A Survey on Media Independent Handover (MIH) and IP Multimedia Subsystem (IMS) in Heterogeneous Wireless Networks

One challenge of wireless networks integration is to provide ubiquitous wireless access abilities and seamless handover for mobile communication devices between different types of technologies (3GPP and non-3GPP), such as Global System for Mobile Communication, Wireless Fidelity, Worldwide Interoperability for Microwave Access, Universal Mobile Telecommunications System and Long Term Evolution. This challenge is critical as mobile users are becoming increasingly demanding for services regardless of the technological complexities associated with them. To fulfil these requirements for seamless vertical handover (VHO) two main interworking frameworks have been proposed by IEEE Group and 3GPP for integration between the aforementioned technologies; namely, Media Independent Handover IEEE 802.21 and IP Multimedia Subsystem, where each of them requires mobility management protocol to complement its work, such as Mobile IP and Session Initiation Protocol, respectively. Various VHO approaches have been proposed in the literature based on these frameworks. In this paper, we survey the VHO approaches proposed in the literature and classify them into four categories based on these frameworks for which we present their objectives and performances issues.


Introduction
With the advancement of wireless communication and computer technologies, mobile communication has been providing more versatile, portable and affordable networks services than ever.Therefore, the number of users of mobile communication networks has increased rapidly as an example; it has been reported that ''today, there are billions of mobile phone subscribers, close to five billion people with access to television and tens of millions of new internet users every year'' [1] and there is a growing demand for services over broadband wireless networks due to diversity of services which can not be provided with a single wireless network anywhere anytime [2][3][4][5][6].This fact means that heterogeneous environment of wireless systems, such as Global System for Mobile Communication (GSM), Wireless Fidelity (Wi-Fi), Worldwide Interoperability for Microwave Access (WiMAX) and Universal Mobile Telecommunications System (UMTS) will coexist providing mobile users (MUs) with roaming capability across different networks.One of the challenging issues in Next Generation Wireless Systems (NGWS) is achieving seamless vertical handover (VHO) while roaming between these technologies; therefore, telecommunication operators will be required to develop a strategy for interoperability of these different types of existing networks to get the best connection anywhere anytime without interruption to the ongoing sessions.To fulfill these requirements for seamless VHO two main interworking frameworks have been proposed by IEEE Group and 3GPP for integration between the different types of technologies (3GPP and non-3GPP); namely, Media Independent Handover IEEE 802.21 (MIH) and IP Multimedia Subsystem (IMS), where each of them requires mobility management protocol to complement its work, such as Mobile IP (MIP) and Session Initiation Protocol (SIP), respectively.Although researches about VHO under MIH and IMS frameworks have been surveyed recently in [7], highlights on their objectives and performances issues have not been considered yet.In this paper, we survey the VHO approaches proposed in the literature and classify them into four categories based on these frameworks for which we present their objectives and performances issues.
The rest of the paper is organized as follows: Sect. 2 describes the VHO procedure, in Sect.3, we overview available techniques of VHO: interworking architectures, mobility management protocols, access network discovery and selection function (ANDSF) mechanism, MIH framework and IMS framework.In Sect.4, we classify VHO approaches proposed in the literature into four categories based on MIH and IMS frameworks.In Sect.5, comparison of the VHO approaches is presented and finally, we conclude the paper in Sect.6.

Vertical Handover Procedure
The mechanism which allows the MUs to continue their ongoing sessions when moving within the same radio access technology (RAT) coverage areas or traversing different RATs, is named horizontal handover and VHO, respectively.In the literature VHO procedure has been divided into three phases: collecting information, decision and execution [8][9][10][11][12][13][14][15] as described below.

Handover Collecting Information
In this phase, all required information for VHO decision is gathered, some related to the user preferences (e.g.cost, security), network (e.g.latency, coverage) and terminal (e.g.battery, velocity).

Handover Decision
In this phase, the best RAT based on aforementioned information is selected and the handover execution phase is informed about that.

