Acta Electrotechnica et Informatica No. 1, Vol. 6, 2006
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PRACTICAL EXPERIMENTATION OF MOBILE IPV6 IN HETEROGENEOUS ENVIRONMENT *
Jani PUTTONEN, *Gábor FEKETE, **1 Pawel RYBCZYK, **Jorma NARIKKA
* University of Jyväskylä, Department of Mathematical Information Technology, PO. Box 35, 40014 University of Jyväskylä, Finland, E-mails:
[email protected],
[email protected] ** Jyväskylä University of Applied Sciences, School of Information Technology, Piippukatu 2, 40100 Jyväskylä, Finland, E-mails:
[email protected],
[email protected]
SUMMARY In this paper we present a Mobile IPv6 analysis related to its performance in heterogeneous multi-access environment. The used access technologies include IEEE 802.3 Ethernet, IEEE 802.11b Wireless LAN and Bluetooth. We also discuss the capability of Mobile IPv6 to provide Always-Best-Connected access in multi-access environment to the user and applications. The analysis is made according to real-life tests in Mobile IPv6 for Linux (MIPL) test network. The Mobile IPv6 protocol by itself cannot handle all the tested scenarios in the best possible way even though it provides a good ground for the All-IP mobility management. We claim that a cross-layer approach would enable intelligent and proactive handovers, and thus improve the end- user experience.
Keywords: mobility, Mobile IPv6, link layer, adaptation, heterogeneous, handover, WLAN 1. INDRODUCTION Wireless and mobile technologies are getting more important and appealing to the end-user as the amount of mobile devices, access technologies and services increase. Cellular networks (e.g. 2G, 2.5G, 3G) with almost complete coverage are accompanied by, for example, unlicensed IEEE 802.11 series wireless LAN hotspots and Bluetooth wireless PANs. The fourth generation (4G) wireless networks are thought of being a combination of several overlapping access technologies with different characteristics such as coverage, bandwidth, price, etc. Networks are converging into one ubiquitous service platform. Also the mobile devices are increasingly having several access interfaces to the services. This fact enables the user to choose the interface to use, thus the user to be able to be Always-Best-Connected (ABC) [1] according to his own preferences related to the access characteristics. More details about various mobile and wireless technologies can be found for example in [2]. Communication networks are moving towards packet switched networks, where IP protocol is the integration layer for both accesses and applications [3]. The research community uses the terms Native IP or All-IP networks. For the IP based mobile terminal to be always globally accessible, some upper layer mobility management technique is necessary, such as Mobile IP (MIP) [4], [5], Mobile Stream Control Transport Protocol (mSCTP) [6], Host Identity Protocol (HIP) [7] or Session Initiation Protocol (SIP) [8]. Mobile IPv6 is seen as the most promising way of handling the mobility in the networks of the future. It handles both horizontal (intra-technology) and vertical (inter-technology) handovers in the IPv6 networks in an application-transparent way by using two
separate addresses, one for identity and one for location. More on Mobile IPv6 functionality in the next section. Even though Mobile IPv6 provides a good and fully functional ground for the IP mobility management, it still has some issues to be improved. When a Mobile IPv6 enabled device moves to a new point of attachment, the handover procedures result a timeslot, when the device cannot send nor receive any packets. Several research studies have been performed to measure Mobile IPv6 handover delays and packet loss related to both horizontal and vertical handovers, such as [9], [10], [11], [12]. In this paper we analyze the Mobile IPv6 protocol in multi-access environment. Mobile IPv6 for Linux (MIPL) [13] is used as the Mobile IPv6 protocol implementation, which is constantly maintained, but not yet in its final state. The analysis includes both performance and ABC concept capability analysis. Application and user transparency needs in addition to the functionality good handover performance, i.e. low handover delay and packet loss. Also, with a constantly changing heterogeneous access environment, application requirements and user preferences the interface selection is not a simple task. All Mobile IPv6 enhancements are out of scope of this paper. Our previous and current work considers mechanisms to improve the Mobile IPv6 functionality both in horizontal and vertical handover contexts. In [14] we proposed a general architecture for a terminal controlled vertical handover system called VerHo. VerHo is a crosslayer mobility management system for Native IP environment using the Mobile IPv6 protocol. VerHo gathers information from different sources (e.g. different protocol layers), processes the best
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Pawel Rybczyk is now with Institute of Computer Science, University of Silesia, Katowice, Poland. E-mail:
[email protected] ISSN 1335-8243 © 2006 Faculty of Electrical Engineering and Informatics, Technical University of Košice, Slovak Republic
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Practical Experimentation of Mobile IPV6 in Heterogeneous Environment
interface and if needed performs a handover with the Mobile IPv6 protocol. The objective is to be capable of providing ABC access in real-time. In [15] we presented a Link Information Provider (LIP) to acquire the link layer information from the interfaces of different technologies. LIP receives information from link layer events, polls for other related parameters and provides them to upper layer consumers supplemented with trigger and hint indications.
