Smooth Handover by Synchronizing Context Transfer Protocol and Fast Mobile IPv6 Reza Farahbakhsh University of Isfahan Computer Engineering Department Isfahan, Iran
[email protected] Abstract— As the Internet continues to shape and reshape our lives, there is a parallel phenomenon taking place in wireless communication which is equally influential. Mobile communication has proved to be a major paradigm in the history of human communication. As both the Internet and mobile telephony continue their dramatic advances, there is a lot of requirement that should be available such as valid IP address. To provide seamless communications for such networks, Fast Mobile IPv6 (FMIPv6) has been proposed. In this paper, to Improve Mobile IPv6 Handover Latency two new schemes has proposed, Predictive and Reactive, for negotiating session parameters and reserve resources synchronize with the fast handover procedure simultaneously to reduce the signaling cost. The performances of the proposed mechanisms are evaluated by analysis. Keywords-component; Mobile IPv6; Context transfer; Fast Handover; mobility management,
I.
INTRODUCTION
One of the most important challenges in Mobile Networks is to provide services for mobile modes (MN) and maintain the connectivity when MN moves from one domain to another, which is referred to as handover. IPv6 designed primarily to provide an abundance of IP addresses for a large portion of devices which are going to be mobile. While Mobile IPv6 is designed to provide basic mobility support on the Internet, there are some newer protocols known as Fast Handover [3] and Context Transfer [6] to enable better performance for realtime applications that serve in mobile networks [1]. When a MN moves to a new location, it must satisfy a number of requirements before it can begin to receive packets. Fast handover enables the MN to send and receive IP packets immediately after regaining link connectivity [3]. The goal of the smooth handover is to maintain uninterrupted access to network resources so that the disruption caused by handover for transport protocols is minimized. Context transfer is a solution to the smooth handover problem [5]. With this background, in order to reduce the disruption time of handover and better QoS provisioning, in this paper two context transfer schemes has been proposed to transfer the session state such as QoS, AAA, header compression and Security information between Previous Access Router (PAR) and New Access Router (NAR). In the proposed schemes, the 978-1-4244-4793-0/09/$25.00 ©2009 IEEE
session context transferring is synchronized by fast handover procedure and combine context transfer with FMIPv6 messages. To evaluate the performance of the proposed schemes, we analyze the handover latency by timing diagram and calculate the signaling cost. The rest of this paper is organized as follows. Next section provides a brief background of the MIPv6 Protocol and context transfer mechanisms and also introduces some related works. In Section III, the proposed handover schemes for improving handover latency have been presented. In Section IV, the proposed scheme is evaluated by using timing diagram and cost analysis. Section V investigates numerical results and finally, we wrap up this paper in Section VI. II.
BACKGROUNDS AND RELATED WORKS
A. Overview of Mobile IPv6 Protocols There have been a lot of research and investigations to improve handover performance. One of these research issues is to reduce the handover latency. FMIPv6 [3] is a modification of MIPv6 that tries to reduce handover latency by utilizing Layer 2 triggers. Fast IP handover allows a mobile node to quickly regain its IP connectivity in order to send and receive its payload immediately following a handover. FMIPv6 aims to reduce the handover delay reduction by delivering the packet in the new point of attachment at the earliest. As mentioned in [3], there are two modes of operations: Predictive and Reactive. The main difference between these two schemes is on the time of establishing the tunnel between the PAR and NAR. In the predictive handover, the tunnel is established before layer 2 handover, but in the reactive handover, the tunnel is established directly after layer 2 handover. Figures 1 and 2 show the packet flows for the predictive and Reactive fast handover scheme. As shown in these pictures, in both modes the MN sends a router solicitation for proxy advertisement (RtSolPr) to its current access router to get the information of a new link. Essentially, the mobile node supplies the link-layer identifiers of one or more access points and requests its default router to resolve them to subnet-specific information in an RtSolPr message. When a PAR receives that message, it sends Proxy Router Advertisement (PrRtAdv) message that provides the information of neighboring links facilitating expedited movement detection. This information includes the prefix, IP
address and link-layer address of the neighbor access router. Then, the MN generates a New Care-of Address (NCoA) that will be used in a new link and sends Fast Binding Update (FBU) prior to disconnecting current link which allows the PAR to tunnel packets and to redirect the traffic destined to the MN from the Previous CoA (PCoA) to the NCoA. A bi-directional tunnel between PAR and NAR is established to prevent routing failure with Handover Initiate (HI) and Handover Acknowledgment (HAck) message exchanges and allows the NAR to allocate necessary buffers beyond what is typically allocated for neighbor discovery procedure. In response to an FBU, PAR sends Fast Binding Acknowledgment (FBack) to acknowledge receipt of a FBU. Thus, bidirectional tunnel is established between them and PAR begins forwarding packets to NAR. After link layer handover, the MN sends Unsolicited Neighbor Advertisement (UNA) message to NAR to announce its movement. Then, NAR sends packets that are stored in its buffer to the MN. Because of scratch, the MN has to invite the CN to the VoIP session [4]. In the reactive mode (see Fig. 2), the MN has already moved to the NAR and does not receive an FBAck. It thus sends an UNA and also sends a FBU via NAR to PAR, then the bi-directional tunnel between PAR and NAR is established with Handover Initiate (HI) and Handover Acknowledgment (HAck) message exchanges if the PAR sends an FBAck to the NAR and starts forwarding packets to the NAR if the NCoA is accepted. Then, the NAR delivers them immediately to the MN. Unlike to the predictive mode that the MN is able to send a FBU when it is attached to the PAR, in reactive mode, the MN is able to send FBU only after attaching to the NAR.
