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S. Jeon et al.: Mobility Management Based on Proxy Mobile IPv6for Multicasting Services in Home Networks

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Mobility Management Based on Proxy Mobile IPv6 for Multicasting Services in Home Networks Seil Jeon, Student Member, IEEE, Namhi Kang, and Younghan Kim, Member, IEEE Abstract — Advances in broadband Internet access and enhanced performance of mobile devices have enabled seamless mobile IPTV service between indoor and outdoor. Mobile IPTV service is based on mobile multicasting to support efficient group communication. However, mobile multicasting has two constraints that we consider: a tunnel convergence problem and high handover latency. To reduce the two constraints, we propose a mobile multicasting model that is feasible for PMIPv6 domain. The proposed model removes tunnel convergence and reduces router processing. We then propose a fast handover scheme using a context transfer mechanism suitable for the proposed model. We also show that the proposed scheme outperforms previously proposed schemes in terms of packet delivery cost and handover latency1. Index Terms — Proxy Mobile IPv6, efficient multicast delivery, fast multicast handover.

I. INTRODUCTION High performance of wired and wireless home network technologies has enabled multimedia streaming services such as IPTV service, which is expected to be a promising service for home use. Furthermore, enhanced CPU performance and memory capacity have made streaming service possible on mobile devices. Such changes in computing have forced many ISPs to migrate simple data services to mobile IPTV service to create new revenue; thus, they need both efficient IP mobility management and multicast mechanisms to provide seamless indoor and outdoor mobile IPTV service. Fig. 1 presents a simple network architecture to introduce the requirement of mobility management, where the home gateway (HGW) is expected to play the role of foreign agent (FA). IPTV service is generally a kind of group communication; therefore, an IP multicasting mechanism is required to allow an IPTV source to transmit a single IP packet to multiple mobile users at the same time. However, we cannot directly apply traditional IP multicasting mechanisms to such a mobile environment, because multicasting mechanisms, including both multicast routing and membership management, have been designed for static hosts [1]. In particular, in this paper, we consider two serious problems in applying multicast mechanisms to the mobile environment.

Home Network IPTV Head End

HGW (FA)

IP Core Network Wireless AP

xDSL

Core Router

AR (FA)

AR (FA)

BS BS

BS

BS

Fig. 1. Network environment to support mobility indoors and outdoors

Several multicasting schemes have been proposed for mobile networks. A common approach of the schemes is delivery of the multicast packet to mobile member nodes located in several foreign networks over bi-directional tunnels. Each tunnel is built per node by using Mobile IP. When a mobile node (MN) running Mobile IP receives multicast packets from a home network, the packets are thus delivered over a bi-directional tunnel via the home agent (HA). If an HA receives multicast packets destined for an MN, the packets are encapsulated twice with the Home-of-Address (HoA) and Care-of-Address (CoA) of the MN. Thus, if each MN located in the region covered by its HA moves to an area covered by a single foreign agent (FA), duplicated multicast packets transmitted over several tunnels increase the delivery cost. We refer to this problem as the tunnel convergence problem [2], as shown in Fig. 2. It causes unnecessary waste of network bandwidth and excessive processing overhead at the FA.

1 Seil Jeon and Younghan Kim are with the School of Electronic Engineering, Soongsil University, Sangdo-Dong, Dongjak-Gu, Seoul 156-743, Republic of Korea (e-mail: [email protected], [email protected]). Namhi Kang is with the Department of Computer Science, Duksung Women's University, Ssangmoon-Dong, Tobong-Gu, Seoul, 132-714, Republic of Korea (e-mail: [email protected]).

Contributed Paper Manuscript received June 10, 2009

Multicast Router

IP Settop Box Mobile Device

Multicast Router

Fig. 2. Tunnel convergence problem

0098 3063/09/$20.00 © 2009 IEEE

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MAG, instead of an MN, performs movement detection and binding updates; therefore, unlike Mobile IP, MNs do not need to install any mobility-related protocol. Moreover, the PMIPv6 does not require IP reconfiguration procedures in the same PMIPv6 domain. A. Proposed Network Model To design a PMIPv6-based multicasting service, we consider the position of MR. Fig. 3(a) shows a simple solution, where both the MAG and the LMA contain the MR function; however, this strategy introduces a tunnel convergence problem similar to Mobile IP-based bidirectional tunneling schemes. Therefore, we separate the MR function from the LMA, as shown in Fig. 3(b), so the MAG can connect to both the LMA and the MR. Thus, multicast packets are delivered from the MR while unicast packets are delivered from the LMA via tunnels. However, the overhead for the routing update from both network models (see Fig. 3(a) and (b)) degrades the performance of PMIPv6 components. Consequently, we propose the network model depicted in Fig. 3(c), where the MAG contains only an MLD forwarding proxy (MLD-FP) function that has been proposed by the IETF [8]. Multicast packets without tunnel header are delivered from a local MR, while unicast packets with PMIPv6 tunnel header are delivered from LMA. An MLD-FP and separated data path of unicast and multicast lift the burden from MAG and LMA. As a result, the tunnel convergence problem is solved and routing processing overhead is reduced. Multicast Core Tree

