Sonifex AVN-GMC, Handbook

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AVN-GMC IEEE1588 PTP Grandmaster Clock with GPS Receiver 1
1. AVN-GMC IEEE1588 PTP Grandmaster Clock with GPS Receiver
Introduction
Fig 1-1: The AVN-GMC Front Panel
The AVN-GMCS is a PTPv2 grandmaster clock for use with AoIP
applications. IEEE1588-2008 PTPv2 (precision time protocol) is used to
synchronise all the nodes within a network. To achieve this one of the
nodes must become the master clock and distribute time packets to
the others. The AVN-GMCS is designed to perform this role simply and
accurately, enabling sub micro second synchronisation between all nodes.
The AVN-GMCS supports the Default Profile and in normal operation, the
unit has PTPv2 time stamping resolution to 8nsec. The AVN-GMCS uses
a combination of a GPS receiver, a PLL (phase lock loop) and a specialist
on-board clock device to create the precise, low jitter clock signals required
to drive the physical transceiver’s time stamping circuitry, also providing
holdover if the GPS signal is lost.
The specialist on board clock , which is used to sustain the PTP clock if the
GPS signal is lost, is available in three different types:
TCXO, OXCO and CSAC (Chip Scale Atomic Clock, Caesium), which vary in
both price and accuracy:
AVN-GMCS – TCXO Temperature Compensated Oscillator accurate to 1 part
per million (worst case 1 sec gain/loss every 11.5 days). *
AVN-GMCOS – OCXO Oven Controlled Oscillator accurate to 0.1 parts per
million (worst case 1 sec gain/loss every 115 days). *
AVN-GMCCS – SAC Quantum Atomic Clock accurate to 0.00050 parts per
million (worst case 1 sec gain/loss every 63 years). *
An external sync clock input can act as an alternative reference source to GPS.
Clock outputs, driven from the physical transceiver, can be used to provide
media clocks for external equipment local to the AVN-GMC when it is in
both ‘master’ and ‘slave’ states. The clock outputs are available as a single
AES-3id output and two outputs which can be selected as either word clock
or variable PPS. The wordclock can operate at 32, 44.1, 48, 96, 176.4 and
192kHz. When set as a variable PPS output, the unit can act as a clock master
to distribute a reference frequency to test and measurement equipment.
The front panel of the unit shows the PTP timebase as standard, which is
always set to International Atomic Time (TAI). It can be reconfigured to display
UTC or ‘Local Time’ instead. Local time allows a fixed time offset from UTC
to be applied (useful for time zones) and the accommodation of automatic
daylight saving time changes by entering Spring Forward and Fall Back dates.
The built-in webserver, or front panel OLED display, can be used to configure
the unit. Front panel LEDs show the synchronisation status, reference lock
status and the status of the AC and DC power supply inputs.
The brightness of the OLED display and LED indicators can be adjusted for low
or high lighting conditions
4 general purpose outputs indicate critical states for the unit using a 9 way
D-type connector mounted on the rear panel. Pull down when active pins are
supplied for reference source, reference lock status, AC power present and DC
power present.
* This figure represents the holdover accuracy should the GPS signal be lost - this is an
approximation based on 1st year stability figures.