Media-independent Handover - Functionality

Functionality

The key functionality provided by MIH is communication among the various wireless layers and between them and the IP layer. The required messages are relayed by the Media Independent Handover Function, MIHF, that is located in the protocol stack between the layer 2 wireless technologies and IP at layer 3. MIH may communicate with various IP protocols including Session Initiation Protocol (SIP) for signaling, Mobile IP for mobility management, and DiffServ and IntServ for QoS.

When a session is handed off from one access point to another access point using the same technology, the handover can usually be performed within that wireless technology itself without involving MIHF or IP. For instance a VoIP call from a Wi-Fi handset to a Wi-Fi access point can be handed over to another Wi-Fi access point within the same network, e.g. a corporate network, using Wi-Fi standards such as 802.11f and 802.11r. However, if the handover is from a Wi-Fi access point in a corporate network to a public Wi-Fi hotspot, then MIH is required, since the two access points cannot communicate with each other at the link layer, and are, in general, on different IP subnets.

When a session is handed off from one wireless technology to another, MIH may assist the handover process by exchanging messages among the Internet access technologies and IP. Message are of three types:

• Event notifications are passed from a lower layer in the protocol stack to a higher layer or between the MIHF of one device to the MIHF of another device. For instance “wireless link quality is degrading” is an event notification that is passed from the wireless layer to the MIHF layer.

• Commands are passed down the protocol stack or between the MIHF of one device to the MIHF of another device. For instance “Initiate Handover” is a command in which the access point MIHF provides the mobile device MIHF with a list of alternative access points that it could use.

• Information Service is of three types. A higher layer may request information from a lower layer, e.g. the MIHF may request performance information, such as delay from the wireless layer. A lower layer may request information from a higher layer, e.g. the MIHF may request to know the ISP Name from the IP layer. One MIHF may request information from another MIHF, e.g. the availability of location-based services.