Arbiter Systems 1200B, Руководство по эксплуатации

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B.11 NTP/PTP Server 159
PTP Terms
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Domain: a collection of one or more PTP subdomains. A subdomain is a logical grouping of 1588
clocks that synchronize to each other using the PTP protocol, but that are not necessarily synchronized
to PTP clocks in another PTP subdomain. Subdomains provide a way of implementing disjoint sets
of clocks, sharing a common network, but maintaining independent synchronization within each set.
ˆ
Announce interval: specifies the interval between the announce messages. The Announce message
is used to establish the synchronization hierarchy.
PTP message intervals are always stated and
communicated as logarithm to the base of 2 So a setting of 0 means that there is an Announce
message being sent every second.
Message interval [ld] Message interval [sec]
-2 0.25
-1 0.5
0 1
1 2
2 4
3 8
Table B.8: PTP Message Intervals
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Sync interval: the time for sending synchronization messages. The default is 1 second.
ˆ
Delay request interval: specifies the time recommended to the member devices to send delay request
messages when the port is in the master state. The range is -1 second to 6 seconds. The default is 5
(32 seconds).
ˆ
Peer Delay Request: the initial value used before receiving an update in a delay response message
from a master clock. It is only used when peer-to-peer (P2P) Delay mechanism is used. Should be ¿=
the Sync Interval but ¡= 32 times the Sync Interval.
ˆ
Announce receipt timeout: the number of Announce Intervals that have to pass without receipt of
an Announce message before another grandmaster capable clock starts sending its own announce
messages. The number is a multiple of the Announce Interval. The minimum number is 3.
ˆ
Delay mechanism: communication delay, end to end or peer to peer.
ˆ
Protocol: UDP IPv4, UDP IPv6 or Layer2.
ˆ
Clock class value: advertises the quality level of the clock. A GNSS clock is given the value of 6.
ˆ
Clock accuracy: 22 is used for clock accuracy to within 250 ns.
ˆ
Priority 1: the user configurable designation that a clock belongs to an ordered set of clocks. It can
bypass the best master clock algorithm. The default is 128 which indicates that the clock is a master.
ˆ
Priority 2: the user configurable designation that sets a clocks selection order among equivalent clocks.
It determines whether the clock is a Boundary Clock or not. A Boundary Clock is a PTP clock with
multiple connections and can act as a master or slave, synchronizing itself to the best master clock.
The NTP/PTP Server is not yet available as a Boundary clock so this should be set to 128.
ˆ
Two Step: the clock step determines whether the timing information is sent along with the sync
message only (one-step) or a subsequent follow-up message (two-step) is sent corresponding to the
previous sync message.