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Data Flow RtSolPr PrRtAdv Detach from PAR Attach to NAR UNA FBU FBU HI Hack FBack Forward packets
buffering
Deliver Packets Invite 100 Trying 180 Ringing 200 OK Ack Data Flow (RTP Media Flow) BYE 200 OK
Figure 2. Reactive mode of FMIPv6 handover
B. Context Transfer Procedure Context Transfer Protocol (CTP) proposed by IETF [6] to allow better node mobility support and avoids re-initiation of signaling to and from a MN. Example features contained in the context are session state information, network and application level QoS information, AAA information, header compression and security features. In all these scenarios, if procedures were conducted without transferring any context related information; descriptive parameters should be re-defined from scratch whenever the MN reaches to a NAR. The re-negotiation of these parameters is too complex and may require longer time than the one that is needed to perform the handover. The best solution is to transfer session context from PAR to the NAR [2, 9]. The key goals are to reduce latency, minimize packet losses and avoid re-initiation of signaling to and from MN. Context transfer is a network level protocol which transfers connection information between access routers; this mechanism is a handover optimization procedure to reduce the length of interruption (handover delay) in user’s ongoing application sessions.
Figure 1. Predictive mode of FMIPv6 handover
Therefore it can get promptly the same forwarding process, minimize the handover service disruption, and avoid initiating the end to end QoS signaling from scratch after an MN performs handovers [7]. By synchronizing Context Transfer in MIPv6 procedure, the access routers could transfer networkresident contexts, such as access control, QoS and header compression, in conjunction with handover and make the handover process smoothly.
III.
PROPOSED HANDOVER SCHEMES
In this section, at the first the handover in the current scheme has presented and then two smooth Fast handover schemes by synchronizing the context transfer procedure in fast MIPv6 handover is proposed. A. Problem Statement We assume that a multimedia session such as VoIP is ongoing between two MIPv6 users. Meanwhile, the MN performs a handover from the PAR where the session was generated to a NAR, where the session should be continued. Due to the mobility, the session at the PAR is terminated, and the MN has to trigger the standard procedures at the NAR. NAR does not have enough information about the MN and its session, so it has to renegotiate by the CN and collect the information again. After scratch, before the MN can continue the session, it has to re-establish and renegotiates session parameters for the ongoing service by the network servers and CN. This will potentially introduce a long interruption of the ongoing session. B. Proposed Context Transfer-based schemes At this paper two context transfer scheme has been proposed that make it possible to have a smooth handover between ARs, without losing session state information. Additionally, fewer messages and shorter handover delay are used for the re-establishment of the session, comparing to the standard schemes which are described in [2]. By transferring the session and QoS context (see Fig. 3), NAR receives profitable information such as session state information, QoS and AAA information, header compression and security features about the MN and its session at the PAR.
latency. After delivery of the buffered packets, the MN only send a re-invite message to the CN and let it know about the handover.
IP/MPLS Core Network Data Flow
CN Access Network
Correspond Network
Access Network
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Figure 3. Network Architecture
At our proposed schemes, we use context transfer signaling within FMIPv6 messages simultaneously and combine these two together. As mentioned in [3], the formats of FMIPv6 messages are ICMPv6 or IPv6 mobility header. Both of these formats operate in the Internet Layer and they can have some extra information in their packets. Therefore it is possible to include the Context Transfer protocol messages in the FMIPv6 packets. C. Proposed Predictive scheme Fig. 4 has shown the proposed predictive handover scheme. In this scheme, the MN knows in advance towards which router it will move or anticipates transferring to the NAR. Note that this knowledge can be acquired by FMIPv6 and Neighbor Discovery (ND). After the negotiation of router advertisement, the MN sends FBU message to the PAR that contains the Context Transfer Activate Request message (CTAR). Then the messages for establishing tunnel between ARs will negotiate. As shown in the Fig. 4 the HI and Hack messages carry the Context Transfer Data message (CTD) and the Hack transmits the Context Transfer Data Reply message (CTDR). This proposed scheme utilizes movement anticipation, tunneling, and session context transfer to alleviate handover delay. It's worthy to mention again that in this scheme the context transfer procedure is performed simultaneously to the MIPv6 handover procedure and doesn’t cause excessive
Figure 4. Proposed Predictivemode of FMIPv6 handover
The time line of the Proposed Predictive FMIPv6 handover is shown in fig. 5.