presented all the essential components of Mobile IPv6 and the handover process. Fig. 2 presents the handover processes in relation to time. When MN changes a Point-of-Attachment (PoA), it first performs the link layer handover, a horizontal or a vertical one. Then the MN needs to perform IP layer movement detection to realize if the IP subnet has changed. This happens by listening periodical Router Advertisements (RAs) sent by the Access Router (AR) or Neighbor Unreachability Detection (NUD). MN can also request the RA by sending Router Solicitation message. In case the subnet has changed, the MN needs to configure a new CoA with either stateless or stateful address autoconfiguration. In the former alternative the CoA is calculated from the RA message, which includes the subnet prefix, and the MAC address of the interface in question. In the latter one, the address is requested from a DHCPv6 server. Finally, the CoA needs to be registered to the HA with a Binding Update process, so that the HA knows the current location of the MN.
Fig. 1 The Mobile IPv6 functionality The rest of the paper is organized as follows. Section II presents the Mobile IPv6 functionality. Section III presents the test scenarios and results. In section IV we discuss mechanisms to improve the suitability of Mobile IPv6 to heterogeneous environments. Section V concludes the paper. 2. MOBILE IPv6 OPERATION Mobility support in IPv6 [5] enables application transparent routing of packets to the Mobile Node (MN) regardless of its location. This is achieved with the use of two addresses, Home Address (HoA) and Care-of-Address (CoA). In the home network, MN is assigned a permanent home address (HoA), which is used in every application layer connection. When MN changes its IP layer attachment in the network, it acquires a new local subnet specific address from the foreign network to be again accessible. The CoA is registered through a Binding Update (BU) process to a special router in the home network called the Home Agent (HA). The HA maintains a binding cache, in which the HoA-CoA bindings are stored, and employs tunneling to redirect the flows to the current CoA of the MN. In the visitor network there exists a bidirectional tunnel between the MN’s CoA and HA, thus all the traffic goes encapsulated via HA. The Mobile IPv6 handover process consists of three phases: movement detection, CoA configuration and CoA registration. In Fig. 1 is
Fig. 2 The handover process The MN can also decide to register its CoA to the Corresponding Nodes (CNs) (i.e. the nodes it is communicating with) in which case also the CNs maintain a binding cache. Now, CNs and MN can communicate directly without tunneling and thus improving the End-to-End communication delay. This happens anyhow at the expense of the handover delay, which is increased by about two round-trip times following from sending BUs to CNs and Return Routability (RR) procedure. This communication option is called Route Optimization and is one of the main improvements of Mobile IPv6 if compared to the Mobile IPv4. Our interest related to Mobile IPv6 protocol lies, in addition to its handover performance, in the interface selection processes related situations where MN is in the coverage area of several access networks. Traditionally the horizontal handover decisions are made according to signal strength with some hysteresis values to avoid ping-ponging. In vertical handover decisions that is not the case anyhow. Mobile IPv6 for Linux (MIPL) implementation provides static interface specific priorities. The following is an example of this in pseudo-code. if (Eth UP) use Eth else if (WLAN UP) use WLAN else no connection
ISSN 1335-8243 © 2006 Faculty of Electrical Engineering and Informatics, Technical University of Košice, Slovak Republic
Acta Electrotechnica et Informatica No. 1, Vol. 6, 2006
