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compression. The channel rate is still 2.4 Kbps. However, 10 Kbps effective throughput can be achieved
depending on content (graphics and images will result in lower effective throughput).
C.5 Short-Burst Data (SBD)
SBD is a simple and efficient bi-directional 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, 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 web pages at a later time.
C.6 Short Messaging Service (SMS)
SMS is a mechanism to deliver short data messages over the Iridium satellite network to the
NIPRNet/Internet. Iridium SMS service 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 service 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 Center (SMSC) which then forwards it to
the destination. In the case that the recipient is not available, the SMSC will attempt to deliver the SMS 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 the short
message has been delivered or not. 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.
C.7 RUDICS
RUDICS is an enhanced gateway termination and origination capability for circuit switched data calls
across the Iridium satellite network. When an Iridium modem places a call to the RUDICS Server located at
the Iridium Gateway, the RUDICS Server connects the call to a pre-defined IP address allowing an end-to-end
IP connection between the Host Application and the Iridium modem. There are three key benefits of using
RUDICS over the conventional PSTN circuit switched data connectivity or mobile-to-mobile data solutions: (1)
elimination of analog modem training time, (2) increased call connection quality, reliability, and maximized
throughput and (3) protocol independence.
