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.

IEEE 802.21 Media Independent Handover [1]

The emerging IEEE 802.21 standard, Media Independent Handover, has the ability to seamlessly handover networks for both wired and wireless networks, which is addresses a prevalent problem when roaming. Interoperability between homogenous network types of 802 and non 802 networks is also a key feature of the 802.21 standard. This report consists of the understanding of 802.21 services and its functionality, specifically at the Data Link and Network Layers of the OSI Networking Model. Currently at the stage of proposal, the 802.21 working group hopes to finalize the standard’s document and begin implementation shortly thereafter. Future outlook of this standard is good when comparing with the existing proprietary UMA (Unlicensed Mobile Access), which is a similar technology, but fails to offer interoperability. The expectations for this standard are, but are not limited to: ability to roam between 802.11 and 3G networks, allowance for use by multiple vendors and users, application for both wired and wireless networks, and ability to engage in a teleconference.


Introduction
Wireless networking has provided us the ability to freely utilize our mobile devices (i.e. computer notebook, cellular phones, PDA, GPS) wherever and whenever a wireless access point is available. With the multitude of existing wireless standards (Wi-Fi, GSM, etc), a smooth transition from one network to another is utterly impossible with the current technology. Existing IEEE 802 standards go through a series of failures before acquiring the correct network access. For instance, as soon as a user unplugs the Ethernet cable from his or her computer, an error appears indicating that the user is no longer connected to a LAN network. If the computer has wireless capability (i.e. 802.11b), then the user may be able to connect to a wireless network, but network discovery would take some time to establish. An interruption of service is inevitable, thus, a network handover standard is necessary. This emerging standard is the IEEE 802.21, which working efforts debuted in March 2004 and implementation is still in progress [4].
IEEE 802.21 is a developing standard which enables handover and interoperability between heterogeneous network types including both 802 and non 802 networks [6]. The standard provides information to allow handing over to and from cellular and wireline, GSM, GPRS, WiFi, WiMAX, Personal Area Network (PAN), Bluetooth and 802.11 networks through different handover mechanisms [1].

Background
Initiated in March 2004, the working group for the 802.21 standard was chaired by Ajay Rajkumar from Lucent Technologies. The members involved include over 50 companies. These companies are the “largest vendors of end-to-end network infrastructure, device companies, chipset developers, and even service providers” [1]. One of the contributing companies, Intel Corporation, expressed enthusiasm towards providing users with the ability to move from a hotspot to a cellular connection without noticing. Envisioned is the idea of a future that unites network connectivity across a wide range of networks. Figure 1 shows a prototype mobile phone that has four different wireless networks: Bluetooth, GPS, GPRS, and Wi-Fi. With the implementation of 802.21, this device is expected to intellectually select available networks, with an ease of transition and without any interruption, when roaming [3].

standards: Bluetooth, GPS, GPRS, and Wi-Fi [3].

Objective
The objective is to enable an innovative fast Layer 2 and Layer 3 handoff algorithm between networks (for both wired and wireless networks). Network discovery and selection are factors that affect the quality of service during a handover decision. With this technology, end-user devices will have the ability to “automatically choose the best available network connection type and to seamlessly hand off sessions among networks during roaming without user involvement” [2]. 802.21 is expected to unite the multitude of existing networks.

Organization
The next immediate section describes the proposed 802.21 standard in detail. The specifics include the four Media Independent Handover services provided, packet format and information, and functionality in Layers 2 and 3 (Data Link and Network, respectively) of the OSI Networking Model. We will discuss the current progress, including accomplished milestones towards completing the 802.21. In addition to this standard’s expectations, we will also mention its future outlook. The report concludes with comparison of 802.21 and existing similar technologies.