the setting is /MODE:NOTIFY, then the commands
are read in character mode (no carriage-return is required;
one merely types the escape character followed by the command) and,
instead of the large prompt, the bell is rung on the terminal.
The setting of /MODE:EXPERT is the same as /MODE:NOTIFY except that
the bell is not rung.  In both of these cases, commands ^&MUST\& use the
single character bbreviations for the command.  The latter two settings are
for the benefit of those who use screen editors which may
have the escape character as a command so that the screen will not
be destroyed immediately if the escape character is typed.
	An additional feature of "NOTIFY" and "EXPERT" modes is that
instead of typing "P" to pass the break character, the user may
simply type the escape character twice sequentially for the same effect.
	Note that in the case of the "R[econnect]" command, after
typing the new escape character to the "C[hange]" command (or REENTEring
after the "M[onitor]" command), CONTINuing after the "M[onitor]"
command, or after the "O[bscure]" command the message
.bl 1
.indent 5
[Reconnected to xxxxx system yyyyyy::]
.bl 1
is output, where "xxxxx" is the operating system type (TOPS-10,
TOPS-20, VMS, RSX, or RSTS) and "yyyyyy" is the node name of
the remote host.  In the case of the "O[bscure]" command, the string
.bl 1
.indent 15
.bl 1
will be output to signify the cancelling of output.
The "Reconnected..."  message is not output if the /MODE switch
is set for /MODE:EXPERT or /MODE:NOTIFY.
	The dialogue for the "C[hange]" command (or REENTEring after
the "M[onitor]" command) is (2):
.fn 4
.bl 1
(2) This can change slightly if NRT is assembled with the performance
analysis feature enabled.  See the section on the performance
analysis feature for details.
.end foot
.bl 1
.indent 5
Enter new escape character: ^&c<CR>\&
("c" is typed by the user and is the desired new escape character)
.bl 1
	Note that this dialogue is output regardless of the setting
of the the /MODE switch, so it is not possible to change the escape
character without destroying the screen contents.
	If any undefined command is input, then NRT will (if in NOVICE
mode) display the message:
.bl 1.nofill
.indent 20
%Illegal command, type "H"<CR> for Help
.bl 1.fill.just
NRT will then return to accept a new command.  The terminal's bell
will be rung if NRT is in NOTIFY mode.
.chapter Assembly Parameters
.subtitle Assembly Parameters
.lm 5
.hl 1 Feature tests
	There are a number of feature tests which may be assembled
into NRT.  The purpose of this section is to describe the defaults
and effects of each feature test.
.list 1
	This feature enables the use of Poor Man's Routing.  If this feature
test switch is enabled, the user may explicity specify the nodes to be
used in routing toward the target.  Also, this enables the usage of
searching the file DCN:DNHOST.TXT for an explicit routing path to the target node.  See the documentation
on the PMR subroutine (located in the PMR.MAC source file)
for an example of the entry format of the DNHOST file.
If this feature is turned on, the subroutine and universal
files PMR.REL and PMR.UNV are required.  The (single) source module for
these files is PMR.MAC which can be foundon the Tools Tape.
If this feature is turned off (the default) all nodes must be
visible on the DECnet network in order to be connected to; the user
may not specify a routing path.
	Enabling this feature also allows one to use NRT to connect to
an ANF node which is running a NRTSRV process (distributed on previous
Customer Supported Tapes) if the local host is also running a PSTHRU
task (also distributed on the DECnet Tools Tape).  The PSTHRU acts as
a DECnet to/from ANF protocol translator in this case.  This is accomplished
by specifying the local host as the first node in the connect string, followed
by the desired remote ANF host.  Example:
.indent 5
.bl 1
(local host: KL1026; remote host: TWINKY)
.bl 1
.indent 5
_.^&SET HOST KL1026::TWINKY::\&
.bl 1
	If this feature is not enabled, NRT will output the following
message (3) to the above command line:
.fn 4
.bl 1
(3) The example assumes verbosity bits are set for prefix and first line.  NRT
observes these bits, except there is no long (continuation) message.
