ITU-T PTP Telecom Profile for Frequency (G.8265.1 Annex A)
| Latest document version: | ITU-T Recommendation G.8265.1, Cor. 1, 04/2016 (full text publication) |
|---|---|
| Location: | http://www.itu.int/rec/T-REC-G.8265.1/en |
| Objective: | Frequency distribution to better than 16ppb (long term fractional frequency offset specified in G.8261.1) |
| Feature/ Parameter | Note | Range | Default Value | G.8265.1 Clause | ||
|---|---|---|---|---|---|---|
| from | to | |||||
Profile Identification | ||||||
| profileName: | ITU-T PTP Profile for Frequency Distribution without timing support from the network (Unicast mode) | Annex A.1 | ||||
| profileVersion: | 1.2 | Annex A.1 | ||||
| profileIdentifier: | 00-19-A7-00-01-02 | Annex A.1 | ||||
| Specified by: | ITU-T | Annex A.1 | ||||
| Location: | www.itu.int | Annex A.1 | ||||
PTP Options | ||||||
| Permitted Nodes | Ordinary clocks (i.e. Grandmasters, slave-only clocks) | Annex A.3.1 | ||||
| Prohibited Nodes | Boundary clocks, transparent clocks | Annex A.3.1 | ||||
| Transport Mechanisms | Both masters and slaves must support IEEE1588-2008 Annex D IPv4/UDP stack Both masters and slaves may support IEEE1588-2008 Annex E IPv6/UDP stack | Annex A.3.2, 6.4 | ||||
| Multicast or Unicast | All messages are sent in unicast. Unicast negotiation is enabled by default (see details below). | Annex A.3.3, 6.3.3 | ||||
| BMCA | Static BMCA specified (see below) | Annex A.4, 6.7 | ||||
| Path Delay Measurement | Uses delay_request/response mechanism, if required (i.e. two-way operation) Peer delay mechanism must not be used. | Annex A.5, 6.3.1, | ||||
| PTP Management | Not specified in this version of the profile. | Annex A.6 | ||||
| Clock Identity | EUI-64 (as specified in clause 7.5.2.2.2 of IEEE1588-2008) | Annex A.7 | ||||
| Message Types | Used: 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. | 6.5 | ||||
| One-step and Two-step clock | Master may support either one-step or two-step clocks, or both. Slaves must support both one-step and two-step clocks, without configuration. | 6.3.2 | ||||
| One-way and Two-way Operation | Masters must support both one-way and two-way operation. Slaves may support either one-way or two-way, or both. | 6.3.1 | ||||
| Security | For further study. IEEE1588-2008 Annex K experimental security protocol is not mentioned. | 8 | ||||
| Unicast negotiation (IEEE1588-2008 clause 16.1) | Mandatory - see details below | A.3.3. 6.6 | ||||
| Path trace (IEEE1588-2008 clause 16.2) | Not mentioned. | |||||
| Alternate timescales (IEEE1588-2008 clause 16.3) | PTP or ARB timescale used. Alternate timescales are not used. | A.2 | ||||
| Grandmaster clusters (IEEE1588-2008 clause 17.3) | Not mentioned. | |||||
| Alternate masters (IEEE1588-2008 clause 17.4) | Not mentioned. | |||||
| Unicast discovery (IEEE1588-2008 clause 17.5) | Not mentioned. | |||||
| Acceptable master table (IEEE1588-2008 clause 17.6) | Not mentioned. | |||||
| Cumulative frequency scale factor offset (IEEE1588-2008 Annex L) | Not mentioned. | |||||
Message Rates | ||||||
| Sync & Follow-up | 1 every 16 seconds to 128 per second | 1/16 | 128 | - | 6.5 | |
| Delay_request/response | 1 every 16 seconds to 128 per second | 1/16 | 128 | - | ||
| Announce | 1 every 16 seconds to 8 per second; default 1 every 2 seconds | 1/16 | 8 | 1/2 | ||
| Peer Delay_request/response | None (uses Delay_request/response mechanism) | |||||
| Signaling | As required for unicast negotiation | |||||
| Management | Not used | |||||
PTP Configurable Attribute Values(all others as per PTP, defined in IEEE1588-2008) | ||||||
Default data set | ||||||
| twoStepFlag | Used as per PTP, according to clock's capability | FALSE | TRUE | 6.3.2, Table A.1 | ||
| clockIdentity | Based on EUI64 format, as per PTP | Table A.1, Annex A.7 | ||||
| numberPorts | Always 1 for ordinary clocks | 1 | 1 | 1 | Table A.1 | |
