Cal Amp VIPER SC+ 100 series User Manual - page 140
Viper SC+™ IP Router for Licensed Spectrum PN 001-5008-000 Rev. C
| Page 130
5. NETWORK OPTIMIZATION
5.1. MAXIMIZING TCP/IP THROUGHPUT
After optimizing the Viper airlink, if there appears to be an unexplained speed loss, you can attempt to maximize
TCP/IP throughput.
TCP/IP throughput can be a challenge to measure, as performance is related not only to the RF link, but to how well
flow control is implemented in the TCP/IP stack and each application’s design. The Viper SC+ has been optimized with
this in mind. When the Tx/Rx LED flashes green or red, this indicates data is moving across the network. It also indicates
(by the LED off periods) when data is not moving across the RF network at full rated speed. LED off periods indicate the
application has not presented data to the Viper radio modem.
Using different client/server combinations or applications may show improvements. For example, one FTP server may
work 30% faster than another, the buffer management is quicker to respond or has larger message buffers, and 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.
5.2. MAXIMIZING THROUGHPUT WITH A WEAK RF LINK
5.2.1. USE ROUTER MODE WITH RF ACKNOWLEDGEMENTS ENABLED
Selecting Router mode is highly recommended when running over a weak RF link. This mode ensures that only the
necessary packets are passed over the RF interface. Using bridge mode often results in passing more traffic than
necessary.
In router mode, you have options to enable Data Retries and enable Collision Avoidance to improve the network
performance. The Data Retries and Collision Avoidance mechanisms are also available in bridge mode when
communication spans only one RF hop.
Router mode requires some IP route planning to and from Viper units, but is well worth the increase in link stability
over the simple bridge mode.
5.2.2. REDUCE RF NETWORK BIT RATE
The Viper SC+ has up to four speeds of operation available for each of the five channel bandwidths. The fastest speeds
utilize 16-level FSK (frequency shift keying). The slower speeds in each bandwidth utilize 2-, 4-, and 8-level FSK, yielding
a higher signal-to-noise level resulting in better sensitivity. When the received RF signal level is strong, the system is
able to utilize faster bit rates. However, if the system has a low RF signal level or the RF signal levels are close to an
elevated noise floor level, you can run at slower over-the-air speed for the system’s bandwidth. It may result in better
overall performance.