.end foot
.bl 1
.indent 5
?NRTNPM Version not compiled with Poor Man's Routing
.bl 1
	The default setting is ^&OFF\&.
	Note that if NRT uses a Poor Man's routing entry from the
DNHOST.TXT file, the entry used will be displayed.  The format of
messages output (which will occur after the user gives the
desired node name and before the connect confirmation message)
are documented in the documentation on the PMR subroutine
package in the PSTHRU area of the DECnet Tools Tape.
	This feature test enables the assembling of the performance
analysis section of NRT.  This feature only works to TOPS-10 or TOPS-20
nodes.  It is intended to give statistics on network line traffic and
utilization.  If enabled, the prompt line output upon entering the
"C[hange]" command to the exit dialogue becomes:
.bl 1
.indent 5
Enter new escape character or [P] to enter performance test mode:
	At this point, entering "P" will ^&NOT\& change the escape
character to "P" but will enter the performance analysis dialogue.
The following questions will be asked:
.bl 1
.indent 5
Comment string for this record (<CR> when done):
.bl 1
This string is an identifying string which is inserted into the data file
for identification purposes.  Any [typable] ASCII string of length less
than 250 (decimal) characters is acceptable.
	After inputting the comment string, NRT will ask:
.bl 1
.indent 5
Number of times to send string:
.bl 1
	NRT has a 30-character test string which is sent character
by character to the host.  This number specifies the number of times
to send the entire string.  Each time a character is sent, the daytime
it was sent is recorded.  When a response comes back from the remote
host, the time differential from the time the character was sent to the
time the response was received is recorded in the data file.
	Performance analysis always appends to the file DSK:NETRSP.DAT.
	After inputting the number of times to send the string, NRT will
.bl 1
.indent 5
[Performance testing for yyyyyy node xxxxxx::]
.bl 1
at which point the user will see the string being sent character
by character.  In the above, "xxxxxx" is the name of the remote host and
"yyyyyy" is the operating system type.
	After sending the performance string the specified number of
times, NRT will type:
.bl 1
.indent 5
End of NRT network performance test
.bl 1
	NRT will then close the file and return to the exit dialogue at
which point the user has all the normal exit dialogue options open to him.
	The data file may be analyzed with the NETDAT program (3).
	The default setting is ^&OFF\&.
.fn 4
.bl 1
(4) Note:  The performance analysis feature and the NETDAT program are
.end foot
	This feature test is for debugging purposes only.  It forces the
error message processor to output, as part of the message, the NSP.
function which encountered the error it is output a message for.
The default and recommended setting is ^&OFF\&.
	This feature test is also for debugging purposes.  It changes
all PJRSTs (or CALLRETs) to PUSHJ/POPJ functions.  This makes it easier
to trace problems on the stack.  The default and recommended setting
is ^&OFF\&.
	This feature test is provided to enable certain consistency
checks, particularly in the core manager.  It should be turned on
only for debugging purposes.  It is automatically turned on if
FTDBUG is enabled.  The default and recommended setting is ^&OFF\&.
	This feature test is defaulted ^&ON\&.  Its purpose is to
enable code to work around certain deficiencies in other operating
system's remote terminal handlers which have not yet been corrected.
	This feature should remain as defaulted; ^&OFF\&.  It causes
NRT to assemble with PSECTs instead of being TWOSEGed.
.end list
.hl 2 Assembly parameters
	The following constitutes a list of assembly time parameters
which may be changed.
.list 1
	This defines the "default default escape character".  In other
words, this is the escape character which is used if the user does
not change it himself either through the long dialogue or through
his SWITCH.INI file.  The "normal" value is Control-P.
	This parameter is applicable only if FTPMR is turned on.  It specifies
the maximum number of nodes which may be specified in a PMR string as
manually typed in by the user.  This has no effect on the size of a PMR
string which may be obtained via the DNHOST.TXT file; the maximum for that
is defined by the assembly parameter PMRSIZ to the PMR subroutine (see the
documentation file for the PMR subroutine on the PSTHRU area of the DECnet
Tools Tape).  The default value is 7.