MR: Multicast Router

LMA: Local Mobility Anchor LMA + MR

LMA

e nn l

MR + MAG

MR + MAG

MR + MAG

MR + MAG

PMPv6 Domain

PMPv6 Domain

(a) Multicast Router on MAG and LMA

(b) Multicast Router on MAG

Multicast Core Tree

MR

LMA

MLD Forwarding Proxy + MAG

MLD Forwarding Proxy + MAG

PMPv6 Domain

II. NETWORK MODEL FOR EFFICIENT MULTICASTING In this section, we propose a novel PMIPv6-based network model allowing for reduction in packet delivery cost for multicasting. PMIPv6 supports network-based local mobility within a PMIPv6 domain consisting of a Mobile Access Gateway (MAG) and a Local Mobility Anchor (LMA) [7]. A

Multicast Core Tree

MAG: Mobile Access Gateway

Tu

To solve the tunnel convergence problem, V. Chikarmane et al. [3] presented the mobile multicast (MoM) scheme, where the FA selects an HA from among several tunneling the same multicast data as a designated multicast service provider (DMSP). Consequently, the scheme can reduce redundant multicast packets; however, this leads to significant signaling overhead and requires complex processing at both the HA and FA. In addition, all MNs experience service disruption caused by DMSP re-selection if the current DMSP is the HA of an MN willing to hand off. Y. Min-hua et al. proposed another alternative [4], the Mobile Multicast Gateway (MMG) scheme, to solve the tunnel convergence problem. MMG can get multicast packets through in two ways. First, it gets multicast packets explicitly by joining a multicast group, but it cannot join the group. Thus, the first MH that wants to join the multicast group should send an IGMP Membership Report message to its home network and get multicast packets through a bidirectional tunnel. Thus, the MMG of the foreign network intercepts the packets implicitly for multicast delivery to other nodes willing to receive them. However, the MMG has difficulty intercepting packets destined for other receiving nodes. In such a case, the scheme increases packet delivery cost in proportion to the distance between the MN of a foreign network and the MMG of a home network. The second problem is the great delay experienced by executing handover, membership management, and multicast tree update for seamless communication whenever MN moves to a foreign network. If an HA does not support multicast router functionalities, an MN should discover a multicast router (MR) and send notification by multicast listener discovery (MLD) query/report messages, including requests to join a group communication. However, the maximum query period for MLD is 125 seconds, as specified in [1]. Such a query/report delay is too long to apply to the real world. To decrease multicast handover latency, J. Wu et al. [5] proposed the multicast support agent (MSA) scheme, and S. Yoo et al. [6] proposed the Fast Mobile IPv6 Multicast (FMIPv6-M) scheme; however, these two schemes require modification of MNs to support fast handover and lack robustness because of sudden breaks in wireless links. To provide efficient mobile multicast service related to above-mentioned two problems, we propose a network model to support mobile multicasting based on Proxy Mobile IPv6 (PMIPv6). Then we propose a faster multicast handover scheme than that of a general PMIPv6 handover. We also evaluate the performance of the proposed scheme in terms of packet delivery cost and handover latency.

(c) MLD Forwarding Proxy on a MAG

Fig. 3 Multicasting architecture in PMIPv6 domain

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S. Jeon et al.: Mobility Management Based on Proxy Mobile IPv6for Multicasting Services in Home Networks

a home network from the source node. The second term is the cost for a multicast packet to arrive at NHA HAs through the binary tree (l layers). The third term is the cost for HAs to forward the tunneled packet to m MNs.

