A Fast Handover System Evaluation in an All-IPv6 Mobility Management - Wireless Broadband Access based Hotspot Network Environment

Transcription

1 A Fast Handover System Evaluation in an All-IPv6 Mobility Management - Wireless Broadband Access based Hotspot Network Environment Norbert JORDAN Institute of Broadband Communications Vienna University of Technology A-14 Vienna, Austria norbert.jordan@ieee.org Peter REICHL Telecommunications Research Center Vienna ftw A-122 Vienna, Austria reichl@ftw.at Abstract The ongoing convergence of wireless networking and IP networking more and more requires solutions for transporting realtime application data to IP enabled mobile devices and mobile networks. Even though the basic Mobile IPv6 protocol suite performs sufficient in macro environments with non realtime traffic, seamless mobility requires some more enhanced protocol procedures in between the mobile node and the involved network entities.limiting the effect of handovers has the potential to considerably improve handover performance in terms of latency, packet loss, signaling overhead, and scalability. This contribution is going to present an extensive simulation study on the performance of the Fast Handovers for Mobile IPv6 approach. The demonstrated simulation scenario comprises 9 access router and up to 7 Mobile Nodes that communicate in accordance with the popular IEEE wireless LAN standard. 1. Introduction Today s second generation s packet service GPRS and the emerging 3G mobile cellular networks are only some of the technologies moving towards a mobile IP future. We consider 3G alone not to be enough for a ubiquitous multimedia-capable IP infrastructure. Wireless access technologies like IEEE WLAN, WiMAX (IEEE 82.16), and the upcoming Digital Video Broadcasting for Handhe (DVB-H) standard will also change the mobile user behavior of today. Moreover, the next generation of mobile networks, 4G, is not likely to be single standardized air interface and networking infrastructure like 3G. Instead, the future 4G network may constitute the integration of heterogeneous networks [1], including a large number of different access technologies. So, in the future mobile Internet, the mobile equipment will be considerably more diverse than nowadays, and the users will have a greater choice of access technologies. However, looking at technologies like Ethernet, ADSL, GPRS, UMTS, IEEE 82.11, WiMAX, or Bluetooth, this is not so far from what is possible today. These technologies offer different quality of service characteristics in terms of range (e.g., global or local coverage), bandwidth, delay, and error rate. Furthermore, the wide deployment of wireless technologies and the integration of various radio access interfaces into a single terminal, allows mobile end-users to be permanently connected to the IP network. But, regardless of whatever future 4G networks may look like, it is foreseeable that heterogeneous IP networking [2] will be a strong driver in future research and commercial deployment. Moreover, it looks as if the one common factor is that 4G networking requires to provide All-IP architectures and connectivity to anywhere and at anytime. Fig. 1. All-IP Network Architecture Concept. In order to support mobile users, the basic Internet protocols have been extended with mobility protocols for intercepting and forwarding packets to a mobile

