14.2
PTP switch types
Within the PTP specification, two types of switches are defined:
l
Boundary clock switches
l
Transparent clock switches
Boundary clock
Boundary clocks are defined within a PTP system to be integrated in place
where standard network switches or routers are used. Boundary clocks are
defined as PTP clocks with more than a single PTP port, with each port
providing access to a separate PTP communication path. The boundary clock
acts as an interface between separate PTP domains intercepting and
processing all PTP messages and passing all other network traffic. The BMC
algorithm is used by the boundary clock to select the best clock any port can
see. The chosen port (the one that receives the best clock) is set as a slave
and all other ports of the boundary clock are asserted as masters to their domain
(to forward the clock).
Transparent clock
Transparent clocks have been added to Version 2 of the standard as an
improved method of forming cascaded topologies. Rather than acting as a
multi
-
port ordinary clock as boundary clocks do, transparent clocks update a
newly introduced time
-
interval field within PTP event messages. This 64 bit
time
-
interval correction field allows for switch delay compensation to a potential
accuracy of less than a picosecond. There are two types of transparent clocks,
End
-
to
-
End and Peer
-
to
-
Peer. End
-
to
-
End transparent clocks update the time
interval field for the delay associated with individual packet transfers, whereas
Peer
-
to
-
Peer transparent clocks measure the line delay associated with the
ingress transmission path and include this delay in the correction field also.
Peer
-
to
-
Peer transparent clocks can allow for faster reconfiguration after
network topology changes.
GEN3t
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I3995-3.1 en HBM: public