Mobile IP is an Internet Engineering Task Force (IETF)6 standard communications protocol that is designed to allow mobile device users to move from one network to another while maintaining a permanent IP address.7 With the original IP protocol, each time a mobile device moved to a new Internet point of attachment, all active network connections had to be restarted. The device possibly needed to be rebooted. Mobile IP instead allows a mobile user to move about transparently while using the same IP address (the user’s “home address”), avoiding these problems and enabling new mobile applications. Mobile IP was designed to support seamless and continuous Internet connectivity. Mobile IP is most often found in wireless environments where users need to carry their mobile devices across multiple Local Area Network (LAN) subnets. Examples of use are in roaming between overlapping wireless systems, e.g., Wireless Local Area Network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), IP over Digital Video Broadcasting (DVB), and Broadband Wireless Access (BWA).8
6 For more information, visit: http://www.ietf.org/
7 For more information, visit http://en.wikipedia.org/wiki/Mobile_IP
8 For more information, visit http://nislab.bu.edu/sc546/sc441Spring2003/mobileIP
Individuals requiring communication services from remote locations (e.g., aviation, emergency services, government, military, etc.) are often equipped with satellite phones. Satellite phones are mobile devices that establish connectivity with satellites rather than cellular towers. Typically, satellite phones require a direct line of sight to the satellite without the obstruction of objects (e.g., buildings, trees, etc.) impacting the signal strength and quality of the call. Depending on the service, coverage may range from a specific area all the way to the entire earth. For example, the Iridium satellite constellation comprises 66 Low Earth Orbiting (LEO) satellites with spares, providing worldwide voice and data communications.
Satellite phones communicate by sending radio signals to a satellite that transmits a signal back down to earth, where a station routes the call to the PSTN. In some cases, the satellite phone provider will transmit from one satellite to another satellite connected to an Earth station. Much like GSM-based mobile devices, satellite phones are equipped with a UICC and provide users with a wide variety of features (e.g., contact list, text messaging, voicemail, call forwarding, etc.).