	This parameter defines the number of output buffers which
are allowed to be queued for output without being output before
NRT blocks waiting for a buffer to become available.  Note that
the buffers need not be full; they must merely be allocated
for output to the TTY:.  Note that NRT waits with PSISER turned
off, so that _^O in particular or the "O[bscure]" command may not
be input to flush output.  Also, due to the mechanics of SCNSER
there is a delay before any interrupt can be granted to NRT siginifying
that input is complete.  Note also that if output is being suspended due to
(for example) a read request on the VAX being "active" the suspension
will be lifted if the output buffer quota is exceeded.
.end list
.chapter General Hints
.hl 1
	This chapter consists of a number of general hints toward
using NRT.  It also contains information on what should be sent
with any SPRs which are submitted for NRT.
	NRT does I/O to device TT:, ^&NOT\& device TTY: during the
main part of the program.  This is a feature to enable using DDT
on NRT without having interference between commands typed to DDT and
commands typed to the program.  This is activated by assigning device
TT: to a terminal other than the user's controlling TTY:.  Note, however,
that commands to the initialization and exit dialogues are typed on
the controlling TTY: only.
.hl 2 Errors
	Upon encountering any kind of error, NRT will save its ACs
in location CRSACS.  It will then output an error message and
usually exit.  The exceptions to the "exit" rule are documented in Appendix A
under the documentation for the specific message which is output.
The user should SAVE the core image if he wishes any action taken for
the problem.  This dump should be included with any SPR which is
sent in for NRT.
	In lieu of sending an SPR, the user may wish to look at the
dump himself.  This is most easily accomplished with FILDDT on
the crash dump file.  NRT by default is assembled with the symbols in
the high segment.  The user may load the ACs used at the time of the
crash which are saved at location CRSACS.
	In debugging many kinds of NRT problems it is many times also
useful to have a trace of the messages being passed between NRT and the
remote host.  This is easily accomplished by using the DNSNUP program
from the Tools Tape, assuming the problem is reproducible.
If this is the case, then a trace covering a time period containing
the error with specifics as to which node is being talked to and
a terminal log of the session should also be submitted along with any
SPR sent on NRT.  This is particularly useful for UED and Link Aborted
type problems (see Appendix A).
.chapter NRT Internals
	This chapter is meant to provide a brief internal look at the basic
algorithms involved in NRT.  It should be read if the user desires to add
additional operating system support or debug NRT crashes.
	Upon being run, NRT initially sets basic defaults; then fills
in values from the user's SWITCH.INI, if applicable.  NRT then enters
the appropriate initialization dialogue.  When all questions have been
answered satisfactorily, NRT OPENs the TTY: in ASCII line mode and initiates
a connection to the desired remote host's network remote terminal server.
Assuming the connection is successful, NRT and the remote host's terminal
server exchange configuration messages as to the features supported by
each and the type of operating system to which NRT is talking.  This
operating system type is displayed in the connect confirmation message.
	NRT then enters an operating specific initialization routine.
This routine decides on default break masks, sends any "bootstrapping"
messages required to the remote system, and sets various flags for the
type of operating system to which it is speaking.
	NRT then enters its main loop (after enabling the software
interrupt system).  NRT is essentially interrupt driven and HIBERs waiting
for either a NSP. interrupt (enabled for input available or state changes),
a TTY: asynchronous I/O complete (input) interrupt, or a timer interrupt
(which is granted only for certain operating systems and under certain
	The exception to the interrupt driven nature of NRT occurs for
the terminal service.  Because changing a terminal break mask does not
grant a PSI interrupt if the new break mask is satisfied by type-ahead,
NRT has the facility to poll the TTY: input service routine while not
at PSI interrupt level.  This is enabled by setting a flag and waking
the job and is done anytime the mask changes if an input would not
be done anyway on the TTY:.