Handover Execution
In this phase, the active session for the MU will be maintained and continued on the new RAT; after that, the resources of the old RAT are eventually released.

Background of Networking Techniques
The NGWS will consist of heterogeneous wireless access networks, such as UMTS, Wi-Fi, WiMAX and Long Term Evolution (LTE), these different RATs have significant different capabilities in terms of system capacity, supported data rate for services, coverage area, cost, etc.For example, The UMTS provides high coverage area, high cost and data rate from 144 Kbps to 2 Mbps at 10 km/h to maximum 500 km/h depending on propagation channel condition, while Wi-Fi provides low coverage area, low cost and high data rate from 1 to 54 Mbps at 30 m to maximum 450 m [3].Therefore, complementarity of these technologies through interworking architectures is essential to provide ubiquitous wireless access abilities with high coverage area, high data rate and low cost to MUs.Consequently, the challenge would be the ability to move MUs seamlessly between these different types of wireless technologies.To fulfil these requirements for seamless VHO many techniques were proposed for integration between the aforementioned technologies; these are discussed next.

Loose and Tight Coupling Interworking Architectures
Loose coupling and tight coupling are two main interworking architectures proposed by European Telecommunication Standards Institute (ETSI) in 2001 [16] for integrating between the different types of technologies [17].

Loose Coupling
In loose coupling architecture, each of the existing access wireless networks, such as UMTS, Wi-Fi and WiMAX is independently deployed.Both of WiMAX and Wi-Fi data do not pass through 3rd Generation Partnership Project (3GPP) core network this in turn means, there is no need to modify current architecture, no additional cost and the interworking point occurs after 3GPP core network in particular, follow Gateway GPRS Support Node (GGSN) with internet.Also, the networks interconnection in this architecture based on MIP as for roaming service the authentication, authorization and accounting (AAA) server connects between different RATs which allows the Wi-Fi and WiMAX data go directly to the internet without requiring for direct link between their components and 3GPP core network [18].

Tight Coupling
In tight coupling architecture, the Wi-Fi and WiMAX data pass through 3GPP core network before going to the internet and significant modifications of existing access wireless networks are necessary for providing seamless service to the MU to move from one network to another [18], this in turn impacts the 3GPP core network performance in terms of complexity, congestion and packet loss due to the overload.The networks interconnection in this architecture is based on the existing 3GPP core network functionalities (e.g., core network resources, subscriber databases and billing systems) that ensure MUs to continue their ongoing sessions when moving within different RATs.There are two types of tight coupling [6]: • Tight coupling integration at GGSN level.
• Tight coupling integration at the RNC level.
• Tight coupling integration at GGSN level.
In this architecture, all of the RATs are connected together by Virtual GPRS Support Node (VGSN) which is responsible to exchange subscriber information and route packets between the wireless access networks, the handover duration (latency) is equivalent with loose coupling where MIP is used (no need of MIP functionalities) and it requires less complexity modification in 3GPP core network [18].• Tight coupling integration at the RNC level.
In this architecture, access point (AP) and base station (BS) in Wi-Fi and WiMAX respectively are connected with Radio Network Controller (RNC) by interworking unit (IWU).The IWU main functionality is to translate protocol and signalling exchange between RNC and another RATs interface, such as AP and BS [6].

Mobility Management Protocols
The mobility management has gained importance due to the rapidly increasing number of MUs requesting services over broadband wireless networks.Mobility management has enabled MUs to maintain their ongoing sessions particularly when traversing between different RATs (3GPP and non-3GPP).In order to fulfill these requirements for seamless mobility the Internet Engineering Task Force (IETF) was produced mobility management protocols; these can be classified into five types [19]:

Host Identity Protocol (HIP)
A new name space used between the IP layer and the transport protocols.The namespace separates IP addresses and the host identifier [19].

Virtual Internet Protocol (VIP)
It is a virtual IP layer that uses the principle of a virtual network address and a physical network address to Internet naming [19].