3. ANALYSIS OF MOBILE IPv6 We used the Mobile IPv6 implementation for Linux (MIPL) [13] version 2 release candidate 3. MIPL2rc3 was patched with our bug fixes for it to operate better in multi-access environment. The MIPLv2 implementation was chosen because it is open, for Linux OS and constantly maintained. The purpose of the tests was to measure the handover performance of Mobile IPv6 in both horizontal and vertical handovers. Here we need to define two handover types; soft and hard handover [16]. Soft handover (i.e. make-before-break) refers to a handover where MN makes the new connection before the old one is broken. In the hard handover (i.e. break-before-make) MN breaks the old connection before the new connection is made. Also, we discuss the handover decision processes both in the case of horizontal and vertical handovers and multi-vendor interoperability. MN uses bidirectional tunneling communication mode, thus Route optimization was not used because it does not have any effect on the ABC analysis. On delay analysis Route Optimization would increase the handover delay about two round-trip delays between MN and CN. However, as Route Optimization is the most important part of Mobile IPv6, we plan to test this feature in the near future. All test cases (i.e. signaling, Ping, TCP and UDP) were made separately, thus they should be analyzed separately and not compared with each other. 3.1. Test environment The IPv6 based test network is presented in Fig. 3. It consists of five Linux computers that has been set up as routers with static routing. The Hunter is set up as Home Agent with Ethernet home link. Each Access Router has RADVD Router Advertisement Daemon installed and RA interval is configured to 0.05-3.00s according to [5]. The network includes IEEE 802.3 Ethernet, IEEE 802.11b WLAN and Bluetooth access points. There are two Ethernet and WLAN accesses to enable also
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horizontal handovers. The MN has the Mobile IPv6 functionality and three accesses corresponding to the access networks (i.e. Realtek, Orinoco Gold, SMC v_1.2). All delay results were a mean of 10 repetitions and measured with Ethereal protocol analyzer and capturing MIPL debug outputs. 3.2. Delay measurements 1) Horizontal handover delay measurements: In the first test we analyze horizontal handovers with Mobile IPv6. We perform both Ethernet to Ethernet handovers and WLAN to WLAN handovers and divide the overall delays into the handover delay components defined in the previous section. In both handover cases only the corresponding interface was up, thus in Ethernet to Ethernet handovers only Ethernet interface was up, the others were down, etc. The Ethernet to Ethernet handovers were made between Hunter (home network, HN) and Wildcat (foreign network, FN). Handovers were performed by plugging out and in the physical cable between the links. The WLAN to WLAN handovers were made between the Wildcat (foreign network) and Wolf (foreign network). Both Access Points were configured to advertise different ESSIDs and the handovers were made by changing the ESSID value of the MN. 2) Vertical handover delay measurements: To measure the vertical handover performance we performed two scenarios: handovers between WLAN (Wolf) and Ethernet (Hunter) and between Bluetooth (Wolf) and Ethernet (Hunter). A handover between the wireless technologies was not performed because we encountered instability problems with Bluetooth connections. Bluetooth connectivity was only unidirectional after setting up the Bluetooth devices and setting on both peers. For bidirectional connectivity one of the peers (the AP) had to send a packet to the client. Probably, it triggered some state in the clients Bluetooth stack. Even when bidirectional connectivity was up and running, the connection tended to break after some time for no visible reason even if there was active communication between the peers (e.g. ping packets).
