Juniper ACX1000 Configuration Manual page 297

Chapter 9: Configuring Timing and Synchronization
about 10 or 12 nodes of MX Series routers and ACX Series routers are present in the
aggregation and access Ethernet rings.
Some of the 4G base stations that are connected to ACX Series routers need to receive
the timing and synchronization information in a packet-based form. Such base station
vendors support only packet interfaces that use Ethernet encapsulation for PTP packets
for time and phase synchronization. Therefore, any node (an ACX Series router) that is
directly connected to a 4G base station must be able to use the Ethernet encapsulation
method for PTP on a master port to support a packet-based timing capability.
PTP over Ethernet encapsulation also facilitates an easier, optimal network deployment
model than PTP over IPv4. Using IPv4, the nodes (master and slave devices) participate
in unicast negotiation in which the slave node is provisioned with the IP address of the
master node and requests unicast messages to be sent to it from the master node. A
master node is the router that functions as the PTP server where the master clock is
located and a slave node is the router that functions as the PTP client where the slave
clock is located. Because PTP over Ethernet uses multicast addresses, the slave node
automatically learns about the master nodes in the network. Also, the slave node is able
to immediately receive the multicast messages from the master node and can begin
sending messages to the master node without the need for any provisioning configuration.
An interface on which the master clock is configured is called a master interface and an
interface on which the slave clock is configured is called a slave interface. A master
interface functions as the master port and a slave interface functions as the slave port.
For PTP over Ethernet, apart from configuring a port or a logical interface to operate as
a master clock or a slave clock, you can also configure a port or a logical interface to
function as both a master clock and a slave clock. This type of port is called a dynamic
port, stateful port, or a bidirectional port. Such a stateful port enables the network to more
efficiently adapt to the introduction and failure of timing sources by forming the shortest
synchronization trees from a particular source. This behavior is implemented as defined
by the best master clock algorithm (BMCA) in the ITU-T G.8265.1 Precision time protocol
telecom profile for frequency synchronization specification.
On both MX Series and ACX Series routers, you can achieve the highest quality
performance if you configure every node in a synchronization chain as a PTP boundary
clock. In Ethernet ring-based topologies, you can configure a port or a logical interface
to function either as a master port or as a slave port to enable redundancy when a node
or link failure occurs. This dynamic port or dual-port functionality is in accordance with
the IEEE 1588-2008 standard and enables the implementation of PTP in data center or
financial applications.
Apart from enabling every node to be available for configuration as a PTP boundary clock,
it is also necessary to enable a logical interface to be configured either as a master port
or a slave port. When you configure a logical interface or even a shared IP address to be
a master port or a slave port, a PTP protocol stack can represent dynamic ports and the
PTP application selects the correct state (master or slave) for any specific port in the
system based on the output of the default PTP BMCA and the states of other ports in
the system.
While an ACX Series router supports the PTP over Ethernet functionality, a Brilliant Grand
Master such as an MX Series router or a TCA Series Timing Client does not support PTP
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