| clockQuality.clockClass | clockClass value is derived from G.781 SSM values, according to Table 1 of G.8265.1. Masters encode clockClass using this table according to their input reference quality. Slaves use clockClass to select master to synchronize to. | GM | 80 | 110 | - | Table A.1, 6.7.3.1 (Table 1) |
| Slave-only | 255 | 255 | ||||
| clockQuality.clockAccuracy | Not used. Should be set to 0xFE if not traceable to a time source. | Table A.1 | ||||
| clockQuality. offsetScaledLogVariance | Not used in this profile. | Table A.1 | ||||
| priority1 | Not used in this profile. | Table A.1 | ||||
| priority2 | Not used in this profile. | Table A.1 | ||||
| domainNumber | No default value. This range should be supported by both grandmaster and slave-only clocks | 4 | 23 | - | Table A.1, 6.2.1 | |
| slaveOnly | FALSE for Grandmasters; | FALSE | FALSE | Table A.1 | ||
| TRUE for slave-only clocks | TRUE | TRUE | ||||
Port data set | ||||||
| portIdentity.clockIdentity | Based on EUI64 format, as per PTP | Table A.5 | ||||
| portIdentity.portNumber | Always 1 for ordinary clocks | 1 | 1 | Table A.5 | ||
| logMinDelayReqInterval | Not used (covered by unicast negotiation - see details below) | Table A.5 | ||||
| logAnnounceInterval | Not used (covered by unicast negotiation - see details below) | Table A.5 | ||||
| announceReceiptTimeout | Timeout period before declaring loss of announce service (in number of missing messages) | 2 | 2 | Table A.5 | ||
| logSyncInterval | Not used (covered by unicast negotiation - see details below) | Table A.5 | ||||
| delayMechanism | Two-way capable slave (E2E mechanism) | 0x01 | 0x01 | Table A.5 | ||
| One-way capable slave (Disabled) | 0xFE | 0xFE | Table A.5 | |||
| logMinPdelayReqInterval | Not used in this profile. | Table A.5 | ||||
| versionNumber | Always set to 2 | 2 | 2 | Table A.5 | ||
PTP common message header flags | ||||||
| alternateMasterFlag | Set FALSE on transmission; ignored on reception. | FALSE | FALSE | Table A.6 | ||
| twoStepFlag | Used as per PTP defined in IEEE1588-2008 | FALSE | TRUE | 6.3.2, Table A.1 | ||
| unicastFlag | Set TRUE on transmission. | TRUE | TRUE | Table A.6 | ||
| PTP profile Specific1 | Set FALSE on transmission; ignored on reception. | FALSE | FALSE | Table A.6 | ||
| PTP profile Specific2 | Set FALSE on transmission; ignored on reception. | FALSE | FALSE | Table A.6 | ||
| Reserved | Set FALSE on transmission; ignored on reception. | FALSE | FALSE | Table A.6 | ||
| leap61 | Not used in this profile. Value as per PTP defined in IEEE1588-2008. | Table A.4 | ||||
| leap59 | Not used in this profile. Value as per PTP defined in IEEE1588-2008. | Table A.4 | ||||
| currentUTCOffsetValid | Not used in this profile. Value as per PTP defined in IEEE1588-2008. | Table A.4 | ||||
| ptpTimescale | Set TRUE if synchronized to reference source of time. Set FALSE otherwise, indicating ARB timescale (e.g. if synchronized to freq. reference) | FALSE | TRUE | Table A.4 | ||
| timeTraceable | Not used in this profile. Value as per PTP defined in IEEE1588-2008. | Table A.4 | ||||
| frequencyTraceable | TRUE if traceable to a PRC, otherrwise FALSE. | FALSE | TRUE | FALSE | Table A.4 | |
| controlField | Not used; ignored on reception. | Annex A.9 | ||||
Unicast and Multicast Operation | ||||||
| Full multicast operation | Not required by this profile. | Appendix I, 6.3.3 | ||||
| Full unicast operation | All messages are sent in unicast. Both masters and slaves must support full unicast operation | Annex A.3.3, 6.3.3 | ||||
| Hybrid unicast/multicast | For further study; see Appendix I. Not required in this version of the profile. | Appendix I, 6.3.3 | ||||
| Unicast negotiation process | Both masters and slaves must support unicast negotiation (IEEE1588-2008 Clause 16.1). Masters must reject any request it can't completely fulfil, rather than grant less than the requested message rate or duration. | Annex A.3.3, 6.6 | ||||
| targetPortIdentity | Requesting 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 field | Duration of unicast service lease | 60 | 1000 | 300 | Annex A.3.4, 6.6 | |
