NTP Correction Field

Document Type Active Internet-Draft (candidate for ntp WG)
Last updated 2019-04-25
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Internet Engineering Task Force                               M. Lichvar
Internet-Draft                                                   Red Hat
Intended status: Experimental                             April 25, 2019
Expires: October 27, 2019

                          NTP Correction Field


   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.

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   This Internet-Draft will expire on October 27, 2019.

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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 receive and transmit timestamps
   from the NTP header.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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.

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    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)          |
   |                                                               |
   +                       Origin Correction                       +
   |                                                               |
   |           Origin ID           | Receive Corr. | Transmit Corr.|
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