Telecoms Circuits; Lowest Telecoms Modulation Mode; Fixed Frequency Operation - Motorola PTP 300 Series User Manual

Point-to-point wireless bridge
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3.9

Telecoms Circuits

The PTP 300 link provides native support for one E1 link, or one T1 link. The link relays
unstructured E1 or T1 data and provides accurate timing transfer.

3.9.1 Lowest Telecoms Modulation Mode

In narrow channel bandwidth and lower modulation modes, the link may have insufficient
capacity to relay the E1/T1 payload; in this case, the wireless link continues to carries timing
information in order to maintain accurate clock synchronization. The relay of telecoms data
resumes automatically when the link reaches a suitable modulation mode.
Links that are able to operate consistently in a high modulation mode can take advantage of
lower link latency. This option is configured by setting the "Lowest Telecoms Modulation
Mode" during installation. Appropriate settings for this control may be determined by using the
LINKPlanner tool. The reduction in latency is achieved by disabling the relay of telecoms data
in lower modulation modes, and this necessarily results in somewhat lower availability for the
telecoms circuit. The loss of availability can be estimated using the LINKPlanner.
The unit will override the user setting of Lowest Telecoms Modulation Mode if the selected
mode has insufficient capacity to carry the telecoms data, or if the mode demands very high
latency and requires more buffering than the link can provide. When the effective mode differs
for Single and Dual Payload operation two modes will be displayed: "Lowest Dual Payload
Modulation Mode" and "Lowest Single Payload Modulation Mode".

3.9.2 Fixed Frequency Operation

In the PTP 300 link, data errors may occur during channel changes on an operational link. It
may be appropriate to minimize channel-change-related errors in a link carrying Telecoms
traffic by preventing channel changes initiated by i-DFS. This can be achieved by barring all
channels except one in the Spectrum Management page, or alternately by selecting Fixed
Frequency mode. These steps disable interference avoidance mechanisms, and should not
be taken if the risk of errors due to interference is more severe than the risk due to channel
changes.
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