rfc869 RFC 869 Host Monitoring Protocol
RFC - 869
A Host Monitoring Protocol
Robert M. Hinden
BBN Communications Corporation
December 1983
RFC-869 December 1983
Table of Contents
1 Introduction.......................................... 1
2 General Description................................... 3
3 Relationship to Other Protocols....................... 6
4 Protocol Operation.................................... 7
5 Header Formats....................................... 12
5.1 IP Headers......................................... 12
5.2 HMP Header......................................... 13
6 HMP Monitoring Center Message Formats................ 16
6.1 Message Type 100: Polling Message.................. 16
6.2 Message Type 101: Error in Poll.................... 18
6.3 Message Type 102: Control acknowledgment........... 20
A Appendix A - IMP Monitoring.......................... 21
A.1 Message Type 1: IMP Trap........................... 21
A.2 Message Type 2: IMP status......................... 24
A.3 Message Type 3: IMP Modem Throughput............... 29
A.4 Message Type 4: IMP Host Throughput................ 32
B Appendix B - TAC Monitoring.......................... 35
B.1 Message Type 1: TAC Trap Message................... 35
B.2 Message Type 2: TAC Status......................... 38
B.3 Message Type 3: TAC Throughput..................... 42
C Appendix C - Gateway Monitoring...................... 47
C.1 Gateway Parameters................................. 47
C.2 Message Type 1: Gateway Trap....................... 48
C.3 Message Type 2: Gateway Status..................... 51
C.4 Message Type 3: Gateway Throughput................. 58
C.5 Message Type 4: Gateway Host Traffic Matrix........ 64
C.6 Message Type 6: Gateway Routing.................... 67
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RFC-869 December 1983
Replaces IEN-197
A Host Monitoring Protocol
1 Introduction
The Host Monitoring Protocol (HMP) is used to collect
information from hosts in various networks. A host is
defined as an addressable Internet entity that can send and
receive messages; this includes hosts such as server hosts,
personal work stations, terminal concentrators, packet switches,
and gateways. At present the Host Monitoring Protocol is being
used to collect information from Internet Gateways and TACs, and
implementations are being designed for other hosts. It is
designed to monitor hosts spread over the internet as well as
hosts in a single network.
This document is organized into three parts. Section 2 and
3 contains a general description of the Host Monitoring protocol
and its relationship to other protocols. Section 4 describes
how it operates. Section 5 and 6 contain the descriptions and
formats of the HMP messages. These are followed by appendices
containing the formats of messages sent by some of the hosts that
use the HMP to collect their monitoring information. These
appendicies included as examples only and are not part of the HMP
protocol.
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This document replaces the previous HMP document "IEN-197, A
Host Monitoring Protocol."
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RFC-869 December 1983
2 General Description
The Host Monitoring Protocol is a transaction-oriented
(i.e., connection-less) transport protocol. It was designed to
facilitate certain simple interactions between two internet
entities, one of which may be considered to be "monitoring" the
other. (In discussing the protocol we will sometimes speak of a
"monitoring host" and a "monitored entity".) HMP was intended to
be a useful transport protocol for applications that involve any
or all of the following three different kinds of interactions:
- The monitored entity sometimes needs to send unsolicited
datagrams to the monitoring host. The monitoring host
should be able to tell when messages from the monitored
entity have been lost in transit, and it should be able to
determine the order in which the messages were sent, but the
application does not require that all messages be received
or that they be received strictly in the same sequence in
which they were sent.
- The monitoring host needs to gather data from the monitored
entity by using a query-response protocol at the application
level. It is important to be able to determine which query
is being answered by a particular response, and to determine
whether successive responses are duplicates of previous
ones.
- The monitoring host must be able to initiate certain control
functions in the monitored entity, possibly including the
setting of parameters in the monitored entity. The
monitoring host needs to know if the control function has
been carried out.
In addition, we assume that a given monitoring host may be
monitoring several different types of entities simultaneously,
and may be gathering several different types of data from a given
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type of monitored entity. Several different monitoring hosts may
be monitoring a given entity, and several processes on the same
host may even be monitoring the same entity.
