Dominating Set-based Location Management Architecture for Mobile IP Networks Haidar Safa
Wiaam Kassab
American University of Beirut Department of Computer Science Beirut, Lebanon
American University of Beirut Department of Computer Science Beirut, Lebanon
E-mail:
[email protected]
E-mail:
[email protected]
ABSTRACT Mobile IPv4 and Mobile IPv6 were proposed to extend the IP protocol to support mobility. They use two IP addresses: a home network address that is used as a permanent identification address, and a care-of-address acquired at the foreign network and used for routing and data delivery. Hosts that want to communicate with a mobile node send packets to the MN’s home network which forwards them to the MN’s current network. In Mobile IP, the MN should keep updating its home network about its current location. Every time a MN is called, the home network is queried. Signaling traffic resulting from the location update and packet delivery procedures has a significant impact on the performance of the Mobile IP networks. In this paper, we propose a new location management architecture that is based on the dominating set theory and aims at reducing the cost of location update and data delivery procedures. The proposed architecture is compared with the MIPv6, Hierarchical MIPv6 and Localized Mobility Management for MIPv6. Obtained results are very promising.
Categories and Subject Descriptors C.2.1 [Computer-Communication Architecture and Design.
Networks]:
Network
General Terms Algorithms, Management, Design.
Keywords Mobile IP, Mobility Management, Location Update, Packet Delivery.
1. INTRODUCTION In Mobile IPv4, every node utilizes two IP addresses: a home network address that is assigned to the MN by its home network and a care-of-address (CoA) acquired at the foreign network (currently visited network) [2]. The major entities of Mobile IP network architecture are shown in Figure 1. There is: 1) the mobile node (MN) which can undergo seamless roaming among the networks; 2) the Home Agent (HA) of the mobile node which located at the home network and should be always aware of the MN’s current location; 3) the Foreign Agent (FA) which is located at the foreign (currently visited) network and cooperates with the HA to successfully deliver packets addressed to the MNs Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Mobility 2009, Sep 2-4, Nice, France Copyright © 2009 ACM 978-1-60558-536-9/00/0009……$5.00
roaming in its vicinity; 4) the Correspondent Node (CN) with which a MN communicates and can either be mobile or stationary. 1 HA MN FA
Internet
Router
1
Home Network
Foreign Network
1
Router
2 Mobile CN CN
Figure 1. Mobile IPv4 Architecture. In mobile IPv4, mobility agents periodically broadcast advertisements messages. Active MNs listen to these advertisements to detect a movement to another network then try to acquire a new CoA from this new network. After acquiring a new CoA, the MN must register it with its HA (also called location update). Computers that want to communicate with a MN send packets to the MN’s home address. When a MN roaming outside its home network receives a data packet, the HA intercepts and tunnels it to the MN’s current location (i.e. CoA). Although this mobility management scheme is simple and scalable, it has some deficiencies. Indeed, all packets destined to a MN must pass through the home agent as shown in Figure 1 (arrow 1) but the MN replies directly to the CN without passing via the HA (arrow 2). Thus, packets sent to the mobile node are redirected via non-optimal paths. An extension to mobile IPv4, known as route optimization [4] has been proposed to overcome this problem. In route optimization, after receiving the first packet, the HA informs the CN about the MN’s CoA, process known also as Binding Cache (BC), to allow data packets to be sent directly from the CN to the MN using MN’s CoA. However, this may increase the signaling and processing load in the network since the MN can handle multiple communication tasks simultaneously. Also route optimization protocol causes several privacy and security problems such as revealing the users’ current location and traffic redirection, in addition to not working properly with routers that perform ingress filtering. MIPv6 was basically designed to overcome the limitations of MIPv4 [3]. It eliminates the need for foreign agents since it uses the IPv6 Neighbor Discovery instead of the address resolution protocol (ARP) which makes it decoupled from any particular link layer. Route optimization is considered as part of the protocol rather than a non-standard set of extensions and coexists
efficiently with routers that perform “ingress filtering”. This is because the MN uses its CoA while communicating with the CN, unlike MIPv4 where the MN uses its home address as a source IP address. Even though MIPv6 solves many MIPv4 bottlenecks, it still has its own weaknesses and concerns. Signaling overhead resulting from the location update and packet delivery procedures is still a problem. In this paper we propose a Dominating setbased Location Management Architecture (DLMA) that reduces the signaling of both, location update and packet delivery procedures. The remaining of this paper is organized as follows. In Section 2, we present the location update and packet delivery procedures of MIPv6 and survey related work. In Section 3, we describe our proposed DLMA. Numerical results are presented in Section 4. Conclusion is presented in Section 5.
