Enhanced Vertical Handover in Mobile IPv6 with Media Independent ...

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Media Independent Handover (MIH) Services as defined in IEEE 802.21 and Advance Duplicate Address. Detection (A-DAD). By utilizing the Layer 2 triggers, ...
Enhanced Vertical Handover in Mobile IPv6 with Media Independent Handover Services and Advance Duplicate Address Detection Son Tran-Trong, Shahnaza Tursunova, and Young-Tak Kim Dept. of Information and Communication Engineering, Graduate School, Yeungnam University 214-1, Dae-Dong, Kyeong-San, Kyeongbuk, 712-749, KOREA

[email protected], [email protected], and [email protected]

Abstract Mobile IPv6 takes long time to perform Layer 2 and Layer 3 handover which seriously affects the Quality of Service (QoS), especially for real-time services. In this paper, we propose an enhanced handover mechanism across heterogeneous environment with multiple network interfaces in a Mobile Node with the Media Independent Handover (MIH) Services as defined in IEEE 802.21 and Advance Duplicate Address Detection (A-DAD). By utilizing the Layer 2 triggers, applying A-DAD, and reducing the number of Layer 3 message exchanges during the handover procedure we can reduce the handover latency in Mobile IPv6 greatly. We perform a simulation on handover between WiMAX and WLAN IEEE 802.11b with the proposed scheme in Mobile IPv6 to get handover performance in terms of handover latency. We analyze the handover performance according to the velocity of Mobile Node and the latency between Mobile Node and its Corresponding Node.

that has been widely accepted in the industry. To keep the ongoing communications of the MN, MIPv6 hides the network movement from the higher layer (transport layer). The long handover latency in MIPv6 degrades the QoS. Also, MIPv6 does not consider the multiple network interfaces for handover. Moreover, when MIPv6-enabled MN moves to a new network, it needs to configure a new address (Care-of Address, CoA) by using the information provided in the Router Advertisement (RtAdv) message. The typical address configuration requires Duplicate Address Detection (DAD) to check validity of the configured address. The DAD procedure easily takes up to 1 second, which is dominant in the handover latency [7]. In this paper, we optimize the handover in MIPv6 by using the MIH services and replacing the typical DAD by Advance DAD [7, 8, and 9]. The rest of this paper is organized as follows. In Section 2, we discuss about related work. In this Section, we emphasize the advantages which are used in our proposal and the disadvantages which are improved. In Section 3, we describe the main idea of the proposal, enhanced handover in MIPv6 with the support of MIH services and A-DAD. In Section 4, we present our performance analysis. Finally, in Section 5, we conclude this paper and figure out the future work.

1. Introduction Mobility management became an important issue since when the Mobile devices are become more and more popular. The trend in telecommunication market is to provide Mobile Nodes with multiple network interfaces, such as Ethernet, IEEE 802.11a/b/g WiFi, WiMAX, and UMTS. Along with the increasing population of advance Mobile Node (MN), there is a requirement for efficient mechanisms for seamless handover among heterogeneous networks. The mechanisms should guarantee the Quality of Service (QoS), i.e., no disruption in service which can be recognized by users. Currently, there are several standard mobility management protocols such as Mobile IPv4/6 (MIPv4/6) [1, 2], Hierarchical Mobile IP [3], Fast Handovers for Mobile IPv6 (FMIPv6) [4], and Proxy Mobile IPv6 (PMIPv6) [5]. Also, there are some schemes introduced which utilizing the Session Initiation Protocol (SIP) for support mobility. All the above proposals obviously focus on the network layer (IP) without the help of layer 2, which can provide much information to support mobility management at Layer 3 or above. Furthermore, they do not take the advantages of multiple network interfaces which are available in recent mobile devices. The IEEE 802.21, Media Independent Handover (MIH) provides generic link-layer intelligence and other networkrelated information to upper layers to optimize handover between different heterogeneous access networks like WiFi, WiMAX, and UMTS. MIPv6 is one of the mobility management solutions