L2 Trigger
Handover Completed
L2 Handover Packet reception latency Location update latency Fast handover latancy
Time
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T-Address
Handover Start epoch
Figure 5. Time line of Proposed Predictive mode of FMIPv6 handover
Start link switching Obtain NCoA
T-UNA
Attached to the new link
FBU and Tunnel will established
T-tunnel
Start Packet Delivery
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Figure 7. Time line of Proposed Reactive mode of FMIPv6 handover
D. Proposed Reactive Scheme In this scheme, the MN has performed a handover before the context transfer is requested. After attachment to the new link and NAR, MN sends UNA message along with CTAR message (see figure 6). Also it sends the FBU and Context Transfer Request message (CTR) to PAR via NAR. After that PAR sent HI message along with CTD to the NAR and receive Hack and CTDR. As mention before, in this proposed scheme the context transfer procedure is performed simultaneously to MIPv6 handover and doesn’t cause excessive latency.
In this section we conduct performance evaluation of the handover delay for the two proposed schemes and compare them with the delay of the original Fast MIPv6 models. The analysis is based on a simple model presented in [8] that takes into account the delay of the different entities involved in the handover procedure. We do not consider the time needed by DAD process and Return Routability procedure and queuing.
The Proposed Reactive FMIPv6 handover Timing Diagram is shown in figure 7.
TL2: The time interval from the moment that MN detaches from PAR to the moment that the MN attaches to the NAR.
IV.
PERFORMANCE EVALUATION
For convenience, the notations are given as follows:
T(A,B): The time required for a packet to pass from A to B. For example, T(MN,PAR) denotes the time required for a packet to pass from the MN to PAR. It is assumed that T(A,B) = T(B,A). T(A): The time required for a packet to be processed at A. A. Performance of the Standard Predictive FMIPv6 As shown in Fig. 1, the handover is performed as follows: first the MN sends router solicitation to all ARs in its domain and receives router advertisements from them. Then selects one of them to migrate and obtains a NCoA which takes 2T(MN,PAR). Afterward The MN sends FBU to the PAR, that also takes T(MN,PAR). Then The ARs, exchange HI and Hack together, which take 2T(PAR,NAR). The PAR sends an FBAck to the NAR and to the MN, which takes at most T(PAR,NAR). After occurring the handover (TL2), the MN sends UNA to the NAR, which takes T(MN,NAR). Finally the MN must invite again the CN to VoIP session, that is 7T(MN,CN). Therefore the overall delay of the standard Predictive FMIPv6 handover would be: Tst-Predictive = 3T(MN,PAR) + 3T(PAR,NAR) + TL2 + T(MN,NAR) + 7T(MN,CN) (1)
Figure 6. Proposed Reactive mode of FMIPv6 handover
B. Performance of the Standard Reactive FMIPv6 As shown in Fig. 2, the first steps are similar to the predictive mode and takes 2T(MN,PAR). But the MN has moved to the NAR (TL2) and has not received an FBAck. Consequently, it sends an UNA to the NAR, (T(MN,NAR)), and sends FBU via the NAR to the PAR that takes T(MN,NAR) + T(NAR) + T(NAR,PAR). Then the ARs, exchange HI and Hack together, which takes 2T(PAR,NAR). Afterward the PAR sends back an FBack to the NAR that takes T(PAR,NAR) and starts
Tst-Reactive = 2T(MN,PAR) + TL2 + 2T(MN,NAR) + T(NAR) + 4T(PAR,NAR) +7T(MN,CN)
(2)
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forwarding packets to the NAR. Then, the NAR delivers the forwarded packets immediately to the MN and start the invitation procedure for VoIP session via CN, (7T(MN,CN)). Totally, the delay of the proposed Reactive FMIPv6 handover would be:
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TPredictive = 3T(MN,PAR) + 3T(PAR,NAR) + TL2 + T(MN,NAR) + (3) 2T(MN,CN) D. Performance of proposed Reactive Scheme In the proposed reactive scheme the handover procedure starts in the same way with proxy router solicitation/advertisement which takes 2T(MN,PAR). But the MN has moved to the NAR and has not received an FBAck (TL2). Consequently, it sends an UNA to the NAR, (T(MN,NAR)) and sends FBU via the NAR to the PAR that takes T(MN,NAR) + T(NAR) + T(NAR,PAR). Then The ARs, exchange (HI + CTD) and (Hack + CTDR) together, which take 2T(PAR,NAR). Afterward the PAR sends back an FBack to the NAR that takes T(PAR,NAR) and starts forwarding packets to the NAR. Then, the NAR delivers the forwarded packets immediately to the MN and reinvite the CN to the ongoing session and let it know about the handover, (2T(MN,CN)). Totally the delay of the proposed Reactive FMIPv6 handover would be: TReactive = 2T(MN,PAR) + TL2 + 2T(MN,NAR) + T(NAR) + 4T(PAR,NAR) + 2T(MN,CN) (4) V.