Session Initiation Protocol (SIP)
It is defined to support real-time multimedia services in mobile networks at application layer such that handles both pre-session mobility and mid-session mobility management.However, the most common protocols used for mobility in VHO are the MIPv4, MIPv6, SIP and HIP [20].

Access Network Discovery and Selection Function (ANDSF) Mechanism
The 3GPP group proposed ANDSF in 2008 (Release 8) [21] to provide a seamless VHO between different RATs and to mitigate the impacts of radio signals impairment between 3GPP and non 3GPP.In this mechanism, there is no need to the measurements reports between the different RATs, and hence, no need to the modification on legacy radio systems (no additional cost).The ANDSF also works as store of RATs information that is queried by MU to make handover decision.This information about neighbor cells, operator's policies and preferences, QoS, capabilities, etc. [22].In [23], new logical element proposed named forward authentication function (FAF), it was collocated with the ANDSF and located in the target network.FAF plays the role of target RAT to perform its functionalities, e.g. if the MU moves toward 3GPP E-UTRAN, the FAF emulates Node-B, while if the MU moves toward WiMAX, the FAF emulates WiMAX BS.The FAF has two main goals: first, to enable the transmission from WiMAX to 3GPP (Authentication).Second, to avoid direct link between 3GPP and WiMAX, i.e. ''avoid the WiMAX access scheduling measurement opportunities to the MU in order to measure neighbor 3GPP sites'' [23].Nevertheless, the authors in [23] lacked to tackle two vital aspects in the VHO procedure: first, the source network was not informed by MU about its movement to the target network which resulted in packet losses and second, it lacked releasing procedure for the resources of the network.In [24], the Data Forwarding Function (DFF) logical entity located in source network was proposed to solve the problems that were raised in [23].

Media Independent Handover (MIH) Framework
The IEEE Group released IEEE 802.21 standard MIH in 2009 to provide seamless VHO between heterogeneous networks that include both wireless (3GPP and non-3GPP) and wired media [25][26][27][28][29][30][31][32].IEEE 802.21 defines two entities: first, Point of Service (PoS) which is responsible for establishing communication between the network and the MU under MIH and second, Point of Attachment (PoA) which is the RAT AP.Also, MIH provides three main services: Media Independent Event Service (MIES), Media Independent Command Service (MICS) and Media Independent Information Service (MIIS) [33] such that MIH relies on the presence of mobility management protocols, such as MIP and SIP, this is shown in Fig. 1.

Media Independent Event Service (MIES)
It is responsible for reporting the events after detecting, e.g.link up on the connection (established), link down (broken), link going down(breakdown imminent), etc. [34].

Media Independent Information Service (MIIS)
It is responsible for collecting all information required to identify if a handover is needed or not and provide them to MUs, e.g.available networks, locations, capabilities, cost, etc.

Media Independent Command Service (MICS)
It is responsible for issuing the commands based on the information which is gathered by MIIS and MIES, e.g.
MIH handover initiate, MIH handover prepare, MIH handover commit and MIH handover complete [34].However no handover decision is made within MIH [35], ''the actual algorithms to be implemented are left to the designers'' [36] and the security for re-authentication at the target network and implementation of the decision algorithm are out of the scope of MIH [26].

IP Multimedia Subsystem (IMS) Framework
The IMS was introduced in 2002 by 3GPP (Released 5) to support multimedia services in UMTS [37][38][39][40] and provides access security to IMS.However, it started supporting multimedia service for both wireless (3GPP and non-3GPP) and wired networks in Release 7 [41].The IMS is defined as a 3-layer architecture consisting of transport layer, control layer and application layer, this is shown in Fig. 3.

Transport Layer
It includes all the entities for the supported access networks which allow IMS devices and MUs connect the IMS through many types of access networks, e.g.Wideband Code Division Multiple Access (WCDMA), UMTS, Wi-Fi, WiMAX, Ethernet, digital subscriber line etc.Also it allows the IMS device to receive/send call either through the public switched telephone network (PSTN) or the media gateway (MGW) [42].