B. Performance Analysis

C MoM =

Fig. 4. Network topology for performance analysis

To analyze the performance of our scheme, we employ the method used in [4]; however, unlike that of [4], we assume that both home and foreign networks can support multicast, as shown in Fig. 4. In addition, we assume the following in calculating the equations presented in this paper: •

• •

• • • • •

•

The architecture is hierarchically formed like a tree structure with an l-layer, where l denotes the number of routers from the highest to the lowest MR within the tree. In two hierarchical trees, all the bottom routers of one tree are HAs and those of the other are FAs. For the proposed PMIPv6 based network model, we consider a single home or foreign network as a single PMIPv6 domain. The hop count is h from the source to the top MR. HAs, FAs, and the MAG receive the same multicast data only when at least one MN exists. The number of HAs, FAs, and MAGs located at the l-th layer in a hierarchical tree is 2l-1. The number of HAs, FAs, and MAGs with at least one MN are NHA, NFA, and NMAG, respectively. When an MN moves to a foreign domain, the identifier of HA (i.e., the number i of HA#i) is equal to the identifier of FA (i.e., j of FA#j), for example, HA3 Æ FA3. Cmulticast (Nx, y) expresses the multicast packet delivery cost from the source node to the Nx nodes located in the bottom layers.

We define the total packet delivery cost as the sum of hop counts of multicast packets passing through routers from the source to the lowest bottom router. An MN is located at an FA of a foreign network from an HA of a home network. For simple evaluation of performance, when the multicast data are delivered from a home network to a foreign network, we consider all multicast data should traverse the top MR of the home network and the top MR of the foreign network. The cost for bi-directional tunneling (B-D), MoM, and MMG schemes is as follows [4]: C B−D =

1 [h + C multicast ( N HA , l ) + m(l − 1 + h + l ). m

1229

(1)

In the B-D case, the first term in brackets in (1) represents the cost for a single multicast packet to arrive at the top MR of

1 [h + C multicast ( N HA , l ) + N FA (l − 1 + h + l − 1) + N FA ]. m

(2)

In the case of an MoM scheme, the first and second terms are the same as in (1). The third term in brackets in (2) represents the cost for tunneled multicast packets to arrive at NFA FAs acting DMSP. The fourth term is the cost to forward a multicast packet to NFA MNs. Two cases are used to calculate the cost of an MMG scheme (see section I). We assume that the top MR of a home network is MMG0 and the top MR of a foreign network is MMG1. Each distance between the source and MMG0, and between MMG0 and MMG1 is h. If MMG0 gets multicast packets from MMG1 by tunnel, then the cost is calculated as in (3) and we call it MMG_A. C MMG _ A =

1 [2 ⋅ h + l + C multicast ( N FA , l ) + N FA ]. m

(3)

In equation (3), the first term in brackets is the sum of the cost required to send a multicast packet from the source node to the MMG0 and the cost required to send the packet via tunnels from MMG0 to MMG1. The second term is the cost required to forward a single tunneled packet from MMG1 to the target MN. The third term is the cost for other MNs interested in the group to forward a multicast packet copied from MMG1. However, when MMG1 gets a multicast packet by joining a multicast group, the cost is calculated as in (4) and we call it MMG_B. C MMG _ B =

1 [ h + C multicast ( N FA , l ) + N FA ]. m

(4)

In equation (4), the first term in brackets is the cost for one multicast packet to arrive at MMG1 from a source node. The second term is the cost for MMG1 to forward multicast packets to NFA FAs. The third term is the cost for NFA FAs to forward multicast packets to MNs. In the proposed model, the cost of a tunneled packet is not required after handoff because PMIPv6 does not require tunneled packet forwarding by HA or MMG. C PMIPv6 =

1 [h + Cmulticast ( N MAG , l ) + N MAG ]. m

(5)

In equation (5), the first term is the cost for the multicast packet to arrive at the top MR from the source node. The second term is the cost to forward a multicast packet to the MAG. The third term is the cost for MAGs to forward the multicast packet to NMAG MNs.

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III. FAST HANDOVER SCHEME

25 Bi-Directional Tunnel (B-D) MoM MMG__A MMG__B PMIPv6

Hop Counts per MN

20

15

10

5

0

3

3.5

4

4.5 5 5.5 The Number of Layers

6

6.5

7

Fig. 5. Hop count per MN as layer increases 25

Hop Counts per MN

20

A. Mobility Pattern and Handover Probability Simply applying a PMIPv6 handover scheme to the proposed network model leads to service disruption as a result of the latency caused by MLD query/report. To solve this problem, we propose a fast handover scheme using the context transfer mechanism, as shown in Fig. 7. When an MN hands off, the MAG with MLD-FP predicts an MN's direction of movement and transfers the context message, which includes the MN ID, the MN home network prefix, the current MAG address, and the multicast group address. The next MAG (nMAG) then checks whether a node is available to receive multicast data corresponding to the group requested by the previous MAG (pMAG). If no hosts are available to receive the requested group from pMAG, the nMAG starts a timer to check the arrival of the MN and joins the group by sending an MLD report. If the MN does not arrive at the nMAG during the specified time, the nMAG sends the MLD leave message to the MR to save bandwidth in wireless networks.

