The Session Initiation Protocol (SIP) is an application-layer control (signalling) protocol for creating, modifying, and terminating sessions. SIP can establish media sessions such as audio/video conferences, multimedia broadcasting and interactive gaming. SIP is the preferred protocol for routing telephone calls over IP networks and has been adopted by 3GPP for IP media services over GSM/GPRS, and 3GPP2 to facilitate control plane and bearer path of all IP media services over CDMA2000.

In 1998, the ITU IMT-2000 initiative was established to standardize competing cellular technologies that were hindering globalization and convergence of digital wireless services (3G). With existing large GSM (2G) networks in Europe and Japan, ETSI standardized UMTS, which is somewhat compatible with existing GSM infrastructure and defines the new W-CDMA radio interface according to the IMT-2000 requirements. In December 1998, ETSI established the Third Generation Partnership Project (3GPP) consortium as a collaboration of telecommunications standards bodies to continue the technical specification work on UMTS.

North America uses the ANSI IS-95 (2G) and IS-2000 interim standards which are largely based on Qualcomm's CDMA technology. ANSI/TIA/EIA developed the ANSI-41 standard for cellular radiocommunication intersystem operations according to IMT-2000 requirements. IS-2000 is an approved radio interface of the IMT-2000 requirements. With the same agenda as the 3GPP consortium, the 3GPP2 consortium was established by ANSI as a collaborative effort of North American and Asian interests to oversee the development of the technical specifications. 3GPP2 networks are entirely based on IP for control plane and bearer path of network and subscriber services.

The 3GPP consortium defined the 3G IP Multimedia Subsystem (IMS) for enhanced services in 2001. IMS is not only to provide new services, but to provide all services that the Internet provides. It is heavily based on SIP. The 3GPP2 consortium has largely adopted IMS (with a few minor differences) and refer to it as IMS-MMD (Multimedia Domain)

WiMAX is a wireless standard belonging to the IEEE 802.16 specification series. IEEE 802.16 provides up to 50 km (31 miles) of linear service area range and allows users connectivity without a direct line of sight to a base station.

An important aspect of IEEE 802.16 is that it defines a scheduling MAC layer, where the subscriber station only has to compete once for initial entry into the network. It is then allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber station. This scheduling algorithm is stable under overload and oversubscription, and is very bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations.

The sophisticated network features available in IEEE 802.16 provide interesting opportunities for interoperability of WiMAX with cellular networks. Amendment 802.16e adds mobility components (at limited velocity) to the standard. Interestingly, 3GPP release 6 defines interworking of IMS over WLAN.

WiMAX uses the same physical layer as existing WiFi networks. Mobile Broadband Wireless Access (MBWA) is the IEEE 802.20 standard built without the limitations of compatibility. It supports higher mobility velocities and concentrates on real-time traffic. It is a much more likely competitor to existing cellular wireless technologies than WiMAX. Some proponents of IEEE 802.20 claim that the existing cellular technologies cannot achieve 3G expectations and IEEE 802.20 is better suited.

In order to increase the range and reliability of wireless systems, the IEEE 802.16 and IEEE 802.20 standards support optional physical layer enhancements which use multiple-antenna techniques such as Alamouti Space-Time Coding (STC), Adaptive Antenna Systems (AAS) and Multiple-Input Multiple-Output (MIMO) systems. IEEE 802.11n is a revision to add MIMO techniques to WiFi.

MIMO is a space-time diversity techniques which exploits the channel dispersion. While the term MIMO has been largely misused by the media and marketing departments to describe antenna switching, the opportunities for MIMO are huge.

Two and three antenna MIMO systems are currently available on the market. Technologies for harnessing the full MIMO capacity have not been realized.