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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.
S
M
HORT
ESSAGING
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
SMSC. Unlike standard GSM, the Iridium SMS can only acknowledge that the message was
delivered to the SMSC and not the end destination.
SMS messages can be sent and received simultaneously while a voice call is in progress. This is
possible because SMS messages travel over and above the radio channel using the signaling
path, whereas the voice call uses a dedicated "traffic" radio channel for the duration of the call.
I
G
RIDIUM
EOLOCATION
The Iridium network makes calculations of the geographical location (geolocation) of an ISU
each time a call is placed. The technique employed to determine the geolocation of an ISU is
based on measurements of the ISU and satellite propagation delay and Doppler frequency shift.
Document Number: 451-01037-001D
S
(SMS)
ERVICE
SHOUT ns/nsx User Guide Version D
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