Easily transportable devices with wireless telecommunications capabilities, such as mobile telephones, personal digital assistants, handheld computers, and similar devices, will be referred to herein as mobile devices. A communications connection between two mobile devices can be referred to as a call or a session. Some mobile devices communicate in a circuit switched mode, wherein a dedicated communication path exists between two devices. For the duration of a call or session, all data exchanged between the two devices travels along the single path.
Some mobile devices also have the capability to communicate in a packet switched mode. In packet switching, a data stream representing a portion of a call or session is divided into packets that are given unique identifiers. The packets might then be transmitted from a source to a destination along different paths and might arrive at the destination at different times. Upon reaching the destination, the packets are reassembled into their original sequence based on the identifiers.
Communications that take place via circuit switching can be said to occur in the circuit switched domain and communications that take place via packet switching can be said to occur in the packet switched domain. Within each domain, several different types of networks, protocols, or technologies can be used. In some cases, the same network, protocol, or technology can be used in both domains. The wireless communication networks may be based on Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), or some other multiple access scheme. A CDMA-based network may implement one or more standards such as 3GPP2 IS-2000 (commonly referred to as CDMA 1x), 3GPP2 IS-856 (commonly referred to as CDMA 1xEV-DO), or 3GPP UMTS (Universal Mobile Telecommunications System). A TDMA-based network may implement one or more standards such as 3GPP Global System for Mobile Communications (GSM) or 3GPP General Packet Radio Service (GPRS).
GSM is an example of a wireless network standard that uses only the circuit switching mode. Examples of wireless network standards that use only packet switching include Wireless Local Area Network (WLAN), GPRS, Worldwide Interoperability for Microwave Access (WiMAX), and CDMA 1x EV-DO. Examples of wireless network standards that may use both circuit switching and packet switching modes include CDMA 1x and UMTS. An example of an application-layer protocol that can be used in a packet switching wireless network is the Session Initiation Protocol (SIP). SIP has been standardized and governed primarily by the Internet Engineering Task Force (IETF).