Specifications

ISU AT Command Reference Modem Overview
Iridium Proprietary Version 2.45
20 June 2011 6
(ATOn) is used to return to the data mode. These mode transitions are made without terminating the call.
2.5 Hardware Failure Reporting
If the ISU detects a hardware problem during initialisation, the ISU may be unable to function correctly.
The ISU notifies the DTE of this situation by issuing an unsolicited result code at the end of initialisation:
HARDWARE FAILURE:<subsys>,<error>
where <subsys> identifies the software subsystem that detected the error, and <error> is the
subsystem-specific error code.
Any AT commands that cannot be handled in the failure condition will terminate with result code 4
(“ERROR”).
2.6 Ring Indicate Signal
Prior to Implementation Phase VI (see section 4), the RI (Ring Indicate) signal was used only to indicate
the presence of an incoming telephony call. From Phase VI, it is also used to indicate reception of an SBD
Ring Alert. This section describes the behaviour of the RI signal in devices supporting both telephony and
SBD ring alerts.
The Ring Indicate signal indicates that an incoming telephony call is ringing, or that an SBD ring alert has
been received. It is accompanied by the unsolicited announcements RING or SBDRING.
In the case of an incoming telephony call, which may be a voice, data or fax call, the RI signal is active for
as long as the call is offered. The RI signal is deactivated when the call is answered or when it is no longer
offered (e.g. the originator terminates the call before it is answered). A RING announcement is issued if
the DTE interface is in command mode. (This behaviour is identical to pre-phase VI versions of 9505A
and 9522A).
In the case of an SBD ring alert, which indicates that there is at least one SBD message at the gateway
awaiting collection, then provided that SBD ring alerts are enabled (see +SBDMTA), the RI signal is
activated on reception of the SBD ring alert. It is held active for a period of 5 seconds from reception of
the SBD ring alert, or until the DTE initiates an SBD session to retrieve the waiting message, whichever
occurs first. An SBDRING announcement is issued if the DTE interface is in command mode, or when it
next returns to command mode. (This behaviour is identical to the 9601).
If the ISU receives an SBD ring alert at the same time as an incoming telephony call, the RI signal
combines both of the above behaviours, remaining active as long as required by either the telephony or
SBD criteria.
The +CRIS command may be used to query the ISU as to the reason for the most recent assertion of the RI
signal.