Mobility Management

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Inter-technology Handover between IP-base Networks: Review


This article is a comparative representation for different strategies for inter-technology handover. The aim of this investigation was to observe the critical issues for inter-technology handover and identify the probable way outs for those issues. This review article abrogates by identifying the speciality and limitations of the related literature and suggests some possible future works.


Intersystem Handover, Vertical Handover, Review, Inter-technology Handover, Mobility Management

I. Introduction

II. Inter-technology handover

Inter-technology has mainly three phases: network discovery, handover decision and handover implementation [1].

A. Handover Decision Algorithms

Intra-technology handover decision is traditionally based on Received Signal Strength (RSS), Signal to Noise Ration (SNR), channel state quality, Bit Error Rate (BER) and others [2]. However, the decision making for handing over to a different access technology is far more complex. Because the access technologies differ in terms of spectrums, bandwidth, media access technologies, security mechanisms, performance, data rate and so on. Hence, only the traditional parameters are not sufficient to perform the decision making for inter-technology handover. There might be some additional parameters to make more efficient decision. However, [3] proposes a detection process of signal strength based on Fast-Fourier-Transform (FFT). The potential advantage shown for this approach was the reduction of unnecessary handover. The algorithm presented in [4] makes the decision of handover based on the presence or absence of the beacon signal. While [5] and [6] considered RSS, data rate and throughput for decision making. A cost function depending on latency, power requirement and bandwidth was the scale for handover decision strategy proposed in [7]. All these algorithms from [3] to [7] used the traditions channel quality parameters. However, [8] represents a decision mechanism naming Distributed Vertical Handoff Decision (DVHD) where the authors considered about call dropping probability, cost and availability of bandwidth as the decision making factors. The simulated results show some potential advantages in terms of handover blocking rate, processing delay and throughput. Additionally, a smart handover decision mechanism was developed in [9], where it was proposed to make the decision in two stages. The first stage was the priority stage where a network was to be selected from a set of available networks. While the second stage dealt with a function based selection criteria and the function used link capacity, cost and power consumption as the input factor. [10] proposed a handover algorithm based on Fuzzy logic. Along with the traditional parameters, it used several additional parameters like availability of bandwidth, user preference, cost, service type, capabilities of the mobile node, network access delay and system performance. The authors urge on the potential advantages of the proposed MUSE-VDA approach for optimizing the benefits for both user and network sides. Furthermore, [11] defined a cost function based on a number of parameters like mobile device velocity, available bandwidth, cost of service, power consumption, security and network performance to take the decision of handover between WiMAX and UMTS networks. The work presented in [12] compared the performance between four different mechanisms of handover decision naming MEW (Multiplicative Exponent Weighting), SAW (Simple Additive Weighting), TOPSIS (Technique for Order Preference by Similarity to Ideal Solution), and GRA (Grey Relational Analysis) proposed in [13] and [14]. All these four approaches were based on Fuzzy logic and the input factors used for the decision metric are bandwidth, delay, packet loss rate and cost. Similarly, the algorithms represented in [15] to [20] are also based on Fuzzy logic. All these works used the similar input factors.

B. Handover Algorithms

Recently many researches have been done so far for handover between WLAN and GPRS/UMTS. Most of these works are based on tight or loose coupling. Tight coupling refers to a system where the elementary subsystems are linked together to form a whole system and as a whole they share a single work load. In the standard tight coupling method used in [21], the UMTS and WLAN networks are connected to each other through SGSN via the traditional Iu-ps interface. The networks in this approach become dependent on each other. This can be considered as a major drawback of that system. An improved tight coupling approach was proposed for interworking between UMTS and WLAN in [22]. An additional wireless link naming Direct Air Interface (DAI) was introduced between UMTS base station and WLAN router. The DAI link was based on [23] and both the networks were assumed to be supporting of IPv6. The approach includes both L2 and L3 mobility and the simulated results serve as a proof of the potential benefits of this approach over traditional tight coupling method.

Loose coupling combines several subsystems through a third party. Its interworking mechanism is very simple. The subsystems depend on each other to the least degree of possible. A loose coupling architecture between GPRS and WLAN proposed in [24] resulted in high latency for handover. Additionally, the hard handover approach caused the in-transit packets to be dropped. The authors proposed these packets to be retransmitted after the establishment of new link. The loose coupling method used in [25], the networks are independent to each other and the data flow directly via the IP network. However, the performance of handover in loose coupling is very poor and the stumbling block for this kind of approach is the high latency.

