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Latest document version:ITU-T Recommendation G.8275.1, Amd. 2, 03/2018 (full text publication)

Objective:Time distribution to better than ±1.5ms, over a full timing support network

Feature/ ParameterNoteRangeDefault ValueG.8275.1 Clause

Profile Identification

profileName:ITU-T PTP profile for phase/time distribution with full timing support from the network

Annex A.1

Annex A.1
profileIdentifier:  00-19-A7-01-02-01

Annex A.1
Specified by:ITU-T

Annex A.1

Annex A.1

PTP Options

Permitted NodesOrdinary clocks (i.e. Grandmasters, slave-only clocks), boundary clocks, end-to-end transparent clocks

Annex A.3.1,
Prohibited NodesPeer-to-peer transparent clocks

Annex A.3.1
Transport MechanismsRequired: IEEE802.3 Ethernet, as per IEEE1588-2008 Annex F.
Both multicast addresses noted in IEEE1588-2008 must be supported by all clocks.
(i.e. 01-80-C2-00-00-0E non-forwardable and 01-1B-19-00-00-00 forwardable address).
The use of VLAN tags is not allowed.
Other transport mechanisms (e.g. IP/UDP as in Annexes D & E) are for further study.

Annex A.3.3,
6.2.6, 6.2.7
Multicast or UnicastFull multicast operation, using both of the addresses noted in IEEE1588-2008 Annex F
Unicast is not permitted.

Annex A.3.4,
BMCAAlternate BMCA specified (see details below)

Annex A.4,
Path Delay MeasurementUses delay_request/response mechanism.
Peer delay mechanism must not be used.

Annex A.5
PTP ManagementNot specified in this version of the profile.

Annex A.7
Clock IdentityEUI-64 (as specified in clause of IEEE1588-2008)

Annex A.6
Message TypesUsed: Announce, Sync, Follow-up, Delay_Req, Delay_Resp
Not used: Pdelay_Req, Pdelay_Resp, Pdelay_Resp_Follow_Up
The use of Signaling and Management messages is for further study.

One-step and Two-step clockClocks may transmit messages using either one-step or two-step modes.
Clocks must be capable of receiving and handling messages from both one-step and two-step clocks, without configuration.

Annex A.3.2,
One-way and Two-way OperationOnly two-way operation is permitted.

SecurityFor further study.
IEEE1588-2008 Annex K experimental security protocol is not used

Annex A.8,
Unicast negotiation
(IEEE1588-2008 clause 16.1)
Not used.

Annex A.9
Path trace
(IEEE1588-2008 clause 16.2)

Annex D
Alternate timescales
(IEEE1588-2008 clause 16.3)
PTP timescale used.
Alternate timescales are not used.

Annex A.9
Grandmaster clusters
(IEEE1588-2008 clause 17.3)
Not used.

Annex A.9
Alternate masters
(IEEE1588-2008 clause 17.4)
Not used.

Annex A.9
Unicast discovery
(IEEE1588-2008 clause 17.5)
Not used.

Annex A.9
Acceptable master table
(IEEE1588-2008 clause 17.6)
Not used.

Annex A.9
Cumulative frequency scale factor offset
(IEEE1588-2008 Annex L)
Not used.

Annex A.9

Message Rates

Sync & Follow-up16 per second16166.2.8
Delay_request/response16 per second1616
Announce8 per second88
Peer Delay_request/responseNone (uses Delay_request/response mechanism)

SignalingNot used

ManagementNot used

PTP Configurable Attribute Values

(all others as per PTP, defined in IEEE1588-2008)

Default data set

twoStepFlagUsed as per PTP, according to clock's capabilityFALSETRUE
Table A.1
clockIdentityBased on EUI64 format, as per PTP

