Cellular access networking has undergone a major transition in the past decade with the convergence toward OFDMA and IP technologies. Multiradio devices will be abundant with advances in device and access technology. As we see, each access technology is designing its own way of integration to other access technologies. A standard way of integration that is agnostic to the underlying access technology is needed. IEEE 802.21 (media-independent handover services) framework aims to develop a common functionality for handover to bridge these accessnetworks via a media independent handover in order to fulfill homogeneous or heterogeneous handovers.
Homogeneous handover is a term defined for horizontal handovers within an access network and heterogenous handover is a term defined for vertical handovers between access networks for global mobility as seen in the illustration below;
IEEE 802.21 desired to bring a common handover solution for multiradio operation for better interworking of various technologies as seen in the illustration below.
Interworking includes handover within 802 services such as 802.3, 802.11, and 802.16, etc. It is also desired to extend 802.21 handover toward cellular or wired services. The handover is defined as a three-step process: handover initiation, handover preparation, and handover execution. The scope of IEEE 802.21 is to cover handover initiation and handover preparation where functionalities include network discovery, selection, and handover negotiation in the former and layer 2 and 3 connectivity in the latter. On the other hand, remaining functionalities such as handover signaling, context transfer, and packet reception fall into handover execution. IEEE 802.21 is being designed to develop smart L2 triggers, media-independent information service, and handover messages in order to provide optimum network selection, seamless roaming, and lower power operation for multiradio devices. L2 triggers consist of link up/down events, link parameters change/going down events, and network-initiated events for load balancing and operator preferences. IEEE 802.21 also proposes a media-independent information service that maintains a global network map that contains list of available networks (802.11/16/22, GSM, UMTS, LTE, etc.) with neighborhood information and available higher layer services such as ISP, MMS, etc. Handover decision is a co-operative feature with respect to triggers and neighbor information. Information element may contain the following in TLV or XML form; List of networks available; Geo-location of Point of Attachment (PoA); Operator ID; Roaming partners; Cost indication for service/network usage; Security; Quality of Service; PoA capabilities such as Emergency Services and IMS.
