User Manual

120 40520-100a ViPR User Manual
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5.1 Maximizing TCP/IP
If after optimizing the airlink there still appears to be an unexplained speed loss, you can look at maxi-
mizing TCP/IP.
TCP/IP throughput can be tricky to measure as performance is related not only to the RF link, but how
well flow control is implemented in the TCP/IP stack and how each application is designed. The ViPR
has been highly optimized with this in mind. When the TX/RX LED flashes amber, this not only indicates
that data is moving but also indicates (by the LED OFF periods) when data is not moving across the RF
network at full rated speed. If you get flashing RED indications on the TX/RX LED, RF reception prob-
lems are present and causing some loss of throughput. OFF periods indicate that the application has not
presented data to the ViPR radio modem.
Using different client/server combinations or applications may show improvements. For instance, one
FTP server may work 30% faster than another, simply because the buffer management is quicker to re-
spond or has bigger message buffers – yet run at nearly the same speed over a pure Ethernet (no RF) link.
Network Address Translation (NAT), payload data compression and encryption have little effect other
than adding a small latency to the flow of traffic.
The TDD mode should be left enabled unless highly specialized protocols are being run. Sometimes,
these protocols and TDD interfere which each other and may run somewhat faster with TDD disabled.
5.2 Maximizing via Setup Pages
Further performance optimization can be done via the User Interface Setup pages. The fundamental ad-
justments described in the following paragraphs can be changed singularly or in conjunction with each
other
Note:
Data Compression (section
4.8.3.5 above) should only be OFF while testing, thereby eliminating
performance differences due only to different compression rates.
5.2.1 Use Router Mode
Selecting Router mode (see section 4.8.2.1) is highly recommended when running over a weak RF link.
This mode ensures that several levels of retry mechanisms are at work, each optimized to minimize TCP
flow control delays or even preventing a dropped TCP/IP link. It requires some IP route planning to and
from the ViPR units but is well worth the increase in link stability over the simpler bridge mode
5.2.2 Reduce RF network bit rate
Normally the system is able to utilize the normal bit rate of xxK (see section 4.8.2.3). If you have a very
low signal level (-90 dBm or less) or the RF signal levels are close to an elevated noise floor level, you
can try running at xxK instead of xxK (changeable on the fly without a reset). It could result in better
overall performance.
5.2.3 Increase OIP Retries Limit
Only available in Router mode, OIP Retries Limit is normally set to two (2). Gradually increasing it up to
five (5) in extreme cases, may provide a slow but reliable link when none was possible with weak signals.
Use in conjunction with a xxK network bit rate.