	The interrupt level of NRT includes five routines:  the NSP
service, the TTY: service, timer service, the ATTACH/DETACH
service, and the WAKE service.  Note that, as mentioned
above, the WAKE service is really a form of TTY: service.  Each interrupt
consists of an operating system independent routine and a routine
whose content depends upon the type of operating system to which NRT
is speaking.  The vectors to the operating system dependent portions of the
interrupt service routines are filled in when NRT determines the type
of operating system from the configuration message.
	Upon any condition which causes the interrupt, PSISER will
dispatch NRT to the appropriate operating system independent interrupt
routine.  This routine will perform various universal functions and,
if there is a reason, will call the associated operating system dependent
	The operating system dependent interrupt routine should perform
the appropriate functions and return to the operating system independent
routine, which will dismiss the interrupt.
	NRT then returns to main loop level and sleeps.
	This continues ad infinitum until the user types the escape character
or the link is aborted by the remote host.  In the former case, the user
will be placed in the exit dialogue and he has the option of continuing
the program (with various options) or exitting.  If he exits, the link is
closed and the user is returned to monitor level.  If he continues, the program
continues until he types the escape character again, or the link is
aborted by the remote host.
	If a non-recoverable error occurs or the remote host aborts the
link, then the user is returned to monitor level.  If continued, NRT restarts
from the beginning.
	The priority level of interrupts is:
.list 1
ATTACH/DETACH service (highest)
TTY: I/O complete service
NSP. I/O complete, WAKE service, and TIMER service.  Note that WAKE
service being on this level means that TTY: I/O service actually
can occur on either of two levels.
.end list
	Although TTY: I/O service can occur at a higher level
than NSP., WAKE, and TIMER service, TTY: service will delay actual
processing of the interrupt if one of the other interrupt
service routines are active.  The interlock is done via AOSE
variable INTLVL.  The requested interrupt bits are IORed into
variable TTYSTS and a routine (FRCTTY) is called to queue a
WAKE interrupt (which is TTY: I/O service).  The original high
level TTY: service interrupt is then dismissed.
	ATTACH/DETACH service occurs at the highest level and never defers
but does not interfere with any of the other data structures.  Its
primary purpose is to change all the terminal UDXs when the job
running NRT changes terminals.

.chapter Adding Additional Operating System Support to NRT
	In order to add additional operating system support to NRT, three
things must be ^&THOROUGHLY\& understood:
.list 1
You should understand NRT's internal structure.  This can be obtained by
studying this document, the PLM for NRT, and the source.
You should understand the internals of the operating system whose support
you are trying to add.  The relevant information is usually contained
in the I/O user's guide or equivalent to the remote operating system.
You should understand the type of protocol which is used to communicate
with the appropriate system.  The types of protocols which NRT knows
can be used as examples for how to handle other protocols.
.end list
	Once these things are understood, it is usally easiest to implement the
"basic" read-from-terminal/write-to-terminal functions first, and then the
more esoteric functions, if those exist.  This depends on the type and
complexity of the protocol.  See the PLM for descriptions of general types
of protocols which exist.
	Again, the DNSNUP/DNTATL programs from the Tools Tape are
invaluable in tracking problems.
.appendix Messages
	NRT has a number of error messages which may be output.
Most of these are the standard DECnet architecture error messages
for which the user is referred to the TOPS-10 DECnet Users' Guide.
Messages which are specific to NRT are documented below.
	NRT observes the user's verbosity bits.  However, there is no
long or continuation message.  Note that this is also true for the DECnet standard error messages.
	The following list is arranged alphabetically by prefix.  Note
that all messages start with "?NRT".
	The normal action for NRT to take on any of the below listed
conditions is to exit, however, there are exceptions.  These are noted
under the specific condition in the list below.
.bl 1
.center 80;^&NRT Specific Error Messages\&
.list 1
?NRTCAT Can't add TIMER traps to PSISER
	This message is output during initialization if NRT is unable to
add PITMR. traps to the software interrupt system.  The error code for
the PISYS. UUO is in AC CX in the dump.
