As per Relevance of the word connection, we have this rfc below:
Network Working Group J.
Request for Comments: 1165
J.
Nottingham
June 1990
Network Time Protocol (NTP) over the
Remote Operations
Status of this
This memo suggests an Experimental Protocol for the OSI and
communities. Hosts in either community, and in particular those
both are encouraged to experiment with this mechanism. Please
to the current edition of the "IAB Official Protocol Standards"
the standardization state and status of this protocol.
of this memo is unlimited
Table of
1. Introduction........................................... 1
1.1 Motivation............................................ 1
2. Protocol Overview...................................... 2
3. Operation of the Protocol.............................. 3
4. Network Considerations................................. 4
5. Implementation Model................................... 4
6. Constructing NTP Data Fields........................... 4
7. Discussion............................................. 4
8. Prototype Experience................................... 5
9. References............................................. 5
10. Acknowledgements...................................... 6
Appendix A. NTP Remote Operations Service Specification... 6
11. Security Considerations............................... 9
12. Authors' Addresses.................................... 9
1.
This document describes the Remote Operations and Abstract Syntax
the operation of the Network Time Protocol (NTP) over an ISO
stack
NTP itself is documented in great detail in RFC 1119.
1.1
The motivation behind the implementation of a Remote
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Service implementation of NTP is fourfold
1. The inclusion of a useful service to an
environment
2. The feasibility of automatically checking a ROS/ASN.1
specification, and automatically generating code
implement the protocol
3. The feasibility of running NTP on connection
network services (CONS or X.25), and consequentially
the ability to use connection success or failure
optimise reachability discovery
4. The generalisation of the last point: the use of
makes NTP independent of the underlying
architecture
The need for time synchronisation is clear, and RFC 1119 indicates
few of the necessary uses of this service. However, it is
clear that OSI applications are very much in need of this
too. Not just in the local context but across the wide area.
example much of the strong authentication outlined in X.511 is
on encrypted packets with time stamps to indicate how long the
is valid for. If two hosts have clocks that are not
synchronised, the host with the faster clock will be more prone
cryptographic attacks from the slower, and the slower host
possibly find it is unauthentable
A similar problem occurs with the X.500 directory and the
control limiting the time allowed for the search
Authentication between NTP peers and between clients and servers
not addressed here, as the choice of mechanism is still the
of some debate
2. Protocol
The NTP application functions exactly as in RFC 1119. The use
remote operations and the underlying Application support means
for NTP daemons to peer with one another, they send an A
ASSOCIATE.REQUEST, and receive an A-ASSOCIATE.INDICATION
On successful association, they subsequently periodically invoke
appropriate Remote Operation with the appropriate parameters at
appropriate frequency
On failure, they mark the peer as unreachable
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The states that an ntp daemon records for each peer are enhanced
RFC 1119 to include
Connected: this indicates the host is connected with its peer
synchronisation data is being exchanged
Connecting: this state indicates that a connection is in progress
Hosts at large distances may take several seconds to connect,
such blocking can perturb the exchange of data with other hosts
Therefore, the connection is made asynchronously
Accepting: this state indicates that a connection is
accepted from another host, but the necessary negotiation
transport session etc has not been fulfilled yet. This is
asynchronous part
Disconnected: this state is reached if the remote host cannot
contacted
3. Operation of the
The use of a connection oriented service means that the operation
the NTP algorithm is slightly different. This stems firstly
some necessary adjustments made to the protocol and secondly
some optimisations that are possible through the use of connections
Firstly, the reachability of the host can be directly determined
The NTP protocol maintains a shift register to determine if it
likely that a peer is still responding and exchanging data.
works by recording over the last eight transfers how many
have been received. If there have been no responses to the
eight packets, then the host is deemed unreachable
Naturally, with a connection to the remote host, the reachability
immediately determinable. Either a connection is established or
connection is broken or not yet made. For this reason it is
necessary to rely on the shift register to determine reachability
Secondly, there are a large number of optimisations that can be
by use of the connection oriented mode. The NTP packet format can
broken into several categories
a) Synchronisation
b) Authentication
c) Protocol
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Of these classes of data, only the first (a) is necessary to
the synchronisation between hosts. Information such as
version and the precision of the local clock are not likely to
over the lifetime of the connection. Likewise the authentication
in use need only be done at connection establishment and is
necessarily required for every packet
For these reason, the NTP protocol can be simplified slightly
remove this information. This can be seen in the specification
the Packet in Appendix A
4. Network
Although on first inspection it might be thought that a high
network is necessary for accurate synchronisation, this is not
case. What is more important is the dispersion of the
traversal times. It is normally the case that a low speed
with little variance in packet transit times will give better
than a high speed network with large differences in individual
transit times. This would lead us to think that connection
networks with resource allocation done at connection time might
to higher accuracies than connectionless networks which can
large swings in packet transit time under high loading. (This
heresy!)
5. Implementation
Ideally, the implementor will provide interoperability between
existing UDP based NTP service, and a ROS based service
To this end, the internal records that hold NTP state information
can be kept the same as existing implementations, and
optimisation reasons, the internal representations of NTP packets
be the same. Translation between these and appropriate ROS/
concrete encodings can be provided by automatic translators such
Rosy [ISODE].
6. Constructing NTP Data
The way in which the data fields in the Packet described in
A is unchanged from RFC 1119. This simplifies implementations
on existing ones, and encourages interworking
7.
