ptp timing everything you need to know! · • if you do not have a microphone, please submit your...

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SMPTE Technology Webcast Series

PTP TimingEverything you need to know!Nick Knez

Director, Processing and Timing Products

Evertz Microsystems SMPTE Technology Webcast Series Sponsored by:

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Today’s Guest Speaker

Nick KnezDirector

Processing and Timing Products

Evertz Microsystems



PTP Timing

• Synchronization

• Overview of PTP

• System Design and Configurations

• Deployment Strategy and Learning

• Monitoring and Robustness

Traditional Video Synchronization

• Distribute fundamental signals• Provide primary frequency and phase reference to terminal equipment

• Carrier waveform conveys frequency (e.g. Hsync)

• Waveform conveys phase (e.g. Vsync, TC preamble)

• When locked to GPS:• Frequency is accurate

• Time can drive time-of-day timecode

• There is no phase reference available via GPS


Using Synchronization

• Slave devices extract frequency and phase from the signal • Frequency is used to clock state machine logic

• Phase is used to identify a specific state

• Signal phase generated by the master is globally arbitrary, locally universal

Free-Running Legacy Synchronization

`

BlackBurst

DARS

Timecode

Master

SPG

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BlackBurst

DARS

Timecode

Distribution TreeCentral Equipment

Facility Equipment

Slave

Single Master produces necessary signals

Non-redundant

Clock quality = Master SPG

Distributed through a DA tree structure

Courtesy – Paul Briscoe – SMPTE 2016


Legacy - External GPS reference

`

BlackBurst

DARS

Timecode

Master

SPG

``

``

`

`

`

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`

`

BlackBurst

DARS

Timecode


Facility Equipment

Slave

GPS

Single Master produces necessary signals

Non-redundant

GPS provides frequency and time

Time for timecode

Frequency for reference signals

Clock quality = GPS

Distributed through a DA tree structure


Legacy - Redundant with GPS

Master 1

`

GPS

BlackBurst

DARS

Timecode

Master 2

Auto

ch

an

ge

over

``

``

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`

`

`

`

BlackBurst

DARS

Timecode

Facility Equipment

Slave

Dual Masters provide redundancy

Autochangeover monitors signal health, switches all

signals on failure of any

Clock quality = GPS

Redundant signals feed distribution tree

Distribution is non-redundant




About GPS

• GPS time is very different from PTP time• Epoch = 1980.01.05 - 00:00:00

“It’s just math” to get from GPS to PTP time

• Grandmasters all support a GPS interface

http://leapsecond.com/java/gpsclock.htm

PTP Overview

• IEEE-1588:2008 Precision Time Protocol• Well defined

• Provides network-distributed precision timestamp to many devices

• Compensates for network delay

• Time anchored = Epoch = 1970.01.01-00:00:00z


PTP Overview

• Profiles describe operation• Convey industry specific metadata

• Power Profile, Telecom Profile, Broadcast (SMPTE 2059) etc.

• Concept of Domains on the network• Private address space for PTP transactions

• A PTP Master is called a “Grandmaster”• One-step / Two-Step Masters

Message Transport

• Primary transport is multicast

• SMPTE Profile allows mixed mode• All messages are multicast except

• Delay request and response can be unicast

• Reduces loading on other slaves• Don’t have to listen to everyone else delay messages

• Grandmasters must support both


PTP Addresses

• PTP uses reserved multicast addresses• 224.0.1.129

• Port 319 for event messages (time-aware)

• Port 320 for general messages (announce, management.)

PTP has a peer-to-peer mode – not used in SMPTE applications.

Boundary / Transparent / PassThru



How does PTP work

• Exchange of well defined messages

• Two phases to the protocol• Initialization (or reconfiguration)

• Synchronization

PTP message types

PTP Grandmaster

GPS

PTP Slave

Sync MessagesPTP Timestamp

Announce Messages

ManagementMessages

Delay RequestSlave to Master

Delay ResponseMaster to Slave


PTP Announce Message

• Carries PTP priority and clock quality info

• Broadcast periodically• Configurable from one every 2 seconds to 8/sec

• SMPTE default 4 per second (val = -2)

• Received by all slaves and masters

Initialization Phase

• Uses announce messages to determine GM

• Best Master Clock Algorithm (BMCA)

1. Priority 1

2. Clock class

3. Clock accuracy

4. Variance

5. Priority 2

6. ID (MAC) - tiebreaker


1. Priority 1

• This parameter overrides anything else.

• Defaults value 128

• Useful to force a specific unit to be master no matter what during maintenance, testing

• If accidentally set higher than other GM(s), it will never enter master state

2. Clock Class

• Enumerated list of clock states

• Relates to clock source types


3. Clock Accuracy

• Class and Accuracy aren’t always related in the same way

• Enumerated list of accuracy wrt exact time

5. Priority 2

• This is the normal way to establish deterministic hierarchy of GMs

• Lowest number wins always

• Default value 128• Evertz recommends lower values


6. ID (MAC) Tiebreaker

… meaning you’ve failed to configure who’s on first with P2 and all else is equal:

- Grandmaster ID

This ensures that there is never a stalemate or lockup situation where no-one is GM

“Or Reconfiguration”

GMs have an “Announce timeout” in slave mode

If an Announce message from the active GM is not received for several expected intervals, the BMCA will run.


PTP Grandmaster

GPS

PTP Slave




Timekeeping Messages

PTP Sync Message

• Carries PTP timestamp value

• Broadcast periodically• Configurable from 2 to 128 per second

• SMPTE default 8 per second (val = -3)• Value chosen to achieve fast slave lock time ~5 sec

• Received by all slaves• Primary source of precision time for all slave use


PTP Delay Management Messages

• Slaves and master conduct periodic dialogue• Delay Request / Delay Response mechanism

• Typically transacted at a 1 second rate • SMPTE default

• Used to measure / manage path delay from master to each slave

Assumes symmetrical path delay

First the slave calculates the master to slave time difference.