Also, when the MN and the CN are in the same network and the CN wants to send packets to the MN, it will have to first send the packets to the MN’s home address where the HA intercepts and forwards them to the MN’s new location (CN’s network) which adds more delay and signalling to the whole network. Network1 2 CN1
1
CN2
3 1
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Movement
1 3 2
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Network2
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Figure 3. Packet deloivery in Mobile IPv6.
2. RELATED WORK The cost of the location update procedure in MIPv6 depends upon the number of MNs, MN’s mobility rate, and the distance between the MN and its communicating CNs and its HA. The procdure is summarized in Figure 2 which shows a MN exchanging packets with two CNs, CN1 and CN2. When the MN moves from the network 1 to network 2, it first acquires a CoA then sends at least three Binding Updates (BU), one to the HA (black arrow-1), one to the CN1 (dashed arrow-2), and one to the CN2 (long-dashed arrow-3) to inform them about its current location. The BU message in MIPv6 is encoded as options in an extension header, called the mobility header [3]. The home agent maintains a binding cache (BC), which contains all bindings for the MNs it serves. Similarly each CN maintains a BC that contains the CoAs of the MNs with which the CN has active sessions. Each entry in the binding cache stores a binding for one home address. Signalling messages of the location update flowing all over the network can add extra load on the network. Therefore, binding updates should be as low as possible. Network1 CN1
CN2 2
MN
3
Movement 3 2
Network2 3 MN
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HA 1
1
1
Several domain-based mobility management mechanisms were proposed in [5][8][9][12]. Each domain contains one or more IP subnets and one or several access routers (ARs). Hierarchical MIPv6 (HMIPv6) [5] was proposed to reduce the signaling between the HA and the MN. It mainly deals with intra-domain mobility by introducing a hierarchical entity called the Mobile Anchor Point (MAP) that is responsible for handling domainbased signaling of the MNs that are visiting foreign networks. In HMIPv6, a MN entering into a new foreign network is assigned two care-of-addresses: a Regional CoA (RCoA) which belongs to the local MAP and an on-Link CoA (LCoA) which changes with each intra-domain movement. Access routers are the point of attachment of the MNs to the MAP as shown in Figure 4. When a packet destined to the MN arrives at the HA, the HA looks up its binding cache to find the MN’s current location then tunnels the packet to the MAP, which looks up its BC to find the LCoA of the MN and tunnels the packet to it. The MN sends a BU to the CN so that the CN can send any further packets directly to the MN’s current RCoA. In HMIPv6’s, any local move performed by the MN only requires the update of the LCoA at the MAP to make it aware of the new AR of the MN. This reduces the amount of signaling sent to the home network. HMIPv6 suffers from the triangle routing problem because every packet sent to the MN goes through the MAP before being tunneled to the MN’s LCoA. Furthermore, if a CN wants to start a session with a MN which is originally in its MAP subnet, the CN will have to send its packets first to the HA which tunnels them back to the MAP.
Figure 2. Location Update in Mobile IPv6. When sending a packet to any destination, the CN checks its binding cache for an entry for the destination. If such entry exists, the CN uses an IPv6 routing header to route the packet to the MN’s CoA. Routing packets directly to the MN’s CoA allows the shortest path to be used, eliminates congestion at the MN’s home agent, and reduces the impact of any possible failure at the home agent or any other network entity. Figure 3 shows the packet delivery procedure. CN1 uses the dashed arrow-1 optimal path to deliver packets directly to the MN’s current CoA without the intervention of the HA. When the MN moves from network1 to network2, CN1 should send its packets via arrow-2 optimal path to the MN’s new CoA. However, if the connection between the MN and CN1 is broken, then CN1 has to use the non-optimal arrow-3 path to deliver the packets to the MN through the HA.
Figure 4. Hierarchical MIPv6. The Localized Mobility Management for mobile IPv6 in Distributed manner (LMMDv6), proposed in [8] uses a Local Mobility Agent (LMA) functionality for proxying a regional COA which remains the same when the MN moves within a Local Mobility Domain (LMD). LMMDv6 re-uses the general idea of [5]. However, it is a different protocol with regard to the formation of LMDs and LMAs which are per-node and created dynamically according to the MN movement. A LMD is
composed of all routers that are sufficiently close to a fixed Center Router (CR). The distance is measured by the hop count between two routers. LMMDv6 distributes the LMA functionality across all access routers. When a MN arrives first to the visited network, its LMA is the first access router to which it is attached. Then, a LMD is formed of the set of routers that are at a distance less than or equal to N hop counts from this first LMA. As a result, this LMA acts as an anchor HA for the MN while roaming within a LMD. Figure 5 depicts an example of the LMD formation with a hop count threshold of two. Notice that AR5 and AR6 are outside the LMD (CR, 2) since they are more than two hops count from the LMA (e.g., CR). Whenever the MN moves to a new router that is within its current LMD, (i.e., AR2, AR3 or AR4) only local binding update to the LMA is needed. However, if it moves to a router which is more than 2 hop counts from its current LMA (i.e., AR5 or AR6), the new router will become the MN’s new LMA and consequently, a new LMD is formed and the MN will have to send binding updates not only to its home network, but also to any CN communicating with.