Fig. 3 The test network topology
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Practical Experimentation of Mobile IPV6 in Heterogeneous Environment
The MN had both interfaces up that took part in the handover process, then Ethernet link was put manually down to cause a handover to the wireless interface and brought up again to cause handover back to home network. Ethernet interface was prioritized over the wireless interface, thus if it is up it was selected to use. The handover to foreign network was a hard one and coming back home a soft one. 3) Ping tests: In this scenario we used Ping with default parameters (e.g. interval is 1s) from MN’s HoA to HA. MN performs all the handover cases as in the previous test case, i.e. both horizontal (EthEth, WLAN-WLAN) and vertical ones (Eth-WLAN, Eth-BT). We measured the delay between the last ping via the old interface and first via the new interface. 4) Application experience: In addition to Ping program we analyzed the real application experience with both UDP and TCP based applications. As in Ping tests all of the handover scenarios were performed. An exception was the handover between Ethernet and Bluetooth, which was not performed because of the Bluetooth specific problems. In both cases the MN received a traffic stream from Moose. As UDP based application we used MGEN [17] traffic generator with 102 Kbps constant bitrate stream (packet size 1024B, interval 100ms). For TCP we used Secure CoPy (SCP) download, which tries to get as good throughput as possible. We measured the delay between the last application packet via the old interface and first via the new interface. 3.3. Delay result analysis All of the handover delay results are presented in Table I. The movement detection is performed by MN sending the Router Solicitation message to which the AR responds with a Router Advertisement. The Link Down event from device driver triggers the solicitation. In [18] is specified that AR has to way a random time between 0 and 0.5 seconds. In vertical handovers (i.e. Eth-WL, EthBT) the movement detection time is nil when moving to foreign network, because the target interface has a valid IPv6 address when Ethernet link is put down.
The CoA configuration phase is a result of DAD process of the new CoA of the MN. In DAD the MN sends a Neighbor Solicitation to the new CoA and then it waits for 1 second for response. If no response is received, the CoA is valid. The CoA registration delay consists of binding process to the HA, thus Binding Update to HA and Binding Acknowledgment in response. A round-trip propagation delay to HA causes the delay. When MN moves to a foreign network the HA performs DAD to verify the validity of the HoA. The overall delay sums up to over 3 seconds which is quite much when thinking that this is calculated from the signaling messages and without any congestion in the network. The results related to Ping, TCP and UDP application experiences are presented in Table II. Vertical handovers seem to be a little faster than the horizontal ones. This might be due the fact that the horizontal handovers were always hard handovers, thus for example movement detection times are longer. In general TCP suffered from the handover a little more time than the UDP, which is related to the congestion control mechanisms of TCP. 3.4. ABC concept test Always-Best-Connected access can be thought from two aspects; horizontal and vertical ones. The purpose was to find out the way MN chooses the AP for use in the horizontal case. The network has two APs configured with the same ESSID, but the other one is configured as 2Mbps AP and the other as 11Mbps AP. The MN has got WLAN interface in down state and it is put up. The purpose is to see how the MN chooses the AP to use. From 10 repetitions we found out that both APs are chosen with an equal probability (i.e. 50%). This shows that MN randomly picks up an AP if it only has the correct ESSID and its signal strength is above the driver defined threshold (in this case 11 SNR). Mobile IPv6 specification [5] does not take into account the interface selection in multi-access environment at all. MIPL implementation on the other hand includes interface specific static priorities, where the link with the biggest priority will be chosen. This approach might be suitable in an environment, where we have two technologies available, but for more complex situations it might not be flexible enough. In a true heterogeneous environment there might exist several access technologies and several APs within the coverage. Furthermore, these APs might provide different quality that might even change quite rapidly because of multipath radio environment. End-to-End paths to CNs differ depending on the AP location in the topology. Different users might have different preferences to the access in use, e.g. cost, coverage, bandwidth. The best connectivity also relates to the applications in use, e.g. VoIP, IP-TV, file transfer. This kind of more complex environment calls for more enhanced interface and AP selection.
ISSN 1335-8243 © 2006 Faculty of Electrical Engineering and Informatics, Technical University of Košice, Slovak Republic
Acta Electrotechnica et Informatica No. 1, Vol. 6, 2006
4. DISCUSSION Mobile IPv6 provides a good ground for IP mobility management, but it also has some issues that could be improved. The delay of each Mobile IPv6 handover component result a quite big overall handover delay, i.e. magnitude of several seconds, which affects at least the real time applications. Also, to put some criticism on our work, we should have made more that 10 repetitions of the tests to get more reliable results. Also the tests scenarios should have not been made separately, so that the results with handover delays and application experiences could have been compared. Numerous optimizations have been proposed due to that fact. For movement detection there exists e.g. link layer triggering [19] and fast RAs [20]. The CoA configuration could be made before the actual handover through the old AR with the help of Candidate Access Router Discovery (CARD) [21] like in Fast Handovers for Mobile IPv6 (FMIPv6) [22]. The CoA registration can be shortened for example with Hierarchical Mobile IPv6 (HMIPv6) [23] or Flow-based Fast Handover For Mobile IPv6 (FFHMIPv6) [24]. We have concentrated more on improving the interface selection than the handover delay. For improving the horizontal handover decision L2 scanning could be improved with more parameters than just the signal strength, AP address and network name. For example available bandwidth and price information would be useful in the AP selection. The scanning phase can be improved by extending the link layer beacon messages, maintaining a connection cache or with some network support such as CARD [21]. The Mobile IPv6 vertical handovers can be improved by designing a cross-layer controller to handle the handovers [14]. In Fig. 4 is a high-level architecture of VerHo handover controller, which gathers important parameters from different sources (e.g. protocol layers), calculates the best link and controls the Mobile IPv6 protocol to do the handovers. Link layer support [15] can improve both the handover delays and the interface selection by providing information about the link states (e.g. Link Up, Link Down) and quality related parameters (e.g. bandwidth, signal strength, power consumption). Proactive handovers can be achieved as well, where MN is able to begin the handover procedures before the connection really breaks (i.e. make-beforebreak). Because VerHo is in control of the Mobile IPv6 handovers it knows the target and timing of the occurring handovers. Thus it can trigger stream adaptation both in transport and application layers (e.g. stream bandwidth change). The aim of the VerHo system is to be fully mobile controlled, but still some information outside the mobile terminal itself can really improve the handover process. The network information such as current load of an AP or End-to-End Quality-of-Service to the corresponding hosts provides really accurate
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information about the connection. Also, positioning information (e.g. from GPS or Galileo) can improve at least the power consumption of the interfaces. 5. CONCLUSION This paper presented the analysis of Mobile IPv6 in heterogeneous multi-access environments. First purpose was to measure the handover delays in both vertical and horizontal handovers and the second to analyze the suitability for achieving Always-BestConnected access for the user. The delays in all the tests cases were considerably large, thus they will affect the applications in use. The interface selection process of Mobile IPv6 requires some more intellect to function well in a more complex multi-access environment and users with different preferences. Our future work includes the VerHo cross-layer mobility management system, which can achieve more intelligent handover decisions. This requires research on link layer support, interface selection algorithms, application adaptability, etc. The final goal is to serve the user in the best possible way in constantly changing heterogeneous environment. REFERENCES [1] [2] [3]
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E. Gustafsson and A. Jonsson, “Always Best Connected,” IEEE Wireless Communications, vol. 10, pp. 49–55, 2003. F. Jakab and Ľ. Doboš, “Multimedia Delivery in Mobile Environments,“ Košice, elfa s.r.o., ISBN 80-89066-98-4, 2005. R. Berezdivin, R. Brenig, and R. Topp, “Next Generation Wireless Communications Concepts and Technologies,” IEEE Communications Magazine, vol. 40, no. 3, pp. 49–55, 2002. C. Perkins, “IP Mobility Support for IPv4,” IETF RFC 3220, January 2002. D. Johnson, C. Perkins, and J. Arkko, “Mobility Support in IPv6,” IETF RFC 3775, June 2004. S. J. Koh, Q. Xie, and S. D. Park, “Mobile SCTP (mSCTP) for IP Handover Support,” IETF draft, December 2005, work in progress. R. Moskowitz, P. Nikander, P. Jokela, and T. Henderson, “Host Identity Protocol,” IETF Draft, October 2005, work in progress. J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, and E. Schooler, “SIP: Session Initiation Protocol,” IETF RFC 3261, June 2002. R. Chakravorty, P. Vidales, L. Patanapongpibul, K. Subramanian, I. Pratt, and J. Crowcroft, “On Inter-network Handover Performance using Mobile IPv6,” Cambridge Open Mobile System, University of Cambridge,” Technical Report, June 2003. M. Bernaschi, F. Cacace, A. Pescape, and S.
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Za, “Analysis and experimentation over heterogeneous wireless networks,” in Proceedings of the 1st International Conference on Testbeds and Research Infrastructures for the Development of Networks and Communities, February 2004, pp. 182–191. M. Dunmore, “Mobile IPv6 Handovers: Performance Analysis and Evaluation,” 6net,” Deliverable D4.1.3, June 2005. C. Vogt, “A Comprehensive Delay Analysis for Reactive and Proactive Handoffs with Mobile IPv6 Route Optimization,” Institute of Telematics, University of Karlsruhe,” Technical Report TM-2006-1, January 2006. “MIPL Mobile IPv6 for Linux,” http://www.mobile-ipv6.org, 2006. J. Mäkelä, T. Hämäläinen, G. Fekete, and J. Narikka, “Intelligent Vertical Handover System for Mobile Clients,” in Proceedings of the 3rd International Conference on Emerging Telecommunications Technologies and Applications (ICETA 2004), September 2004, pp. 151–155. J. Puttonen, G. Fekete, J. Mäkelä, T. Hämäläinen, and J. Narikka, “Using Link Layer Information for Improving Vertical Handovers,” in Proceedings of the 16th Annual IEEE International Symposium on Personal Indoor and Mobile Radio Communications, September 2005. J. Manner and M. Kojo, “Mobility Related Terminology,” IETF RFC 3753, June 2004. “The Multi-Generator Toolset,” http://pf.itd.nrl.navy.mil/mgen/, 2006. T. Narten, E. Nordmark, and W. Simpson, “Neighbor Discovery for IP Version 6 (IPv6),” IETF RFC 2461, December 1998. A. Yegin, “Link-layer Event Notifications for Detecting Network Attachments,” IETF Draft, October 2005, work in progress. G. Daley, B. Pentland, and R. Nelson, “Effects of Fast Router Advertisement on Mobile IPv6 Handovers,” in Proceedings of the Eighth IEEE International Symposium on Computers and Communication 2003 (ISCC 2003), 2003, pp. 557–562. M. Liebch, A. Signh, H. Chaskar, D. Funato, and E. Shim, “Candidate Access Router Discovery (CARD),” IETF RFC 4066, July 2005.
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BIOGRAPHIES Jani Puttonen received his M.Sc. degree in information technology from the field of data communications from the University of Jyväskylä in 2003. After that he has begun his Ph.D. studies in the subject of IP mobility and especially handover techniques. His current research interests are related to intelligent handovers in ubiquitous heterogeneous All-IP environment. Gábor Fekete received his M.Sc. degree in Software Engineering and Mathematics at the University of Debrecen, Hungary in 2005. Currently he is a PhD candidate at the University of Jyväskylä. He researches in the field of mobility in IP networks and related areas. Pawel Rybczyk received his B.Sc. degree in Information Technology from the Jyväskylä University of Applied Sciences in 2006. His bachelor’s thesis was about performance analysis of Mobile IPv6 in heterogeneous environments. Currently he is doing his M.Sc. thesis at the Silesian University in Katowice, Poland. Jorma Narikka was born on 1.3.1955. In 1979 he graduated (M.Sc. Engineering) from Tampere University of Technology. After several positions in industry he has held the position of lecturer in Jyväskylä University of Applied Sciences since 1992. He is currently also a post-graduate student in University of Jyväskylä, studying data network technologies, emphasis on mobile and wireless technologies.
ISSN 1335-8243 © 2006 Faculty of Electrical Engineering and Informatics, Technical University of Košice, Slovak Republic
