Configuration using Web Based Management and Command Line Interface
4.5 The Switch menu
SCALANCE X-300 / X-400
238 Configuration Manual, 10/2014, C79000-G8976-C187-22
The deviation of the slave clock is
Δ
t
= Δ
Sync
- Δ
D
= 14 μs - 6 μs = 8 μs
The slave clock is therefore "fast" and needs to be corrected by 8 μs.
The aim of the peer delay mechanism is to calculate the delay time of a message between
two ports of PTP-compliant devices. In contrast to a delay request response message that is
transported between the slave and master also over several network nodes, peer delay
messages are only exchanged with the relevant neighbor node, hence the name "peer
delay".
The delay requester sends a peer delay request message to a neighboring node, the delay
responder, and stores the time t
0
at which this message was sent. The delay responder then
immediately sends back a peer delay response message. In the correction field of the peer
delay response follow-up message, it enters the time difference between the send time t
2
of
the peer delay response message and the time t
1
when the peer delay request message was
received:
Δ
R
= t
2
- t
1
At the time of receipt t
3
of the peer delay response message, the delay requester then has all
the data required to calculate the message delay time to the neighboring node:
Δ
PDelReq
= Δ
PDelRes
= ( t
3
- t
0
- Δ
R
) / 2
To calculate the deviation of a slave clock, sync messages and follow-up messages must be
evaluated with the peer delay mechanism as well. The section "Peer-to-peer transparent
clock" contains a description of the complete synchronization cycle.
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