2) Dominating Agent (DA) which is an AR that belongs to the DS nodes and can reach all of the other nodes in the domain/subnet, 3) Home/Foreign Gateway Dominating Agent (GDA) which connects one domain to other domains and each MN has a Home GDA in its home network and associates with a Foreign GDA when visiting foreign networks, 4) the Roaming Mobile Nodes List (R-MN-L) which is a list used by the home GDA to track the current locations of the roaming MNs (the Home GDA maintains in this list entries of the mobile nodes that have this GDA as their Home GDA but roaming outside their home networks), and 5) the Visitors Mobile Nodes List (V-MN-L) which is a list in which the Foreign GDA maintains entries of the mobile nodes that are visiting this Foreign GDA’s network.
Figure 5. LMMDv6 example
3. PROPOSED SCHEME In this section we describe our proposed Dominating set based Location Management Architecture (DLMA) that aims at reducing the signaling of both, location update and packet delivery procedures. The proposed scheme obtains first the dominating set of the Internet routers backbone. Then, it selects some nodes from the dominating set and designates them to play the role of the mobility agents. Gateway mobility agents will maintain two lists: one to track the nodes that belong to the networks it serves but are roaming outside its vicinity, and another one to track the visiting nodes. In a Dominating Set (DS), any other vertex in the graph should be connected to one DS vertex [10]. Each node exchanges its neighborhood information with all of its one-hop neighbors. Any node with two unconnected neighbors becomes a dominator. The set of all the dominator nodes forms a DS. An example is shown in Figure 4 where there is graph of five nodes a, b, c, d, e. After applying the domintaing set theory in this graph only vertices b and c are marked as dominators. The resulting dominating set is generally not minimal, but [11] proposed some rules to reduce its cardinality.
Figure 6. Dominating Set example Our proposed architecture designates certain nodes of the DS to play the roles of mobility agents. Its main components are shown in Figure 7. They are: 1) the Access Router (AR) which can be any node in the network to which the MNs are directly attached,
Figure 7. Architeture of DLMA In Figure 7 the gateway dominating nodes are encircled (e.g., node 4). Several location update scenarios may exist in our architecture depending on the type of movement whether it is an intra-domain or an inter-domain movement. For example, when a MN moves from its HA subnet to another subnet under its HomeGDA, it acquires a new CoA then sends a BU to its HA via the AR. However, when the MN moves from a subnet in its home domain to another subnet in a foreign domain, it acquires a new CoA and registers it with the Foreign-GDA (which adds a new entry for MN to its visitors list), then the Foreign GDA updates the MN’s Home GDA with MN’s new location (i.e., MN’s HGDA updates MN’s entry in its roaming list). Another scenario is when the MN moves between two subnets that belong to two different foreign domains. The MN first acquires a new CoA and registers it with the new Foreign GDA which updates, in its turn, the MN’s Home GDA with MN’s current Regional CoA and also updates the old Foreign GDA to delete the MN’s entry from its visitors’ list. In the case of a MN moving from one subnet to another one under the same Foreign GDA, the MN acquires a new CoA then performs regional registration with the Foreign GDA to update its local-CoA entry in the visitors’ list. As a result of these scenarios, the HA of the MN will be accessed and updated only during local moves in the home domain. Similarly, several packet delivery scenarios may exist in our architecture. For example, when the MN is in its home domain and the CN is in another domain. The CN sends the packet to the MN’s home agent. The packet should go through the CN’s current subnet’s Foreign GDA. If the Foreign GDA does not find an entry for the MN in its visitors’ list (V-MN-L), it forwards it toward the MN’s HA where the packet should reach first the MN’s Home GDA. The Home GDA checks if it has an entry for the MN in its
roaming list. If it does not have, it forwards the data to the MN’s HA which tunnels it to the MN’s current AR to deliver it to the MN. A different scenario will occur when the CN and the MN are in the same foreign domain. In this case, the CN sends the packet to the MN’s HA through the MN’s Foreign GDA. However, the Foreign GDA finds the MN in its visitors’ list (VMN-L) and forwards the data to MN’s AR (local CoA) which delivers it to the MN. Another scenario occurs when the MN is in a foreign domain and the CN is in another foreign domain. In this case, the CN sends the data to the MN’s HA through its Foreign GDA. The Foreign GDA does not find an entry for the MN in its visitors’ list (V-MN-L) and therefore forwards the data to the MN’s HA where they are intercepted by the MN’s Home GDA. The MN’s Home GDA finds the MN in its roaming list (R-MN-L) and forwards the data to the MN’s current Foreign GDA which forwards it to the MN’s current AR to deliver it to the MN.
nodes are designated as Gateway Dominating Agents, GDAs. The proposed DLMA can reduce the cost of location update and data delivery procedures by using these new gateway mobility agents. We have studied all the possible location update and data delivery scenarios. We have evaluated the performance of the proposed scheme considering the call to mobility ratio parameter. The obtained results showed that the proposed scheme outperforms other schemes found in the literature.
