Network Time Protocol (NTP) over the OSI Remote Operations Service
RFC 1165

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Network Working Group                                       J. Crowcroft
Request for Comments:  1165                                          UCL
                                                               J. Onions
                                                   Nottingham University
                                                               June 1990

                Network Time Protocol (NTP) over the OSI
                       Remote Operations Service

Status of this Memo

   This memo suggests an Experimental Protocol for the OSI and Internet
   communities.  Hosts in either community, and in particular those on
   both are encouraged to experiment with this mechanism.  Please refer
   to the current edition of the "IAB Official Protocol Standards" for
   the standardization state and status of this protocol.  Distribution
   of this memo is unlimited.

Table of Contents

   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.  Introduction

   This document describes the Remote Operations and Abstract Syntax for
   the operation of the Network Time Protocol (NTP) over an ISO OSI
   stack.

   NTP itself is documented in great detail in RFC 1119.

1.1  Motivation

   The motivation behind the implementation of a Remote Operations

Crowcroft & Onions                                              [Page 1]
RFC 1165                      NTP over OSI                     June 1990

   Service implementation of NTP is fourfold.

      1.  The inclusion of a useful service to an OSI
          environment.

      2.  The feasibility of automatically checking a ROS/ASN.1
          specification, and automatically generating code to
          implement the protocol.

      3.  The feasibility of running NTP on connection oriented
          network services (CONS or X.25), and consequentially,
          the ability to use connection success or failure to
          optimise reachability discovery.

      4.  The generalisation of the last point: the use of ROS
          makes NTP independent of the underlying communications
          architecture.

   The need for time synchronisation is clear, and RFC 1119 indicates a
   few of the necessary uses of this service.  However, it is becoming
   clear that OSI applications are very much in need of this service
   too.  Not just in the local context but across the wide area.  For
   example much of the strong authentication outlined in X.511 is based
   on encrypted packets with time stamps to indicate how long the packet
   is valid for.  If two hosts have clocks that are not closely
   synchronised, the host with the faster clock will be more prone to
   cryptographic attacks from the slower, and the slower host will
   possibly find it is unauthentable.

   A similar problem occurs with the X.500 directory and the service
   control limiting the time allowed for the search.

   Authentication between NTP peers and between clients and servers is
   not addressed here, as the choice of mechanism is still the subject
   of some debate.

2.  Protocol Overview

   The NTP application functions exactly as in RFC 1119.  The use of
   remote operations and the underlying Application support means that
   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 the
   appropriate Remote Operation with the appropriate parameters at the
   appropriate frequency.

   On failure, they mark the peer as unreachable.

Crowcroft & Onions                                              [Page 2]
RFC 1165                      NTP over OSI                     June 1990

   The states that an ntp daemon records for each peer are enhanced from
   RFC 1119 to include:

      Connected: this indicates the host is connected with its peer and
      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, and
      such blocking can perturb the exchange of data with other hosts.