An Enchanced MAG Forwarding Scheme for Proxy Mobile IPv6 Yong JIANG1，Bo HU1 ，Shanzhi CHEN2 1
State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications, Beijing CHINA 2 State Key Lab of Wireless Mobile Communication, China Academy of Telecommunication Technology ,Beijing CHINA
[email protected] Abstract—Long registration delay and signaling cost restrict the practical deployment of MIP. Proxy Mobile IPv6 has been proposed to overcome limitation of Mobile IP, which can avoid tunneling overhead and support of hosts in the mobility management. In this paper, we propose an extension protocol based on Proxy Mobile IPv6 to reduce the overhead of Local Mobile Anchor and decrease handoff delay. When the MN is moving in a Registration Area(RA),current MAG directly sends redirection message to Primary MAG avoiding remote signaling cost to LMA. Analysis results demonstrate that our extension scheme reduces the overhead by decreasing the network signaling cost and optimizes handoff capability. Keywords- MIPv6,PMIPv6,LMA,Primary MAG
I.
INTRODUCTION
As the amount of mobile host increases sharply, the protocol to support mobility has been proposed. Especially, the host-based global mobility protocols such as Mobile IPv6[1] and Hierarchical Mobile IPv6[2] protocol have been considered as a mainstream for enabling IPv6 mobility. However, they are still not deployed in real communication market. Why? The reason is the inherent characteristic involving in using global mobility protocol for every movement between access routers such as remote update latency, signaling overhead and location privacy[3]. Moreover, mobility stack has to be installed into all mobile hosts, which usually have the limited computer capacity and power. Due to such reasons, other standard such as 3GPP+ and WiMax Forum have requested the IETF to develop a new mobility support protocol. Motivated by above observation, Proxy Mobile IPv6(PMIPv6)[4] has been developed from the concept of network-based and local mobility support in IETF. PMIPv6 provides a solution for network-based mobility management that can avoid both tunneling overhead over the air and stack updates in the mobile host. Furthermore, the IETF expects that scaling benefits can be realized by introducing PMIPv6 for localized mobility management. Among these benefits, we can summarize the following four aspects[5] since they are also the major important goals for the Network-based Localized Mobility Management(NETLMM)[6]. Compared with MIPv6, the PMIPv6 has exclusive superiority including handoff performance optimization, reduction in handover-related signaling overhead, location
privacy and having on host participation. Apparently, the distinguishing mark of PMIPv6 would solve a number of challenges of host-based protocol. However, several drawbacks exist in PMIPv6. The most important one identified is that all mobility signaling is controlled through the mobility entities, especially the LMA, which is responsible for not only forwarding of data packets but also processing signaling overhead. So the LMA is easy to become the bottleneck of the whole networks. The scalability in support of very large numbers of MNs suffers limitation. Moreover, the PMIPv6 can cause high handoff delay if the LMA is located far from the current MAG [6].To overcome these drawbacks, we propose an extension scheme to minimize the signaling overhead and optimize mobility management cost in PMIPv6. The major contributions of this paper are: firstly, we give a brief overview of PMIPv6. Section Ⅲ presents extension scheme to expand the capacity of networks and reduce the signaling cost associated with the registration process performed by the LMA. In section Ⅳ, the numerical analysis . II.
PMIPV6 OVERVIEW
PMIPv6 introduces the network-based mobility management concept. A MN’s mobility service is supported by the LMA and the MAG. As the MN hands off between different links, the MAG detects its movement and then registers the location to the LMA by sending the proxy binding update (PBU) message. Notice that the signaling owner is the MAG, not the MN. Because the LMA acts as a home agent(HA) for the MN as described in [1], the location tracking for the MN is managed in the LMA. The LMA replies the proxy binding acknowledgement (PBA) message including the home network prefix (HNP) for the MN to the MAG. The MAG on receiving the PBA message sends the route advertisement message with the HNP to the MN. At that time, the bi-directional tunnel between the MAG and the LMA is established. The end point addresses for the tunnel is the MAG address called proxy Careof Address (pCoA) and the LMA address (LMAA), respectively. Finally, the MN configures its home address (HoA) based on the HNP obtained from the route advertisement message. From the perspective of the MN, the LMA is a topological anchor point due to the HNP for the MN belongs to the same LMA.
This work is supported by the China Next Generation Internet (CNGI) project: No. CNGI-09-02-08; Doctorate Fund of the Ministry of Education project: No. 20090005120013 and Sino-Swedish Strategic Cooperative Program on Next Generation Networks project No. 2008DFA12110 and the Special Funds for Key Program of the China: No. 2009ZX01039-002-001-07.
978-1-4244-3709-2/10/$25.00 ©2010 IEEE
Figure 2. Network Architecture of a PMIP PMIP domain Figure 1. PMIPv6 Handoff Signaling Procedure
Furthermore, all data packets sent to the MN are forwarded through the bi-directional tunnel established between the LMA and the serving MAG for the MN in its PMIP domain.The process is shown in Figure 1. III.