T1 is the precise time of the sync message from the master. In two-step mode, it’s exact value is sent in a follow-up message.

T2 is the precise time of receipt by the slave (on it’s own clock)

Master to slave time difference is calculated by T2 – T1


Next we find the slave to master time difference.

T3 is the precise time of the delay request message from the slave.

T4 is the precise time of receipt by the master (on it’s own clock)

Slave to master time difference is calculated by T4 – T3

Slave now knows T1, T2, T3 and T4.

Master to Slave = T2 - T1

Slave to Master = T4 – T3

One way path delay:

(Master to Slave + Slave to Master) / 2

Offset Correction:

(Master to Slave – One-way delay) / 2

Slave can now accurately set it’s clock. It uses this mechanism to maintain local time and frequency lock.


SMPTE 2059

• SMPTE Standard for use of PTP• 2059-1: Epoch and Signal Alignment

• Video, AES3, Timecode specifications and formulae

• 2059-2: SMPTE Profile• Message types and rates

• Network Parameters

• Synchronization Metadata

Slave only mode

• A provision in ST 2059 calls for “slave-only” mode in terminal equipment (i.e. 2110 gear)

• Prevents rogue masters on the network• Misconfiguration of a slave

• Broken link to slave

• This is not standard in IEEE-1588


Clock Hierarchy in 2110

• In ST 2110, PTP is the fundamental timing reference

• In 2110 transmitters:• PTP creates the Media Clock

• Media Clock creates the RTP Clock (timestamp)

• In 2110 receivers: • RTP Clock is used to align streams together

• PTP is used to manage receiver buffers

Deployment Strategy

• Timing must be 1 + 1 Redundant

• PTP Network Considerations

• Keep it close to blackburst for now

• Limit the slave count

• Choice of clocks

• Random Grandmasters

• Security


Grandmaster

1

GPS

PTP

Grandmaster 2

BM

CA

PT

Network Fabric (cloud of switches)Centralized Equipment

Facility Equipment

PTP Slave

Masters provide native redundancy (2+)

Autochangeover is virtual between masters (PTP BMCA)

With external reference, they lock to that, one ‘drives’ the network

Without external reference, one becomes master, other(s) lock to it.

With failure of master, another picks up the role


Redundant PTP with GPS

GPS

PTP

Network Fabric (cloud of switches)Centralized Equipment

Facility Equipment

PTP Slave

PTP Slave1

Legacy

Master 1 BlackBurst

DARS

TimecodePTP Slave2

Legacy

Master 2

Au

toch

an

ge

ove

r

PTP

Grandmaster

1

Grandmaster 2

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`

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`

`

BlackBurst

DARS

Timecode

Facility Equipment

Legacy

Slave


Hybrid PTP with GPS


PTP on the Essence Network

• Sharing network with dense media traffic• 1080p60 is over 200,000 packets per second

• Jitter happens

Video A

Video B

PTP

Timing Layer Isolation

MasterMaster

Timing Layer Switch

Timed Layer Switch Timed Layer Switch

Slave Slave Slave Slave Slave

Timing Layer

PTP ONLY

BMCA

Flat or TC switch

Timed Layer

Essence + PTP

TC, BC, SDVN


Deployed Systems Examples

Deployed Systems Examples


Learned with Deployments

• Understanding of PTP is still lacking• Comfort with PTP

• 2 way communication

• Improvements needed• Commissioning and Monitoring

• Hybrid systems work

Locked to PTP


Locked to Blackburst

Rogue Master

PTP Grandmaster

GPS

PTP Slave


Announce Messages



X XIncoming Network

Link Breaks


Rogue Master

PTP Grandmaster

GPS

PTP Slave


Announce Messages

Slave hears no Announce messages, assumes it is the best

master, assumes master role. Commences

sending messages into network.

X XIncoming Network

Link Breaks


Announce Messages

Rogue Master

PTP Grandmaster

GPS

PTP Slave Rogue GM


Announce Messages

Network now has two GMs with the same

Domain ID. Panic ensues on the network.

X XIncoming Network

Link Breaks

This master just keeps on running, unaware

of the conflict


Announce Messages


Rogue Master

Why is this a problem?

• Slave devices will be listening to two different grandmasters, randomly.

• Will get both timestamps

• Can only transact delay measurement with one

• As the rogue drifts away (in holdover mode), slaves begin to get two different times which diverge. Eventually slave unlocks.

Monitoring

• Monitor the timing of your network• Get Insight into what is happening

• Logging

• Understanding the ACO of the system

• Free / Opensource / commercial tools• Insite

• PTP Trackhound

• Wireshark

• Various commercial products


Monitoring

Monitoring


Advancements

• Next version of PTP to be released soon• No significant changes to our usage

• SMPTE Study Group on PTP security• Aligned with work on 2110 security

• Proposed methodology for PTP and 2022-7

• One-year review of 2059 documents nearly complete with only minor changes.

Thank you! Questions?

Nick KnezDirector

Processing and Timing Products

Evertz Microsystems



SMPTE Technology Webcast Sponsors

• Thank you to our sponsor for their generous support:


Additional Thanks

• This webcast also brought to you by:



SMPTE Technology Webcast Series

PTP TimingEverything you need to know!Nick Knez

Director, Processing and Timing Products

Evertz Microsystems SMPTE Technology Webcast Series Sponsored by:

ptp timing everything you need to know! · • if you do not have a microphone, please submit your...

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