In [26], the specifications related to usage of Mobile IP in GSM network was proposed and the IETF introduced the IP mobility management for IPv4 in [27]. In (Thinh Q et al., 2006) a Mobile IP method is used to interwork between WiMAX and UMTS where a mobile device with single interface is used and the handover is not seamless. As with single interface it is not possible to communicate with the two networks at the same time and so it obviously is a break-before-make type of handover which will force the on-going session to be dropped. However, (Choi and Cho, 2003) represents the potential advantages of Mobile IP in a mixed IPv4 and IPv6 network environment. Furthermore, (Min-hua et al., 2003) describes the conceivable advantages of using Mobile IP to maintain IP mobility in the hybrid network environment. (Chang, 2005) introduces the Mobile IP WMAN. (Santhi and Kumaran, 2006) introduces with the opportunity towards the migration of 4G by interworking 3G and fixed or wireless networks. However, the Mobile IP method is not good for the user moving at high speed. In this method the user must notify its change of CoA to the Home Agent (HA) that instigates to a high latency, especially when the HA is at a far distance from the visited network. The triangular routing also increases the total latency of handover (Sanguankotchakorn and Jaiton 2008). The in-transit packets during the binding-update may also be lost causing a high packet loss.

IMS was introduced in (3GPP TS 23.228, 2005) to control the IP multimedia services in the application layer and it uses the SIP as the base protocol. 3GPP IMS can support negotiation and management for real-time sessions in the heterogeneous networks environment (Marquez et al., 2005). This can be considered as a positive way out for session mobility management (Vingarzan and Weik, 2007). A 3GPP IMS based handover was proposed in (Fangmin et al., 2007). But the service continuity was not focused there. In IMS the user sends a “Re-Invite” message to the CN when the decision of handover is made from one network to another which causes the IP address of the user to be changed and this forces the on-going session to be dropped. In addition, the frameworks based on IMS presented in (Renier et al., 2007), (Gourraud, 2007) and (O'Connell, 2007) lack in considering issues related to mobility management. Furthermore, the work presented in (Wei et al., 2005) also applies the IMS where it describes how the SIP protocol handles session management for between UMTS and WLAN. But again the issue of mobility management was not addressed. Similarly, IMS was applied only for session mobility management focusing on aspects related to QoS and AAA in (Fangmin X et al., 2007). This framework also was not capable of providing seamless inter-technology handover.

(Faccin et al., 2002) first introduced Mobile IP and SIP based mobility within 3G networks. In addition, (Jung et al., 2003) suggested a two layered mobility management framework by developing a hybrid version of Mobile IP and IMS. Furthermore, (Zeadally et al., 2004) and (Wang and Abu-Rgheff, 2004) putted forward the same idea to manage session negotiation and IP mobility together. At a later stage, (Munasinghe and Jamalipour, 2007a) and (Munasinghe and Jamalipour, 2007b) used the same idea of applying IMS along with Mobile IP to handover between WLAN and UMTS/CDMA2000. In (Munasinghe and Jamalipour, 2008) this combined method was used for the handover between WiMAX and UMTS. But a major stumbling block of these three works is that the handover procedure starts after the link layer registration completed in each individual networks which is only possible in the overlapping areas. And of course the mobile device must have multiple interfaces to communicate with the different networks at the same time. In the non-overlapping areas the procedure of handover must start from the link layer registration which will cause a latency of few seconds and this is not expected. For example, in a non-overlapping area to handover from WiMAX to GPRS, the procedure should start from RRC connection, GPRS Attach, PDP Activation and finally the MIP-SIP service registration used in (Munasinghe and Jamalipour, 2007b). But the delay will be high enough to exit the limits for all types of QoS.

III. discussion

When the intersystem handover is the matter to be concerned, there are so many critical issues related to it. However, the most critical elements to be resolved for intersystem handover can be stated as: a) Continuity of an on-going session which is an application layer issue and b) Preventing the change of IP for a roaming user which is a network layer issue

Henceforth, Mobile IP and IMS can be considered as the two potential candidates for interworking between different access technologies.

However, the approaches of using Mobile IP and IMS resulted in more efficient outcome than the previous works.

IV. Conclusions


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