User guide

Planning 1+1 Hot Standby links Chapter 2: Planning considerations
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phn-2513_004v000 (Oct 2012)
• At the Ethernet Switch, configure the Receive Diversity VLAN for tagged operation. At
the ingress, the ports in this VLAN must accept tagged frames which arrive with the
Receive Diversity VID and forward them to the other port which is also a member of
this VLAN. At the egress, the Ethernet Switch must NOT strip the Receive Diversity
tag.
Performance considerations for Receive Diversity
As the Ethernet Switch multiplexes the Receive Diversity Frames with customer traffic,
consider the impact of Receive Diversity on latency and jitter.
When the link is not fading, the maximum latency increases by 12 µs in all configurations.
When the link fades to the point where the Active unit can no longer demodulate a signal
and where the data stream from the Inactive unit is being used, the maximum latency
increases to a value which is dependent on the frames size of the customer traffic as
shown in Table 12.
Table 12 Frame size and latency relationship in Rx SD links
Maximum Customer
Frame Size (octets)
Latency increase with
Receive Diversity enabled
(µs)
64 53
1500 64
9600 150
In all cases, the minimum latency does not change hence jitter is increased.
Link Planning for Spatial Diversity
Spatial Diversity can significantly improve the availability of a link, particularly for long
links. Indeed regulations can recommend or even mandate that Spatial Diversity is
deployed for links which are longer than a specific range.
LINKPlanner calculates link availability for all link configurations and provides a very
convenient way of seeing the effect of enabling Spatial Diversity.
When ACM is enabled, Spatial Diversity only increases the availability of the lowest
configured modulation mode. The availability of higher order modes is not increased.