2 and possibly roaming node. Mobile IPv6 [3] is expected to become the standard mechanism for mobility in any IPv6-based Internet. It is often termed as a macro-mobility approach since it will be global, and independent of mechanisms (such as routing protocols, link-layer technologies, and security architectures) in different administrative IP-domains. However, this generality has its prize in that the standard Mobile IPv6 protocol is not optimized to take advantage of specific link-layer mechanisms that may be deployed in different administrative domains. Hence, the standard MIPv6 handover procedure often leads to an increase of the signaling load, the handover latency, and the packet loss. One of the MIPv6 enhancement protocols, Fast Handovers for Mobile IPv6 or sometimes referred to as Fast Mobile IPv6 (FMIPv6) [4], has its focus on the minimization of delays during the handover. However, in general little is known about the performance of different MIPv6 approaches in an actual network. This paper presents a simulative performance comparison of FMIPv6 with unmodified standard MIPv6 in a wireless broadband environment. We investigate the impact of various parameters on the overall performance as experienced by a single Mobile Node (MN) in a wireless IPv6 access network. The scenario chosen for this study comprises 9 access router and up to 7 MNs that communicate in accordance with the IEEE wireless LAN standard. The rest of the paper is organized as follows. Section 2 describes the Fast Handovers for Mobile IPv6 approach. In Section 3 we discuss the simulation environment and Section 4 presents the simulation setup. Performance evaluation results are provided and discussed in Section Fast Handovers for Mobile IPv6 Fast Handovers for Mobile IPv6 [4] or sometimes referred to as Fast Mobile IPv6 has its focus on the minimization of delays during the handover. Standard Mobile IPv6 suffers considerable delays during the handover from one Access Router (AR) to another. This includes movement detection at IP-layer, IPv6 address configuration, and Binding Updates to all peer entities. All these processes and the signaling related to the handover to another subnet shou be kept away from the critical handover-time. In order to achieve this goal, FMIPv6 allows the MN to anticipate its movement and ideally to discover the new router and its prefix, before being disconnected from the current AR. The Fast Mobile IPv6 protocol enables a MN to quickly detect at the IP layer that it has moved to a new subnet by receiving link-related information from the link-layer [5] and furthermore it gathers anticipative information about the new Access Point (AP) and the associated subnet prefix when the MN is still connected to the previous subnet (see Figure 2). Figure 2. Reference Scenario for Fast Handovers. A new message proposed in [4], the Router Solicitation for Proxy Advertisement (RtSolPr) message, is utilized by the MN and sent to its current AR to request this information about likely candidate APs. The response by the present AR is called a Proxy Router Advertisement (PrRtAdv) messages, containing the neighboring router s advertisement (including its prefix). As the MN receives this information, it can immediately formulate a prospective New CoA (NCoA) for the New AR (NAR), while still present on the Previous AR s (PAR) link. This prefix discovery and IPv6 address generation in an early stage will help to eliminate associated latency normally suffered when the MN arrives in the new subnet. The FMIPv6 message flow for a scenario in which the Mobile Node sends a Fast Bindung Update (FBU) message and also has enough time to receive the Fast Binding Acknowledgment (FBAck) message on the PAR s link is illustrated in Figure 3. This full sequence of messages exchanged during Fast Handover is often characterized as the predictive mode of operation. disconnect connect MN RtSolPr PrRtAdv FBU FNA FBack PAR Figure 3. Predictive Fast Handover. forward packets HI HAck FBack packet delivery NAR

3 The message flow for a general scenario in which the MN sends FBU from the NAR s link is termed as the reactive mode of operation. The reactive mode also includes the case when FBU has been sent from the PAR s link but the FBAck has not been received timely at the previous link (see Figure 4). disconnect connect MN RtSolPr PrRtAdv FNA [FBU] Figure 4. Reactive Fast Handover. PAR forward packets FBU FBack packet delivery In IEEE networks the MN may initiate the handover by link-layer triggering [6, 7], which is aware that a handover is imminent. Even though IEEE WLAN networking is mobile-initiated, there are also wireless technologies where the handovercontrol resides in the fixed network-infrastructure. NAR After waiting a certain interruption time, it selects a new destination and speed, and moves with this constant speed to the new destination. The movement of a node from a starting position to its next destination is referred to as one movement period or transition. The destination points are uniformly random distributed over the complete system area. A more detailed discussion of the random waypoint mobility model and its stochastic properties is presented in [1]. 4. Simulation Setup The studied scenario was designed in a way to provide realistic and also significant results as well as being manageable via large scale simulations. Figure 5 illustrates the chosen scenario. It comprises a single Home Agent (HA) and multiple Correspondent Nodes (CN) which are connected to a Central Router (CR). The link delay () between the CR and the CNs and between the CR and the single HA can be modified for comprehensive performance evaluation. CN 1 CN 2 CN n HA 3. Simulation Environment CR Due to the complexity of the performed studies, a simulation seems to be the most suitable analysis method. The simulation code used for the experiments is based on the INRIA/Motorola MIPv6 [8] extension for the ns-2 (ns-2.1.b6) [9] implementation. Further code extensions have been developed by NEC Europe Ltd. Network Laboratories. Some modifications have also been performed in order to extend the code to work with more than one simultaneous MN and to realize the FMIPv6 approach. Worth mentioning is the fact that the movement pattern of mobile users plays an important role in the performance analysis of wireless communication networks. In cellular networks, for example, a user s mobility behavior directly affects the signaling traffic necessary for handover management. If the model is unrealistic, invalid or doubtable conclusions may be the result. A very popular mobility model is the Random Waypoint (RWP) [1] model which has been applied for this simulative study. This mobility model is a simple and straightforward stochastic model that describes the movement behavior of a mobile network node in a specified system area as follows. A node randomly chooses a destination point (waypoint) within the system area and moves with constant speed. MAP MAP AR 1 AR 2 AR 3 AR 4 AR 5 AR 6 AR 7 AR 8 AR 9 MN Figure 5. Simulation Scenario for MIPv6 Comparison. The nine AR in Figure 6 represent different IPv6 subnets and are connected via intermediate routers to the CR. Figure 6. Access Router Positioning and Radio Ranges. MAP

