rfc802.txt
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RFC 802 Andrew G. Malis
Bits 1-4: Unused and set to zero.
Bits 5-8: 1822L IMP-to-Host Flag:
This field is set to decimal 14 (1110 in binary).
Bits 9-16: Handling Type:
This has the value assigned by the source host (see section
3.1). This field is only used in message types 0, 5-9, 11
and 15.
Bits 17-20: Unused and set to zero.
Bit 21: Trace Bit:
If equal to one, the source host designated this message for
tracing as it proceeds through the network. See 1822(5.5).
Bits 22-24: Leader Flags:
Bit 22: Available as a destination host flag.
Bits 23-24: Reserved for future use, set to zero.
Bits 25-32: Message Type:
Type 0: Regular Message - All host-to-host communication
occurs via regular messages, which have several sub-
types. The sub-type field (bits 77-80) is the same as
sent in the host-to-IMP leader (see section 3.1).
Type 1: Error in Leader - See 1822(3.4).
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Type 2: IMP Going Down - See 1822(3.4).
Type 3: NDM Reply - This is a reply to the NDM host-to-IMP
message (see section 3.1). It will have the same
number of entries as the NDM message that is being
replying to, and each listed 1822L name will be
accompanied by a zero or a one. A zero signifies that
the name is not effective, and a one means that the
name is now effective.
Type 4: NOP - The host should discard this message. It is
used during initialization of the IMP/host
communication. The Destination Host field will contain
the 1822L Address of the host port over which the NOP
is being sent. All other fields are unused.
Type 5: Ready for Next Message (RFNM) - See 1822(3.4).
Type 6: Dead Host Status - See 1822(3.4).
Type 7: Destination Host or IMP Dead (or unknown) - This
message is sent in response to a message for a
destination which the IMP cannot reach. The message to
the "dead" destination is discarded. See 1822(3.4) for
a complete list of the applicable sub-types. If this
message is in response to a standard (type 0, sub-type
0 or 1) message, it will be followed by a Dead Host
Status message, which gives further information about
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RFC 802 Andrew G. Malis
the status of the dead host. If this message is in
response to an uncontrolled (type 0, sub-type 2 or 3)
message, only sub-type 1 (The destination host is not
up) will be used, and it will not be followed by a Dead
Host Status message.
Type 8: Error in Data - See 1822(3.4).
Type 9: Incomplete Transmission - The transmission of the
named message was incomplete for some reason. An
incomplete transmission message is similar to a RFNM,
but is a failure indication rather than a success
indication. This message is also used by the short-
blocking feature to indicate that the named message was
rejected because it would have caused to IMP to block
the host for a long amount of time. See section 2.4
for more details concerning the short-blocking feature.
The message's sub-types are:
0: The destination host did not accept the message
quickly enough.
1: The message was too long.
2: The host took more than 15 seconds to transmit the
message to the IMP. This time is measured from
the last bit of the leader through the last bit of
the message.
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RFC 802 Andrew G. Malis
3: The message was lost in the network due to IMP or
circuit failures.
4: The IMP could not accept the entire message within
15 seconds because of unavailable resources. This
sub-type is only used in response to non-short-
blocking messages. If a short-blocking message
timed out, it will be responded to with one of the
sub-types 6-10.
5: Source IMP I/O failure occurred during receipt of
this message.
Sub-types 6-10 are all issued in response to a short-
blocking message that timed out (would have caused the
host to become blocked for a long amount of time). The
sub-types are designed to give the host some indication
of why it timed out and what other messages would also
time out. See section 2.4.2 for further details
concerning each of these sub-types.
6: The message timed out because of connection set-up
delay. Further messages to the same host (if on
the same connection) may also be affected.
7: The message timed out because of end-to-end flow
control. Further messages to the same host on the
same connection will also be affected.
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RFC 802 Andrew G. Malis
8: Destination IMP buffer shortage caused the message
to time out. This affects multi-packet standard
messages to the specified host, but shorter
messages or messages to hosts on other IMPs may
not be affected.