From the limited testing of this model so far done, the results
seem to indicate that the ROS based model running over an X.25
service is of similar reliability as the UDP model. Until
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experimentation can be performed, specific data can not be given
However, in the UK where the most common method of
synchronisation is the system administrators watch and typing in
time to the nearest minute, this method is clearly far superior
Connection management is transparent to NTP since it is
beneath the Remote Operations Service. However, an
implementation must have access to the status of connections,
uses this not only for reachability information but also to find
information gleaned at connect time and no longer exchanged in
operations
8. Prototype
There are a number of UK sites running NTP over ROS over X.25 with
earlier ROS specification, with at least one site peering both
ROS with UK sites on X.25, and over UDP with US Internet sites
Initial experience is promising. The table below shows
reachabilities, delays, offsets and dispersions for the central
site peering with 2 JANET sites (IP addresses not meaningful,
shown as 126.0.0.1), and three US sites
Address Strat Poll Reach Delay Offset
=============================================================
+126.0.0.1 3 64 377 718.0 0.0 3.0
+umd1.umd.edu 1 1024 177 535.0 13.0 13.0
*128.4.0.5 1 64 167 545.0 10.0 524.0
9.
1. Mills, D., "Network Time Protocol (Version 2) Specification
Implementation", RFC-1119, UDEL, September 1989.
2. Mills, D., "Algorithms for Synchronizing Network Clocks", RFC
956, M/A-COM Linkabit, September 1985.
3. Postel, J. "User Datagram Protocol", RFC-768, USC
Sciences Institute, August 1980.
4. ISO TC97, "Specification of Abstract Syntax Notation
(ASN.1)", Draft International Standard ISO/DIS 8824, 6 June 1985.
5. CCITT, "Remote Operations: Model, Notation and
Definition", CCITT X.ros0 or ISO/DP 9072/1, Geneva, October 1986.
6. Mills, D., "Internet Time Synchronization: The Network
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RFC 1165 NTP over OSI June 1990
Protocol (NTP)", RFC 1129, UDEL, October 1989.
7. Mills, D., "Measured Performance of the Network Time Protocol
the Internet System", RFC 1128, October 1989.
8. Rose M., et al, "The ISO Development Environment: User's Manual".
10.
The Authors would like to thank Dave Mills for his
comments on an earlier version of this document
Appendix A. ROS "Header"
-- NTP definitions for ROS
--
-- Julian Onions, Nottingham University, UK
--
-- Mon Jun 5 10:07:07 1989
--
NTP DEFINITIONS ::=
update
ARGUMENT
::= 0
query
ARGUMENT
RESULT
::= 1
-- Data
BindArgument ::=
fullbind SEQUENCE {
psap[0] IA5String OPTIONAL
version[1] BITSTRING {
version-0(0),
version-1(1),
version-2(2)
} DEFAULT version-2,
authentication[2] Authentication OPTIONAL
mode[3]
}
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Authentication ::=
BindMode ::= ENUMERATED {
normal(0), -- standard
query(1) -- queries
}
BindResult ::=
SEQUENCE {
version[1] INTEGER DEFAULT 2,
authentication[2] Authentication OPTIONAL
mode[3]
}
BindError ::=
SEQUENCE {
reason[0] INTEGER {
refused(0),
validation(1),
version(2), -- version not
badarg(3), -- bad bind
congested(4) -- catch all
},
supplementary[1] IA5String
}
-- basic exchange
Packet ::= SEQUENCE {
leap Leap
mode Mode
stratum[1] INTEGER
pollInterval[2] INTEGER
precision[3] INTEGER
synchDistance SmallFixed
synchDispersion SmallFixed
referenceClockIdentifier ClockIdentifier
referenceTimestamp TimeStamp
originateTimestamp TimeStamp
receiveTimestamp TimeStamp
transmitTimestamp
}
ClockInfoList ::= SET OF
ClockInfo ::= SEQUENCE {
remoteAddress Address
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localAddress Address
flags[0] BIT STRING {
configured(0),
authentable(1),
sane(2),
candidate(3),
sync(4),
broadcast(5),
referenceClock(6),
selected(7),
inactive(8)
},
packetsSent[1] INTEGER
packetsReceived[2] INTEGER
packetsDropped[3] INTEGER
timer[4] INTEGER
leap Leap
stratum[5] INTEGER
ppoll[6] INTEGER
hpoll[7] INTEGER
precision[8] INTEGER
reachability[9] INTEGER
estdisp[10] INTEGER
estdelay[11] INTEGER
estoffset[12] INTEGER
reference[13] ClockIdentifier OPTIONAL
reftime TimeStamp
filters SEQUENCE OF
}
Leap ::= [APPLICATION 0] ENUMERATED {
nowarning(0),
plussecond(1),
minussecond(2),
alarm(3)
}
SmallFixed ::= [APPLICATION 1] IMPLICIT SEQUENCE {
integer INTEGER
fraction
}
ClockIdentifier ::= CHOICE {
referenceClock[0] PrintableString
inetaddr[1] OCTET STRING
psapaddr[2] OCTET
}
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TimeStamp ::= [APPLICATION 2] IMPLICIT SEQUENCE {
integer INTEGER
fraction
}
KeyId ::= [APPLICATION 4]
Mode ::= [APPLICATION 4] ENUMERATED {
unspecified (0),
symmetricActive (1),
symmetricPassive (2),
client (3),
server (4),
broadcast (5),
reservered (6),
private (7)
}
Filter ::= SEQUENCE {
offset INTEGER
delay
}
Address ::= OCTET STRING -- for
11. Security
Security issues are not discussed in this memo
12. Authors'
Jon
Computer Science
University College
Gower
London WC1E 6BT
EMail: JON@CS.UCL.AC.
Julian P.
Computer Science
Nottingham
University
Nottingham, NG7 2RD
EMail: JPO@CS.NOTT.AC.
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RFC 1165 NTP over OSI June 1990
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if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
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