4 Figure 6 also demonstrates the exact position of the ARs, the transmission range of 15 meter, and the overall coverage area of approximately 636 x 636 square meter. At the starting point of the simulation, all MNs are uniformly distributed within the rectangular system area. The performance studies are conducted by observation of a single MN that moves deterministically while all other MNs move randomly all the time providing realistic interference with respect to the observed MN. As the wireless access technology an IEEE [11,12] link is applied in each AR which operates according to the Distributed Coordination Function (DCF) mode. All wired links within the micro-mobility domain provide up to 1 Mbit/s maximum throughput with a 2 ms delay. The connection between the CR and the HA or CNs is also modelled as a 1 Mbit/s link with a default link delay () of 1 ms. 5. Performance Evaluation This section presents the performance evaluation of the basis Mobile IPv6 protocol in comparison with the Fast Signaling approach. The parameters are studied from the point of view of a single MN that follows a deterministic path while all other MNs in the system area follow the RWP mobility model. By default all the simulations have been performed for a maximum speed of 5 m/s and a UDP probing traffic is selected between the CN and the observed MN of 25 bytes transmitted at an interval of 1 ms. All other MNs generate background traffic in that a UDP stream of 25 kbit/s is sent or received. As will be demonstrated, this traffic is chosen in order to saturate the wireless channel not until a high number of MNs share the medium. Furthermore, it shou be notices that all simulations have a duration of 245 s including a 5 s warm-up period. A sample size of up to 1 has been chosen for each point in the following graphs in order to achieve a confidence interval of 99 %. Due to the fact that all work presented in this performance evaluation is optimized in relation to handovers with low disruption time, an Optimistic Duplicate Address Detection (odad) [13] scheme is applied. The observed MN exactly performs 8 handovers during a simulation run moving at 5 m/s from center to center of the ARs coverage area until it reaches the initial point again. An increase of the handover latency and the packet loss is expected as the number of MNs sharing the wireless channel is increased. The presented comparison studies are focused on the quantitative evaluation of the improvements that mobile users wou experience in a system using the FMIPv6 approach. The parameters to be studied are listed below: Bandwidth per Station - The probability to obtain the required bandwidth is studied in dependence on an increasing number of competing stations. Handover Latency - The handover latency for a MN is defined as the time that elapses between the last packet received via the o AR and the arrival of the first packet via the new AR after a handover is finished. This is an important parameter for delay-sensitive applications like VoIP or video streaming. Packet Loss - The packet loss can be defined as the number of packets lost during the handover procedure. While it may be assumed that packet losses are directly proportional to the latency, the study will show that this is not valid in general. Signaling Load - The signaling load for MIPv6 is defined as the number of BUs and BAcks received during the simulation. In addition, for the case of FMIPv6 deployment the BUs, BAcks, PrRtAdv, PrRtSol, F-NA, F-BU, F-BAck, HI and HAck messages have to be taken into account. Figure 7 represents interesting results in association with the obtained bandwidth for the tracked MN. The observed MN obtains more bandwidth in comparison to standard Mobile IPv6. Furthermore, this figure depicts the saturation of the wireless IEEE channels for both schemes, starting at about 3 concurrent mobile user. As will be observable later, these results correlate to the succeeding graphs. Bandwidth [kbit/s] FMIPv Number of Stations Figure 7. Obtained Bandwidth for the Observed Mobile Node Depending on the Number of Stations.

5 The partially better behavior for standard MIPv6 is a consequence of the higher wireless load of the Fast Handover approach. A higher number of signaling messages sent via the wireless medium yies to a higher channel access delay and higher collision rate, resulting in a lower bandwidth achieved. Figure 8 and Figure 9 illustrate the increase in the handover latency and the packet loss due to an increase in the number of MNs sharing the wireless channel. The gained results for up to 3 MNs point out that the dominating factor of the handover latency is the wired link delay for a small number of MNs. As can be seen, the Fast MIPv6 approach performs better in terms of the handover latency and the packet loss. Handoff Latency [s] FMIPv6 saturation arises. Under high load conditions, the additional signaling messages of fast handover schemes in the local domain result in reaching earlier the saturation level on the wireless channel. The following signaling load study considers a fix scenario of 2 MNs, as this represents a case with many MNs while the wireless channel is still not in saturation (see Figure 7). As now can be observed in Figure 1, the FMIPv6 scheme requires a higher signaling load within the local domain, since it introduces the FMIPv6 signaling load. However, baseline MIPv6 and FMIPv6 introduce the same signaling load outside the local domain since all the additional FMIPv6 messages are only sent within the local domain. Signaling Load [bit/s] FMIPv6 outside Local Domain FMIPv6 within Local Domain Number of Stations Figure 8. Impact of the Number of Simultaneous Stations on the Handover Latency. Packet Loss FMIPv Number of Stations Figure 9. Impact of the Number of Simultaneous Stations on the Packet Loss. Although the fast handover protocol is designed to minimize the packet loss and the latency during a handover, a worse performance is observed with respect to standard MIPv6 protocol when the channel Number of Handoffs/min Figure 1. Impact of the Handover Rate on the Signaling Load. Finally, it shou be noticed that even if a complete set of performance metrics has been recorded for all simulation cycles, only the most relevant results are presented in this initial evaluation. Containing all results wou go beyond the scope of this work. 6. Conclusions and Future Work This paper has been addressed to an initial simulative performance evaluation of standard Mobile IPv6 in comparison to the Fast Handovers for MIPv6 approach, using the network simulator ns-2 for the case of a wireless broadband access hot spot deployment scenario. The simulation study has considered the effects of the number of concurrent mobile stations on parameters such as the handover latency, packet loss rate, the obtained bandwidth, and dependence on variation of the wired link delay. The behavior of the MIPv6 protocols for a general case considering random movement and realistic traffic