9: Network congestion control caused the message to be
rejected. Messages to hosts on other IMPs may not
be affected, however.
10: Local resource shortage kept the IMP from being
able to accept the message within the short-
blocking timeout period.
11-15: Unassigned.
Type 10: Interface Reset - See 1822(3.4).
Type 15: 1822L Name or Address Error - This message is sent
in response to a type 0 message from a host that
contained an erroneous Source Host or Destination Host
field. Its sub-types are:
0: The Source Host 1822L name is not authorized or not
effective.
1: The Source Host 1822L address does not match the
host port used to send the message.
2: The Destination Host 1822L name is not authorized.
3: The Destination Host 1822L name is authorized but
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not effective, even though the named host is up.
If the host were actually down, a type 7 message
would be returned, not a type 15.
4: The Source or Destination Host field contains a
1822L name, but the host being addressed is on a
non-C/30 IMP (see Figure 4 in section 2.2).
5-15: Unassigned.
Types 11-14,16-255: Unassigned.
Bits 33-48: Source Host:
For type 0 messages, this field contains the 1822L name or
address of the host that originated the message. All
replies to the message should be sent to the host specified
herein. For message types 5-9, 11 and 15, this field
contains the source host field used in a previous type 0
message sent by this host.
Bits 49-64: Destination Host:
For type 0 messages, this field contains the 1822L name or
address that the message was sent to. This allows the
destination host to detect how it was specified by the
source host. For message types 5-9, 11 and 15, this field
contains the destination host field used in a previous type
0 message sent by this host.
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RFC 802 Andrew G. Malis
Bits 65-76: Message ID:
For message types 0, 5, 7-9, 11 and 15, this is the value
assigned by the source host to identify the message (see
section 3.1). This field is also used by message types 2
and 6.
Bits 77-80: Sub-type:
This field is used as a modifier by message types 0-2, 4-7,
9, 11 and 15.
Bits 81-96: Message Length:
This field is contained in type 0 and type 3 messages only,
and is the actual length in bits of the message (exclusive
of leader, leader padding, and hardware padding) as computed
by the IMP.
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RFC 802 Andrew G. Malis
4 REFERENCES
[1] Specifications for the Interconnection of a Host and an IMP,
BBN Report 1822, May 1978 Revision.
[2] E. C. Rosen et. al., ARPANET Routing Algorithm Improvements,
IEN 183 (also published as BBN Report 4473, Vol. 1), August
1980, pp. 55-107.
[3] J. Postel, Assigned Numbers, RFC 790, September 1981, p. 10.
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RFC 802 Andrew G. Malis
INDEX
1822...................................................... 4
1822 address.............................................. 6
1822 host................................................. 5
1822L..................................................... 4
1822L address............................................. 7
1822L host................................................ 5
1822L name................................................ 6
authorized................................................ 9
blocking................................................. 16
congestion control................................... 22, 39
connection........................................... 20, 38
destination host..................................... 32, 40
effective................................................ 10
flow control......................................... 20, 38
handing type......................................... 27, 35
incomplete transmission message...................... 19, 37
leader flags......................................... 27, 35
link field............................................... 32
logical addressing........................................ 4
message ID........................................... 32, 41
message length........................................... 41
message type......................................... 28, 35
multi-homing.............................................. 4
NDM.................................................. 10, 28
NDM reply............................................ 10, 36
NOC....................................................... 9
NOP........................................... 5, 22, 30, 36
outstanding.............................................. 21
priority bit............................................. 27
regular message...................................... 28, 35
RFNM..................................................... 36
short-blocking feature................................... 15
short-blocking message............................... 19, 28
source host.......................................... 31, 40
standard message......................................... 28
sub-type............................................. 32, 41
symmetric................................................. 5
trace bit............................................ 27, 35
uncontrolled message................................. 14, 28
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