Cisco CX-FEIP-1TX= Installation and con?guration User's Guide download pdf (Page 108)

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1+1 Hot Standby link protection Chapter 1: Product description

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phn-2513_004v000 (Oct 2012)

Effects of Receive Diversity on 1+1 operation

In almost all aspects, the 1+1 Hot Standby feature operates in the same way regardless of

whether or not Receive Diversity has been enabled. Of most significance is the concept of

the Active and Inactive units, where it is the Active ODU or IRFU transceiver which always

radiates at the antenna and the Active CMU which forwards Ethernet frames to the

network. The Inactive unit remains on standby to take over the role of the Active unit in

case of a fault. However, there are some subtle differences as follows:

• When Receive Diversity is enabled, then a protection switch will not occur if the fault

only affects the wireless receiver of the Active CMU, ODU or IRFU transceiver. This is

because the Active CMU will seamlessly use the data received at the wireless interface

of the Inactive CMU. The Active ODU or IRFU transceiver will continue to radiate at

the antenna. Receiver faults in this category are the RFU Rx Synthesizer faults and

complete loss of the wireless receive signal.

• The Fiber-Y configuration is useful in a network which requires a single Ethernet

interface for customer traffic. In order to support Receiver Diversity in Fiber-Y

configurations, the CMU copper data ports must also be connected to the same

Ethernet Switch as the Fiber-Y interface. This is because the Fiber port of the Inactive

CMU is necessarily disabled in Fiber-Y configurations. The copper port is therefore

required in order for the Inactive CMU to send Receive Diversity Ethernet Frames.

Note that the copper port will never carry customer traffic hence the single interface

for customer traffic is not compromised.

When Receive Diversity is enabled, there is a small impact on maximum Latency, and

hence jitter. When there is significant fading and the Active CMU is using data which has

been received at the wireless interface of the Inactive CMU, the latency increase will be

affected by the customer traffic. The worst case is where jumbo frames are included in

the customer traffic in which case the maximum increase in latency will be 150 μs. In

periods where there is no significant fading, the Active CMU will use the data from its

own wireless receiver in which case there will be a fixed increase in maximum latency of

12 μs.

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