An Approach
Optimal Hierarchical Mobility Management Network Architecture for
'Iti Saha Misra,2Mohuya Chakraborty 'ETCE Dept., Jadavpur University,Kolkata-700032
3Debashish Saha & 4Amitava Mukherjee 3MIS & CSc Group, IIMC, Joka, Calcutta-700104 4IBM Global Services, Salt Lake, Kolkata,India dsgiimcal.ac.i,amitava.mukherjee(in. ibm.com
2ECE Dept., NSEC, Kolkata-700152, India
[email protected],
Abstract -The focus of this paper is to get the optimal hierarchical mobility management solution for next generation wireless IPbased networks. Hierarchical architectures prove advantageous in minimizing signaling overhead by limiting registration signaling locally. Our ultimate goal is to find the optimum hierarchy level, which should provide best performance in terms of networks parameters like signaling overhead, handoff latency and frequency of location updates. For this purpose an n-tiered architecture has been considered and optimality test on the number of tiers has been performed through analytical and ns-2 based simulation results. From the performance evaluation it is seen that time-bandwidth product is minimum for three-tiered network architecture leading as the optimal solution.
Keywords- Foreign Agent; Gateway Mobility Agent; handoff latency; location update; mobility management; signaling overhead; optimal level ofhierarchy. I.
INTRODUCTION
With the rapid growth of wireless networks, seamless user mobility has become the need of the hour. Hence, networks of tomorrow have to be robust enough to deal different mobility patterns of the users efficiently. Many protocols have been designed and implemented that support IP mobility. Among them Mobile IPv4 (MIPv4) [1], MIPv4 Regional Registration (MIPv4 RR) [2], MIPv6 [3] and Hierarchical MIPv6 [4] are noticeable. MIPv4 requires a Mobile Node (MN) to have a static Home Agent (HA) and a home address. For some big network domains, the MN's current network attach point could be far away from the static HA and hence could cause severe triangular routing problems. Route optimization takes the edge off this problem but it still requires substantial remote HA signaling and does not help much when the MN is moving very fast. It also imposes high signaling overhead on the Correspondent Node (CN) for processing binding update messages and data encapsulation. Finally, for a fast moving MN, when it keeps migrating to a nearby Foreign Agent (FA), which is typical for wireless network subscribers, the signaling with the remote HA will cause an unacceptable long delay. MIPv4 RR uses a hierarchy of FAs in a visited domain so as to efficiently handle local movements of MNs without the need of frequent registrations with the HA [5]. The idea here is that the movement of an MN within the visited domain and in
particular under one globally routable entity, denoted as the Gateway Foreign agent (GFA), is hidden from the HA so that the number of signaling messages to the home network, in conjunction with the time needed for the MN to update the path to its current location is reduced. This is because a change on the MN's path within a visited network is handled locally. This proposal uses a tree-like hierarchy of FAs where the FA located at the root of the tree is called the GFA. It is possible that several levels of regional FAs (RFA) are supported between the GFA and the lowest-level FAs. After an MN moves to new foreign domain, it registers with its home network where it uses the IP address of the GFA as its care-ofaddress (CoA). In MIPv6, the MN is obliged to send binding update message to its CNs and HA each time it changes its point of attachment. This causes significant processing overhead as the number of MNs increases. In addition, handoff-speed performance is aggravated because the MN waits for an end-toend path establishment so that it can receive packets on the new access router (AR). To overcome these limitations, Hierarchical MIPv6 (HIMIPv6) introduced a local entity within the access network, the Mobility Anchor Point (MAP), which can be located at any level in a hierarchy of routers, including the AR. The idea is that the movement of the MN within MAP domain is not visible to the CNs and HA. So the latter need not be notified for MN movements within the MAP's subnet. The MAP intercepts the packets destined for MN and tunnels them to the actual location of the MN [4]. Review of the different hierarchical protocols show that increasing the number of hierarchical levels proves advantageous in the performance of signaling overhead but deficiently deteriorates the handoff latency and frequency of location updates as the MN moves very fast across multiple subnets in a domain. Performance further degrades with the increase in the number of MNs [6]. So, in this paper we investigate for a hierarchical protocol architecture that should provide most favorable handoff latency, signaling overhead and frequency of location updates in an IP-based network scenario. For this purpose we consider an n-tiered architecture and execute optimality test on the number of tiers. The rest of the paper is organized as follows. After an introduction in section I, the analytical model of an n-tiered architecture is presented in section II. Section III provides the optimality test results. Both analytical as well as simulation
Iti Saha Misra is thankful to AICTE, India, for the financial support ofthis research under CAYT scheme
0-7803-9392-9/06/$20.00 (c) 2006 IEEE 481
results using ns-2 support the claim for three-tiered model. Finally, section IV concludes the paper with some highlights on extended works.
B. Signaling Overhead Model The expression for Per-Hop Signaling Overhead (SOPH) for an n-tiered architecture is shown in Fig. 2.
ANALYTICAL MODEL OF TIERED ARCHITECTURE We consider some important network parameters of interest are as location update frequency, handoff latency and signaling overhead. It is well known that terminal mobility management in wireless network environment consists of two components: location management and handoff management [7]. Location management is taken care of by location update (LU) or registration, which is a process that enables a network to discover the current point of attachment of an MN for information delivery. Handoff management enables a network to maintain a connection as an MN continues to move and change its point of attachment to the network. Signaling overhead is the total load on the network in the entire process of LU and handoff [8]. Accordingly we require three different types of analytical models as required by the above three network parameters. We consider an n-tiered hierarchical mobility model, where there are several layers of FAs i.e., layer-I FAs (LIFA) at the lowest layer, L2FAs at layer-2 and so on. The FAs at one layer are under the control of FAs immediately above their layer. So LIFAs are under the scope of L2FAs, L2FAs are under the scope of L3FAs and so on. So we define here a tree-like hierarchy of FAs, where FA located at the root of the tree (nth layer) is called the Root FA (RFA) where, FA located at the root of the tree (nth layer) is called the Root FA (RFA). II.
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where
Whenever an MN attaches to a foreign domain in an ntiered architecture, it has to acquire n-levels of CoAs starting from the lowest layer FA to the RFA as shown in Fig. 1. It registers the RFA-CoA with its HA. After initial registration with HA, the mobility of the MN is handled locally so long it is under the same RFA. If, however the host changes its RFA, it has to register with HA. If, on the other hand the MN continues to move to different LIFAs under the same L2FA, it has to register with the latter. If the MN changes its L2FA, registration has to be made to L3FA and so on. So HA need not be notified of the current point of attachment of MN until eventually the MN changes its RFA.
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