Control Layer
This layer includes three SIP signaling servers that are known as Call Session Control Functions (CSCFs) which are responsible for establishing, managing and terminating media sessions.Also it includes another entities i.e.Home Subscriber Service (HSS), breakout gateway control function (BGCF), Media Gateway Control Function (MGCF), Media Resource Function Controller (MRFC), Multimedia Resource Function Processor (MRFP) [42], this shown in Table 1.

Application Layer
In this layer the AS is responsible for hosting and executing all the services offered by IMS.
However, in this framework handover decision is out of its scope and unlike the MIH framework the MU obliges to discover neighbor cells with no assistance by periodically conducting a radio scanning in the background which results in: • The MU needs two receivers work concurrently one for scanning and another for ongoing session, while one receiver may be incurred probability of missing data from serving cell.[2, 25 and 43] and [35,[44][45][46][47], respectively [48].In [2], the authors proposed an approach called tunneling mechanism to guarantee the continuity of service during a communication session in heterogeneous wireless technologies between Wi-Fi, WiMAX and 3G technologies such that a set of components organized in three layers which offered the MU the possibility to monitor its resources and its network performance.
In [25], the authors presented the integration process of MIH with Wi-Fi, WiMAX and UMTS scenarios in order to provide seamless VHO with low latency and zero packet loss.The RSS parameter was considered to make VHO decision before source PoA link was disconnected due to fading RSS.The latency was divided into two phases: handover preparation latency (HPL) and handover execution latency (HEL).The HPL was the time interval in which the MU queried the MIIS about available RATs for handover, the HEL was the time since the MU sent/ received authentication messages to its target network (new PoA) until the reception of the first packet on the target network.The ns-2 simulator was used considering two types of traffic IPTV and VoIP.The results for handover between Wi-Fi and WiMAX shown that HPL was *125 ms, HEL was 45 ms and jitter was 1.5 ms, and for handover between WiMAX and UMTS results shown that latency due to HPL was *36 ms, HEL was 110 ms and jitter was 4.3 ms.Finally, handover between UMTS and Wi-Fi results shown that HPL was *31 ms, HEL was 48 ms and jitter was 6.3 ms [25], while no performance evaluation provided regarding packet loss.
In [35], a new approach that combined MIH and ANDSF mechanism was proposed for improving the VHO behavior such that the ANDSF is an entity produced by 3GPP to provide seamless VHO between different RATs.The aim of the proposed approach was to eliminate packet loss and improve the resource release mechanism in the source access network between WiMAX and LTE scenario.However; no evaluations or validation about the work has been provided.
In [43], the authors presented MIH vertical handover approach in order to provide seamless VHO with low latency, they also presented MIH Layer 2 (MIH L2) trigger handover decision algorithm based on RSS taking into account Wi-Fi and WiMAX scenario.Analytical modeling and ns-2 simulator were used considering FTP traffic.The result shown that latency was considerably reduced compared with MIPv4 through the pre-registration process using the L2 trigger.
In [44], the authors presented fast handover approach for heterogeneous networks that utilized MIH with Proxy Mobile IPv6 (PMIPv6) to support heterogeneous networks performance between Wi-Fi and WiMAX scenario taking into account RSS to make VHO decision.The analytical modeling results shown that the proposed approach reduced latency time by 26 % and packet losses by 90 % [44].
In [46] a new approach that enabled seamless VHO handovers in wireless heterogeneous environments was presented.The proposed approach combined the MIPv6 mobility management protocol, the MIH, and a mobility control entity to perform VHO with minimal packet loss and latency between Wi-Fi and 3G (HSPA) scenario taking into account the RSS parameter to make VHO decision.The Network Mobility Manager (MM_NET) and Mobile Node Mobility Manger (MM_MN) were two logical entities developed in the proposed approach.The MM_NET was the network entity that controls, with the help of MM_MN which placed on the MU device.The authors divided the latency into two periods: handover latency (HL) and HEL.The HL was the time interval in which the MU did not receive any packets as a result of handover until the first packet received by target network (new PoA), the HEL was the time since the MU sent a binding update to its home agent until the reception of the first packet on the new target network.Testbed experiment was developed considering two types of traffic video and VoIP.The results shown that latency was zero when using video or VoIP traffic at HL, while at HEL was *0.5 s, whereas packet loss was *0.18 % [46].
In [47], the authors presented analytical modeling of VHO latency for PMIPv6 under MIH between Wi-Fi and WiMAX scenario in [49], [50] taking into account RSS to make VHO decision.The analytical results shown that L2 latency was *50 ms, while between MU and source network/target network was 50-150 ms [47].