6 sources has also been taken into account. As demonstrated, all these factors may have a significant influence on the performance metrics. In a next step we will compare various real-wor traffic sources such as TCP, VoIP, and video streaming. Also, we eagerly work on bringing more different wireless access technologies inside of the simulation environment (e.g., 3G, WiMAX) in order to be able to evaluate also vertical handover scenarios. 7. Acknowledgement Part of this work has been performed within the project CAMPARI - Configuration, Architecture, Migration, Performance Analysis and Requirements of IMS at the Telecommunications Research Center Vienna (ftw.) and has been funded in the framework of the Austrian Kplus Competence Center Programme. 8. References [1] J.-Z. Sun, J. Sauvola, and D. Howie. Features in future: 4G visions from a technical perspective. In The Proceedings of the Global Telecommunications Conference (GLOBECOM 21), San Antonio, USA, pages , November 21. [2] N. Jordan, A. Poropatich, and J. Fabini. Mobility Adaptation Layer Framework for Heterogeneous Wireless Networks based on Mobile IPv6. In The 4th IEEE International Conference on Networking 25 (ICN 5), Reunion Island, pages , April 25. [3] D. Johnson, C. Perkins, and J. Arkko. Mobility Support in IPv6. RFC 3775, IETF Network Working Group, June 24. [4] R. Koodli. Fast Handovers for Mobile IPv6. RFC 468, IETF Network Working Group, July 25. [5] A. Yegin, E. Njedjou, S. Veerepalli, N. Montavont, and T. Noel. Link-layer Triggers and Hints for Detecting Network Attachments. Internet draft, work in progress, IETF DNA Network Working Group, draft-yegin-dna-l2-hints- 1.txt, February 24. [6] A. Yegin, D. Funato, K. El-Malki, Y. Gwon, J. Kempf, M. Pettersson, P. Roberts, H. Soliman, and A. Takeshita. Supporting Optimized Handover for IP Mobility - Requirements for Underlying Systems. Internet draft, work in progress, IETF DNA Network Working Group, draftmanyfolks-l2-mobilereq-2.txt, June 22. [7] N. Jordan, A. Poropatich, and R. Fleck. Link Layer Support for Fast Mobile IPv6 Handover in Wireless LAN based Networks. In The Proceedings of the 13th IEEE Workshop on Local and Metropolitan Area Networks (LANMAN 24), San Francisco, USA, pages , April 24. [8] T. Ernst. MobiWan: A NS-2.1b6 simulation platform for Mobile IPv6 inwide Area Networks. ns-2 extension, INRIA Rhone-Alpes, /mobiwan, May 22. [9] NS. The Network Simulator - ns-2. Simulation tool, version 2.1b6, University of California, Berkeley, January 2. [1] C. Bettstetter, H. Hartenstein, and X. Perez-Costa. Stochastic Properties of the Random Waypoint Mobility Model. ACM/Kluwer Wireless Networks, vol. 1, no. 5, pp , September 24. [11] IEEE. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. IEEE Std , IEEE Computer Society, June [12] IEEE. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Higher- Speed Physical Layer Extension in the 2.4 GHz Band. IEEE Std 82.11b-1999, IEEE Computer Society, June [13] Nick Sharkey Moore. Optimistic Duplicate Address Detection. Internet-draft, work in progress, IETF IPv6 Working Group, draft-ietf-ipv6-optimistic-dad-6.txt, September 25.