C. The Procedure of Proposed Extension Solution Here, we will introduce the procedure of ExPMIPv6 scheme as the Figure 3 shows. •
When MN enters into a RA, it selects a MAG that it meets with as Primary MAG. Here we assume it is MAG1. The MAG1 detects the MN’s attachment and then registers the location to the LMA by sending PBU message. Once the MAG1 receives PBA message from LMA it sends RS message with the HNP to the MN. At the same time, it also informs other MAGs in the RA by multicast message including MN-ID, the HNP and MAG1’s IP address.
•
Once MN breaks current connection and starts to construct connection with MAG2 in the RA, the MAG2 retrieves the cache directory according to the MN-ID. If there is no entry about the MN, the MAG assumes that it is the first MAG the MN meets. The MAG2 starts the above step’s process. Otherwise, the MAG2 sends RA message including HNP in the cache directory. Meanwhile, it sends a Registration Area Redirection(RAR) message to previous MAG1. Receiving the PAR message, the MAG1 sends the Registration Area Redirection Acknowledgement (RARA) message and constructs the bidirectional tunnel from MAG1 to MAG2. The packets destined for MN are forwarded to the MAG2 by the tunnel.
•
When MN leaves the RA1, it will reconnect to other MAGs in another RA. And above process is continued. The bidirectional tunnel built in previous RA will be deleted and the cache info in each MAG is also updated by the MAG1’s broadcast message.
AN EXTENSION SCHEME FOR PMIPV6
A. Design Considerations To further improve the performance of PMIPv6, we propose the extension scheme which can offer following requirements and benefits. We call our scheme ExPMIPv6. •
Keeping the independence of MN:PMIPv6 is not in accordance with host-based mobility protocols. So our extension scheme should not be permitted to change MN’s stack nor send any registration signaling. The independence of MN remains still.
•
Decreasing the mobility signaling cost in LMA:In the PMIPv6, MAG all need to renew the registration to LMA for each MN’s handoff between MAGs. Our scheme should decrease the registration signaling to LMA and increase scalability in support of very large numbers of MNs.
•
Reducing the handoff delay:High handoff latency may happen if the LMA is far away from MAG. We should consider to further lower handoff delay.
B. PMIPv6 Architecture Before proposing our scheme, we firstly devise the PMIPv6 architecture. Figure 2 illustrates the architecture of a PMIP domain. The PMIP domain consists of a LMA and several MAGs. According to neighboring relations and separate ISPs, we assume the MAGs are divided into different RA. When a MN enters a RA, only the first MAG to which MN is attached need to register to the LMA. We name the first MAG as Primary MAG. If the MN moves to another MAG in the RA, the new MAG doesn’t have to send PBU message. And the first MAG which the MN attaches to is in charge of forwarding the packets to relative MAG.The delay between MAGs is shorter than that between MAG and LMA. The MAGs that involve in the same RA belong to the same multicast group.
After adopting our proposed scheme, the procedure of sending and receiving packets can be described in the following content. The downstream packets, in which the destination address is MN-HoA, are sent to LMA. The LMA encapsulates the packets with the tunnel between LMA and MAG1 relying on looking up binding cache entry(BCE) and sends them to primay MAG which is MAG1. The MAG1 decapsulates the packet .If MN is connected to current primary MAG, the packet will be forwarded to the MN directly. Otherwise,MAG1 will tunnel them to MAG2 by looking up
H S = HC − H A =
route table. The packets whose destination is MN-HoA have to be forwarded to MAG2 by the tunnel. Because the intermediate routers between MAG1 and MAG2 can’t forward the packet automatically. For the upstream packets, the reverse tunnel is needed. The MAG2 can use the tunnel to forward packets to the MAG1 and the later process obeys the fundamental PMIPv6 protocol. PERFORMANCE ANALYSIS
In this section, we describe our analytical models. They are used as evaluation environment for our scheme’s performance. A.
Network Model
The LMA localized domain is composed of M cells in where MAGs are connected by a meshed topology. Then we assume that all cell in the given domain has the circular shape with the same size S. Note that the cell area may be calculated as S=∏*R2，where R is the radius of the cell. As our mobility model, we use the model[9] which is suitable for MN having a high mobility and static velocity. The direction of a MN is distributed uniformly in the range of （0 ，2∏）.Suppose HC and HA be the cell crossing rate and RA crossing rate, respectively. We define v as the average velocity of the MN. Then, the HC and HA are expressed as follows:
HC =
HA =
ρ .v.LC 2 ρ ⋅ v ⋅ S = π π HC N
(3)
A. Cost Analysis In what follows we focus on the benefit obtained related to the most important two factors in mobility management: signaling cost and handoff latency. We compare these metrics of our scheme with that of basic PMIPv6. In the basic PMIPv6, the registration update for an MN occurs whenever the MN hand off between MAGs. An MN in extension scheme calls forth registration update only when the MN moves between RAs. In the same time, the scheme also increases extra costs.
