AROSP: Advanced Route Optimization Scheme in PMIPv6 Networks for Seamless Multimedia Service

Transcription

1 26 IJCSNS International Journal of Computer Science and Network Security, VOL.8 No.9, September 2008 AROSP: Advanced Route Optimization Scheme in PMIPv6 Networks for Seamless Multimedia Service Byungjoo Park 0, Dongcheul Lee and Jaejin Lee KT Network Technology Laboratory, Internet Research Department, Yuseong-Gu, Daejeon, South Korea Summary In standard Mobile IPv6 networks multi-media streaming suffer from packet disruptions and packet loss resulting from high handover latency as well as available bandwidth fluctuation. To decrease high handover latency, Fast Handover for MIPv6 can be adopted where the client stores quickly sufficient amount of stream in advance. However, under the both conventional protocols which based host mobility, handover latency may take up to several seconds, it is extremely difficult to maintain seamless media playback.for network-based mobility management, the Internet Engineering Task Force (IETF) is standardizing Proxy Mobile IPv6 (PMIPv6). In this paper, we propose an optimal fast handover scheme using Optimal Proxy Binding Update and Snoop mechanism in network based proxy Mobile IPv6 networks, and we then evaluate it against IETF s convention protocols in terms of deployment, proceeding latency. Key words: Multimedia, PMIPv6, Handover, Route Optimization. 1. Introduction In multimedia streaming applications such as Mobile IPTV, media stream has to be transmitted seamlessly to the client. Beside the handover problem under the Mobile IPv6 (MIPv6) networks to be discussed in this paper, the media streaming applications have to overcome the network variation challenges [1]. IETF MIPv6 is designed to manage the movement of mobile nodes (MNs) between wireless IPv6 networks. The protocol provides seamless connectivity to MNs when they move from one wireless point of attachment to another in a different subnet. Mobile IPv6 notifies the correspondent(s) of an MN about its new location by binding the MN addresses. Nevertheless, the MN cannot receive IP packets on its new point of attachment until the handover finishes. MIPv6 supports mobility by binding Home Address(HoA) and Care-of Address(CoA) to Home Agent(HA) when MN attempts to connect to new Access Router(AR) after being disconnected from current AR. However, movement detection, address configuration and confirmation, and a registration process are needed when it tries to handover. Consequently, MN loses packets during this process [2]. Recent work has been aimed at improving Mobile IPv6 handover performance in order to support real time and other delay sensitive traffic. Packet losses during handover are treated as an indication of network congestion, which causes TCP to take unnecessary congestion avoiding measures [3]. For this work, some trials have been proposed such as Smooth handover for Mobile IP by Route optimization in mobile IP [4] and Fast Handover for Mobile IPv6 (FMIPv6) [5]. By the help of link layer, the fast handover detects change of link connectivity and sets up a routing path, so called tunnel, between two access routers (AR). The tunnel is used to forward packets to a new AR from a previous AR, until a mobile anchor point (MAP) changes the routing path from the previous AR to the new AR. However, the Fast Mobile IPv6 (FMIPv6) [5] may cause packet mis-ordering problem between tunneling packets from PAR, HA and directly delivered packets from CN. These mis-ordered packets encounter performance decline of TCP by duplication of the ACKs from the TCP congestion control on the transport layer and induce useless packet retransmissions from CN. Proxy Mobile IPv6 (PMIPv6) has been proposed by IETF NetLMM working group and this protocol defines two network entities; Mobility Access Gateway and Localized Mobility Anchor (LMA). Therefore, PMIPv6 protocol guarantees the localized mobility solution for the MN whenever the MN handover within an local mobility domain area. However, the current PMIPv6 does not provide the specific route optimization scheme for reducing packet disruption. Thus, PMIPv6 needs the technology that reduces packet loss by efficient buffering before MN moves to new Mobile Access Gate(MAG). Therefore, even though MN did not send handover prediction information, MAG can detect handover [6]. Manuscript received September 5, Manuscript revised September 20, 2008.

2 IJCSNS International Journal of Computer Science and Network Security, VOL.8 No.9, September In this paper, we propose an efficient and reliable media streaming scheme in Proxy MIPv6 to support seamless media streaming without packet disruptions during a handover. It is done by using optimal proxy binding update message and pre-buffering mechanisms with snoop agent. The remainder of this paper is organized as follows. Section 2 introduces PMIPv6 and previous works about seamless handover. Section 3 explains a proposed scheme. Section 4 compares the performance between the proposed scheme and conventional protocols. 2. Related Works and Problems 2.1 IETF Standard MIPv6 (MIPv6) The basic idea in Mobile IPv6 is to allow a HA to work as a stationary proxy for a MN [2]. Whenever the mobile node is away from its home network, the home agent intercepts packets destined to the node, and forwards the packets by tunneling them to the mobile node addressed to NCoA. The transport layer uses the home address as a stationary identifier for the mobile node. The basic solution requires tunneling through the home agent, thereby leading to longer paths and degraded performance. To improve the performance, Mobile IPv6 includes route optimization [4]. In route optimization a CN discovers a binding which is then used to modify the handling of outgoing packets between the mobile node s stationary home address and its NCoA. When route optimization is used, the mobile node sends its NCoA to the CN using binding update (BU) messages. After receiving BU, the packets leaving the CN are routed directly to the NCoA. However, before the CN receives the BU, it continues to route packets to the NCoA via HA. Consequently, these two types of packets will arrive at the NAR with mis-ordered packets. 2.2 IETF Fast Handover for Mobile IPv6 (FMIPv6) While an MN is connected to its PAR and is about to move to an NAR, FMIPv6 requires that the MN obtains a new CoA at the NAR while still connected to the PAR. Furthermore, the MN must send a Binding Update message to its PAR to update its binding cache with the MN s new CoA, and finally the PAR must start forwarding packets, originally destined for the MN, to the NAR. Either the MN or the PAR may initiate the Fast Handover procedure by using the L2 trigger. The linklayer information indicates that the MN is moving from the current access point (AP) to another; that is, from the PAR to the NAR. If the L2 trigger is received at the MN (Mobile-initiated handover), the MN will initiate an L3 handover by sending a Router Solicitation for Proxy (RtSoPr) message to the PAR. On the other hand, if the L2 trigger is received at the PAR (Network-controlled handover), then the PAR will transmit a Proxy Router Advertisement (PrRtAdv) message to the appropriate MN, without any solicitation message. The MN obtains a new CoA (NCoA) while still connected to the PAR by means of router advertisements containing network information from the NAR. The PAR validates the MN s new CoA and initiates the process of establishing a bidirectional tunnel between the PAR and the NAR by sending a Handover Initiate (HI) message to the NAR. Then, the NAR verifies that its new CoA can be used on the NAR s link. Also, in response to the HA message, the NAR sets up a host route for the MN s previous CoA (PCoA) and responds with a Handover Acknowledge (HACK) message. When the MN receives a PrRtAdv message, it should send a Fast Binding Update (F-BU) message, preferably prior to disconnecting its link. When the PAR receives an FBU message, it must verify that the requested handover is accepted by the NAR as indicated in the HACK message status code. Then, the PAR begins forwarding packets intended for the PCoA to the NAR and sends a Fast Binding Acknowledgement (F- BACK) message to the MN. After changing link connectivity with the NAR, the MN and NAR exchange a Router Solicitation (RS) Message including the Fast neighbor Advertisement (FNA) option and a Router Advertisement message (RA) with the Neighbor Advertisement Acknowledgment (NAACK) option. After the NAR sends a Router Advertisement message with the NAACK option, it starts to deliver buffered packets tunneled from the PAR and buffered packets from the CN directly. Until the CN receives a BU, the packets sent from the CN are tunneled from the PAR to the NAR. After the CN receives a BU, the CN directly delivers the packets to the MN. Consequently, if the distance between the CN and NAR is shorter than the tunneled distance from the CN to the NAR via the PAR, the MN may receive out-of-sequence packets. After the PAR receives an F-BU message, packets four through eight are tunneled from the PAR to the NAR and buffered until the NAR receives an RS message with FNA from the MN. When the CN receives a BU from the MN, the CN sends packet nine to ten directly to the NAR. These packets are also buffered in the NAR until the NAR sends an RA with NAACK option to the MN. Consequently, if the distance between the CN and NAR is shorter than the tunneled distance from the CN to the NAR via the PAR, buffered packets in the NAR would be out of sequence due to the packet delay time inccurred by tunneling. So when an MN receives mis-ordered packets, the use of TCP in the MN creates a duplicate

3 28 IJCSNS International Journal of Computer Science and Network Security, VOL.8 No.9, September 2008 ACK (DACK) for packets six and seven in accordance with its congestion control procedure. accepted address modes, loaming policies, etc. for providing network based mobile services. Fig. 1 IETF PMIPv6 Handover Procedure. 2.3 IETF Proxy Mobile IPv6 (PMIPv6) IETF standardizes PMIPv6 that manages mobility on the basis of network, not in MN. Fig.1 shows the comparison between standard MIPv6 and PMIPv6. It expands MIPv6 signaling by using a proxy mobility agent and supports the mobility of MN by reusing HA. This kinds of mobility-supporting schemes do not include MN in a signaling exchange process for the mobility management [6][7]. That is, MAG in a network and LMA which manages domain network do MIPv6 signaling and manage the mobility which was managed by MN. Normally, LMA is located between the domain gateways. Fig. 2 shows the flow of PMIPv6 protocol messages. PMIPv6 supports MNs that do not support MIPv6 while they connect to IPv6 based network. MN defines the scheme for sustaining connection with CN when it changes network connection point while being connected with CN. Therefore, PMIPv6 should get a home address at the link if MN enters a PMIPv6 domain and authenticates. And the network should emulate that MN is always in a home network by assigning a home network prefix to MN. Then MN considers PMIPv6 domain as the domain that consists of same home link. MN sends MN-identifier messages to new MAG for authentication. And it obtains a MN s profile after the L2 link layer handover completed so that it can notify its movement by policy store (AAA server, Authentication Authorization Accounting). The profile contains information about MN-ID, LMA, Fig. 2 IETF PMIPv6 Handover Procedure. After MAG gets MN s profile from the policy store, it sends router advertisement messages with a home network prefix to MN if the profile contains a MN s home network prefix. MN which received RA (Router Advertisement) messages from connected links can set IPv6 addresses to its interfaces by the method which the links permit. MAG which receives the profile sends PBU (Proxy Binding Update) messages to LMA for registering MN s location information. PBU message contains MN s NAI (Network Access Identifier) options, home network prefix of the mobile node, and other required options. After receiving PBU, LMA checks whether its binding cache tree has mobile nodes ID. If not, it creates information about mobile nodes, and sets tunneling between LMA and NMAG, and sends PBA (Proxy Binding Acknowledgement) messages to NMAG with MN s home network prefix options.

4 IJCSNS International Journal of Computer Science and Network Security, VOL.8 No.9, September The proposed Optimal Fast Handover Scheme (RPMIPv6) The purpose of PMIPv6 with route optimization is to support seamless handover and to reduce the packet loss with the help of connectivity information of link layer. In PMIPv6 which was proposed by IETF, MAG supports mobility when MN moves without changing the configurations of MN. However, this scheme may cause a packet mis-ordering problem between tunneling packets from the PMAG, LMA/HA and directly delivered packets from the CN. These out-of-sequence packets encounter performance decline of TCP by duplicated ACKs according to TCP congestion control on the transport layer and induce useless packet retransmissions from the CN. In real time service applications, it is difficult to remedy the out-of-sequence packets correctly. In proposed scheme, after process of establishing a bidirectional tunnel from the PMAG to the NMAG is made, the PMAG sends Optimal Proxy Binding Update message to the CN as soon as an MN start moving so that the number of packets which need to be forwarded from PMAG to NMAG could be decreased. Certainly this optimal proxy binding update (OP-BU) message can be modified by adding a 2-bit P-flag to the reserved flag and including the NMAG address and MNs ID as options in the option field. Table 1: The P-flag of Optimal Proxy binding Update Message P-Flag Meaning 00 Don t Apply in IEEE-802 case 01 Send Data Packet to the NMAG 10 Send Data Packet to the PMAG 11 Use standard PBU messa. From NMAG Table 1 defines the P-bits. When LMA/CN receives an optimal proxy binding update message, the LMMA/CN has to be operated by P-bits. First, our assumptions for proposed scheme are as follows: 1) MN receives L2 trigger messages which contain MAG addresses. 2) PMIPv6 Access Points (NAPs) are connected with MAG on the same level. 3) PAP consists of PAP ACK Controller, PAP Dual Stack Buffer and Sequence Checker for ACK. 4) MN s mobility in PMIPv6 network is based on localized mobility. Fig. 3 The Proposed Optimal PMIPv6 (RPMIPv6) Handover Procedure. Fig. 3 shows the flow of proposed PMIPv6 based fast handover scheme with route optimization. PMAG receives L2 HO signaling message which included trigger messages (AP-ID, Proxy CoA) from previous AP (PAP) when MN passes by a base station. PMAG can identify NMAG address before the link down by checking neighbor cache. Initiate (HI) message to NMAG. Then, the NMAG verifies that its Proxy CoA can be used on the NMAG s link. Also, the NMAG start to set up a bidirectional tunnel between PMAG and NMAG) and responds with a Handover Acknowledge (HACK) message. As soon as receiving HACK message, NMAG sends optimal proxy binding update message (OP-BU) to LMA/CN in order to reduce tunneled packet from CN. Therefore, we can reduce both packet loss and out-of sequence packets which cause TCP performance

5 30 IJCSNS International Journal of Computer Science and Network Security, VOL.8 No.9, September 2008 degradation in proxy mobile IPv6 networks using optimal proxy binding update message. Also, if the LMA/CN receives this message quickly, the LMA/CN can transmit new media packets to NMAG with modified TCP data packet header. That is, the CN can send new media packets quickly to the mobile node without long time wait to exchange standard biding update message. If NMAG receives packets from LMA/CN directly, it starts to check modified TCP header flag (T-flag) of received packets. Using T-flag, MAG can distinguish tunneled packet from PMAG and new packet from NMAG. When the T-flag is 0, the packet acts as tunneled packet from PMAG. However, if the T-flag is 1, this packet acts as the new packet from the CN. Then, NMAG can store new packet and tunneled packet separately in the Dual Stack Buffer. The snoop protocol [8] works by deploying a snoop agent with link level buffers at the base station to cache packets passing across the wireless link. Doing so prevents retransmission of unacknowledged packets and avoids unnecessary timeouts; in addition, snoop filters copy acknowledgements to avoid duplicated packets. Our proposed scheme based on snoop protocol to handle duplicated packets. When an MN receives data packets from the NMAG, the MN sends ACKs for the received data packets. The PAP sequence checkers process the ACKs to see whether the received ACKs are duplicates or not. If duplication of an ACK does not occur, the ACK is forwarded to the CN. Therefore, this ACK act as the final ACK for received data packet. On the other hand, if duplication occurred, a snoop agent for the ACK processes the optimized snoop for ACK algorithm to accommodate out-of-sequence packets by delaying the ACK segment processing. To prevent out-of-sequence packets, we use an Sequence Timer (ST) to delay ACKs. We denote TST as the Sequence delay, which is the time required to postpone ACKs during the schedule time. TST is derived by TST = max(ts PN; TOSP ) (1) Where, TS PN is the snoop information transmission delay between the PMAG and NMAG via the PAP. TOSP is the time period in which out-of-sequence packets can arrive during a handover. we define some parameters for comparison. TC P is the packet transmission delay between a CN and a PAP. TP P and TN P are the packet transmission delay between the PAP and the PMAG and NMAG. TWTD is the wireless transmission delay. QP is the queuing delay in the PAP. QPM and QNM are the queuing delay in the PMAG and NMAG, respectively. TPM NM is the packet transmission delay between the PMAG and NMAG, where tunneling is used. Thus, TPM NM is denoted by TPM NM = TP P + TN P + QP (2) TD is the difference between the delay times of a normal packet transmitted directly from the CN to the NMAG via the PAP and a last packet transmitted by the CN via tunneling from the PAP to the NMAG via the PMAG. Therefore, TD is affected by the distance between the PAP and the PMAG. To calculate TD, we denote the last packet transmission delay from the CN to the NMAG via the PMAG as TD T. Thus, TD T is be derived by TD T = TC P + QP + TP P + QPM + TPM NM (3) Also, we denote the packet transmission delay from the CN to the NMAG directly via the NAP as TD D. The TD D is represented by TD D = TC P + QP + TN P (4) Thus, TD can be described as follows. TD = TD T TD D = TP P + QPM + TPM NM TN P (5) Therefore, we can solve the duplicated ACK problem by delaying ACKs during TD. After TD, the PAP transmits delayed ACKs of the content in the Dual Stack Buffer to the CN. That is, after the NMAG waits a maximum time between TS PN and TD, if the sequence timer has expired, the NMAG sends stored ACKs to the CN by arranging the ACK packets with respect to transmission order. After finding the DACK, the PAP controller determines whether the received packet is the first DACK or not. Consequently, the proposed scheme keeps data transmission and ACK transmission in sequence to prevent the retransmission of packets from the CN. 4. Discussion There are the performance impacts on NMAG due to the support of proposed protocol. The main impacts are as follows. First there is the actual CPU and IO load to check duplication procedure for ACKs using sequence checker. Secondly, NMAG s neighbor cache have to keep neighbors information in accordance with the proposed scheme. This is unavoidable, but can be countered with additional CPUs, sufficient IO bandwidth and buffer. The impact largely depends on MNs movement frequency. The impact will be large with a high rate of MNs movement, while it will be small with a relatively low movement frequency.

6 IJCSNS International Journal of Computer Science and Network Security, VOL.8 No.9, September Conclusions The use of a Proxy Mobile IPv6 has advantages in easy implementation and deployment. However conventional Proxy Mobile IPv6 have to consider route efficient optimization scheme for reducing packet loss rate. In this paper, we have introduced the proposed an optimal fast handover scheme in Proxy Mobile IPv6 Networks to support seamless media streaming without packet disruption and mis-ordering packets during handover. By adapting optimal proxy binding update and snoop mechanism, we have many advantages, such as a faster packet route checking speed, which solves the packet delay caused by tunneling between PMAG and NMAG when a router has more than two links. Also, the use of a proposed scheme can prevent the out-of sequence packets problem in conventional protocols. References [1] E. Steinbach, N. Farber, and B. Girod, Adaptive play out for low latency video streaming, in Proc. IEEE ICIP 01, [2] D.Johnson, C. Perkins, J. Arkko, Mobility Support in IPv6, RFC 3775, June [3] V. Tsaotissidis, Open Issues on TCP for Mobile Computing, Journal of Wireless Communications and Mobile Computing, v01.2, no. 1, 2002, pp.3-20 [4] D. B. Johnson, Route Optimization in Mobile IP, draftietf-mobileip-optim-07.txt, Nov, 1997 [5] Koodli, R., Fast Handovers for Mobile IPv6, RFC 4068, July 2005 [6] S. Gundavelli, K. Leung, V. Devarapalli, K. Chowdhury, B. Patil, Proxy Mobile IPv6, IETF Netlmm, Internet Draft, March, 2007 [7] F. Xia, B. Sarikaya, Mobile Node Agnostic Fast Handovers for Proxy Mobile IPv6, IETF Netlmm, Internet Draft, Feb [8] Vangala. S, Labrador.M.A., Performance of TCP over wireless networks with the snoop protocol, in Proc. IEEE LCN, Nov.2002, pp Byungjoo Park received the B.S. degree in Electronics Engineering from Yonsei University, Seoul, Korea in 2002, and the M.S. and Ph.D. degrees (First Class Honors) in Electrical and Computer Engineering from University of Florida, Gainesville, USA, in 2004 and 2007, respectively. He is currently a senior researcher in the KT Network Technology Laboratory, Korea. He is a member of the IEEE, IEICE, IEEK, KIISE and KICS. His primary research interests include theory and application of mobile computing, including protocol design and performance analysis in the next generation wireless/mobile networks. Since 2004, his activities have focused on IPv6, IPv6 mobility management, End-to-End QoS provisions and crosslayer optimization for efficient mobility support on IEEE 802 wireless networks. He has published approximately 25 research papers on mobile computing. He is an honor society member of Tau Beta Pi and Eta Kappa Nu. Dungcheul Lee.received the B.S. and M.S. degrees in Computer Science and Engineering from Pohang University of Science and Technology, Pohang, Korea in 2002 and 2004, respectively. He is currently a junior researcher in the KT Network Technology Laboratory, Korea. He is a member of the KISS. His primary research interests include algorithm and application of mobile communications, including routing protocol design and network engineering in the ubiquitous network. Jaejin Lee is an assistant vice president and the group leader in IP Network Research Group, Network Technology Laboratory, KT, Korea. He received the B.S. and M.S. degrees in Electrical Engineering from Kyungpook National University, Daegu, Korea in 1985 and 1987, respectively, and the Ph.D. degree in Electrical Engineering from Korea University, Seoul, Korea, in Since he joined KT in 1987, for 21 years he worked for the research and development of various IP network management systems including PSTN, ATM, Fixed and Mobile Internet NMSs. His research interest include Broadband Convergence Network, routing algorithms, traffic network management engineering, fixed and mobile IP network architecture and NGOSS (Next Generation Operation Support Systems).