User guide

Canopy System User Guide Understanding Bandwidth Management
pmp-0229 (Mar 2013)
91
Competition for Bandwidth
When multiple SMs vie for bandwidth, the AP divides its bandwidth among them, considering
their effective CIR and MIR values. However, 2X operation uses bandwidth twice as efficiently as
1X, even where MIR values apply. This is because, in 2X operation, the modules transmit their
data in 4-level frequency shift keying (FSK), not
2-level as they would in 1X operation. This moves twice the data per slot. Thus, for the sum of all
bandwidth that 2X-eligible customers use, the bandwidth available to the remaining customers
increases by half of that sum when these eligible customers are transmitting and receiving in 2X
operation.
Checking Link Efficiencies in 2X Operation
Unlike in 1X operation, efficiencies below 90% on the Link Capacity Test tab in the Tools web
page of the SM may be acceptable for stable operation. An efficiency of 60% in 2X operation is
equivalent to an efficiency of 120% in 1X. If you read efficiency between 60% and 90%, check
the status of 2X operation (as described below) to confirm that the link is operating at 2X.
Since received signal strength typically varies over time, you should perform link tests at various
times of day and on various days of the week. Efficiencies should consistently be 60% or greater
for 2X operation. You may be able to achieve better efficiencies by re-aiming the SM, mounting it
elsewhere, or adding a reflector dish.
Checking the Status of 2X Operation
The Session Status tab in the Home page of the AP provides operation status information about
each SM-to-AP link. Under the MAC address of each SM, the data in this tab includes a line such
as the following:
RATE : VC 19 Rate 2X/2X VC 255 Rate 2X/1X
Interpret this information is as follows:
• VC means virtual channel. If one VC is displayed, the high-priority channel is disabled. If two
are displayed, the high-priority channel is enabled and is using the higher number VC (255 in
the above example).
• 2X/2X indicates that the SM-to-AP link is in 2X operation.
• 2X/1X indicates that the SM is capable of 2X operation but the SM-to-AP link is in 1X
operation. This can be for either of the following reasons:
o The SM has not sent data on the channel yet.
o The received signal does not support 2X operation.
• 1X/1X indicates that the SM is capable of only 1X operation. This can be for either of the
following reasons:
o The SM does not support 2X operation (SM is of the hardware series P7 or P8).
o The 2X Rate parameter is disabled in the General tab of the Configuration page in the
SM or the AP.