A Hierarchical Approach of Integrating Mobile Ad Hoc Network and the Internet

Khaleel Ur Rahman Khan Rafi U Zaman A Venugopal Reddy Dept. of CSE Dept. of CSE Dept. of CSE M J College of Engg. M J College of Engg Univ. College of Engg.. Hyderabad, INDIA Hyderabad, INDIA Osmania Univ., Hyderabad khaleelrkhan@gmail.com rafi.u.zaman@gmail.com avgreddy@osmania.ac.in Kashifa Hafeez Tabassum Sultana Dept. of CSE Dept. of CSE M J College of Engg. M J College of Engg. Hyderabad, INDIA Hyderabad, INDIA kashifahafeez20@yahoo.com tabassum_sultana7@yahoo.co.in

Abstract- Connecting the wired and wireless networks particularly the Mobile ad hoc Network is interesting in real world situations due to its usefulness and practicality. Different mechanisms have been proposed to integrate MANETs and the Internet. These strategies differ in gateway discovery mechanism, cell switching criteria, ad hoc routing protocol. In this paper, Mobile-IP is integrated with Hierarchical Cluster-Head Gateway Switch Routing (CGSR) Protocol to provide Internet access to the mobile node of the ad hoc Network. This paper discusses a mechanism for selecting an alternate route in case if the Cluster Head is unable to forward the packets to the destination. The proposed framework provides bi-directional connectivity between the MANET and the Internet nodes. A detailed performance evaluation is made based on mobility of cluster heads and cluster gateways and other network parameters.

I. INTRODUCTION

The main challenge to the deployment and acceptance of mobile applications is the requirement of better connectivity. Solutions like Mobile IP [1] have no doubt contributed to the enlargement of the connectivity to include nodes with a wireless last hop. On the contrary, MANET is visualized as a standalone network, with communication being supported between nodes in the network. In order to enable the connectivity outside of the ad hoc network, a bridge between ad hoc network and the Internet is required, which would expand the communication base of the ad hoc Network. In our proposed architecture, we integrated the CGSR [2] and the mobile IP protocols to provide the bi-directional connectivity. The basic requirement for providing the Internet connectivity is that the MANET nodes should be registered with the Cluster Head in order to access the Internet. In turn the Cluster Heads must be registered with the Foreign Agents. The mobile ad hoc nodes using CGSR forwards the packets to the Cluster Head and the Cluster Head in turn forwards them to the Internet node using the Mobile IP protocol via the Foreign Agent. In case if any Cluster Head is not registered with the FA or is not in a position to deliver the packets in the Internet, then it uses as alternate route to forward the packets to another Cluster Head via a Cluster Gateway. This will certainly increase the route length but will ensure the delivery of the packets and thereby

improves the performance. In other strategies, the packets will be dropped if the gateway is unable to transmit the packets. This will reduce the end-end delay and improves the packet delivery ratio with less control overhead. The remainder of this paper is organized as follows: Section II provides the related work done in this area. Section III describes the architecture of the Integrated Protocol. Section IV discusses the simulation results. Section V concludes the paper.

II. PREVIOUS WORK

The existing approaches for integrating MANET and the Internet are classified into two categories based on two criteria. The outer most criteria is related to the type of architecture of the hybrid network. This classification leads to two-tier and three-tier strategies. Further, the gateway discovery process and their selection are considered as other criteria to produce a finer classification of the existing approaches. Few of the two-tier strategies are given in [3-9]. A couple of three-tier strategies can be found in [10-11].

III. INTEGRATED PROTOCOL DESIGN

A. Proposed Architecture

The proposed architecture shown in Figure 1 consists of the Mobile ad hoc Network (MANET), with Clusters either overlapped or non-overlapped. Each Cluster has a Cluster Head and the overlapping Clusters have a Cluster Gateway. At least one Cluster Head shall be in the transmission range of the Foreign Agent (FA) in the Internet backbone. The Correspondent Node (CN) is assumed to be present in the wired Internet. The Integrated Protocol uses the basic functionalities of the Mobile IP as well as CGSR. We assume that the CHs are close to FA in order to provide the Internet connectivity to the MANET nodes. The CHs are assumed to be registered with an FA at any time.

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The Agent advertisements issued by the FA are meant only for the CHs. They are ignored by the ad hoc hosts and CGs. So, we use proactive approach of registration of the CH with the FA. If any CH receives advertisements from multiple FAs, then it selects that FA which is lightly loaded. All the communication from the MANET nodes towards the Internet side is through the CH. Therefore the CHs acts like a Mobile IP proxy for the MANET mobile nodes and the visiting mobile nodes.

Figure 1. Proposed Architecture

B. Bi-Directional Communication between the MANET and the Internet

The CH doesn’t broadcast the Agent advertisements for the purpose of registration of the hosts. This broadcast is the source of the overhead in the other strategies [4, 6, and 8]. In the proposed protocol, ad hoc hosts and the CHs know each others presence via routing update of the DSDV protocol, as the DSDV is the underlying protocol in the CGSR. