Cambium PTP 670 Series, Руководство пользователя

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Chapter 1: Product description TDM bridging
Page 1-44
The NIDU always connects to the ODU using the Main PSU port of the ODU. This constrains
the flexible allocation of ports to services somewhat.
Timing transfer for TDM circuits
Accurate timing transfer for TDM circuits in the PTP 670 Series is based on the same
underlying technology as the IEEE 1588 Transparent Clock and Synchronous Ethernet features.
Consequently, the IEEE 588 and Synchronous Ethernet features are not available when TDM
bridging is enabled. Similarly, TDM bridging is not available if either IEEE 1588 or Sync E is in
use. The Adaptive setting for Link Symmetry is not compatible with TDM bridging.
TDM bridging is a licensed feature, and may require an optional upgrade for the ODU
firmware.
Lowest TDM modulation mode
In narrow channel bandwidths and lower modulation modes, the link may have insufficient
capacity to relay the E1/T1 payload; in this case, the wireless link continues to carry timing
information in order to maintain accurate clock synchronization. The relay of TDM 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 TDM 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 TDM data in
lower modulation modes, and this necessarily results in somewhat lower availability for the
TDM circuit. The loss of availability can be estimated using the LINKPlanner.
The unit will override the user setting of Lowest TDM Modulation Mode if the selected mode
has insufficient capacity to carry the TDM data, or if the mode demands very high latency and
requires more buffering than the link can provide.
Fixed frequency operation
In the PTP 670 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 TDM traffic by
preventing channel changes initiated by DSO. This can be achieved by barring all channels
except one in the Spectrum Expert or Spectrum Management pages, or alternatively by
selecting Fixed Frequency mode. These steps unavoidably 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.
Fixed frequency operation is not available when radar detection requirements exist in the
frequency band. Channel barring is allowed in radar regions, but it is unwise to bar all channels
except one, as any radar signals detected on that channel will drop the link for up to 30
minutes.