AL3A-RM User Guide Version B
Document Number: 451-93156-002B
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effective data throughput is achieved through the use of user-transparent data compression.
The channel rate is still 2.4 kbps. However, 10 kbps effective throughput can be achieved
depending on content (graphics and images result in lower effective throughput).
G.4 S
HORT
B
URST
D
ATA
SBD is a simple and efficient bidirectional transport capability used to transfer messages with
sizes ranging from zero (a mailbox check) to 1960 bytes. SBD takes advantage of signals within
the existing air interface but without using the dedicated traffic channels. As a result, small
amounts of data can be transferred more efficiently than those associated with circuit-switched
data calls. Messages that originate from an Iridium modem can be delivered to a variety of
destinations. Commonly, data are delivered across terrestrial communications networks
(NIPRNet and internet) to servers and applications that process data from one or multiple
fielded Iridium modems. SBD service also supports the transfer of messages to Iridium
modems, where messages may originate from terrestrial sources. Delivery methods and
options are initially configured when the Iridium modem is first purchased and may be easily
modified via webpages at a later time.
G.5 S
HORT
M
ESSAGING
S
ERVICE
SMS is a mechanism to deliver short data messages over the Iridium satellite network to the
NIPRNet/internet. Iridium SMS incorporates a subset of the GSM SMS features. Each SMS
message can be up to 160 text characters (7-bit coded) in length. The text characters are based
on a 7-bit alphabet, which is encoded and transmitted as 8-bit data, hence the 140 octet (byte)
maximum message size.
SMS is a store-and-forward method of transmitting messages to and from an Iridium modem.
The short message from the modem is stored in a central Short Message Service Center (SMSC),
which then forwards it to the destination. If the recipient is not available, the SMSC attempts to
deliver the SMS message until it is delivered or the validity period expires. SMS supports a
limited confirmation of message delivery. The sender of the short message can request to
receive a return message notifying them whether or not the short message has been delivered.
With this option, the originator gets a confirmation that the message was delivered to the