Messages from the monitoring host to the monitored entity
are called "polls". They need to contain enough information to
allow the monitored entity to make the following determinations:
- The monitored entity must be able to determine that this
message is in fact a poll from a monitoring host. The
"system type," "message type," and "password" fields in the
HMP header have been defined to meet this need.
- The monitored entity may need to be able to identify the
particular process on the monitoring host that sent this
poll, so it can send its response back to the right process.
The "port number" field in the HMP header has been defined
to meet this need.
- The monitored entity must be able to indicate to the
monitoring host, in its response, precisely which query is
being answered by a particular response. The "sequence
number field" has been defined to meet this need.
- The monitored entity must be able to determine just what
kind of action the monitoring host is requesting. That is,
the HMP transport protocol must provide some way of
multiplexing and demultiplexing the various higher-level
applications which use it. The "R-message type" and "R-
subtype" fields of the polling message have been defined to
meet this need.
Messages from the monitored entity to the monitoring host
need to contain enough information to enable the monitoring host
to make the following determination:
- The monitoring host must be able to route this message to
the correct process. The "port number" field meets this
need.
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- The monitoring host must be able to match up received
messages with the polls, if any, that elicited them. The
"returned sequence number" field in the HMP header has been
defined to meet this need.
- The monitoring host must be able to determine which higher
level application should receive a particular message. The
"system type" and "message type" fields are used for this
purpose.
- The monitoring host must be able to determine whether some
messages of a given type were lost in transit, and whether
messages have arrived out of sequence. Although this
function, strictly speaking, belongs to the application and
not to the transport layer, the HMP header contains a
"sequence number" for this purpose.
In addition, a simple one's complement checksum is provided
in the HMP header to detect data corruption during transmission.
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3 Relationship to Other Protocols
The Host Monitoring Protocol is a transport protocol
designed to fit into the layered internet protocol environment.
It operates on top of the Internet/ICMP protocol and under
applications that require its services. This relationship is
illustrated in the following diagram:
+------+ +------+ +-------+ +------+
|TELNET| ...| FTP | |GATEWAY| ... | TAC | Application Layer
+------+ +------+ +-------+ +------+
| | | |
| | | |
|__________| |_____________|
| |
+------+ +-------+
| TCP | | HMP | Transport Layer
+------+ +-------+
| |
| |
+-------------------------------------+
| Internet Protocol & ICMP | Internetwork Layer
+-------------------------------------+
|
+------------------------+
| Local Network Protocol | Network Layer
+------------------------+
If internetwork services are not required it should be possible
to run the HMP without an Internetwork layer. As long as HMPs'
service requirnments (addressing, protocol demultiplexing, and
occasional delivery) are met it should run over a variety of
protocols.
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4 Protocol Operation
The HMP is built around the idea that most of the
intelligence needed to monitor a host should reside in a
monitoring center, not in the host. The host should be required
only to collect data and send it to the monitoring center, either
spontaneously or on request from the monitoring center. The host
is not responsible for insuring that the data arrives reliably
(except that it checksums the data); instead, the monitoring
center is responsible for ensuring that the data it requests is
received correctly.
Consequently, the HMP is based on polling hosts for
messages. When the monitoring center requires a particular type
of data (e.g., throughput data), it sends a poll to the host
requesting that type of report. The host, upon receiving the
poll, responds with its latest set of collected data. If the
host finds that the poll is incorrect (e.g., if the poll was for
throughput data and the host is not collecting throughput data),
it responds with an error message. The monitoring center waits a
reasonable length of time for the host to answer its poll. If no
response is received, it sends another poll for the same data.
In this way, if either a poll or the response is lost, the
correct data is still collected.
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The HMP is used to collect three different classes of data:
o Spontaneous Events (or Traps)
o Current status
o Statistical data collected over time
These classes of data allow a host to send data in a manner best
suited to the data. For instance, the host may quickly inform
the monitoring center that a particular event has happened by
sending a trap message, while the monitoring center is reliably
collecting the host's throughput and accounting data.