Figure 3. ExPMIPv6 handoff signaling procedure
IV.
H C ⋅ ( N − 1) N
SCBA = Hs ⋅ (Ta + Tc) =
2ρv S
π
(N − N ) (Ta + Tc) (4)
The signaling cost for the basic PMIPv6 SCBA is expressed as follows. We assume the number of cells in the LMA domain is N, each RA contains M cells. Where Ta is the signaling cost between the MAGs and LMA, and Tc is the process cost for tunnel. The signaling cost of proposed extensive scheme is:
SCES = H S 1 (Tb + Te) + H S 2 (Ta + Tc + Td ) =
N 2ρ v S ( M − M )(Tb + Tc) + M π
2ρv S
π Where
(5)
N − N )(Ta + Tc + Td ) M
( H
S1
is the cell crossing rate in a RA, and the H S 2 is
the cell crossing rate in a LMA domain. Tb and Td is the signaling cost between the MAGs and the multicast cost in the RA. In the Equation(5), the former is the overhead of intra-RA handoff and the latter is the cost of inter-RA handoff. Then, handoff latency of PMIPv6 can be calculated as follows:
(1)
H L B A = d M H -M A G + 2d M A G -LM A + d LM A
(6)
The handoff latency in the RA can be expressed as follows: (2)
Where v is the average velocity of the MN , ρ is the MN’s density and LC is the cell perimeter. And N means the number of cells in an area. According to Equation(1), we define HS as the cell crossing rate for which the MN still keeps its residence in the same area.
H L E S = d M H -M A G + 2d M A G -M A G + d M A G Suppose that entities(X and Y).
(7)
d X −Y means processing time between two d MH − MAG is transmission delay of wireless
d MAG − LMA means transmission delay between LMA and d MAG. MAG − MAG decided by hop number between MAGs,
link.
represents transmission delay between LMA and MAG, which can be calculated by C .Where C is the number of MAGs in a domain. B. Numerical Results In this part, we analyze and compare the performance between basic PMIPv6 and extension scheme by numerical results. We set the system parameters listed in TableⅠas the typical scheme for performance analysis. First, we investigate the impact of velocity. Here, we set ρ =0.01. And other parameters are set as default values shown in Table1. Then we vary the speed form 5m/s to 20m/s, and calculate the signaling cost. The NSCLe is signal cost of basic PMIPv6 and the NSCEx means the cost of ExPMIPv6. We can conclude that with the increase of speed, the signaling cost both the proposed extensive scheme based on MAG forwarding and basic PMIPv6 gradually raise. Because the increase of MN’s speed leads to more number of handoff. But, the MAG forwarding scheme is generally smaller than the basic PMIPv6 as its signaling cost is reduced when MNs hand off between MAGs in the same RA. The figure also shows that the registration messages of LMA are also decreased owning to MN registering to LMA when only it handoff between different RAs , which cuts down the load of LMA. When we fix the value of velocity and gradually change the value of ρ .The same situation happens. Because increasing ρ value leads to the augment of MN. V.
mathematical model to testify the effectiveness of our scheme. The simulation demonstrates that our proposed scheme is superior to the basic PMIPv6 due to the reduced signaling load on the whole network and LMA. PMIPv6 is the newest micro mobility management protocol. Thus, there are still some avenues left for future work. For example, how to improve the handover performance for both latency and signaling overhead will be further work. Furthermore, the link layer intelligent detection technique and hierarchical architecture have been developed in the community and being considered useful, how to incorporate these techniques into PMIPv6 for further performance improvement is a meaningful work in the future. In addition, PMIPv6 has no specific concerns on global mobility management.
CONCLUSIONS
In the paper, we study the PMIPv6,considering inherent defect of PMIPv6.Then, we present an extension scheme based on fundamental PMIPv6 in order to enhance the scalability of PMIPv6 and reduce load on the LMA. Lastly, we introduce a TABLE I. NOTA TIONS N
Figure 4. Signaling cost of the entire network and LMA
SYSTEM PARAMETER TABLE MEANINGS
The cell number of LMA domain
S
The area of one cell
M
The cell number of a RA
v
The average speed of MNs
ρ
The density of MNs in a cell
Tc Ta
The process cost for tunnel between MAG and LMA Sig cost between the MAG and LMA
Tb
Sig cost between the MAGs
Td
The broadcast cost in the RA
Te
The process cost for tunnel between MAGs
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[3] VALUE 100
[4] 2
250 m
[5]
9 5～20 0.005～0.02
[6]
5
[7]
10 [8] M M M
1
[9]
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