| logInterMessagePeriod | Masters must accept at least the entire ranges specified. Slaves must operate within these ranges, but do not have to cover the entire ranges. | Annex A.3.4, 6.5 | ||||
| Sync & Follow-up (from 128 per s to 1 per 16s) | -7 | 4 | - | |||
| Delay_request/response (from 128 per s to 1 per 16s) | -7 | 4 | - | |||
| Announce (from 8 per s to 1 per 16s, default 1 every 2s) | -3 | 4 | 1 | |||
| R (Renewal Invited) | Set FALSE on transmission; ignored on reception. | FALSE | FALSE | Annex A.8 | ||
| logQueryInterval | Slaves 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. | 1 | 6.6 | |||
| number of TLVs | Master 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 | 1 | 3 | 6.6 | ||
Master Selection Process | ||||||
| BMCA type: | Static BMCA | 6.7.1 | ||||
| State decision algorithm | Masters must implement static BMCA, with state BMC_MASTER, and state decision code M1 Slaves must implement static BMCA, with state BMC_SLAVE, and state decision code S1 | 6.7.1.1, 6.7.1.2 | ||||
| Data set comparison algorithm (master selection process) | Slaves select a master from a locally-provisioned list of grandmasters using the following criteria: - grandmaster not in PTSF state (Packet Timing Signal Fail), e.g. loss of sync or announce service, (or optionally, unusable timing signal) - lowest clockClass (SSM QL) value - local priority value | 6.7.3 | ||||
| clockClass | clockClass value is derived from G.781 SSM values, according to Table 1 of G.8265.1. Masters must encode clockClass using this table according to their input reference quality. Slaves must use clockClass to select master to synchronize to. | 6.7.3.1 | ||||
| PTSF-lossAnnounce | A slave must set the PTSF-lossAnnounce signal when it has not received any announce messages for a period longer than the announceReceiptTimeout attribute | 6.7.3.2 | ||||
| PTSF-lossSync | A slave must set the PTSF-lossSync signal when it has not received any sync messages for a period longer than the syncReceiptTimeout attribute, or has not received any delay_response messages for a period longer than the delayRespReceiptTimeout attribute (these are locally-configured attributes, not part of PTP itself) | |||||
| PTSF-unusable | A slave must set the PTSF-unusable signal if it is not able to achieve the required performance target. The criteria for establishing this are not specified and for further study. | |||||
Protection switching | ||||||
| Protection switching | A slave must switch to an alternative master under one or more of the following conditions: - clockClass (QL value) degraded (i.e. lower quality) than an alternative master - PTSF-lossSync or PTSF-lossAnnounce conditions on the current master - (optional) PTSF-unusable on the current master (by configuration) If no master is acceptable (e.g. all in PTSF condition), slave MUST enter holdover or free-run | 6.7.3 | ||||
| Temporary master exclusion | A slave must have the ability to temporarily exclude a grandmaster from the list of grandmasters (by configuration) | 6.8.1 | ||||
| Wait to Restore time | After a protection switch, when the traceability of the highest priority grandmaster has been restored, a slave must wait before switching back to the highest-priority grandmaster. (delay time by configuration) | delay time not specified | 6.8.2 | |||
| Non-reversion | A slave may optionally provide non-revertive switching (by configuration) | 6.8.3 | ||||
| Forced traceability | A grandmaster must provide the ability to force the QL value to a specified value (by configuration) | 6.8.4 | ||||
| QL Hold-off | A slave must be capable of delaying a change in QL value to downstream devices (delay time by configuration) | delay time not specified | 6.8.5 | |||
| Output squelch | A slave must be capable of squelching the output timing signal in case all masters are in PTSF, or QL value of all masters is less than a pre-determined threshold (by configuration) | 6.8.6 | ||||