ITU-T PTP Telecom Profile for Phase/Time, (G.8275.2 Annex A)

Latest document version:ITU-T Recommendation G.8275.2, 11/2022 (full text publication)
Location:http://www.itu.int/rec/T-REC-G.8275.2/en
Objective:Time distribution to better than ±1.5µs over a partial timing support network
Feature/ ParameterNoteRangeDefault ValueG.8275.2 Clause
fromto

Profile Identification

profileName:ITU-T PTP profile for phase/time distribution with partial timing support from the network (unicast mode)


Annex A.1
profileVersion:2.2 (IEEE1588-2008) / 2.3 (IEEE1588-2019)


Annex A.1
profileIdentifier:  00-19-A7-02-02-02 / 00-19-A7-02-02-03


Annex A.1
Specified by:ITU-T


Annex A.1
Location:www.itu.int


Annex A.1

PTP Options

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


Annex A.3.1, 6.2.3
Prohibited NodesNone. Transparent Clocks are for further study.


Annex A.3.1
Transport MechanismsBoth masters and slaves must support IEEE1588-2008 Annex D IPv4/UDP stack. Bit 0 of the transportSpecific field must be set to "0".
Both masters and slaves may support IEEE1588-2008 Annex E IPv6/UDP stack



Annex A.3.2,
6.4
Multicast or UnicastBoth masters and slaves must support full unicast operation
(see details below)



Annex A.3.3, 6.3.3
BMCAAlternate BMCA specified (see details below)


Annex A.4,
6.7
Path Delay MeasurementUses delay_request/response mechanism, if required (i.e. for two-way operation)
Peer delay mechanism must not be used.



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


Annex A.6
Clock IdentityEUI-64 (as specified in clause 7.5.2.2.2 of IEEE1588-2008)


Annex A.7
Message TypesUsed: Announce, Sync, Follow-up, Delay_Req, Delay_Resp, Signaling
Not used: Pdelay_Req, Pdelay_Resp, Pdelay_Resp_Follow_Up
The use of Management messages is for further study.



6.2.2
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.



6.3.2
One-way and Two-way OperationMasters must support both one-way and two-way operation.
Slaves may support either one-way or two-way, or both.



6.3.1
SecurityFor further study.
IEEE1588-2008 Annex K experimental security protocol is not used



Annex A.8,
8
Unicast negotiation
(IEEE1588-2008 clause 16.1)
Mandatory - see details below


Annex A.3.4, A.3.5, 6.6
Path trace
(IEEE1588-2008 clause 16.2)
Not mentioned.


-
Alternate timescales
(IEEE1588-2008 clause 16.3)
PTP timescale used.
Alternate timescales are not used in this profile.



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


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


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


-
Acceptable master table
(IEEE1588-2008 clause 17.6)
Not used in this profile


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


Annex A.9

Message Rates

Sync & Follow-up1 per second to 128 per second1128-6.5
Delay_request/response1 per second to 128 per second1128-
Announce1 per second to 8 per second18-
Peer Delay_request/responseNone (uses Delay_request/response mechanism)


SignalingAs required for unicast negotiation


ManagementNot used


PTP Configurable Attribute Values

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

Default data set (configurable members)

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 clocksBC, TC1N
clockQuality.clockClass
Grandmaster clocks6, 7, 140, 150, 160, 248248Table A.1,
6.7.5, Table 2

Boundary clocks135, 165, 248248

Slave-only clocks255255
clockQuality.clockAccuracy
Grandmaster clocks locked to an ePRTC0x200xFETable A.1,
6.7.6

Grandmaster clocks locked to a PRTC0x21

Grandmaster clocks not locked to a PRTC0xFE

Boundary clocks and slave-only clocks0xFE
clockQuality. offsetScaledLogVariance
Grandmaster clocks locked to an ePRTC0x4B320xFFFFTable A.1,
6.7.7

Grandmaster clocks locked to a PRTC0x4E5D

Grandmaster clocks not locked to a PRTC 0xFFFF

Boundary clocks and slave-only clocks0xFFFF
priority1Not used. For all clock types, must be set to default value.
128128Table A.1, 6.7.3
priority2Used to set network and protection topology, as described in Appendix IGrandmasters, boundary clocks0255128Table A.1,
6.7.4
Slave-only clocks255255
domainNumberAll clock types446344Table A.1
 6.2.1
slaveOnlyGrandmasters and boundary clocksFALSEFALSETable A.1
Slave-only clocksTRUETRUE

Profile-specific defaultDS attributes

localPriorityNew dataset member defined in profile, allowing operators to manually configure topology (Annex B)1255128Table A.1, 6.7.2

Port data set (configurable members)

portIdentity.clockIdentityBased on EUI64 format, as per PTP


Table A.5
portIdentity.portNumberAlways 1 for ordinary clocks
Boundary clocks as required for device
Ordinary clocks11Table A.5
Boundary clocks1N
logMinDelayReqIntervalDelay_Req message rate: covered by unicast negotiation (see details below)

