NTP Interleaved Modes
draft-ietf-ntp-interleaved-modes-04

Document Type Active Internet-Draft (ntp WG)
Last updated 2020-09-17
Replaces draft-mlichvar-ntp-interleaved-modes
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Internet Engineering Task Force                               M. Lichvar
Internet-Draft                                                   Red Hat
Updates: 5905 (if approved)                                  A. Malhotra
Intended status: Standards Track                       Boston University
Expires: March 21, 2021                                     Sep 17, 2020

                         NTP Interleaved Modes
                  draft-ietf-ntp-interleaved-modes-04

Abstract

   This document extends the specification of Network Time Protocol
   (NTP) version 4 in RFC 5905 with special modes called the NTP
   interleaved modes, that enable NTP servers to provide their clients
   and peers with more accurate transmit timestamps that are available
   only after transmitting NTP packets.  More specifically, this
   document describes three modes: interleaved client/server,
   interleaved symmetric, and interleaved broadcast.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on March 21, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must

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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Interleaved Client/server mode  . . . . . . . . . . . . . . .   4
   3.  Interleaved Symmetric mode  . . . . . . . . . . . . . . . . .   7
   4.  Interleaved Broadcast mode  . . . . . . . . . . . . . . . . .   9
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
     8.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   RFC 5905 [RFC5905] describes the operations of NTPv4 in a client/
   server, symmetric, and broadcast mode.  The transmit and receive
   timestamps are two of the four timestamps included in every NTPv4
   packet used for time synchronization.

   For a highly accurate and stable synchronization, the transmit and
   receive timestamp should be captured close to the beginning of the
   actual transmission and the end of the reception respectively.  An
   asymmetry in the timestamping causes the offset measured by NTP to
   have an error.

   There are at least four options where a timestamp of an NTP packet
   may be captured with a software NTP implementation running on an
   operating system:

   1.  User space (software)

   2.  Network device driver or kernel (software)

   3.  Data link layer (hardware - MAC chip)

   4.  Physical layer (hardware - PHY chip)

   Software timestamps captured in the user space in the NTP
   implementation itself are least accurate.  They do not include system
   calls used for sending and receiving packets, processing and queuing

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   delays in the system, network device drivers, and hardware.  Hardware
   timestamps captured at the physical layer are most accurate.

   A transmit timestamp captured in the driver or hardware is more
   accurate than the user-space timestamp, but it is available to the
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