Media Independent Handover (802.21) Reference Model

Media Independent Handover Reference Model (MIH) is a new layer that resides between the Network Layer (Layer 3 of OSI model) and lower layers: MAC and PHY (IEEE interfaces) or RRC and LAC ( 3GPP or 3GPP2). It provides asynchronous and synchronous services through Service Access Points (SAPs) for lower layers and upper layers. MIH Function (MIHF) helps Layer 3 Mobility Protocol in maintaining service continuity between different interfaces, adaptation to reach Quality of Service (QoS), link selection and network discovery.

The communication between MIHF on the network side is depends on MIHF location and type of scenario. When MIHF is in the access network such as Access Point (AP), Layer 2 or Layer 3 transport can be used over access. When network decides where and when to handover, the source MIHF can send messages to destination MIHF to inform destination MIHF to begin “preparation”. The preparation includes checking availability of appropriate resources including acceptable QoS levels at new PoA, procuring an IP address for the mobile station, etc. Another possible scenario is where the MIHF in an AP communicates with MIHF in an Access Router (AR). This type of communication includes events such as Link Up, Link Down, etc.
The IEEE 802.21 standard supports the Media Independent Event service, Media Independent Command service and Media Independent Information service. A management protocol is required for the exchange of information between MIH entities within a terminal and a network.

MIH Reference Model for Ethernet (802.3)
For 802.3 there are no peer management facilities in CSMA/CD. Thus, if the MIH services are supported over wired ethernet networks, in order to carry the payload over normal ethernet data frames, a L2 protocol with a new ethertype is necessary. The MIH ethertype is encoded in the SNAP header. At the same time 802 networks don’t support data frames in unauthenticated state. Hence the MIH Protocol cannot be used in this case. Only management frames can be used to transport information in the unauthenticated state.
The IEEE 802.21 standard should define the packet format and payloads in media independent manner in standard TLV format. Thereafter these packets can be encapsulated in a L2 MIH Protocol using MIH ethertype when the payload needs to be sent over normal data frames as in case of ethernet. In other cases the TLV based messages and payload can be directly encapsulated in media specific management frames.

MIH Reference Model for Wi-Fi (802.11)
The above figure shows the MIH functions for 802.11 stations and network PoA (APs). The MIH_MAC_SAP is the MIH interface to the data plane and can encapsulate MIH protocol packets in data packets. However since 802.11 does not currently support Class 1 data frames, traffic can be sent over the data plane only when the client is connected with the AP. The MIH_MGMT_SAP provides interface with the management plane (MLME) and allows MIH protocol packets to be stored in management frames.
The MIH_SAP shows the interface of MIH Function with other higher layer entities such as Transport, Handover policy, L3 Mobility protocol, etc. The MIH Function may interface with the OS or the system using the MIH_ME_SAP.

MIH Reference Model for WiMAX (802.16)
In 802.16 based system, the MIH_MGMT_SAP provides the MIH functionality over management plane and help with transporting MIH protocol messages across peer MIHFs. The MIH_SAP shows the interface of MIHF with other higher layer such as Transport, Handover policy, L3 Mobility protocol, etc. The MIH Function may interface with the OS or the system using the MIH_ME_SAP.

MIH Reference Model for 3rd Generation Mobile System (3GPP)
A potential realization of MIH functions for 3GPP enabled Mobile Stations is illustrated above. The MIH_RRC_SAP defines the MIH interface to the 3GPP Radio Resource Control (RRC) layer. The MIH_MGMT_SAP defines the MIH interface to the 3GPP GPRS Mobility Management or Global System (GMM) for Mobile Communication (GSM). Most of the MIH services may utilize the information that is already defined in the RRC layer and GMM/SM. The desired information from MIH Event Services, Command Services and Information Services will be provided to MIH_RRC_SAP and MIH_MGMT_SAP which will be further defined by 3GPP SDO. In the case of MIH in the Mobile Stations, the PHY and MAC SAPs communicate to the RRC as defined in the 3GPP standards. No new interfaces and primitives need to be defined for these SAPs.

Spanning Across Different Media
This figure shows how the MIH Function spans across different media specific technologies and provides a common abstraction of handover services to higher layers.