IMS Category
In the literature there are many approaches which have been proposed about VHO based on SIP under IMS [51][52][53][54].
In [51], the authors presented an internetworking approach to provide the continuity of service during and after VHO session while moving between Wi-Fi and UMTS scenario.The OPNET simulator was used considering VoIP traffic and result shown that latency was *150 ms [51].
In [52], the authors presented two WiMAX-3G interworking approaches: the loosely coupled WiMAX-cellular (LCWC) and the tightly coupled WiMAX-cellular (TCWC) based on loosely and tightly coupling interworking architectures, respectively, to investigate the effects of these interworking architectures on the SIP-based IMS registration and session setup procedures such that tight coupling required significant modifications of existing access network for providing seamless service to MU to move from one network to another which resulted in additional cost.Also they analyzed the effects of their WiMAX-3G interworking approach on the IMS signaling latency.Analytical modeling and ns-2 simulator were used considering VoIP, MPEG, FTP, and HTTP traffics.The results shown that the IMS registration latency for WiMAX in the TCWC architecture was lower than in the LCWC architecture, whereas The IMS registration latency for 3G was the same for both TCWC and LCWC, Also, the IMS session setup latency in the TCWC architecture was lower than latency in the LCWC architecture when the SN (source node) was in a 128 kbps 3G network and the correspondent node (CN) was in a 24 Mbps WiMAX [52].
In [53], analytical modeling was presented in order to evaluate the signalling cost of mobility management during VHO between WiMAX and UMTS scenario.The results shown that transmission signalling cost, the transmission processing cost and the queuing signalling cost increased linearly with the increasing value of IMS arrival rate.
In [54], the authors presented Wi-Fi and WiMAX scenario and three coupling architectures, such as tight coupling (TC), loose coupling (LC) and hybrid coupling (HC) to investigate VHO latency, mobile scanning interval activity and neighboring advertisement received.The OP-NET simulator shown that HC obtained less latency than LC and TC such that the latency at the 50th minute was *0.022 s [54].

MIP under IMS Category
In the literature there are many approaches which have been proposed about VHO based on MIP under IMS [55][56][57][58].
In [55], the authors presented a new cross-layer mobility management approach to provide smaller VHO latency and lower signaling overhead.Analytical modeling shown latency between MU and HA, MU and CN was *52-76 and 47-87 ms, respectively, while signalling cost between MU and HA, MU and CN was *2,000-8,750 and 2,500-7,500, respectively [55].
In [56], the authors presented new approach to investigate various performances, such as VHO latency, packet loss, jitter and signaling cost.Analytical modeling and OPNET simulator were used considering VoIP traffic.The simulator shown the average session setup and VHO latency between UMTS to WiMAX scenario was 190 and 210 ms, respectively, while packet loss was *0.34 when number of VHO was reached to 6, also it shown that the signaling cost exponentially reduced with increasing call-to-mobility ratio when the session arrival rate and service rate were constant, while jitter was exponentially increasing [56].
In [57], the authors presented an approach in order to provide seamless VHO between WiMAX and UMTS scenario with no packet loss and minimum latency taking into account the RSS parameter to make VHO decision.The OPNET simulator was used considering FTP and VoIP traffics and results shown that the average latency using FTP was *45.7 ms in UMTS and 28.8 ms in WiMAX, while the latency was *31.6 ms in UMTS and 19.8 ms in WiMAX using VoIP [57].However, no performance evolution provided regarding packet loss.
In [58], the authors presented an approach in order to provide seamless VHO with QoS support between Wi-MAX and UMTS scenario taking into account the RSS and QoS for video conference to make VHO decision, while no performance evolution provided regarding VHO.

