IEEE 802.21

802.21 is an IEEE standard published in 2008. The standard supports algorithms enabling seamless handover between networks of the same type as well as handover between different network types also called Media independent handover (MIH) or vertical handover. The standard provides information to allow handing over to and from 802.3, 802.11, 802.15, 802.16, 3GPP and 3GPP2 networks through different handover mechanisms.

The IEEE 802.21 working group started work in March 2004. More than 30 companies have joined the working group. The group produced a first draft of the standard including the protocol definition in May 2005. The standard was published January 2009.

Cellular networks and 802.11 networks employ handover mechanisms for handover within the same network type (aka horizontal handover). Mobile IP provides handover mechanisms for handover across subnets of different types of networks, but can be slow in the process. Current 802 standards do not support handover between different types of networks. They also do not provide triggers or other services to accelerate mobile IP based handovers. Moreover, existing 802 standards provide mechanisms for detecting and selecting network access points, but do not allow for detection and selection of network access points in a way that is independent of the network type.

Many vendors are building wireless products and participating in the development of the 802.21 standard. Current technologies such as 802.11 that accomplish handover use software to accomplish handovers and suggest that software will also be the way that handover will be implemented by 802.21. The use of software as a means to implement 802.21 should not cause large increases in the cost of networking devices. An open source software implementation is provided by ODTONE.

Unlicensed Mobile Access (UMA) technology is basically a mobile-centric version of 802.21. UMA is said to provide roaming and handover between GSM, UMTS, Bluetooth and 802.11 networks. Since June 19, 2005, UMA is a part of the ETSI 3GPP standardization process under the GAN (Generic Access Network) Group.

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