RuggedCom RX1000, RX1100 Configuring Irigb And IEEE1588, IEEE1588 Fundamentals, PTP Network Roles

RuggedRouter™ User Guide

Chapter 24 – Configuring IRIGB And IEEE1588

Introduction

This chapter familiarizes the user with:

∙IEEE 1588 Configuration

∙IRIGB Configuration

∙Viewing IRIGB and IEEE1588 Status

IEEE1588 Fundamentals

The IEEE 1588 working group Precise Timing Protocol (PTP) standard details a method of synchronizing a clocks over networks, including Ethernet. The RuggedRouter provides a special hardware assisted PTP capability as provided by the RuggedCom PTP card. When used in conjunction with the cards Global Positioning System (GPS) receiver, the router can provide nanosecond accuracy via IEEE1588.

Additionally, IEEE1588 may be used (in GPS failure situations) to synchronize to a remote source and provide accurate time for IRIG-B.

PTP Network Roles

The IEEE 1588 standard describes regular clocks as devices having a single PTP port that can issue and receive PTP messages. PTP boundary clocks are clocks have have multiple PTP ports, offering the ability to serve time to more than one subnet at a time. The RuggedRouter can serve as a regular clock and communicate with boundary clocks.

The set of devices that can communicate using the PTP protocol IP multicast transmissions are said to be in the PTP subdomain. This is usually a set of PTP devices connected by a switched network or direct links. The “best” clock in the subdomain is known as the master clock. The master clock of a boundary clock is known as the grandmaster clock.

The protocol negotiates among PTP ports to identify the device with the highest quality clock source. Ports issuing messages from the master clock are said to be masters, while those that will receive the messages are slaves. When a port will not participate in the protocol its status is passive. When the network architect knows the relative quality their clock's time sources, they may configure a specific clock to be the preferred master.

PTP Master Election

PTP clocks exchange SYNC messages containing information which is used by the PTP Best Master Clock (BMC) algorithm. Several factors will affect the choice of best master clock, including the preferred master clock setting, the clock identifier, grandmaster settings and clock stability.

The clock identifier is the measure of PTP clock quality and is one of the following:

PTP Identifier	Descrption
GPS	The PTP clock is a primary reference standard traceable to a recognized standard
	source of time such as GPS. The router uses this identifier when GPS is locked.

222 RuggedCom