2. Related work 2.1. xMIPv6: Overview and Problem Statement

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MIPv6 is developed to support global mobility management [1]. In MIPv6 every MN has two IP addresses: permanent (HoA) and temporary (CoA). When a MN enters to a foreign domain, it updates its location at the HA and at the CN. The MN will create a CoA using address prefix from received router advertisement message (RtSolPr or PrRtAdv), and then performs Duplicate Address Detection (DAD) procedure. Using this CoA, the MN registers with HA and CN through binding update (BU) messages. In MIPv6 layer 3 handover latency mainly consists of following three factors: i) movement detection latency – in average 1.5 sec., ii) address auto-configuration latency (consists of DAD) – typically takes 1 sec., and iii) binding update latency [11]. HMIPv6 [3] introduces a new entity called mobility anchor point (MAP), which replaces FA and helps to decrease the handover latency as a local MAP can be updated more quickly than remote HA [3]. The main components of handover latency are still movement detection and DAD procedure which belong to the Layer 3 handover. In FMIPv6 [4], decreasing of handover latency is achieved by delivering the packet to the new point of attachment, some of the layer 3 messages exchanging will be performed before the link layer handover. The MN gets network parameters and configures a new CoA before the handover (in the predictive mode) or just before the handover (in the reactive mode). Both of the MIPv6 extensions requires some changes in MN. PMIPv6 [5] is based on MIPv6 signaling and does not require the MN to be involved in the signaling phase required for mobility management. The Mobility Access Gateway (MAG) in the network performs the signaling and does the mobility management on behalf of the MN. The Local Mobility Anchor (LMA) is a modified MIPv6 HA, which maintains the address bindings for MNs in PMIPv6 domain.

Going Down”, and “Link Detected”. MICS refers to the commands sent from MIH Users to the lower layers in the reference model. The MICS commands are utilized to determine the status of the connected links and facilitate optimal handover policies. Moreover, they carry the decisions of upper layer on mobility and connectivity to the lower layer. The MICS commands also can be both local and remote. Some examples of MICS commands are MIH Poll, MIH Scan, and MIH Configure. MIIS provides framework and mechanism to discover available neighboring network information within a geographical area to facilitate network selection and handovers. The MIIS defines information elements (IE) and corresponding query-response mechanisms for the transfer of information. In order to represent information across different access technologies, the MIIS specifies a common way of representing this information by using a standard format. Both static and dynamic information can be provided by MIIS, and classified into three groups: general or access network specific information, PoA specific information, and vendor specific information. 2.3. Advance Duplicate Address Detection After detecting that it has moved a MN should generate a new primary care-of address using normal IPv6 mechanism [1]. As normal scenario, the MN sends a Router Solicitation (RtSol) message and waits for RtAdv. Whenever, it receives the RtAdv the MN will use the information included in the message to derive a tentative address. After that the MN must perform DAD procedure to verify the uniqueness of the tentative address. During the DAD procedure, the MN sends a neighbor solicitation message to ask whether its new address is being used. If there is no reply in a certain time, the MN can assume that the new address is valid in that network. The DAD procedure takes a long time, as much as 1 second [7], and it increases the handover latency. In our proposal we suggest to use a fast DAD for MIPv6. The candidate fast DAD is Advance DAD (ADAD) [7, 8, and 9]. A-DAD tries to reduce the typical DAD latency by keeping a list of duplicate-free addresses at an Access Router (AR). Each AR randomly generates an address and performs DAD. If the checking address is unique then the AR will store it in a cache called Passive Proxy Cache. AR acts as a passive proxy for addresses. It listens to neighbor discovery from other nodes in the network. If the AR hears another node performing DAD on the same address in it pool, it must silently remove that address in its cache and perform another DAD to keep the list of duplicate-free addresses constant. The A-DAD procedure is depicted in Figure 1. When the MN receives an L2 switching trigger, it sends RtSol message to all-router multicast address (FF02::2). The RtSol must be modified to include the NCoA-request option which indicates a request for a unique address. This option field contains the previous CoA and the MAC address of MN. Whenever the AR receives the RtSol with NCoA-request it will reply with the modified RtAdv