Traps report spontaneous events, as they occur, to the
monitoring center. In order to insure their prompt delivery, the
traps are sent as datagrams with no reliability mechanisms
(except checksums) such as acknowledgments and retransmissions.
Trap messages usually contain an identifier to indicate which
event is being reported, the local time in the host that the
event occured, and data pertinent to the event. The data portion
is intended to be host and event specific.
Status information, the second type of data collected by the
Host Monitoring Protocol describes the current state of the host.
Status information is useful at one point, but it does not have
to be collected cumulatively over a certain period of time. Only
the latest status is of interest; old status provides no useful
information. The monitoring center collects status information
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by sending a poll for status to a host. Upon receiving the poll,
the host responds with its latest status information, always
creating a new status message. If the monitoring center does not
receive a response to its poll, it sends another poll. The
monitoring center can decide if the host is up or down based on
whether the host responds to its polls.
The third type of data collected by the HMP is statistical
data. These are measurements taken over time, such as the number
of packets sent or received by a host and the count of packets
dropped for a particular reason. It is important that none of
this type of data be lost. Statistical data is collected in a
host over a time interval. When the collection time interval
expires, the current data is copied to another area, and the
counters are cleared. The copied data is sent to the monitoring
center when the host receives a poll requesting statistical
information. If another poll is received before the collection
time interval has expired, the data in the buffer is sent again.
The monitoring center can detect duplicate messages by using the
sequence number in the header of the message, since each type of
statistical data has its own sequence number counter.
The collection frequency for statistics messages from a
particular host must be relatively long compared to the average
round trip message time between the monitoring center and that
host inorder to allow the monitoring center to re-poll if it does
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not receive an answer. With this restriction, it should be
possible to avoid missing any statistics messages. Each
statistics message contains a field giving the local time when
the data was collected and the time at which the message was
sent. This information allows the monitoring center to schedule
when it sends a poll so that the poll arrives near the beginning
of each collection period. This ensures that if a message is
lost, the monitoring center will have sufficient time to poll
again for the statistics message for that period.
The HMP also includes a provision to send data to and read
parameters in hosts. The data may be used to set switches or
interval timers used to control measurements in a host, or to
control the host itself (e.g. a restart switch). The format of
the data and parameters is host specific.
To send data to a host, the monitoring center sends the host
a poll for a control-acknowledgment message. This poll message
includes the type of the data and the data being sent. When the
host receives this poll, it processes the data and responds with
a control-acknowledgment message.
To read parameters in a host, the monitoring center will
send a poll for parameters to the host. This poll includes the
type of the parameters being read. When the host receives this
poll, it will send the parameters of the requested type to the
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monitoring center in a parameters message.
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5 Header Formats
Host Monitor Protocol messages have the following format:
+----------------+
| Local Network |
| Header(s) |
+----------------+
| IP header |
+----------------+
| HMP |
| Header |
| |
+----------------+
| D |
| A |
| T |
| A |
+----------------+
| Padding |
+----------------+
5.1 IP Headers
HMP messages are sent using the version 4 IP header as described
in RFC-791 "Internet Protocol." The HMP protocol number is 20
(decimal). The time to live field should be set to a reasonable
value for the hosts being monitored.
All other fields should be set as specified in RFC-791.
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5.2 HMP Header
The HMP header format is:
0 0 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------+---------------+
0 | System Type | Message Type |
+---------------+---------------+
1 | Port Number | Control Flag |
+---------------+---------------+
2 | Sequence Number |
+---------------+---------------+
3 | Password or Returned Seq. # |
+---------------+---------------+
4 | One's Complement Checksum |
+---------------+---------------+
HMP FIELDS:
System Type
Message Type
The combination of system type and message type determines
the format of the data in the monitoring message.
