Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Release 3.5 Software Configuration Guide, Cisco IOS Release 15.1(3)MR
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Chapter 16 Configuring Clocking and Timing
Network Clocking Overview
Precision Timing Protocol (PTP)
The Cisco MWR 2941 supports the Precision Time Protocol (PTP) as defined by the IEEE 1588-2008
standard. PTP provides for accurate time synchronization on over packet-switched networks. Nodes
within a PTP network can act in one of the following roles:
• Grandmaster—A device on the network physically attached to the primary time source. All other
clocks are ultimately synchronized to the grandmaster clock.
• Ordinary clock—An ordinary clock is a 1588 clock with a single PTP port that can serve in one of
the following roles:
– Master mode—Distributes timing information over the network to one or more slave clocks,
thus allowing the slave to synchronize its clock to the master.
– Slave mode—Synchronizes its clock to a master clock. You can enable slave clocking on up to
two interfaces simultaneously in order to connect to two different master clocks.
• Boundary clock—The device participates in selecting the best master clock and can act as the master
clock if no better clocks are detected.
• Transparent clock—A device such as a switch that calculates the time it requires to forward traffic
and updates the PTP time correction field to account for the delay, making the device transparent in
terms of timing calculations.
Note The Cisco MWR 2941 does not currently act as a transparent clock.
Note The Cisco MWR 2941 does not currently act as a boundary clock.
Note The 1588-2008 standard defines other clocking devices that are not described here.
PTP Domains
PTP devices use a best master clock algorithm to determine the most accurate clock on a network and
construct a clocking hierarchy based on the grandmaster clock. A given clocking hierarchy is called a
PTP domain.
Clock Synchronization
PTP master devices periodically launch an exchange of messages with slave devices to help each slave
clock recompute the offset between its clock and the master clock. Periodic clock synchronization
mitigates any drift between the master and slave clocks.
PTP Redundancy
The Cisco MWR 2941 supports the multicast- and unicast-based timing as specified in the 1588-2008
standard. The Cisco MWR 2941 can use multicast routing to establish redundant paths between an
external PTP client and one or more PTP multicast master clocks. The Cisco MWR 2941 functions as a
multicast router only for PTP traffic and only allows multicast traffic to pass from the PTP master clocks
to the PTP client (the PTP client can send unicast traffic).