synchronizationuncertain feature in ieee p1588-rev (for...
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IEEE 802.1, March 2019, Vancouver
synchronizationUncertain
feature in IEEE P1588-rev
(for IEEE P802.1AS-rev comment i-368)
Rodney Cummings
National Instruments
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IEEE 802.1, March 2019, Vancouver
1588-rev syncUncertain History
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IEEE 802.1, March 2019, Vancouver 3
Application Profile Requirements
• Applications have timing requirements
• e.g. telecom, power grid, industrial, automotive
• Applications specify profiles of 1588
• Transitive for app profile of 802.1AS (e.g. IEEE/IEC 60802)
• How does a 1588 device know that app profile
requirements are met along the entire path from the
Grandmaster?
• Solution brought into 1588-rev from ITU-T:
synchronizationUncertain
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IEEE 802.1, March 2019, Vancouver 4
Spec in 1588-rev Initial Sponsor
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IEEE 802.1, March 2019, Vancouver 5
Benefit of Flag in Announce
• Application in 1588 device knows when it has stable
synchronization along the complete path
• Stable according to the application's requirements
• It is impossible to instantaneously know
if "all" devices in the network have stable sync
• For a given device, this tells me what matters:
• Is my sync stable?
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IEEE 802.1, March 2019, Vancouver 6
Remote Management
• What if we have a remote management client?
• Client might not be running 1588
• Client wants to read syncUncertain in node(s)
• This is not related to operation of the application
• Non-essential, but still important
• Presenter submitted comment to 1588 initial sponsor ballot
• Must-be-satisfied=No
• So far, comment's response is Accept In Principle
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IEEE 802.1, March 2019, Vancouver 7
Coming in 1588-rev Sponsor Recirc 1
• currentDS.synchronizationUncertain
• Read-only value of this node's flag (boolean)
• Transmitted in Announce (when applicable)
• parentDS.synchronizationUncertain
• Read-only value received from parent
• Received in Announce (when applicable)
• Recirc 1 has not started as of this date
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IEEE 802.1, March 2019, Vancouver
Comment i-368 of
802.1AS-rev Initial Sponsor
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IEEE 802.1, March 2019, Vancouver 9
Comment i-368
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IEEE 802.1, March 2019, Vancouver 10
Proposal
• 802.1AS-rev Response for i-368
• REJECT: This comment is addressed by the
synchronizationUncertain feature of 1588-rev, and therefore
it is not needed in 802.1AS-rev
• IEC/IEEE 60802
• "shall support the synchronizationUncertain
feature of 1588-2019"
• Application-specific performance metrics for syncUncertain
• As expected by the 1588-rev specs
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IEEE 802.1, March 2019, Vancouver 11
Benefits of Proposal
• Short and simple
• Avoids delay of 802.1AS-rev
• Avoids major new feature, coordinating with app profiles
• Should be done in task or working group, not sponsor ballot
• Meets essential need for 60802
• Operation of the application
• Industrial controllers/sensors/actuators already have
mechanisms to detect and react to faults in a device
• This is a fault like any other
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IEEE 802.1, March 2019, Vancouver 12
Remote Management
• In presenter's opinion, this is non-essential for 60802
• YANG: syncUncertain will be in 1588's YANG
• If 802.1AS YANG is an augment, inherited
• If 60802 requires for MIB, changes needed in 802.1AS
• Two data set members: Managed objects and MIB
• Extra features
• Statistics counter: Managed object and MIB
• Notification: MIB only
• Application-specific managed objects in 802.1AS
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IEEE 802.1, March 2019, Vancouver
Duplication of 1588 Text
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IEEE 802.1, March 2019, Vancouver 14
Presenter's Opinion on Duplication
• If 802.1AS integrates syncUncertain, do so by reference
• Do not duplicate text from 1588 in 802.1AS document
• In past this duplication was targeted at
recommendations to read 802.1AS and ignore 1588
• In other words, read a profile and ignore its base standard
• Thankfully, most implementers ignore this advice
• Following this advice can lead to bugs
• Duplication is harmful to standards development
• Conformance contradictions, re-invention, more editor work
• Leave existing duplication, but avoid in future
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IEEE 802.1, March 2019, Vancouver
Thank You