IDP 100 Modem Series - Developer Guide
T203, Version 04 8
©
SkyWave Proprietary
2.3.1.1 Priority
The host can specify up to four priorities when submitting a from-mobile message
(Figure 3). The priority field is not transmitted to the Gateway. The modem selects the
message with the highest priority from the message queue to transmit.
The modem can deliver up to eight messages (Figure 4), or two for each priority in the Tx
Sending state. Once a message is in the Tx Sending state, it cannot be deleted, although a
higher priority message can be submitted.
Figure 4
Priority Messages
The modem always gives priority to the high priority message when selecting the next
message fragment to transmit. However, if there are network slots available for a lower
priority message, the modem interleaves this message to maximize the network
resources. The number of network slots available for low priority messages depends on
message size, coding rate and the number of outstanding acknowledgements at any one
time.
A high priority does not guarantee that the message is delivered before a lower priority
message. As the modem can process up to eight messages at once time, a low priority
message may arrive before a high priority message depending on its length and number
of message retries.
If the host wants to ensure a priority message transmission, it is recommended to use
priority levels appropriately.
2.3.2 To-Mobile Messages
Figure 5 describes the message flow for a to-mobile message. Like the from-mobile
messages, to-mobile messages are sent as a sequence of message fragments.
The IDP modem creates an
incoming message name
based on the network reference
number. The modem receives the network reference number and the message length in
the first packet. As the incoming message name is based on the network reference
number, it is in the form FMaa.ss
n
where aa.ss is the network reference number and
n
is a
number assigned by the modem. In most cases
n
is absent. However, if the message
partition contains an older message with a matching network reference number,
n
is
incremented.
The host does not send an unsolicited message when a to-mobile message is received. If
the host does not use the hardware notification (Section 2.6), the host can poll the to-
mobile message state (Figure 5) to determine if there are new un-retrieved messages. AT
commands can be used to obtain a list of un-retrieved messages, or all messages stored in
the message buffer. The number of messages in the list could be as large as the maximum
number of messages stored in the message buffer.
Msg 1
Msg 2
Priority 1
Msg 3
Msg 4
Priority 2
Msg 5
Msg 6
Priority 3
Msg 7
Msg 8
Priority 4
Summary of Contents for IDP 100 Series
Page 106: ...www SkyWave com ...