MIH and IMS Combination Category
In the literature there are two approaches which have been proposed about VHO based on combination between MIH and IMS [59,60].
In [59], the authors presented an approach between Wi-Fi, WiMAX and UMTS scenarios in order to perform intelligent and accurate VHO with better latency and packet loss taking into account the RSS to make VHO decision.The authors divided the latency into two periods: handover latency between MU and advertisement router (MU-AR) and handover latency between MU and HA (MU-HA).The analytical modeling results taking into account video streaming shown that latency was *50-100 ms at MU-AR and 50 ms at MU-HA time, while packet loss was zero [59].
In [60], the author presented new approach to minimize handover latency and improving perceived video quality in terms of peak signal-to-noise ratio (PSNR).The PSNR or signal-to-noise ratio (SNR) parameters was considered to make VHO decision.Analytical modeling and testbed experiment between 3G and Wi-Fi indicated that VHO latency was reduced by 12 s compared to non-integrated MIH/IMS frameworks [60].

Comparison of the VHO Approaches
In Sect. 4 we have discussed eighteen VHO recent approaches found in the literature [2,25,35,[43][44][45][46][47][51][52][53][54][55][56][57][58][59][60] and classified them into four categories based on MIH and IMS frameworks in order to present their objectives and performances issues.To offer a systematic and exhaustive comparison in this survey, we present two types of comparison: comparison between the frameworks (MIH and IMS) and a comparison between the four categories based on these frameworks (MIH based category, IMS based category, MIP under IMS based category and MIH and IMS combination based category).
In order to provide comparison of the two frameworks, we summarize their specifications on fourteen aspects: producer, released, mobility management protocol, legacy RATs, security, implementation of the decision algorithm, wired and wireless multimedia service, available RATs provider, available RATs provider capability, upgrade, additional cost, components, battery consumptions (MU) and receivers (MU), this is shown in Table 2.
As shown in Sect.3.5, the IMS framework includes large number of components, it is based on SIP for mobility management, the MU obliges to discover neighbor cells with no assistance by periodically conducting a radio scanning in the background which results in: (a) Limited information is discovered, (b) the MU needs two receivers work concurrently one for scanning and another for ongoing session, while one receiver may be incurred probability of missing data from serving cell, (c) high MU power consumption, and (d) upgrades legacy cells (2G/3G) due to broadcast information about 4G neighbors cells, such as WiMAX and LTE which results in additional cost.
As shown in Sect.3.4, MIH presents less number of components compared with IMS, it is based on various mobility management protocols, such as MIPv4 and MIPv6 which are best standard for VHO and presents MIIS which is responsible for collecting all information required to identify if a handover is needed or not and provide them to MUs (e.g.available networks, locations, capabilities, cost.etc.)which results in: (a) large amount of information is provided, (b) one receiver for ongoing session, (c) low MU power consumption, and (d) no need to upgrade legacy cells (no additional cost); hence, the majority of approaches in the literature are based on MIH framework.However, security check is out of its scope.Whereas the commen area between them includes support wired and wireless multimedia service and legacy RATs, while implementation of the decision algorithm is out of their scope.
In order to provide comparison of the four categories, we summarize their features on eight aspects: objective, VHO decision criteria, applicable area, additional entity, cost, complexity, evaluation method and traffic, this is shown in Table 3.We observe that MIH is the only category which presents solutions include all existing networks: 3G (e.g.UMTS, HSPA) and 4G (e.g.WiMAX, LTE), also the approaches [2,25 and 45] present comprehensive solutions to ensure the VHO between three types of different RATs: Wi-Fi, WiMAX and 3G, followed by MIH and IMS combination category which deals with three types of different RATs in approach [59], whereas the rest of categories are content with two types of RATs, this is shown in Fig. 4.
As for the main objective, the MIH category's performance focuses on two vital parameters that make VHO seamless: latency and packet loss, followed by MIP under IMS category which also focuses on signaling cost, followed by MIH and IMS combination category and finally, the majority approaches of IMS category focus on latency, while packet loss is out of its scope, this is shown in Fig. 5.For VHO decision criteria, the MIH category presents approaches to make VHO decision based on the various network parameters as in [2,45], followed by MIH and IMS combination category and MIP under IMS category due to (PSNR, SNR, RSS), (QoS, RSS), respectively, whereas in IMS category the VHO decision criteria is not mentioned.
In terms of complexity, the MIH and IMS combination category is high complex due to the combination between the frameworks (MIH and IMS) which results in additional entities and cost, followed by MIP under IMS category due to the MIP components (HA and FA), followed by IMS with less complexity due to the large number of its components that require for VHO session, lastly, MIH category is simple compared to above categories due to less number of components which are able to play vital role for providing seamless VHO by selecting target RAT.
Finally, the evolution methods in the survey are various between real environment, testbed, simulation tools and analytical modeling.We observe that the MIH category is mostly in the practical and it is sole providing one empirical work real environment [2], followed by IMS Category, MIP under IMS and MIH and IMS combination category, this is shown in Fig. 6.