?NRTCDP Can't add DECnet NSP. traps to PSISER
	This message is output if NRT is unable to add NSP. traps to the
software interrupt system.  The error code for PISYS. UUO is in
AC CX in the dump.
?NRTCSC Couldn't find specified character
	This error occurs if NRT is scanning its internal input stream
for the last break character in the input stream before a specified point.
The routine SCNLBK is called with the "final" byte pointer to the input
stream.  SCNLBK scans characters until the "final" byte pointer is
encountered, remembering the last break chraracter.  This error occurs
if the "final" byte pointer is not encountered before the end of the
input stream.
?NRTCTP Can't add TTY: to PSI system
	NRT does asynchronous input to the terminal and thus requires
getting software interrupts on input complete.  This error occurs when
NRT is unable to add the TTY: to the software interrupt system at initialization
time.  There error code for the PISYS. UUO is in AC T1 in the dump.
	This error occurs if NRT is unable to increase its size to buffer
?NRTCWT Can't add WAKE Traps
	NRT could not enable PSI traps for WAKE UUOs.  The error code
from the PISYS. UUO is in AC T1 in the dump.
?NRTDNI DEBRK. not implemented
	The DEBRK. UUO to dismiss a software interrupt failed with the
non-skip return.
?NRTDSF DEVSIZ for device TTY: failed
	The DEVSIZ UUO to find the buffer size for the TTY: failed.
The error code for the failure is in AC T1 in the dump.  Submit an
SPR and a dump.
?NRTEDC Expecting Double colon in PMR string
	Also applicable only if FTPMR is on, this message is output if the
user specifies a PMR string with a single colon in it.
?NRTFUF FILOP. UUO failed to open performance file
	NRT could not do the FILOP. UUO to append to the performance
file.  Use the monitor command "SET WATCH FILES" to find the error code,
or examine AC T1 in the dump.  This error can only occur if FTPERF is turned
?NRTIBP Illegal byte pointer
	Routine BPLENG is called to compute the number of bytes to output
to the network in a message from the beginning and final destination pointers.
This routine is coded to work only if the beginning byte pointer specifies
eight-bit bytes and is word aligned.  This error occurs if the initial
byte pointer does not one of those conditions.  The specified byte pointer
is in AC P1 in the dump.
?NRTIBS Illegal byte size
	This error is also part of the BPLENG routine described in the
NRTIBP error immediately above.  It occurs if the byte size specified
in the final byte pointer does not specify eight-bit bytes.
?NRTICA Illegal core allocation
	This error occurs only if FTPARANOID is turned on.  It occurs
if the memory manager is requested to allocate a negative or zero sized
block of core.  AC T1 in the dump contains the requested size; examine the
stack to find the offending calling routine.
?NRTICD Illegal core deallocation
	This occurs only if FTPARANOID is turned on.  It occurs if
the memory manager is requested to return a core block which
is zero length or whose starting address is out of bounds for the
free core pool.  AC T1 in the dump is the starting address; AC T2 is
the size to deallocate.  Examine the stack to find the offending
routine.  Note that it is only the absolute value of the size which is
important (i.e., T2 can be negative).
?NRTILD Illegal digit in number - re-input number
	This error occurs when parsing the number of times to send
the performance analysis string.  The program will not be aborted
and the correct number should be input (this message means the
user typed a non-numeric character in the number).
?NRTINA Interlock not available
	The interrupt level data base interlock was not available to
the lowest level interrupt routine.  This implies that some routine
dismissed without returning the interlock.  Submit an SPR with a dump.
?NRTIOR Illegal operating system type returned in configuration message
	The byte in the configuration message returned by the remote system
upon initiating the connection was of a value larger than the maximum
value known by NRT.  The problem is at the fault of remote system unless
NRT is supposed to understand a new operating system type in which case
symbol MAXOS must be re-defined to include this type and all values
between the default value of MAXOS and the new value must have dispatches
in the OS dispatch tables.  This problem can also occur if the message
which NRT expected to be the configuration message was not.  Currently,
this can happen if a VMS system which is being used as a Poor Man's Routing
node has PSTHRU "logging" "enabled", in which case the PSTHRU task on the
VMS system returns a non-standard PSTHRU ACK message which is followed
by extra text messages which NRT does not know how to interpret.  If this
is the case, turn off PSTHRU "logging" on the VMS system.
