Specifications
ISU AT Command Reference  Introduction 
Iridium Proprietary Version 2.45 
20 June 2011     3 
CI 
Cell Identifier 
CTS 
(V.24 Signal) Clear To Send. This signal is normally used in controlling the flow of data to the ISU. 
(See RTS) 
DCD 
(V.24 Signal) Data Carrier Detect. This is a signal from the ISU that indicates that it is connected to 
the far-end modem for data transfer. 
DCE 
Data Communications Equipment, i.e., a data adaptor or modem. In this product, DCE refers to the 
ISU. 
DSR 
(V.24 Signal) Data Set Ready. This signal, from the ISU, indicates the readiness of the phone to 
receive data. 
DTE 
Data Terminal Equipment, such as a dumb terminal, or a PC running communications software. 
DTR 
(V.24 Signal) Data Terminal Ready. A signal from the DTE to the ISU. Can be used to terminate 
calls. 
ESS 
  ETC SBD Subsystem (synonymous with GSS) 
ETC 
 Earth Terminal Controller 
ETSI 
European Telecommunications Standards Institute. 
FA 
 Field Application 
GSM 
Global System for Mobile communications. 
GSS 
  Gateway SBD Subsystem (synonymous with ESS) 
IRLP 
Iridium Radio Link Protocol 
ISU 
Individual Subscriber Unit 
LAC 
Location Area Code 
Modem 
MOdulator/DEModulator. A device used to convert digital signals to analog signals for transmission 
and reception of telephone lines. 
MO 