2.2. 802.21 Media Independent Handover Services IEEE 802.21 Media Independent Handover (MIH) [6] defines supporting functions to improve mobility between heterogeneous networks. MIH provides link layer intelligence and other related network information to upper layers. The Media Independent Handover Functions (MIHF) provides abstracted services to higher layers by means of a unified interface. This unified interface exposes service primitives that are independent of the access technology. The MIHF defines three main asynchronous and synchronous services: the Media Independent Event Services (MIES), the Media Independent Command Services (MICS), and the Media Independent Information Services (MIIS). MIES provides services to the upper layer by reporting event classification, event filtering, and event reporting corresponding to dynamic changes in link characteristics, link status, and link quality. It reports both local (from the local stack of the mobile node) and remote events (from another MIHF in the network). Some of the common events that have been specified by the standard are “Link Up”, “Link Down”, “Link Parameters Report”, “Link

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message. The modified RtAdv message includes the NCoA-reply option. This option contains the duplicate-free address from the AR’s cache. After sending the RtAdv message, the AR must remove the assigned address, perform another DAD on a random address, and store the assigned address together with the MN’s MAC address in its neighbor cache. On reception of RtAdv message, the MN can perform BU to Home Agent and Corresponding Node (CN) without any delay.

Response Option, the MN configures the NCoA for the Interface 2 but it does not send BU to both HA and CN. MN needs to keep the ongoing communications through Interface 1 until there is an L2 event reporting from this interface indicating the decreased QoS (i.e., Link Going Down, Link Parameters Report events). Whenever the MIH User/MIPv6 receives such events it will immediately send BU to the CNs. To reduce the handover latency, it’s better to send BU to CN first, and whenever MN successfully receives packets on the Interface 2, it sends BU to HA. The all interactions are described in Figure 2.

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Figure 1. Advance DAD signaling in Mobile IPv6

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Using the A-DAD, we can reduce the time spending on IPv6 address configuration and DAD. As the performance analysis in [7], A-DAD for MIPv6 only takes less than 10ms. For this reason, we suggest to use A-DAD during the handover in MIPv6.

MIH_Link_Down.indication

Figure 2. Enhanced handover in MIPv6 By utilization of MIH services, our proposal prepares another network interface for handover before the current interface is going down. Also, with the support of A-DAD, the DAD time is reduced significantly; therefore, whenever there is a request for handover, which is indicated by MIH_Link_Going_Down.indication event in Figure 2, the MIH User/MIPv6 only needs to send the BU and waits for Binding Acknowledgement (BA) message. When MN receives BA message, it starts delivering data through new interface. The time for sending BU and receiving BA is often small then the MN can successfully switch to new interface before the previous interface is actually down. As the results, we can reduce both handover latency and packet loss.

3. Enhanced Vertical Handover in Mobile IPv6 with MIH Services and A-DAD for Multiple Network Interfaces Mobile Nodes 3.1. Enhanced Vertical Handover Procedure with MIH and A-DAD In this proposal, we take the advantages of multiple network interfaces Mobile device and we mainly focus on the enhancement of vertical handover across different access network technologies. Assume that the MN is currently connected to certain access network using one of its network interfaces (Interface 1). Other interfaces listen to the other access networks. By deploying the MIH User/MIPv6 and the MIHF into the MN, whenever it moves into the coverage area of another access network, the corresponding interface (Interface 2) in the MN will generate and report a trigger (Link Detect event) to the MIHF and then to the MIH User/MIPv6. After that the MN establishes the L2 connection on that link interface. Note that the MN is still communicating with CN through Interface 1. The above events are used for preparation of handover which probably occurs. From now we can prepare for L3 handover. The MIH User/MIPv6 performs the RtSol with the NCoA-request option as described in Section 2 through Interface 2 to request for a New CoA (NCoA) on the new access network. On receiving the RtAdv with NCoA-

