GEN7iB
288
GEN series SYNCHRONIZATION METHODS
GEN series SYNCHRONIZATION METHODS
14
Switches using transparent clocks
Switches using transparent clocks forward the master clock synchronization mes-
sage to every port of the switch. The time required to transfer the message from the
incoming port to the outgoing port must be measured and transferred together with
the original synchronization message. There are two methods used to communicate
the internal delay information to the original synchronization messages:
● End-to-End
● Peer-to-Peer
Each of these two methods has its advantages and disadvantages.
End-to-End transparent clocks
End-to-End transparent clocks create a higher load on the master clock, as the master
“sees” all the slaves. End-to-End transparent clocks support a 1:N topology with one
master communicating with a large number of slaves. They are, however, good for
linear systems with a number of daisy-chained clocks.
Peer-to-Peer transparent clocks
Peer-to-Peer clocks avoid the higher master load, but introduce the need to be aware
of how the synchronization messages are routed through the network topology. They
cannot resolve 1:N topologies, as they cannot determine which line delay is being
calculated and they must also maintain path delay measurements.
One-Step and Two-Step clock synchronization
PTP allows for two different types of time stamping methods:
● One-Step clock synchronization
One-Step clocks update time information by adjusting the time information within
theoriginalsynchronizationmessages(syncanddelayrequest)on-the-y.
● Two-Step clock synchronization
Two-Step clocks transmit the precise timestamps of packets using additional
general messages (follow-up and delay response).
A One-Step End-to-End transparent clock updates for switch delay in sync and delay
request messages as they pass through the switch while a Two-Step transparent clock
updatesaeldinthenon-time-criticalgeneralmessage.
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