User's Manual

#9 ViPR User Manual_Rev2.doc Page 91
MAXIMIZING THROUGHPUT WITH A WEAK RF LINK
Further performance optimization can be done via the User Interface Setup web pages.
Fundamental adjustments, described in the following paragraphs, can be changed singularly
or in conjunction with each other.
Use Router Mode with RF Acknowledgements Enabled
Selecting Router mode and enabling RF Acknowledgements is highly recommended when
running over a weak RF link. This mode ensures several levels of retry mechanisms are at
work, each optimized to minimize TCP flow control delays or prevent a dropped TCP/IP link.
It requires some IP route planning to and from ViPR units, but is well worth the increase in
link stability over the simple Bridge mode.
RF Acknowledgements can be enabled on ViPR web pages under Setup (Advanced) D IP
Optimization. RF Acknowledgements must be enabled or disabled on all ViPRs in the
network.
ViPRs are tested for BER at the factory with the optimizations described above. The units
are configured for Router Mode, RF Acknowledgements are enabled, MAC retries are set for
2, and OIP retries are set for 2.
Reduce RF Network Bit Rate
ViPR has two speeds of operation available for each of the three channel bandwidths. The
faster speeds in each bandwidth utilize 4-level FSK (frequency shift keying.) The slower
speeds in each bandwidth utilize 2-level FSK, yielding a higher Signal-to-Noise level
resulting in better sensitivity. Normally the system is able to utilize the faster bit rate.
However, if the system has a very low signal level (-95 dBm or less) or the RF signal levels
are close to an elevated noise floor level, you can try running at a slower over-the-air speed
for the system’s bandwidth. It may result in better overall performance.
Increase OIP and MAC Retries Limit
OIP retries and MAC retries are only available in Router mode. The MAC Retry Limit is
normally set to 1 and the OIP Retry Limit is normally set to 2. Gradually increasing these
limits (up to 3 in extreme cases), may provide a slower, but more reliable link impossible
with weak signals. Use in conjunction with the slower over-the-air network bit rate for the
system’s bandwidth.
The number of MAC retries can be configured on the ViPR’s web pages under Setup
(Advanced) D RF Optimizations. The number of OIP retries can be configured under Setup
(Advanced) D IP Optimization.