Bi-Directional Tunnel (B-D) MoM MMG__A MMG__B PMIPv6

15

10

5

0

20

40

60

80 100 The Number of MNs

120

140

160

Fig. 6. Hop counts per MN as increase of MN Fig. 7. Proposed fast multicast handover procedure using PMIPv6

Fig. 5 shows the total multicast delivery cost per MN when the number of MNs is 100. As the layer increases, delivery cost of the tunneled packet increases more rapidly than that of the multicast packet. The cost of bi-directional tunneling and the MoM scheme depends on the number of layers. In the case of MMG_B, no tunnel cost is needed, compared with B-D and MoM. In the case of MMG_A, tunnel cost is incurred for only a single MN. Thus, we can see that MMG increases slightly as the layer increases. The proposed PMIPv6-based multicasting technique also requires tunnel cost for only a single MN, like MMG_B. Fig. 6 indicates that changes occur in hop counts per MN when the number of h and l is 8 and 6, respectively. When the number of MNs increases, the hop counts of the B-D, MMG, and PMIPv6 schemes converge into a constant value because tunnel cost increases in proportion to the growing number of MNs. Therefore, the PMIPv6-based network model has better performance with MMG in terms of delivery cost for multicasting, but PMIPv6 has no mobility related protocol on a mobile device and can easily deploy with no additional multicast agent like MMG. Thus, we propose that the PMIPv6-based network model is suitable for mobile multicasting services.

To analyze handover latency, as in [9], we use hierarchical cell structures consisting of a k-layer, as shown in Fig. 8.

Fig. 8. Mobility pattern for performance analysis

Fig. 8(a) shows movement of an MN from di to di+4 when the layer, k, is 2. Fig. 8(b) shows minimum and maximum distance range that an MN can move in a cell. Before attempting to calculate handover latency, we need frequency of occurrence of inter-MAG handover whenever an MN crosses a cell boundary; thus, we calculate the number of cells belonging to the MAG in (6).

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S. Jeon et al.: Mobility Management Based on Proxy Mobile IPv6for Multicasting Services in Home Networks k

k

i =1

i =1

1231

(6)

C total = C 0 + ∑ C i =1 + ∑ 6i = 1 + 3k ( k + 1).

We note that the real inter-MAG handover occurs at the border line, as given in (7), because only three of the six lines are adjacent to other cells. Pa =

Ck = Ctotal

6k k

1 + ∑ 6i

(7)

.

i =1

Thus probability Pb, which is 1/2, should be multiplied by Pa to obtain inter-MAG handover probability PMAG-HO as shown in (8). PMAG − HO = Pa × Pb =

6k k

1 + ∑ 6i

×

1 = 2

i =1

3k k

1 + ∑ 6i

(8)

.

Fig. 10. Accumulated handover delay according to k-layer

i =1

B. Multicast Handover Latency Total PMIPv6 handover time can be classified with L2 handover time and Proxy Binding Update (PBU) / Proxy Binding Acknowledgment (PBA) time, as in (9). Equation (10) shows MLD latency due to membership update. t PMIPv 6 = t L 2 + t PBU / PBA .

(9)

t MLD = t MLD −Query + t MLD −Re port .

(10)

Consequently, we can determine total handover latency by multiplying the inter-MAG handoff probability by the individual handover delay. Equations (11) and (12) show the latency. In the proposed scheme, an MN does not experience the delay caused by MLD operation. n

MAG − HO t PMIPv 6 − M (i ) = ∑ (t PMIPv 6 + t MLD ) × PMAG − HO .

(11)

i =1

n

MAG − HO t Fast PMIPv 6 − M (i ) = ∑ (t PMIPv 6 ) × PMAG − HO .

