Digi M10 - Manual (Page 14)

Digi m10 Technical Overview
Digi International, Inc. © 2009 Page 14 of 26
inaccessible by the satellite constellation. The stored messages are transmitted when an
ORBCOMM Gateway comes into satellite-transmission range. This concept applies to both
sending (SC-Originated) and receiving (SC-Terminated) from a satellite modem point of view.
More documentation can be found on the kit installation CD. To learn more, navigate to
C:\Program Files\Digi\Digi m10 JumpStart Kit\documents please refer to either ORBCOMM Serial
Interface Specification > Figure 4.5 SC-Originated Globalgram & Figure 4.6 SC-Terminated
Globalgram or ORBCOMM Serial Interface Specification > SC-ORIGINATED GLOBALGRAM &
SC-TERMINATED GLOBAL.
3.7 Message Blocking
Message Blocking is an optional feature that allows customers to restrict the addresses to which
their satellite modems can send messages, and those addresses that are allowed to send to a
satellite modem. The Speed Dial addresses are used as permitted addresses.
3.8 Message Priority
Message priority is a feature that allows messages to be processed in order of importance. The
higher the priority, the faster the message moves through the network. However, the ORBCOMM
message switch (OMS) does not terminate message sessions in progress; a new urgent
message will remain queued until any active lower-priority message is completed.
ORBCOMM will only implement priority restrictions during periods of very heavy usage. If the
system is lightly loaded and no queues, or only very short queues, are formed, there is little user
benefit gained from the priority feature.
Functionally, within the ORBCOMM gateway congestion control mechanisms use priority to stop
satellite modems from sending messages not meeting a customer-designated priority threshold.
The satellite broadcasts the identification number of connected gateways and their minimum
message priority thresholds in the downlink control information. All listening satellite modems that
have messages queued for a listed gateway must refrain from sending messages below the
specified priority threshold. Only queued messages with a priority at or above the minimum
priority threshold are sent. Messages below the minimum priority remain in the queue until
channel utilization falls below the threshold.
The available priority levels are:
0. Non-urgent
1. Normal
2. Urgent
3. Special Delivery