3.2. Handover Latency of Proposed Scheme Figure 3 shows the standard MIPv6 handover procedure in terms of taken time. The L2 handover time depends on the actual network interface and access point, base station types. For the case of IEEE 802.11 network, the L2 latency varies from about 100ms to 400ms [10]. The L3 handover even takes more time. L3 handover latency mainly depends on the DAD time and the distances between the MN and CN, HA, and it easily takes up to several seconds [11]. Such long handover latency seriously affects the QoS, especially for real-time services. In Figure 4, we explain the handover latency of our proposal regarding to the L2 and L3 messages needed to be exchanged. By taking the advantages of multiple network interfaces, in our proposal, the MN always prepares a new

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detects new network, WiMAX in this case, it configures the new interface (WiMAX interface), but still uses the previous interface for communications. The MN only performs handover when it receives the Link Going Down event, which indicates that the loss of connection will occur soon, from previous link layer. The duration between MIH_Link_Detection.indication and MIH_Link_Up.indication messages arriving at MIH User/MIPv6 is about 16ms. The time for sending RtSol and receiving RtAdv is only about 12ms. But in current implementation MIPv6 and MIH, there is no support for the A-DAD, therefore we need to count the time for ADAD to the handover latency in our experiment, assume that it is 10ms [7]. So the handover preparation latency in our proposal is about 40ms. The actual handover latency as shown in Figure 4 is about 96ms.

interface whenever it detects a new network. Also, we suggest using the A-DAD to reduce the handover preparation time. Movement detection (RtSol/RtAdv message exchange) Channel Scanning

Authentication

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L2 Handover L3 Handover

Figure 3. Handover latency in Mobile IPv6 The actual handover in our proposal only takes place if the MIH User/MIPv6 in the MN receives the event from current interface indicating the degradation of QoS on this interface. Such events can be Link Going Down or Link Parameters Report. On receiving such events, the Local MIH User/MIPv6 decides to handover, and the actual handover latency in our proposal is only from MIH_Link_Going_Down.indication until BA message reaching the MIH User/MIPv6, as depicted in Figure 4. Also, in our proposal, we just need to use few MIH services; therefore it can be easily deployed.

Old L2 New L2

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Figure 5. The effect of overlap area on handover performance

Link_Detected. MIH_Link_Up. indication indication

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In our proposal, the handover performance is affected by the MN’s velocity. If the MN moves very fast then even though it receives the handover decision, for example indicated by Link_Going_Down.indication, it cannot complete the sending BU and receiving BA before the previous link interface is down. Therefore, the length of overlap between two cells is important and affects to the performance. We illustrate the problem of overlap area in Figure 5.

RtSol with NCoA-request Opt.

RtAdv with NCoA-response Opt. Link_Going_Down. MIH_Link_Going_Down. indication indication Handover latency

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Figure 4. Enhanced handover latency in Mobile IPv6

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4. Performance evaluation

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We make the simulation on ns-2 based on the MIH and MIPv6 implementations from NIST [12]. We simulate the handover scenario from IEEE 802.11b WLAN to WiMAX network. The MN is equipped with two interfaces (IEEE 802.11b WLAN and WiMAX). The WiMAX and WLAN cell radius are 1000m and 50m, respectively. The WiMAX and WLAN Point of Attachments (PoA) are connected to the core network through 100 Mbps connection. The CN is connected to the core network through 100 Mbps and 30ms latency connection. In this simulation, we assume that the MN currently communicates with CN through WLAN interface. When it

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Figure 6. The overlap area against MN’s velocity As depicted in Figure 5, the overlap in length is D. In our scenario the MN performs handover preparation and makes actual handover in the overlap area. Therefore, to avoid the previous link interface from down, the whole procedures need to be completed while MN is moving in the overlap area, then: (1) THO + THO _ P ≤ t

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And then:

THO _ P

: the handover preparation latency

handover performance. Our proposal takes effect on the MN’s power consumption and it is our future work. Currently, we are deploying the PMIPv6 in ns-2 for investigating the optimization handover in PMIPv6 by using MIH services.