NUMERICAL RESULTS
In this section, we present the numerical performance evaluations for the standard and the proposed schemes. To evaluate the disruption time, we assume T(MN,PAR) = 10ms, T(PAR,NAR) = 20ms, T(MN,NAR) = 15ms, T(MN,CN) = 10ms, TL2= 100ms and T(NAR) =20ms. We do not consider the delay introduced by the Internet depends on the number of routers and the type of links here. Fig. 8 shows the impact of the delay between MN and CN on the total disruption time.
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C. Performance of proposed Predictive Scheme As mentioned before, in the proposed predictive scheme the handover procedure starts in the same way as for standard scheme with proxy router solicitation/advertisement which takes 2T(MN,PAR). Afterward The MN sends FBU to the PAR that also takes T(MN,PAR). Then The ARs exchange (HI + CTD) and (Hack + CTDR) together, which take 2T(PAR,NAR). The PAR sends an FBAck to the NAR and to the MN, which takes at most T(PAR,NAR). After occurring the handover (TL2), the MN sends UNA to the NAR, which takes T(MN,NAR). As referred earlier, the context transfer procedure proceeds concurrently with the fast handover process avoiding extra latency for invitation procedure, there is only need to re-invite the CN to the ongoing session and let it know about the handover, (2T(MN,CN)). So the total delay of the proposed predictive FMIPv6 handover would be:
de la y MN-C N [m s]
Figure 8. Disruption time VS. delay between the MN and CN
VI.
CONCLUSION
In this paper, we deal with the fast handover, which is to provide rapid handover for the delay-sensitive and real-time applications. In order to improve the performance of the handover procedure, we proposed two handover schemes for MIPv6 networks. To lessen the handover latency, the predictive and reactive proposals make use of context transfer procedure between the previous and new Access Routers simultaneity by FMIPv6 messages. The session state information such as QoS, AAA, header compression and Security information will transferred concurrently by the handover and decrease the total time needed for the transactions of the handover process. We analyzed the performance of the proposed schemes and compared them with the standard modes. The performance evaluation shows that in proposed schemes, the handover latency is reduced in compare of the existing fast handover schemes. REFERENCES [1] [2] [3] [4]
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D. B. Johnson, C. E. Perkins, and J. Arkko, “Mobility support in IPv6,” IEFT RFC 3775, June 2004. R. Koodli, , C. E. Perkins, “Fast Handovers and Context Transfers in Mobile Networks”, ACM, 2001. R. Koodli, Ed, “ Mobile IPv6 Fast Handovers,” IETF RFC 5268, June 2008. H. Fathi, S. Chakraborty, and R. Prasad “Optimization of Mobile IPv6Based Handovers to Support VoIP Services in Wireless Heterogeneous Networks”, IEEE Transactions on Vehicular Technology, vol. 56, no. 1, Jan. 2007. J. Kempf, “Problem Description: Reasons For Performing Context Transfers Between Nodes in an IP Access Network”, IETF RFC 3374, September 2002. J. Loughney, M. Nakhjiri, C. Perkins and R. Koodli, “Context Transfer Protocol (CXTP)”, IETF RFC 4067, July 2005. C. Liu1, D. Qian1, Y. Liu1, and K. Xiao, “A Framework for End-to-End QoS Context Transfer in Mobile IPv6”, PWC 04, LNCS 3260, pp. 466– 475, 2004. R. Li, J. Li, K. Wu and Ed., “An Enhanced Fast Handover with Low Latency for Mobile IPv6”, IEEE Transactions On Wireless Communications, Vol. 7, No. 1, Jan 2008. R. Farahbakhsh, N. Movahhedinia, “Using context transfer mechanisms to Improve Mobile IMS-IPv6 Handover Latency and QoS provisioning”, IMSAA 08, Bangalore, 2008.