(12)

i =1

Fig. 9 shows accumulated handover latency as a function of the number of handovers. MLD query time is assumed to be 0 to 1 second depending on the mobile environment. Once an MN receives an MLD query, it transmits an MLD report to its MAG. We suggest that MLD query transmission follows uniform distribution with 1 second periodicity. The MLD query delay is calculated with uniform random variables according to each handoff. Fig. 10 shows handover latency according to the number of k-layers. When the number of layers increases, the number of cells belonging to one MAG is increased. As a result, the incidence of whole handoffs decreases. Consequently, we can confirm that the proposed handover scheme with the PMIPv6 context transfer mechanism outperforms the original PMIPv6 in terms of handover latency. IX. CONCLUSION Advanced radio technology such as fixed mobile convergence (FMC) and femtocell technologies may enable seamless indoor and outdoor mobile service; however, in terms of IP mobility management, mobile IPTV based on IP multicasting has two constraints: the tunnel convergence problem and high handover latency. In this paper, we proposed a multicast network model using PMIPv6 to ensure efficient delivery of multicast packets. Moreover, we proposed a fast handover procedure that reduces multicast handover delay in the proposed network model. For the evaluation, we performed a numerical analysis. The results prove that our network model and handover scheme are well suited to mobile multicasting. ACKNOWLEDGMENT

Fig. 9. Accumulated handover delay as the number of handoffs

This work was partly supported by the IT R&D program of MKE/IITA [2008-F015-2] Research on Ubiquitous Mobility Management Methods for Higher Service Availability, and the Ubiquitous Computing and Network (UCN) Project of MKE [09C1-C1-20S].

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REFERENCES [1] [2] [3]

[4]

[5] [6] [7] [8]

[9]

R. Vida and L. Costa “Multicast Listener Discovery Version (MLDv2) for IPv6,” IETF RFC 3810, June 2004. I. Romdhani, M. Kellil, and H. Lach, “IP Mobile Multicast: Challenges and Solutions,” IEEE Communications Surveys & Tutorials, vol. 6, no. 1, pp. 18-41, 2004. V. Chikarmane, C. L. Williamson, R. B. Bunt, and W. L. Mackrell, “Multicast Support for Mobile Hosts using Mobile IP: Design Issues and Proposed Architecture (MoM Protocol),” ACM/Baltzer Mobile Network and Applications, vol. 3, no. 4, pp. 365-379, Jan. 1998. Y. Min-hua, Y. Lv-yun, and Z. Hui-min, “Implementation of Multicast in Mobile IP,” Proc. of Wireless Communications and Networking Conference (WCNC 2003), vol. 3, pp. 1796-1800, Mar 2003. J. Wu, and G. Q. Maguire Jr., “Agent-Based Seamless IP Multicast Receiver Handover,” Proc. IFIP Conference Personal Wireless Communication (PWC 2000), Sept. 2000. S. Yoo, and S. Shin, “Fast Handover Mechanism for Seamless Multicasting Service in Mobile IPv6 Wireless Networks,” Wireless Personal Communications, vol. 42, pp. 509-26, Sep. 2006. S. Gundavelli, K. Leung, V. Devarapalli, K. Chowdhury, and B. Patil, “Proxy Mobile IPv6,” IETF RFC 5213, Aug. 2008. B. Fenner, H. He, B. Haberman, and H. Sandick, “Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding (“IGMP/MLD Proxying”)”, IETF RFC 4605, Aug. 2006. C. Cho, S. Jun, E. Paik, and K. Park, “Rate Control for Streaming Services Based on Mobility Prediction in Wireless Mobile Networks,” Proc. of Wireless Communications and Networking Conference (WCNC 2005), vol. 4, pp. 2534-2539

Seil Jeon received B.E. and M.S. degrees in electrical and communication engineering from Soongsil University, Korea, in 2006 and 2008. He is currently a Ph.D. candidate in electrical and communication engineering at Soongsil University. His current research interests include mobile communication, IP mobility protocol, and peer-to-peer (P2P) streaming mechanism for IPTV. He has been a student member of IEEE since 2008. Namhi Kang received B.E. and M.S. degrees in electrical and communication engineering from Soongsil University, Korea, in 1999 and 2001, respectively. He received a Ph.D. in information and communication engineering from Siegen University, Germany, in December 2004. In 2005, he joined Ubiquitous Network Research Center, DASAN Networks, where he was a senior engineer. Since 2009, he has been a professor in the Department of Computer Science, Duksung Women's University. His research interests include QoS and security in wired and wireless networks, and design of communication protocols for future oriented ubiquitous networks. Younghan Kim received a B.E. in electrical engineering from Seoul University, Korea, in 1984. He received an M.S. and Ph.D. in electrical engineering from KAIST, Korea, in 1986 and 1990, respectively. Since 1994, he has been a professor in the electrical and communication department at Soongsil University in Korea. Currently, he is a director of Ubiquitous Network Research Center (13year research program) supported by the Ubiquitous Computing and Network (UCN) Project, the Ministry of Information and Communication (MIC) 21st Century Frontier R&D Program in Korea. His research interests include wired and wireless networking, QoS, mobile computing, and ubiquitous networking. He is a member of IEICE and IEEE.

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