Westermo U200 Operator manal - Manual (Page 37)

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the corresponding DELAY_RESP packet is then modified with this measured delay. The
sequenceId
is used for pairing the DEL_REQ packet the corresponding DEL_RESP packet.
See Figure 17 for the handling of the DEL_REQ/DEL_RESP packets at the switch with
IEEE1588 Transparent Clock functionality.
A switch with IEEE1588 Transparent Clock support maintains a list of ports, where SYNC and
FOLLOW-UP packets are received. Any DEL_REQ packets received are only forwarded on
these ports.
Figure 17, IEEE1588 DEL_REQ/DEL_RESP Transparent Clock functionality
A network of switches with IEEE1588 Transparent Clock support can in fact be considered as
one big LAN segment as if all the Ethernet switches were Ethernet hubs with the difference
that full duplex connectivity and bandwidth scalability of Ethernet switches are maintained.
12.3 IEEE1588 Transparent Clock version 1 and 2
IEEE1588 version 2 (launched 2008) defines the IEEE1588 Transparent Clock principles.
New payloads for all IEEE1588 packets are defined in this version of the IEEE1588 standard.
A new “correction” field is defined for FOLLOW_UP and DEL_RESP packets. The correction
field is meant to be used by the version 2 Transparent Clocks. The correction field shall be
updated with the measured switch delay (ingress – egress timestamp) for the SYNC or
DEL_REQ packets forwarded by each Transparent Clock.
The T200 switch supports both IEEE1588 version 1 and 2 packets. That means that the
switch can handle both version 1 and 2 IEEE1588 Grand Masters/Slaves in the same
network.
IEEE1588 version 2 also defines a new principle for how to measure and compensate for the
propagation delay between the Slaves and the Grand Master. The two methods are:
- End-to-End (E2E) propagation delay measurement