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: the actual handover latency

6. References

D ≥ v × (THO + THO _ P )

(2)

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: the MN’s velocity [1] D. Johnson, C. Perkins and J. Arkko, Mobility Support in IPv6, RFC 3775, June 2004. [2] Perkins, C., Ed., IP Mobility Support for IPv4, RFC 3344, August 2002. [3] H.S. Flarion, C.Castellucia, K. El-Malki, and L. Bellver, Hierarchical Mobile IPv6 mobility management (HMIPv6), IETF RFC 4140, August 2005. [4] R. Koodly, Fast Handovers for Mobile IPv6 (FMIPv6), IETF RFC 4068, July 2005. [5] S. Gundavellu, K. Leung, V. Devarapalli, K. Chowdhury, and B. Patil, Proxy Mobile IPv6, IETF draft-ietf-netlmm-proxymip6-11.txt, February 2008. [6] IEEE 802.21 WG, Draft Standard for Local and Metropolitan Area Networks: Media Independent Handover Services, IEEE P802.21/D9.0, February 2008. [7] Panita Pongpaibool, Pahol Sotthivirat, Sukumal I. Kitisin, Chavalit Srisathapornphat, Fast Duplicate Address Detection for Mobile IPv6, ICON 2007, 15th IEEE International Conference on Networks, Nov. 2007. [8] Y. Han, J. Choi and H. Jang, Advance Duplicate Address Detection, Internet Draft, Dec 2003, expired. [9] Y.-H.Han, S.-H. Hwang, Care of address provisioning for efficient IPv6 mobility support, Computer Communications 29 (2006), pp. 1422-1432. [10] Arunesh Mishra, Minho Shin, Willicam Arbaugh, An Empirical Analysis of the IEEE 802.11 MAC layer Handoff Process, ACM SIFCOMM Computer Communication Review, 2003; 33(2): 93 ~ 102. [11] Gaogang Xie, Ji Chen, Hongxia Zheng, Jianhua Yang, Yu Zhang, Handover Latency of MIPv6 Implementation in Linux, IEEE GLOBECOM 2007. [12] http://w3.antd.nist.gov/seamlessandsecure/doc.html [13] Quazi Bouland Mussabbir, Wenbing Yao, Zeyun Niu, and Xiaoming Fu, Optimized FMIPv6 Using IEEE 802.21 MIH Services in Vehicular Networks, IEEE Transactions on Vehicular Technology, Vol. 56, No. 6, Nov. 2007. [14] Yoon Young An, Byung Ho Yae, Kang Won Lee, You Ze Cho, and Woo Young Jung, Reduction of Handover Latency Using MIH Services in MIPv6, Proceeding of the 20th International Conference on Advanced Information Networking and Applications (AINA’06).

For example, in our simulation the MN’s speed is 36 km/h, the total time need for handover preparation and actual handover is 136ms, and then the overlap area D has to be greater than 1.36m to guarantee the handover success without any disruption in service. In Figure 6, we show the relation between the overlap area in length with the MN’s velocity in the case the latency between CN and MN is 30ms. The handover preparation time is not affected by the latency between MN and CN, because all messages exchanged in this phase are inside the access networks. While the actual handover latency is affect by the latency for sending BU and receiving BA. Figure 7 shows the handover latency against the latency between MN and CN. 500 450

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Figure 7. The handover latency against latency between MN and CN

5. Conclusion and future work In this paper, we proposed an enhanced handover scheme in MIPv6 by utilizing the MIH services and ADAD. In our scheme, we always prepare the new link connection on available network interface whenever the MN detects a new network. This approach can reduce the handover latency as well as can prevent the service from disruption. For improving handover performance, we suggest using a fast Duplicate Address Detection for IP address configuration, and in our scheme, we use A-DAD for this purpose. We analyzed the performance by simulating the proposed scheme in ns-2 to get the handover performance results in terms of latency. Also, we analyzed the effects of MN’s velocity and latency between MN and CN on the

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