Sierra Wireless DART 200 CDPD Modem - Manual (Page 55)

PN1197-00 Revision 1.0
5 DART Supported Protocols
UDP
User Datagram Protocol (UDP) is the most basic transmission protocol
provided by the Data Access Radio Transceiver (DART) 200. It is a thin
protocol, adding only a port specification to the underlying Internet
Protocol (IP). It has the same features as IP, that is a best effort,
connectionless delivery service with the chief benefit being minimum
overhead.
UDP is not considered reliable because packet delivery is not guaranteed.
Packets can be lost, duplicated, delayed, or delivered out of sequence.
These conditions are not detected, and the sender or receiver is not
informed.
UDP is connectionless because sender and receiver are never logically
connected. If the intended receiver is not active the message is lost. It is a
best effort delivery, because the IP software makes an earnest attempt to
deliver the packets, failing only if system resources are overloaded or the
underlying networks fail.
Application programs using UDP must accept full responsibility for
handling the problems of reliability, including message loss, duplication,
delay, out-of-order delivery, and loss of connectivity.
These problems are often treated casually be programmers. Testing done
when using highly reliable, low delay local networks may not expose
potential failures. This explains why many applications that use UDP
work well in a local environment but often fail in dramatic ways on a
more global network.
Despite these warnings, UDP is still the most efficient and widely used
protocol. Take care in analyzing the application being implemented, the
network being used, and the Mobile Application Subsystem (MAS)
device involved to determine if an application implementation using
UDP is feasible.
• How likely is it that the network being used can cause these
problems?
Small, non-Internet networks are not likely to cause problems.
• How much compute power and programming capability does the
MAS device have?
Lack of available memory or programming capability can preclude
adding the needed reliability features into the application.