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DXD/PTP/GPS User Manual (rev 2.10)

Page 15

12. General Information on PTP 

12.1. TIME AND PHASE 

Precise time information has always been crucial in traditional production and broadcast environments. To keep the different 
video and audio sources synchronized properly, two different references were typically used, one providing time information 
(time code), the other phase information (black & burst or try-level sync for Video and DARS or Word Clock for Audio). With 
IP networks, PTP provides both Time Of Day and phase information, replacing and/or coexisting with the traditional ‘legacy’ 
references. 

12.2. WHAT IS PTP? 

PTP (Precision Time Protocol) is a method for precisely synchronizing devices over a computer network. On a LAN, PTP can 
achieve clock accuracy to within a microsecond. Originally designed for network measurements, PTP has been broadly 
adopted in applications ranging from real-time automations to telecom transmissions and financial transactions. 

Published in 2002 by IEEE under the 1588-2002 standard (PTP v1) it was revised in 2008 as 1588-2008 (PTP v2). Version 2 
brought several improvements but is not backward compatible with version 1. 

12.3. A/V OVER IP APPLICATIONS 

PTP has been widely adopted in A/V over IP applications. It is the protocol chosen by AES and SMPTE with PTP profiles 
included in both the AES67 and ST-2059 standards. The SMPTE ST-2110 suite of standards (digital video over IP with audio, 
video and ancillary data as separate streams) uses PTP for synchronization as it is based on ST-2059. 

Major A/V over IP systems such as Q-LAN, LiveWire, Wheatnet-IP, Ravenna and Dante all use PTP. Although the original 
Dante used PTP v1, with the release of the Dante Domain Manager version 1.1, a Dante system has the ability to clock to a 
non-Dante PTP v2 clock. 

AVB (Audio Video Bridging) is a set of IEEE standards that facilitate the transport of high performance audio and video on a 
LAN. One of those standards, IEEE 802.1AS, defines a specific profile of IEEE 1588-2008 with additional timing features 
called gPTP (Generalized Precision Time Protocol). 

12.4. PTP DESCRIPTION 

Per IEEE 1588, PTP uses a hierarchical Master-Slave architecture for clock distribution. The primary timing source is called the 
PTP Grandmaster. Precise timestamps are captured at the Master and Slaves and exchanged to determine the offset between 
the two and the network latency so that the Slaves can synchronize their internal clocks to the Master’s. 

With the PTP protocol, two activities continually occur on the network: 

-  All grandmaster-capable devices negotiate to select a grandmaster. 
-  All devices synchronize to the grandmaster. 

BMCA: The Grandmaster is elected autonomously without any user interaction. Grandmaster-capable devices broadcast 
their clock “quality” and other parameters with Announce messages. They each compare the received Announce messages 
and, independently of the other devices, determine the most suitable grandmaster. This determination is done through the 
Best Master Clock Algorithm (BMCA), which by design ensures that all clocks reach the same conclusion. This best master 
clock negotiation continues even after a grandmaster has been selected so that in case the current grandmaster fails another 
clock can quickly replace it. 

SYNC: Synchronization to the grandmaster is done using a series of messages. Sync messages are broadcasted periodically 
by the grandmaster and contain timestamps from its internal clock. Slaves read these messages and adjust their internal 
clocks match exactly the master’s. Every update cycle, the slaves calculate corrections for offset and network latency to 
achieve high precision synchronization. 

Содержание DXD/GPS

Страница 1: ...k DXD OCXO OCXO option for the DXD Universal Clock Operations manual Version 2 10 January 2021 All materials herein Brainstorm Electronics Inc Brainstorm Electronics reserves the right to change or mo...

Страница 2: ...6 GPS Menus 8 6 1 SATELLITES SELECTION MENU 6 1 8 6 2 GPS SETTINGS MENU 6 2 8 6 3 ADVANCED GPS SETTINGS MENU 6 3 8 7 DXD OCXO 9 8 Time of Day 9 8 1 RTC Real Time Clock 10 8 2 Time Jam 10 8 2 1 TIME JA...

Страница 3: ...9 15 Typical PTP use 20 15 1 HYBRID SYNC GENERATOR ACCEPTING MULTIPLE REFERENCES 20 15 2 DISTRIBUTED PTP VS INDIVIDUAL GRANDMASTERS WITH GNSS 21 16 Guidelines for con fi guring PTP Precision Time Prot...

Страница 4: ...a series of 4 numbers separated by periods This key is only valid for the DXD 8 with the serial number used when you placed the order Note that PTP is optional on the DXD 8 only A feature key is not r...

Страница 5: ...ng LOCAL REF WHEN GM When PTP Mode is selected if GPS is available this fields enables GPS to be set as the reference when the DXD 8 is the Grandmaster Enabling this field will announce the DXD 8 as G...