?NRTIRS Illegal RSTS function
	This error occurs if a RSTS remote hosts requests a function
which NRT does not know how to handle.  This class of problem should be
traced with DNSNUP.
?NRTITF IN UUO for TTY: failed
	The IN UUO for the TTY: channel failed with a GETSTS bit
on other than IO.EOF.  The GETSTS bits are in AC T1 in the dump.
?NRTIVQ Illegal VMS QIO function
	This error occurs if a VMS remote host requests a QIO function
which we do not know how to perform.  Trace this problem with DNSNUP.
?NRTIXF Illegal RSX function
	This error occurs if a remote RSX host requests an unimplemented
or illegal function.  This should be traced with DNSNUP.
?NRTN10 Not connected to TOPS-10 or TOPS-20, command ignored
	This occurs when the usuer attempts to use the "O[bscure]"
command for the exit dialogue while connected to a remote host
which does not speak TOPS-10/20 protocol.  This error does
not cause NRT to abort; the command is simply ignored.
?NRTNPI NSP. UUO to set PSI mask failed
	NRT was unable to set the PSI mask for the channel to the remote
host in order for it to get a PSI interrupt when status on the channel
changed.  The error code for the NSP. UUO is in AC T1
in the dump.
?NRTNPM Version not compiled with Poor Man's Routing
	This message is output when the user attempts to specify a multi-node
path to a destination node (e.g. KL1026::TWINKY::), but the version of NRT
was not compiled to accept Poor Man's Routing.
?NRTODT OPEN of device TTY failed
	NRT was unable to open device TT: for asynchronous I/O.
?NRTOTF OUT to TTY: failed
	NRT uses non-blocking buffered I/O to the terminal.  This
error occurs if the OUT UUO fails with some error bit (other than
IO.EOF) turned on.  Submit an SPR, a dump, and a test case if this
is repeatable.  The GETSTS bits for the TTY: channel are in AC T1
in the dump.
	This message is output if NRT fails to initialize the software
interrupt system.  Submit a dump and an SPR if this is repeatable.
?NRTPMR Can't send PMR string
	The NSP. UUO to send the Poor Man's Routing string to the remote
PSTHRU task failed.  The error code is in T1.
?NRTPOF Performance file output failure
	An OUT UUO to the performance file failed.  AC T1 in the dump will
contain the GETSTS bits for the channel.
?NRTTMN Too many nodes in PMR string
	This message is output if the user attempts to specify too many nodes
in PMR string (applicable only if FTPMR is on).  This can be changed by
recompiling NRT with a different value for the assembly constant MAXPMR.
?NRTUED Unexpected end to network data
	This message is caused by NRT expecting more 
data in an incoming network message than
it received.  It should occur only for system such as RSX or VMS whose
protocol involves well-defined message headers which specify expected
lengths to various fields.  If sent as SPRs, UED problems should be sent
with a dump ^&AND\& with a trace file generated by the DNSNUP program
(supplied on the DECnet Tools Tape) run over the interval in which the
UED error occurs.  The program and the files necessary to run it on the remote
system are also very useful.
?NRTUSP Unsupported Protocol found
	This error occurs if the user attempts to connect to a remote host
whose protocol NRT does not understand.
?NRTUTF PISYS. UUO Unable to turn off interrupts
	NRT was unable to temporarily turn the software interrupt system
off.  The error code for the PISYS. UUO is in AC T1 in the dump.
?NRTUTN PISYS. UUO Unable to turn on interrupts
	NRT was unable to re-enable the software interrupt system after
turning it off.  The error code for the PISYS. UUO is in Ac T1 in the dump.
.end list