The system types which have been defined are:
System Type | Meaning
----------------+-----------------
1 | Monitoring Host
2 | IMP
3 | TAC
4 | Gateway
5 | SIMP
6 | BBN VAX/C70 TCP
7 | PAD
8 | Reserved
9 | TIU
10 | FEP
11 | Cronus Host
12 | Cronus MCS
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Message types are defined and used for each system type
according to the needs of that system. The message types
currently defined are:
Type | Description
----------+--------------------------
|
1 | Trap
2 | Status
3 | Thruput
4 | HTM - Host Traffic Matrix
5 | Parameters
6 | Routing
7 | Call Accounting
|
100 | Poll
101 | Error
102 | Control Acknowledgment
Port Number
This field can be used to multiplex similar messages to/from
different processes in one host. It is currently unused.
Control Flag
This field is used to pass control information. Currently
Bit 15 is defined as the "More bit" which is used in a
message in responce to a poll to indicate that there is more
data to poll for.
Sequence Number
Every message contains a sequence number. The sequence
number is incremented when each new message of that type is
sent.
Password or Returned Sequence Number
The Password field of a polling message from an monitoring
center contains a password to verify that the monitoring
center is allowed to gather information. Responses to
polling messages copy the Sequence Number from the
polling message and return it in this field for
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identification and round-trip time calculations.
Checksum
The Checksum field is the one's complement of the one's
complement sum of all the 16-bit words in the header and
data area.
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6 HMP Monitoring Center Message Formats
6.1 Message Type 100: Polling Message
Description
The monitoring center will send polls to the hosts it is
monitoring to collect their monitoring data. When the host
receives a poll it will return a message of the type
requested. It will only answer a poll with the correct
system type and password and will return an error message
(Message Type 101) if it receives a poll for the wrong
system type or an unsupported message type.
The Poll message includes a facility to send data to a
monitored host. The poll message to send data consists of a
poll for a Control Acknowledgment message (type 102)
followed by the data. The R-Subtype specifies the type of
the data that is being sent. When the monitored host
receives a Poll for a Control acknowledgment, it processes
the data, and then responds with an Control acknowledgment
message. If the monitored host can not process the data, it
should respond with an error message.
A poll to read parameters consists a poll for a Parameters
message. The R-Subtype specifies the type of parameters
being read. When the monitored host receives a poll for a
Parameters message, it responds with a Parameters message
containing the requested information.
A polling message has the following form:
0 0 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------+---------------+
0 | R-Message Type| R-Subtype |
+---------------+---------------+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | Data |
+ +
2 | |
+ +
. .
. .
n | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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HMP FIELDS
System Type
The type of machine being polled.
Message Type
Polling Message = 100
Port Number
Unused
Control Flag
Unused
Sequence Number
The sequence number identifies the polling request. The
Monitoring Center will maintain separate sequence numbers
for each host it monitors. This sequence number is returned
in the response to a poll and the monitoring center will use
this information to associate polls with their responses and
to determine round trip times.
Password
The monitoring password.
POLL FIELDS
R-Message Type
The message type requested.
R-Subtype
This field is used when sending data and reading parameters
and it specifies the type of the data being sent or
parameters being read.
Data
When the poll is requesting a Control Acknowledgment
message, data is included in the poll message. A poll for
any other type of message does not include any data . The
contents of the data is host specific.
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6.2 Message Type 101: Error in Poll
Description
This message is sent in response to a faulty poll and
specifies the nature of the error.
An error message has the following form:
0 0 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------+---------------+
0 | Error Type |
+---------------+---------------+
1 | R-Message Type| R-Subtype |
+---------------+---------------+
HMP FIELDS
System Type
The type of machine sending message.
Message Type
Error Message = 101
Port Number
Unused
Control Flag
Unused
Sequence Number
A 16 bit number incremented each time an error message is
sent.
Returned Sequence Number
The Sequence Number of the polling message which caused the
error.
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ERROR MESSAGE FIELDS
Error Type
This field specifies the nature of the error in the poll.
The following error types have been defined.
1 = Reason unspecified.
2 = Bad R-Message Type.
3 = Bad R-Subtype.
4 = Unknown parameter
5 = Invalid parameter value
6 = Invalid parameter/value format
7 = Machine in Loader
R-Message Type
R-Subtype
These fields identify the poll request in error.
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6.3 Message Type 102: Control acknowledgment
Description
This message is sent in response to a poll for this type of
message. It is used to acknowledge poll messages that are
used to set parameters in the monitored host.