Table A.5
logAnnounceIntervalAnnounce message rate: covered by unicast negotiation (see details below)

Table A.5
announceReceiptTimeoutTimeout period before declaring loss of announce service2 missing messages22Table A.5
logSyncIntervalSync message rate: covered by unicast negotiation (see details below)

Table A.5
delayMechanismTwo-way capable slave (E2E mechanism)0x010x01Table A.5
One-way capable slave (Disabled)0xFE0xFETable 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, allowing multiple simultaneous active GMs.
TRUE for ports that are always in master state.
Grandmaster clocksTRUETRUETable A.5,
6.7.1
Boundary clocksFALSETRUETRUE
 Slave clocksFALSEFALSE
localPriorityNew dataset member defined in profile, allowing operators to manually configure topology (Annex B)1255128Table A.5,
6.7.1
SFNew dataset member defined in profile
TRUE when a slave port is in signal failure
TRUEFALSE
Table A.5

PTP common message header flags

alternateMasterFlagIn Announce messages: set FALSE on transmission when port state is MASTER.
Announce messages discarded on reception if flag is TRUE.
FALSETRUE
6.9,
Table A.6
twoStepFlagUsed as per PTP defined in IEEE1588-2008FALSETRUE
Table A.6
unicastFlagSet TRUE on transmission.TRUETRUETable A.6
PTP profile Specific1Set FALSE on transmission; ignored on reception.FALSEFALSETable A.6
PTP profile Specific2Set FALSE on transmission; ignored on reception.FALSEFALSETable A.6
ReservedSet FALSE on transmission; ignored on reception.FALSEFALSETable A.6
leap61Used as per PTP defined in IEEE1588-2008FALSETRUE
Table A.6
leap59Used as per PTP defined in IEEE1588-2008FALSETRUE
Table A.6
currentUTCOffsetValidUsed as per PTP defined in IEEE1588-2008FALSETRUE
Table A.6
ptpTimescaleSet TRUE on transmission.TRUETRUETable A.6
timeTraceableUsed as in Table 2FALSETRUE
Table A.6,
Table 2
frequencyTraceableUsed as in Table 2FALSETRUE
Table A.6,
Table 2
controlFieldNot used; ignored on reception.


6.7.10

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.6,
Annex E

Unicast and Multicast Operation

Full multicast operationNot used in this profile.


Annex A.3.3
Full unicast operationBoth master ports and slave ports must support full unicast operation


6.3.3,
Annex A.3.3
Hybrid unicast/multicastNot used in this profile.


Annex A.3.3
Unicast negotiation processBoth masters and slaves must support unicast negotiation (IEEE1588-2008 Clause 16.1).
Unicast connection establishment without negotiation is for further study.



Annex A.3.3,
6.6
targetPortIdentityRequesting port may use all 1's as the initial value.
On receiving a response, it may use all 1's, or use the clockIdentity/portNumber of grant port
Grant port may use all 1's, or use the clockIdentity/portNumber of requesting port



6.6
duration fieldDuration of unicast service lease601000300Annex A.3.4,
6.6
logInterMessagePeriod


Masters must be capable of accepting the entire ranges specified.
Slaves must operate within these ranges, but do not have to use the entire ranges.



Annex A.3.4,
6.5
Sync & Follow-up (from 128 to 1 messages per second)-70-
Delay_request/response (from 128 to 1 messages per second)-70-
Announce (from 8 to 1 messages per second)-30-
R (Renewal Invited)Set FALSE on transmission; ignored on reception.FALSEFALSE6.6
logQueryIntervalSlaves must wait a minimum of 1 second before repeating a unicast negotiation request.
Note: If three consecutive requests are denied or not answered, slaves must wait 60s before repeating the request to the same master.


16.6
number of TLVsMaster must accept multiple unicast request TLVs in the same signaling message
Slaves may include multiple unicast request TLVs in the same signaling message
Master may include multiple unicast grant TLVs in the same signaling message
Slaves must accept multiple unicast grant TLVs in the same signaling message
13
6.6

Best Master Clock Algorithm (BMCA)

BMCA type:Alternate BMCA (modified default BMCA)


6.7
State decision algorithmBased on default state decision algorithm, adding check for new parameter masterOnly


6.7.8
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)



6.7.9

Additional flags/fields

PTSF-lossSyncIf the slave no longer receives the timing messages sent by a master (i.e., Sync and subsequently Follow_up and Delay_Resp messages), then a PTSF‑lossSync associated to this master must occur. FALSETRUEFALSE6.7.11
PTSF-unusableIf the PTP packet timing signal is not usable for the slave to achieve the performance target, then a PTSF-unusable associated to this master must occur. FALSETRUEFALSE6.7.11

Profile-specific TLVs

PTP Interface RateOptional TLV communicating the bit rate of the master port. Used to determine rate asymmetry on the path between master and slave port, allowing the slave port to compensate for the resulting delay asymmetry. 
Attached to the signalling message containing the GRANT_UNICAST_TRANSMISSION TLV.



Annex D

On this page: