Media Independent Handover (MIH) is a standard being developed by IEEE 802.21 to enable the handover of IP sessions from one layer 2 access technology to another, to achieve mobility of end user devices (MIH).
The importance of MIH derives from the fact that a diverse range of broadband wireless access technologies is available and in course of development, including GSM, UMTS, CDMA2000, WiMAX, Mobile-Fi and WPANs. Multimode wireless devices that incorporate more than one of these wireless interfaces require the ability to switch among them during the course of an IP session, and devices such as laptops with Ethernet and wireless interfaces need to switch similarly between wired and wireless access.
Handover may be required, e.g. because a mobile device experiences a degradation in the radio signal, or because an access point experiences a heavy traffic load.
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 quality of service (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.
Implementation
The MIH function, MIHF, is implemented:
• in mobile devices that have more than one wireless/wired interface;
• in access points that have at least one wireless interface;
• in core network equipment that may have no wireless interface.
Mobile devices and access points clearly need to implement MIHF in order to communicate in a standard way between each other and between the wireless and IP layers. This allows them to make their own local decisions as to whether and how to handover a session. The reason for MIHF in core network equipment with no wireless interface is to enable the design of “handover servers” which can make centralized decisions about the handover of sessions among multiple access points and multiple access technologies. Such servers allow a wireless network operator to balance the traffic load so as to alleviate congestion on specific access points, and deliver sufficient QoS to all users.
Short-lived sessions such as accessing a single web page typically do not require handover or QoS. Longer duration sessions, which may well require handover, such as VoIP, audio/video streaming (including live TV and VoD), and VPNs, typically have QoS requirements including delay, delay variation and packet loss.
It is important that QoS is maintained, not just before and after a handover, but also during the handover, and this can be achieved by using MIH to plan ahead. Before a handover is required, the MIHFs communicate to identify which access points using which wireless technologies are within range and what QoS is available from them. MIH can also be used to pre-authenticate the mobile device with alternative potential access points and to reserve capacity prior to handover. For instance WiMAX allows resources to be reserved for a session before they are actually allocated to that session. When a handover becomes necessary, much of the ground-work is therefore already in place and the session can be handed over with minimal delay and packet loss. Incoming packets to the mobile device that are delivered to the old access point after the handover can be forwarded via the new access point, thus further reducing packet loss.
QoS is handled differently by each technology, including both the wireless access technologies and also IP, which has two QoS approaches, DiffServ and IntServ. Some technologies divide traffic into “Service Classes”, e.g. streaming, while others allow users to specify quantitative “QoS Parameters”, e.g. transfer delay. WiFi, Mobile-Fi and DiffServ use the service class approach and although they do not have exactly the same service classes, it is possible to make a correspondence among them. WiMAX and IntServ use the QoS parameter approach, and UMTS uses both approaches. Again correspondences among parameters can be made, [1].
MIH can be used to exchange information about service class and QoS parameter availability from one wireless technology to another and to the IP layer. One source of such information is performance measurements made by the wireless layer, e.g. 802.11k for WiFi and 802.16f for WiMAX.
Example MIH Scenario
To illustrate the operation of MIH, let us take an example of a real-time gaming application, using DiffServ at the IP layer, being handed over from Mobile-Fi to WiMAX. The application is currently using the Assured Forwarding Class 1, AF1, DiffServ service, and the Class 2 Real-Time Interactive Mobile-Fi service.
Since the MIH standard is not yet finalized, this example is illustrative of the type of functionality that may be provided, as opposed to a firm guarantee of what will become available. Also the standard specifies the MIH messages. The use of those messages in any particular application is implementation dependent. The example below is for illustrative purposes only.
1. The mobile device notices a degradation in the Mobile-Fi wireless signal strength and uses the MIH Event Notification Service to inform the MIHF layer in the mobile device. This information is passed to the MIHF in the access point.
2. The access point uses the MIH Command Service to tell the mobile device to initiate handover and includes a list of potential access points.
3. The mobile device MIHF passes this list to its various wireless layers and, using the MIH Information Service, requests them to determine the signal strength of each access point and report back to the MIHF.
4. The MIHF in the mobile device determines that the best signal strength comes from a WiMAX access point, and passes that information to its IP layer, using the Event Notification Service.
5. DiffServ at the IP layer in the mobile device uses the Information Service to request performance information from the WiMAX access point. This request is passed through the mobile device MIHF, via the WiMAX access point MIHF, to the WiMAX access point wireless layer.
6. The WiMAX layer in the access point uses IEEE 802.16f to obtain the performance information and reports back that it can schedule the session using its Unsolicited Grant Service, UGS, with a link delay of 5ms, or on its Real-Time Polling Service with a link delay of 18ms.
7. DiffServ selects the WiMAX UGS, and uses the MIH Command Service to tell the mobile device to commit to handover. It may also use Mobile IP if a change in the mobile device IP address is required.
Related Standards
Another standard that can be used for handover from one wireless technology to another is UMA, Unlicensed Mobile Access, which provides handover between WiFi and GSM/GPRS/UMTS. It was originally developed by an independent industry consortium and was incorporated into the 3GPP standards in 2005 under the name GAN (Generic Access Network).
Another standard of interest is 802.11u which provides roaming between 802.11 networks and other networks, so that services from one network can be accessed when the user is subscribed to services from another network. However it does not provide handover of IP sessions in progress.
Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network or a cloud computing service, particularly the performance seen by the users of the network. To quantitatively measure quality of service, several related aspects of the network service are often considered, such as packet loss, bit rate, throughput, transmission delay, availability, jitter, etc.
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A wireless network is a computer network that uses wireless data connections between network nodes.
Wi-Fi is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves. These are the most widely used computer networks in the world, used globally in home and small office networks to link desktop and laptop computers, tablet computers, smartphones, smart TVs, printers, and smart speakers together and to a wireless router to connect them to the Internet, and in wireless access points in public places like coffee shops, hotels, libraries and airports to provide the public Internet access for mobile devices.
IEEE 802.11e-2005 or 802.11e is an approved amendment to the IEEE 802.11 standard that defines a set of quality of service (QoS) enhancements for wireless LAN applications through modifications to the media access control (MAC) layer. The standard is considered of critical importance for delay-sensitive applications, such as Voice over Wireless LAN and streaming multimedia. The amendment has been incorporated into the published IEEE 802.11-2007 standard.
WiMAX is a family of wireless broadband communication standards based on the IEEE 802.16 set of standards, which provide multiple physical layer (PHY) and Media Access Control (MAC) options.
In IEEE 802.11 wireless local area networking standards, a service set is a group of wireless network devices which share a service set identifier (SSID)—typically the natural language label that users see as a network name. A service set forms a logical network of nodes operating with shared link-layer networking parameters; they form one logical network segment.
The Wi-Fi Alliance owns the Wi-Fi trademark. Manufacturers may use the trademark to brand certified products that have been tested for interoperability.
IEEE 802.16 is a series of wireless broadband standards written by the Institute of Electrical and Electronics Engineers (IEEE). The IEEE Standards Board established a working group in 1999 to develop standards for broadband for wireless metropolitan area networks. The Workgroup is a unit of the IEEE 802 local area network and metropolitan area network standards committee.
Wireless Multimedia Extensions (WME), also known as Wi-Fi Multimedia (WMM), is a Wi-Fi Alliance interoperability certification, based on the IEEE 802.11e standard. It provides basic Quality of service (QoS) features to IEEE 802.11 networks. WMM prioritizes traffic according to four Access Categories (AC): voice (AC_VO), video (AC_VI), best effort (AC_BE), and background (AC_BK). However, it does not provide guaranteed throughput. It is suitable for well-defined applications that require QoS, such as Voice over IP (VoIP) on Wi-Fi phones (VoWLAN).
IEEE 802.11r-2008 or fast BSS transition (FT), also called fast roaming, is an amendment to the IEEE 802.11 standard to permit continuous connectivity aboard wireless devices in motion, with fast and secure handoffs from one base station to another managed in a seamless manner. It was published on July 15, 2008. IEEE 802.11r-2008 was rolled up into 802.11-2012.
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The IEEE 802.21 refers to Media Independent Handoff (MIH) and is an IEEE standard published in 2008. The standard supports algorithms enabling seamless handover between wired and wireless networks of the same type as well as handover between different wired and wireless network types also called Media independent handover (MIH) or vertical handover. Vertical handover was first introduced by Mark Stemn and Randy Katz at U C Berkeley. The standard provides information to allow handing over to and from wired 802.3 network to wireless 802.11, 802.15, 802.16, 3GPP and 3GPP2 networks through different handover mechanisms.
Wireless security is the prevention of unauthorized access or damage to computers or data using wireless networks, which include Wi-Fi networks. The most common type is Wi-Fi security, which includes Wired Equivalent Privacy (WEP) and Wi-Fi Protected Access (WPA). WEP is a notoriously weak security standard: the password it uses can often be cracked in a few minutes with a basic laptop computer and widely available software tools. WEP is an old IEEE 802.11 standard from 1997, which was superseded in 2003 by WPA, or Wi-Fi Protected Access. WPA was a quick alternative to improve security over WEP. The current standard is WPA2; some hardware cannot support WPA2 without firmware upgrade or replacement. WPA2 uses an encryption device that encrypts the network with a 256-bit key; the longer key length improves security over WEP. Enterprises often enforce security using a certificate-based system to authenticate the connecting device, following the standard 802.11X.
IEEE 802.11u-2011 is an amendment to the IEEE 802.11-2007 standard to add features that improve interworking with external networks.
Vertical handover or vertical handoff refers to a network node changing the type of connectivity it uses to access a supporting infrastructure, usually to support node mobility. For example, a suitably equipped laptop might be able to use both a high speed wireless LAN and a cellular technology for Internet access. Wireless LAN connections generally provide higher speeds, while cellular technologies generally provide more ubiquitous coverage. Thus the laptop user might want to use a wireless LAN connection whenever one is available, and to 'fall over' to a cellular connection when the wireless LAN is unavailable. Vertical handovers refer to the automatic fallover from one technology to another in order to maintain communication. This is different from a 'horizontal handover' between different wireless access points that use the same technology in that a vertical handover involves changing the data link layer technology used to access the network.
Generic Access Network (GAN) is a protocol that extends mobile voice, data and multimedia applications over IP networks. Unlicensed Mobile Access (UMA) is the commercial name used by mobile carriers for external IP access into their core networks. The latest generation system is named Wi-Fi Calling or VoWiFi by a number of handset manufacturers, including Apple and Samsung, a move that is being mirrored by carriers like T-Mobile US and Vodafone. The service is dependent on IMS, IPsec, IWLAN and ePDG.
Mobile VoIP or simply mVoIP is an extension of mobility to a Voice over IP network. Two types of communication are generally supported: cordless/DECT/PCS protocols for short range or campus communications where all base stations are linked into the same LAN, and wider area communications using 3G/4G protocols.
A wide variety of different wireless data technologies exist, some in direct competition with one another, others designed for specific applications. Wireless technologies can be evaluated by a variety of different metrics of which some are described in this entry.
Mobile data offloading is the use of complementary network technologies for delivering data originally targeted for cellular networks. Offloading reduces the amount of data being carried on the cellular bands, freeing bandwidth for other users. It is also used in situations where local cell reception may be poor, allowing the user to connect via wired services with better connectivity.
References
David J Wright; Maintaining QoS During Handover Among Multiple Wireless Access Technologies, International Conference on Mobile Commerce, Toronto, July 2007.
Ok Sik Yang; Seong Gon Choi; Jun Kyun Choi; Jung Soo Park; Hyoung Jun Kim; A handover framework for seamless service support between wired and wireless networks, Advanced Communication Technology, 2006. ICACT 2006. The 8th International Conference, Volume 3, 20-22 Feb. 2006 Page(s):6 pp.
Al Mosawi, T.; Wisely, D.; Aghvami, H.; A Novel Micro Mobility Solution Based on Media Independent Handover and SIP, Vehicular Technology Conference, 2006. VTC-2006 Fall.2006 IEEE 64th, Sept. 2006 Page(s):1 - 5
Yoon Young An; Byung Ho Yae; Kang Won Lee; You Ze Cho; Woo Young Jung; Reduction of Handover Latency Using MIH Services in MIPv6, Advanced Information Networking and Applications, 2006. AINA 2006. 20th International Conference on, Volume 2, 18-20 April 2006 Page(s):229 - 234
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