The Control acknowledgment has no fields other than the HMP
header.
HMP FIELDS
System Type
The type of the system sending the message.
Message Type
Control acknowledgment = 102
Port Number
Unused
Control Flag
Unused
Sequence Number
A 16 bit number incremented each time a Control
acknowledgment message is sent.
Returned Sequence Number
The Sequence Number of the polling message which requested
this message.
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A Appendix A - IMP Monitoring
A.1 Message Type 1: IMP Trap
Description
When a trap occurs, it is buffered in the IMP and sent as
soon as possible. Trap messages are unsolicited. If traps
happen in close sequence, several traps may be sent in one
message.
Through the use of sequence numbers, it will be possible to
determine how many traps are being lost. If it is
discovered that many are lost, a polling scheme might be
implemented for traps.
A IMP trap message has the following form:
0 0 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------+---------------+
0 | # of traps lost |
+---------------+---------------+
1 : first :
. : trap :
. : data :
. +---------------+---------------+
. : additional :
. : trap :
. : data :
+---------------+---------------+
HMP Fields
System Type
IMP = 2
Message Type
IMP Trap Message = 1
Port Number
Unused
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Control Flag
Unused
Password
Unused
Sequence Number
A 16 bit number incremented each time a trap message is sent
so that the HM can order the received trap messages and
detect missed messages.
IMP TRAP FIELDS
# of traps lost
Under certain conditions, an IMP may overflow its internal
trap buffers and be unable to save traps to send. This
counter keeps track of such occurrences.
Trap Reports
There can be several blocks of trap data in each message.
The format for each such block is below.
+---------------+---------------+
| Size |
+---------------+---------------+
| Time |
+---------------+---------------+
| Trap ID |
+---------------+---------------+
: Trap :
: Data :
+---------------+---------------+
Size
Size is the number of 16 bit words in the trap, not counting
the size field.
Time
The time (in 640 ms. units) at which the trap occurred.
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This field is used to sequence the traps in a message and
associate groups of traps.
Trap ID
This is usually the program counter at the trap. The ID
identifies the trap, and does not have to be a program
counter, provided it uniquely identifies the trap.
Trap Data
The IMP returns data giving more information about the trap.
There are usually two entries: the values in the accumulator
and the index register at the occurrence of the trap.
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A.2 Message Type 2: IMP status
Description
The status message gives a quick summary of the state of the
IMP. Status of the most important features of the IMP are
reported as well as the current configuration of the
machine.
The format of the status message is as follows:
0 0 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------+---------------+
0 | Software Version Number |
+---------------+---------------+
| Last Trap Message |
+---------------+---------------+
| Max # Hosts | Max # Modems |
+---------------+---------------+
| Max # Channels| Max # IMPs |
+---------------+---------------+
| Package bits 0-15. |
+---------------+---------------+
5 | Package bits 16.-31. |
+---------------+---------------+
| |
+ Crash +
| |
+ Data +
| |
+---------------+---------------+
| Anomalies |
+---------------+---------------+
10 | Free Pool | S+F Pool |
+---------------+---------------+
|Reassembly Pool| Allocated Pool|
+---------------+---------------+
| HIHD0 | HIHD1 | HIHD2 | HIHD3 |
. +---------------+---------------+
. : HIHD4 | ............... :
. +---------------+---------------+
(cont.)
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Imp Status (cont.)
. +---------------+---------------+
. | Modem |
. + State +
. | Data |
. +---------------+---------------+
. : Modem State :
. : Data...... :
+---------------+---------------+
HMP FIELDS
System Type
IMP = 2
Message Type
IMP status message = 2
Port Number
Unused
Control Flag
Unused
Sequence Number
A 16 bit number incremented each time a status message is
sent.
Password
The password contains the sequence number of the polling
message to which this message responds.
IMP STATUS FIELDS
Software Version Number
The IMP version number.
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Last Trap Message
Contains the sequence number of the last trap message sent
to the HM. This will allow the HM to detect how many trap
messages are being lost.