Table A.1,
Annex A.7
numberPortsAlways 1 for ordinary clocks (Grandmasters, slaves)Ordinary clocks11Table A.1
As required for Boundary or Transparent clocksBoundary, Transparent Clocks1N
Grandmaster clocks6, 7, 140, 150, 160, 248248Table A.1,
6.4 (Table 2)
Boundary clocks135, 165, 248248
Slave-only clocks255255
clockQuality.clockAccuracyGrandmaster clocks traceable to a GNSS-locked ePRTC0x200xFETable A.1,
Grandmaster clocks traceable to a GNSS-locked PRTC0x21
Grandmaster clocks not traceable to a PRTC0xFE
Boundary clocks and slave-only clocks0xFE
clockQuality. offsetScaledLogVarianceGrandmaster clocks traceable to a GNSS-locked ePRTC0x4B320xFFFF
Grandmaster clocks traceable to a GNSS-locked PRTC0x4E5D
Grandmaster clocks not traceable to a PRTC 0xFFFF
Boundary clocks and slave-only clocks0xFFFF
priority1All clock types128128Table A.1, 6.3.3
priority2Use cases to aid network topology establishment and configure protection paths described in Appendices IV and XGrandmasters, boundary clocks0255128Table A.1,
Slave-only clocks255255
domainNumberAll clock types244324Table A.1
slaveOnlyGrandmasters and boundary clocksFALSEFALSETable A.1
Slave-only clocksTRUETRUE

Profile-specific defaultDS attributes

localPriorityNew dataset member defined in profile
Allows operators to manually configure the topology of the synchronization network (see Annex B)
1255128Table A.1,
maxStepsRemovedNew dataset member defined in profile
Allows operators to configure the maximum distance between a T-GM and a T-TSC
1255255Table A.1,
Annex F

Port data set (configurable members)

portIdentity.clockIdentityBased on EUI64 format, as per PTP

Table A.5
portIdentity.portNumberAlways 1 for ordinary clocks
Boundary and transparent clocks as required for device
Ordinary clocks11Table A.5
Boundary, Transparent clocks1N
logMinDelayReqIntervalDelay_Req message rate: 16 messages/second-4-4Table A.5
logAnnounceIntervalAnnounce message rate: 8 messages/second-3-3Table A.5
announceReceiptTimeoutTimeout period before declaring loss of announce service: 3 missing messages3FFS3Table A.5
logSyncIntervalSync message rate: 16 messages/second-4-4Table A.5
delayMechanismUses end-to-end delay mechanism11Table A.5
logMinPdelayReqIntervalPdelay message rate: not used in this profile

Table A.5
versionNumberPTP protocol version number: Version 2 only22Table A.5

Profile-specific portDS attributes

masterOnlyNew dataset member defined in profile.
Renamed from notSlave
Grandmaster clocksTRUETRUETable A.5,
Boundary clocksFALSETRUETRUE
Slave clocksFALSEFALSE
localPriorityNew dataset member defined in profile
Allows operators to manually configure the topology of the synchronization network
1255128Table A.5,

PTP common message header flags

alternateMasterFlagSet FALSE on transmission; used as per PTP by receiving nodesFALSEFALSETable A.8
twoStepFlagUsed as per PTP defined in IEEE1588-2008FALSETRUE
unicastFlagSet FALSE on transmission; ignored on reception.FALSEFALSE
PTP profile Specific1Set FALSE on transmission; ignored on reception.FALSEFALSE
PTP profile Specific2Set FALSE on transmission; ignored on reception.FALSEFALSE
ReservedSet FALSE on transmission; ignored on reception.FALSEFALSE
leap61Used as per PTP defined in IEEE1588-2008FALSETRUE
leap59Used as per PTP defined in IEEE1588-2008FALSETRUE
currentUTCOffsetValidUsed as per PTP defined in IEEE1588-2008FALSETRUE
ptpTimescaleSet TRUE on transmission.TRUETRUE
timeTraceableUsed as defined in Table 2 of G.8275.1FALSETRUE
Table A.8,
Table 2
frequencyTraceableUsed as defined in Table 2 of G.8275.1FALSETRUE
controlFieldNot used; ignored on reception.


Profile-specific common message header flags

synchronizationUncertainProfile specific optional flag in octet 1, bit 6, indicating that the source of synchronization is uncertain (e.g. clock is in UNCALIBRATED state while switching to a new T-GM).FALSETRUEFALSETable A.8,
Annex E

Unicast and Multicast Operation

Full multicast operationFully multicast operation

Annex A.3.4
Full unicast operationNot used.

Hybrid unicast/multicastNot used.

Unicast negotiation processNot used.

Best Master Clock Algorithm (BMCA)

BMCA type:Alternate BMCA (modified default BMCA)

State decision algorithmBased on default state decision algorithm, adding check for new parameter masterOnly

Data set comparison algorithmBased on default data set comparison with following changes:
- moves check on GM clockIdentity to end
- removes check on GM priority1 values
- adds check for new parameter localPriority value (after GM priority2)


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