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IEEE Std 802.1AS-2020 pdf free download
IEEE Std 802.1AS-2020 pdf free download.IEEE Standard for Local and Metropolitan Area Networks Timing and Synchronization for Time-Sensitive Applications.
Each PTP Instance measures, at each PTP Port. the ratio of the frequency of the PTP Instance at the other end of the link attached to that PTP Port to the frequency of its own clock. The cumulative ratio of the Grandmaster (‘lock frequency to the local clock frequency is accumulated in a standard organizational type, length, value (TLV) attached to the Follow_Up message (or the Sync message if the optional one-step processing is enabled). The frequency ratio of the Grandmaster Clock relative to the local clock is used in computing synchronized time, and the frequency ratio of the neighbor relative to the local clock is used in correcting the propagation time measurement.
The Grandinaster Clock frequency ratio is measured by accumulating neighbor frequency ratios for two main reasons. First. if there is a network reconfiguration and a new Grandinaster PTP Instance is elected, the nearest neighbor frequency ratios do not have to be newly measured as they are constantly measured using the Pdelay messages. This results in the frequency offset relative to the new Grandmaster (‘lock being known when the first Follow Up message (or first Sync message if the optional one-step processing is enabled) is received, which reduces the duration of any transient error in synchronized time during the reconfiguration. This is beneficial to many high-end audio applications. Second, there are no gain peaking ctiects because an error in frequency offset at one PTP Relay Instance, and resulting residence time error, does not directly affect the frequency offset at a downstream PTP Relay Instance.
7.3.4 Grandmaster PTP Instance (best master) selection and network establishment
All PTP Instances participate in best master selection so that the IEEE 802.IAS protocol can determine the synchronization spanning tree. This synchronization spanning tree can be different from the forwarding spanning tree determined by IEEE 802. IQTM Rapid Spanning Tree Protocol (RSTP) since the spanning tree determined by RSTP can be suboptimal or even inadequate for synchronization or can he fbr a different topology of nodes from the synchronization spanning tree.
gPTP requires that all systems in the gPTP domain be time-aware systems, i.e., the protocol does not transfer timing over systems that are not time-aware (e.g., those that meet the requirements of IEEE Std 802.IQ- 2018. but do NOT meet the requirements of the present standard). A time-aware system uses the peer-to- peer delay mechanism on each PTP Port to determine if a non-time-aware system is at the other end of the link or between itself and the Pdelay responder. If, on sending Pdelay Req.IEEE Std 802.1AS-2020 pdf free download.
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