User's Manual

36 Interface specification: MASC and RAP link-layer protocols
Integrator’s Guide – RIM 902M OEM Radio Modem
is designed to be extremely robust and redundant, and should be used when the
serial link is unreliable or when the serial cable to the RIM 902M is very long.
Advances in mobile computing technology have helped to ensure that serial
links are short enough to make bit errors extremely unlikely. This is especially
true for smaller devices such as laptops and PDAs. The complexity of MASC is
unnecessary for these applications, and involves complex and lengthy software
development.
RAP was designed to take advantage of the reliability inherent to a short serial
link. The primary benefit of RAP is that it is easy to describe and implement.
As a result, RAP reduces software development time, complexity, and memory
consumption. It also provides double the throughput of MASC, by using binary
frame data transfers instead of hex-ASCII encoding.
Since every application is different, the choice of protocol should be made
carefully. The following chart is provided as a guide to comparing the relative
advantage of each protocol.
MASC RAP
Serial cable between
RIM 902M and device
Designed for long serial
cable prone to bit errors
Assumes a short, reliable
serial cable
Operating environment Withstands harsh, hostile
electrical interference
Best suited for laptops,
PDAs, other small devices
Software complexity Complex Simple
Implementation time
(typical)
Weeks or months,
or use third-party API’s
Days
Memory requirements 10 to 50 kilobytes 1 to 3 kilobytes
Hardware flow control RTS/CTS is required RTS/CTS is optional
Throughput at 9600 bps 4800 bps 9600 bps
Cost Free, open specification,
or pay for third-party API’s
Free, open specification,
sample source code is free