Hosts
The number of configured hosts in this system.
Modems
The number of configured modems in this system.
Channels
The maximum possible number of IMP-IMP channels in this
system.
IMPs
The maximum possible number of IMPs in this system.
Package Bits
This is a bit encoded word that reports the set of packages
currently loaded in the system. The table below defines the
bits.
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Bit Package
(octal)
(1st Word)
1 VDH
2 Logical address tables
4 Mezmode
10 Cumulative Statistics
20 Trace
40 TTY
100 DDT
200 HDLC
400 HDH
1000 Cassette Writer
2000 Propagation Delay Measurement
4000 X25
10000 Profile Measurements
20000 Self Authenticating Password
40000 Host traffic Matrix
100000 Experimental/Special
(2nd Word)
1 End-to-end Statistics
2 Store and Forward statistics
Crash Data
Crash data reports the circumstances surrounding an
unexpected crash. The first word reports the location of
the crash and the following two are the contents of the
accumulator and index registers.
Anomalies
Anomalies is a collection of bit flags that indicate the
state of various switches or processes in the IMP. These
are very machine dependent and only a representative
sampling of bits is listed below.
Bit Meaning
(octal)
20 Override ON
200 Trace ON
1000 Statistics ON
2000 Message Generator ON
4000 Packet Trace ON
10000 Host Data Checksum is BAD
20000 Reload Location SET
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Buffer Pool Counts
These are four bytes of counters indicating the current
usage of buffers in the IMP. The four counters are: free
buffers, store-and-forward buffers, reassembly buffers and
allocated buffers.
HIHD0 - HIHDn
Each four bit HIHD field gives the state of the
corresponding host.
Value Meaning
0 UP
1 ready line down
2 tardy
3 non-existent
Modem State Data
Modem state data contains six fields of data distributed
over four words. The first field (4 bits) indicates the
line speed; the second field (4 bits) is the number of the
modem that is used by the neighboring IMP on this line; the
third field (8 bits) is the number of line protocol ticks
covered by this report; the fourth (1 bit) indicates line
down(1) or up(0); the fifth (7 bits) is the IMP number of
neighbor IMP on the line; and the sixth (8 bits) is a count
of missed protocol packets over the interval specified in
the third field.
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A.3 Message Type 3: IMP Modem Throughput
Description
The modem throughput message reports traffic statistics for
each modem in the system. The IMP will collect these data at
regular intervals and save them awaiting a poll from the HM.
If a period is missed by the HM, the new results simply
overwrite the old. Two time stamps bracket the collection
interval (data-time and prev-time) and are an indicator of
missed reports. In addition, mess-time indicates the time
at which the message was sent.
The modem throughput message will accommodate up to fourteen
modems in one packet. A provision is made to split this
into multiple packets by including a modem number for the
first entry in the packet. This field is not immediately
useful, but if machine sizes grow beyond fourteen modems or
if modem statistics become more detailed and use more than
three words per modem, this can be used to keep the message
within a single ARPANET packet.
The format of the modem throughput message is as follows:
0 0 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------+---------------+
0 | Mess-Time |
+---------------+---------------+
| Software Version Number |
+---------------+---------------+
| Data-Time |
+---------------+---------------+
| Prev-Time |
+---------------+---------------+
| Total Modems | This Modem |
+---------------+---------------+
5 | |
. + modem +
. | |
. + throughput +
. | |
. +---------------+---------------+
. : modem :
. : :
. : throughput :
+---------------+---------------+
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HMP FIELDS
System Type
IMP = 2
Message Type
IMP Modem Throughput message = 3
Port Number
Unused
Control Flag
Unused
Sequence Number
A 16 bit number incremented at each collection interval
(i.e. when a new throughput message is assembled). The HM
will be able to detect lost or duplicate messages by
checking the sequence numbers.
Password
The password contains the sequence number of the polling
message to which this message responds.
IMP MODEM THROUGHPUT FIELDS
Mess-time
The time (in 640ms. units) at which the message was sent to
the HM.
Software Version Number
The IMP version number.
