NTP Correction Field
draft-mlichvar-ntp-correction-field-02

Document Type Active Internet-Draft (individual)
Last updated 2018-06-18
Stream (None)
Intended RFC status (None)
Formats plain text xml pdf html bibtex
Stream Stream state (No stream defined)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date
Responsible AD (None)
Send notices to (None)
Internet Engineering Task Force                               M. Lichvar
Internet-Draft                                                   Red Hat
Intended status: Experimental                              June 18, 2018
Expires: December 20, 2018

                          NTP Correction Field
                 draft-mlichvar-ntp-correction-field-02

Abstract

   This document specifies an extension field for the Network Time
   Protocol (NTP) which improves resolution of specific fields in the
   NTP header and allows network devices such as switches and routers to
   modify NTP packets with corrections to improve accuracy of the
   synchronization in the network.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 20, 2018.

Copyright Notice

   Copyright (c) 2018 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
   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.

Lichvar                 Expires December 20, 2018               [Page 1]
Internet-Draft            NTP Correction Field                 June 2018

1.  Introduction

   Processing and queueing delays in network switches and routers may be
   a significant source of jitter and asymmetry in network delay, which
   has a negative impact on accuracy and stability of clocks
   synchronized by NTP [RFC5905].

   If all network devices on the paths between NTP clients and servers
   implemented NTP and supported an operation as a server and client,
   the impact of the delays could be avoided by configuring NTP to make
   measurements only between devices and hosts that are directly
   connected to one another.  In the Precision Time Protocol (PTP)
   [IEEE1588], which is a different protocol for synchronization of
   clocks in networks, such devices are called Boundary Clocks (BC).

   A different approach supported by PTP to improve the accuracy uses
   Transparent Clocks (TC).  Instead of fully implementing PTP in order
   to support an operation as a BC, the devices only modify a correction
   field in forwarded PTP packets with the time that the packets had to
   wait for transmission.  The final value of the correction is included
   in the calculation of the delay and offset, which may significantly
   improve the accuracy and stability of the synchronization.

   This document describes an NTP extension field which allows the
   devices to make a similar correction in forwarded NTP packets.

   To better support a highly accurate synchronization, the extension
   field also improves resolution of the following fields in the NTP
   header: root delay, root dispersion, receive timestamp, transmit
   timestamp.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Format of Correction Field

   The Correction Field is an NTP extension field following RFC 7822
   [RFC7822].  The format of the extension field is shown in Figure 1.

Lichvar                 Expires December 20, 2018               [Page 2]
Internet-Draft            NTP Correction Field                 June 2018

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Field Type           |          Length (28)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Root Delay Correction     |  Root Dispersion Correction   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Receive Corr. | Transmit Corr.|                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
Show full document text