Страница 6: ...a quick set up This menu gives you the option to set the timing values to the pro fi le default values 4 4 PORT TIMING MENU 5 4 Announce Interval 3 to 4 1 8sec 16sec Sets the rate at which the master...

Страница 7: ...in your DXD an antenna will need to be connected to the receiver s SMA connector an antenna is not included with the DXD GPS The cable needs an SMA Male connector on the DXD side Ideally the antenna s...

Страница 8: ...sideration as it can not only impact the signal strength but also cause a delay in the signal Under typical conditions however the expected cable delay is negligible in the nanoseconds range The follo...

Страница 9: ...e reference sources include time and rate information GPS and PTP for example carry precise time and date information as well as frequency However traditional reference signals such as video sync or w...

Страница 10: ...nd wanting all of the cross frame outputs 25 etc to be in correct phase and epoch as well as wordclocks and AES In a primarily legacy application this is the way to increase the number of legacy outpu...

Страница 11: ...to use Local Time instead while others may even prefer different standards for different times Be aware that even though the time source may give Time Of Day it may not correspond to the time indicate...

Страница 12: ...on Jan 1 1970 This process occurs everyday at the same time as set in the DAILY JAM TIME fi eld Daily Jam Time The value entered in the DAILY JAM TIME field is the amount of time after midnight local...

Страница 13: ...to LOCKED GRANDMASTER In case the DXD is or becomes a PTP Salve when locked it changes to LOCKED PTP SLAVE Note that if another source was selected in the reference menu such as Video Sync and the DXD...

Страница 14: ...lock and the Grandmaster in sec Additional times may appear on this page such as Time Code based on the installed options 11 2 2 GPS RECEIVER STATUS PAGE The GPS RECEIVER status page displays the foll...

Страница 15: ...as the ability to clock to a non Dante PTP v2 clock AVB Audio Video Bridging is a set of IEEE standards that facilitate the transport of high performance audio and video on a LAN One of those standard...

Страница 16: ...suited clock is found it will become the Grandmaster 12 6 SYNCHRONIZATION There are several different PTP messages used during synchronization sequenced as follows 1 The grandmaster sends a Sync messa...

Страница 17: ...clocks on a single PTP communication path must use the same method to measure the time delay 12 8 TYPES OF CLOCKS IEEE 1588 de fi nes three different types of clocks Ordinary Clock OC Boundary Clock...

Страница 18: ...ate of the port can change The BMCA determines what unit becomes the Grandmaster If the current Grandmaster disappears or looses GPS another Grandmaster is selected For more on the Grandmaster selecti...

Страница 19: ...it has been set by the operator 14 1 JUMP TO RELOCK When the time difference detected between the external PTP GM and the DXD System Time is above the Jump Threshold value the DXD will jump to the ne...

Страница 20: ...t all equipment could be kept perfectly synchronized But for added fl exibility the DXD s can also be set up to lock to any legacy sync or to PTP as illustrated below These choices are available in th...

Страница 21: ...TP slaves to an external Grandmaster in the second illustration the DXD 8 s are all Grandmaster for their networks and each is locked to GNSS This second solution is particularly useful when distances...

Страница 22: ...ith any other domain number will be ignored menu 5 2 Ports Timing per IEEE 1588 all devices on a PTP domain must have the same value set for these ports timing Announce Interval Announce Receipt Timeo...

Страница 23: ...GMPv2 On larger networks a router is required to manage multicast group membership Switches that support IGMP snooping are also recommended 17 Troubleshooting Error Warning Messages 17 1 PTP NO PORT W...

Страница 24: ...3 Menu 5 1 If PTP was selected TIME JAM BNC INPUT will automatically show in menu 5 1 in blue blue status information The words Time Jam will also appear on the REFERENCE line at the bottom of the ma...

Страница 25: ...the ribbon cable to J23 the GPS connector on the motherboard B J23 is the designator number on both DXD 8 and DXD 16 PCB As always with ribbon cables make sure the connectors are properly oriented do...

Страница 26: ...Including cable loss Low Gain mode FLNA High 3 For best jammer resistance and lower power consumption use 10 dB lower gain than the max gain 18 3 2 RECOMMENDED PASSIVE ANTENNA 1 High Gain mode FLNA Op...

Страница 27: ...TIMEOUT 3 announce intervals SYNC INTERVAL 1 sec log 0 MINIMUM DELAY REQUEST INTERVAL 1 sync interval GLONASS Yes GALLILEO No QZSS LIC A Yes SBAS QZSS LIS SBAS DIF FIX ANTENNA CABLE DELAY 0 ANTENNA H...

Страница 28: ...Page 28 DXD PTP GPS User Manual rev 2 10...

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