4. NUMERICAL RESULTS We have derived the location update cost, LU, and the packet delivery cost, PD, for each scheme using an analytical model similar to the one presented in [12] . In this model, the total cost of DLMA, DLMAtot, can be given as: DLMAtot = μLU DLMA + λ a PD DLMA where μ is the average number of times the MN changes its location per unit time and λa is the packet arrival rate at the MN. Similarly, the total signaling costs of mobile IPv6, MIPtot, of HMIPv6, HMIPtot, and of LMMDv6, LMMDtot can be given as SCHEMEtot = μLU SCHEME + λa PDSCHEME where LUSCHEME and PDSCHEME are the location update cost and the packet delivery cost of the concerned scheme. We define the call-to-mobility ratio (CMR)[6] to be ratio of the average packet arrival rate, λa, to the average mobility rate of the
λ ). When the mobility rate dominates, the μ CMR decreases and when the packet arrival rate dominates, the CMR increases. To compare the three schemes DLMA, HMIPv6 and LMMDv6 with that of MIPv6, we define the relative cost (RC) of a scheme to be the ratio of the total cost of the scheme divided by the total cost of MIPv6 (e,g., RC > 1 means that MIPv6 outperforms the scheme while RC < 1 means that the scheme outperforms MIPv6). The scheme relative cost is given as: MN, μ (i.e., CMR =
RCSCHEME =
SHEMEtot LU SCHEME + (CMR * PDSCHEME ) = MIPtot LU MIP + (CMR * PDMIP )
We have outputed some numerical results measuring the relative cost of each scheme when varying the call-to-mobility ratio. Figure 8 shows the significant cost reduction obtained with the proposed DLMA while varying the CMR.
Figure 8. Relative Cost vs. CMR
6. REFERENCES [1] Charles E. Perkins, Mobile IP, IEEE Communications Magazine, Volume 35, Number 5, May 1997, pp. 68-70
[2] C. Perkins, IP mobility Support for IPv4, internet draft, draft-ietf, mobileiprfc2002- bis-08.txt, Sept. 2001.
[3] D. Johnson, C. Perkins, and J.Arkko, Mobility Support in IPv6, [4] [5] [6] [7] [8] [9]
[10] [11]
[12]
5. CONCLUSION We have proposed a Dominating Set-based Location Management Architecture for Mobile IP networks, called DLMA. The proposed DLMA uses the dominating set theory to form a set of gateway nodes that can cover the whole network. This set is reduced by applying some reduction rules and the final gateway
Internet Engineering Task Force (IETF), internet draft, draft-ietfmobileip-ipv6-24.txt June 2003. C. Perkins and D. Johnson, Route Optimization in Mobile IP, internet draft, draft-ietf-mobileip-optim-09.txt Feb 2000. H. Soliman, C. Castelluccia, K. El-Malki, and L. Bellier, Hierarchical MIPv6 Mobility Management, Internet draft, draft-ietfmobileip-hmipv6-o4.txt, Oct. 2002. Safa H., Pierre S., and Conan, J., An Efficient Location Management Scheme for PCS Networks, Computer Communications, Elsevier Science, Vol. 24, No. 14, August 2001, pp. 1355-1369. Soliman H., (Mobile IPv6. Mobility in a Wireless Internet), pp. 8487, 2004. C. Williams, (Localized Mobility Management Requirements), draftietfmobileip-lmm-requirements-03.txt, March 2003. W. Chang, J. Li, and H. Kameda, (A Dynamic and Distributed Domain-Based Mobility Management Method for Mobile IPv6), IEEE Communications Magazine, Volume 3, Oct 2003, pp. 19641968. T. W. Haynes, Hedetniemi S. T., and P. J. Slater., (Fundamentals of Domination in Graphs), A Series of Monographs and Text books. Marcel Dekker, Inc., 1998. Wu, F. Dai, M. Gao and I. Stojmenovic, (On calculating poweraware connected dominating sets for efficient routing in ad hoc wireless networks), Journal of Communications and Networks, Vol.4, Mar 2002, pp. 59-70. Jiang Xie, and Ian F. Akyildiz, (A Novel Distributed Dynamic Location Management Scheme for Minimizing Signaling Costs in Mobile IP), IEEE transactions on mobile computing, vol. 1, no. 3, july-september 2002, pp. 163-