Data-Time
Data-time is the time (in 640ms. units) when this set of
data was collected. (See Description.)
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Prev-Time
Prev-time is the time (in 640 ms. units) of the previous
collection of data (and therefore, is the time when the data
in this message began accumulating.)
Total Modems
This is the number of modems in the system.
This Modem
This Modem is the number of the first modem reported in this
message. Large systems that are unable to fit all their
modem reports into a single packet may use this field to
separate their message into smaller chunks to take advantage
of single packet message efficiencies.
Modem Throughput
Modem throughput consists of three words of data
reporting packets and words output on each modem. The
first word counts packets output and the following two
count word throughput. The double precision words are
arranged high order first. (Note also that messages from
Honeywell type machines (316s, 516s and C30s) use a fifteen
bit low order word.) The first block reports output on the
modem specified by "This Modem". The following blocks
report on consecutive modems.
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A.4 Message Type 4: IMP Host Throughput
Description
The host throughput message reports traffic statistics for
each host in the system. The IMP will collect these data at
regular intervals and save them awaiting a poll from the HM.
If a period is missed by the HM, the new results simply
overwrite the old. Two time stamps bracket the collection
interval (data-time and prev-time) and are an indicator of
missed reports. In addition, mess-time indicates the time
at which the message was sent.
The host throughput format will hold only three hosts if
packet boundaries are to be respected. A provision is made
to split this into multiple packets by including a host
number for the first entry in the packet.
The format of the host throughput message is as follows:
0 0 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------+---------------+
0 | Mess-Time |
+---------------+---------------+
| Software Version Number |
+---------------+---------------+
| Data-Time |
+---------------+---------------+
| Prev-Time |
+---------------+---------------+
| Total Hosts | This Host |
+---------------+---------------+
5 : host :
. : throughput :
+---------------+---------------+
HMP FIELDS
System Type
IMP = 2
Message Type
IMP host Throughput message = 4
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RFC-869 December 1983
Port Number
Unused
Control Flag
Unused
Sequence Number
A 16 bit number incremented at each collection interval
(i.e. when a new throughput message is assembled). The HM
will be able to detect lost or duplicate messages by
checking the sequence numbers.
Password
The password contains the sequence number of the polling
message to which this message responds.
IMP HOST THROUGHPUT FIELDS
Mess-time
The time (in 640ms. units) at which the message was sent to
the HM.
Software Version Number
The IMP version number.
Data-Time
Data-time is the time (in 640ms. units) when this set of
data was collected. (See Description.)
Prev-Time
Prev-time is the time (in 640 ms. units) of the previous
collection of data (and therefore, is the time when the data
in this message began accumulating.)
Total Hosts
The total number of hosts in this system.
This Host
This host is the number of the first host reported in this
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RFC-869 December 1983
message. Large systems that are unable to fit all their
host reports into a single packet may use this field to
separate their message into smaller chunks to take advantage
of single packet message efficiencies.
Host Throughput
Each host throughput block consists of eight words in the
following format:
+---------------+---------------+
| messages to network |
+---------------+---------------+
| messages from network |
+---------------+---------------+
| packets to net |
+---------------+---------------+
| packets from net |
+---------------+---------------+
| messages to local |
+---------------+---------------+
| messages from local |
+---------------+---------------+
| packets to local |
+---------------+---------------+
| packets from local |
+---------------+---------------+
Each host throughput message will contain several blocks of
data. The first block will contain data for the host
specified in First Host Number. Following blocks will
contain data for consecutive hosts. All counters are single
precision.
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RFC-869 December 1983
B Appendix B - TAC Monitoring
B.1 Message Type 1: TAC Trap Message
Description
When a trap occurs, it is buffered in the TAC and sent as
soon as possible. Trap messages are unsolicited. If traps
happen in close sequence, several traps may be sent in one
message.
Through the use of sequence numbers, it will be possible to
determine how many traps are being lost. If it is
discovered that many are lost, a polling scheme might be
implemented for traps.
A TAC trap message has the following form:
0 0 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------+---------------+
0 | Version # |
+---------------+---------------+
1 : first :
. : 