Conclusion
In this paper, we have overviewed two main interworking frameworks that have been proposed by IEEE Group and 3GPP for integration between the different types of technologies (3GPP and non-3GPP); namely, MIH and IMS, where each of them requires mobility management protocol to complement its work, such as MIP and SIP, respectively.Also, we have surveyed the VHO approaches proposed in the literature and classified them into four categories based on the above frameworks for which we have presented their objectives and performances issues.To offer a systematic and exhaustive comparison in this survey, we have presented two types of comparison: comparison between the frameworks (MIH and IMS) and comparison between the four categories (MIH based category, IMS based category, MIP under IMS based category and MIH and IMS combination based category).
The comparison between the frameworks has shown that MIH framework plays critical role in providing seamless VHO with less number of vital components which result in: (a) large amount of information is provided, (b) one receiver for ongoing session, (c) low MU power consumption), and (d) no need to upgrade legacy cells (no additional cost).However, the security for re-authentication at the target network and implementation of the decision algorithm are still required improving by designers.
The comparison between the four categories has shown that MIH is the only category which presents solutions include all existing networks 3G (e.g., UMTS, HSPA) and 4G (e.g.WiMAX, LTE), it presents comprehensive solutions to ensure VHO between three types of different RATs: Wi-Fi, WiMAX and 3G, it deals with multiple parameters to make VHO decision, it has been practically tested, it is simple compared to other categories and finally, there is one approach uses empirical work in real environment.

Table 1 Control
• High MU power consumption.•Upgradeslegacycells (2G/3G) due to broadcast information about 4G neighbors cells, such as WiMAX and LTE.4 Vertical Handover Approaches ClassificationsIn this section, we classify VHO approaches proposed in the literature into four categories based on MIH and IMS frameworks in order to present their objectives and Available of PoAs (GSM, UMTS, Wi-Fi, WiMAX..) RATs MUs Fig. 2 Media Independent Information Service (MIIS) passing information about RATs to Mobile Users (MUs) layer of an IP Multimedia Subsystem (IMS) Components Roles Breakout Gateway Control Function (BGCF) Select the network in which the connection to the PSTN will be made Home Subscriber Service (HSS) Database stores user authorization and profile information which is queried by SCSCF server for providing the service to the user The Radio Signal Strength (RSS), link layer throughput, link quality, loss rate and contention rate parameters were considered to make VHO decision.The implementation of their approach which was in real environment by Meditel Telecommunication operator in Morocco shown throughput (KBite/s) and latency (ms) considering streaming traffic for WiMAX, Wi-Fi and 3G were (62.24,60.48,55.99)and(20.1, 22.4,  46