User's Manual

Appendix D - Application Development __________________________ Boomer II User Manual & Integrator’s Guide
Copyright Wavenet Technology © November 2003 122 BM210012WT37
Outbound SDU Failure
Due to the unreliable delivery of RF data packets (and their responses),
a client application must consider the possibility of an outbound SDU
being delivered to the client, with the transport confirmation of that
data packet being lost (RF acknowledgment and/or transport level
acknowledgment).
Note: When developing a centralized server and distributed-mobile
client wireless enabled application, outbound SDU failure is primarily
a server application issue.
When this occurs, the client and server transport levels must
resynchronise to a common level before proceeding. Such an
understanding might require retransmission of the transaction or
retransmission of the transport confirmation.
Loss of Network Contact
When a wireless modem experiences a loss of network contact, queued
SDUs are returned with the out-of-range response code and with out-
of-range event indicated. A loss of contact can occur for the following
reasons:
Moving beyond network coverage
When the device moves beyond the network boundary, network contact
loss could occur for an extended period. Depending upon the user route
and network coverage area, this interval could extend from a few
minutes to several hours (or longer). Once network contact is re-
established, the client and server application must be resynchronised if
applications transactions have failed during the interval. After network
contact has been announced, further delays should be minimised, as the
user becomes acquainted with the coverage area.
Moving between areas of network coverage
Small movements within the area of network coverage can result in the
loss and reacquisition of network contact, as a result of RF penetration
difficulties with specific network topology and terrain. It might take
from a few tenths of a second to a few minutes to recognize the channel
has degraded to an unusable level, to qualify a new channel, and to re-
establish network contact. Again, the client and server application must
be resynchronised if application transactions failed during this interval.
Acquiring improved network coverage
A channel might originally have been marginal, or might have
degraded from a good to a marginal level, or might be negatively
impacted by the presence of other objects that influence its capability
to send and receive data. Under such circumstances, the wireless
modem seeks a preferred alternate channel, as previously described.
Usually this situation does not produce notification of network contact
and reacquisition.