EP80579 Datasheet, PDF (1623/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
The end-to-end transparent clock forwards all messages just as a normal switch,
router or repeater. However for PTP-event messages, the time the message takes to
traverse the switch is measured and appended to the forwarded event messages.
The peer-to-peer transparent clock is similar to the end-to-end transparent clock
however, it also measures peer-to-peer link delays in addition to the internal message
traversal time.
A management node is a PTP device that is physically connected to the network and
provides an user interface to the PTP management messages. It will not be discussed
further here
Figure 41-2. Example Network Topology
41.5.1.1
41.5.1.2
The operation of a PTP enabled network is divided into two stages, Initialization and
time synchronization.
Initialization
At the initialization stage every master enabled node starts by sending Sync packets
that include the clock parameters of its clock. These parameters include the source of
the clock, the accuracy of the clock, it’s variance, etc. Upon reception of a Sync packet,
a node compares the received clock parameters to its own and if the received
parameters are better, then this node moves to Slave state and stops sending Sync
packets. When in slave state the node continuously compares the incoming packet to
its currently chosen master and if the new clock parameters are better then the master
selection is transferred to this master clock. Eventually the best master clock is chosen.
Every node has a defined time-out interval in which if no Sync packet was received
from its chosen master clock it moves back to master state and starts sending Sync
packets until a new best master clock (BMC) is chosen.
Time Synchronization
The time synchronization stage is different to master and slave nodes. If a node is at
master state it should periodically send a Sync packet which is time stamped by
hardware on the TX path (as close as possible to the PHY). After the Sync packet is
sent, a Follow_Up packet is sent which includes the value of the timestamp captured
from the Sync packet. In addition the master should timestamp Delay_Req packets on
its RX path and return to the slave that sent it the timestamp value using a
Delay_Response packet. A node in Slave state should timestamp every incoming Sync
packet and if it came from its selected master keep this value for time offset
calculation. In addition it should periodically send Delay_Req packets in order to
August 2009
Order Number: 320066-003US
Intel^® EP80579 Integrated Processor Product Line Datasheet
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