System Management
230
Basic System Configuration Guide
3HE 11010 AAAC TQZZA Edition: 01
There is no CLI configuration requirement for PCR; it is turned on automatically when
a microwave link is enabled on an MWA RJ-45 port or on a copper SFP Ethernet port
(ports 3 and 4).
PCR provides the same frequency recovery capability as standard-based copper
synchronous Ethernet without having to endure a traffic hit whenever a synchronous
source switching occurs. See Figure 13.
Figure 13 Proprietary Clock Recovery
By running PCR between the MPR-e radio and the MWA port, frequency
synchronization can be delivered in either direction.With standard-based copper
synchronous Ethernet, there is a traffic hit every time a clock source change occurs
on a 7705 SAR-8 or 7705 SAR-18 because the 7705 SAR-8 or 7705 SAR-18 and
the MPR-e radio to which it is connected must bring down the Ethernet link MAC
layer before it can renegotiate and reverse the master and slave clock role. This MAC
layer renegotiation affects the data plane and the signaling and routing plane. All
MPLS signaling links and the label switched path (LSP) are taken down during the
renegotiation process; the routing signaling advertises the down state of the link
throughout the network.
However, with PCR running on the microwave link, the physical layer transmit clock
on a copper synchronous Ethernet port on the Packet Microwave Adapter card is
always set to master. The reversal of the clock role only occurs at the PCR “layer”.
This means that a synchronous source change does not disrupt the data plane and
the signaling and routing plane on the 7705 SAR-8 or 7705 SAR-18.
Note: On the MPR-e side, PCR requires that the MAC address of the 7705 SAR-8 or
7705 SAR-18 be configured on the MPR-e radio that is connected to the 7705 SAR-8 or
7705 SAR-18 chassis. Refer to the latest version of the MPR-e user manual for the required
information.
7705 SAR 7705 SAR
Synchronous RFPCR over copper PCR over copper
F1F1 F1
F1
Primary Clock
Reference
frequency 1F1 =
Legend:
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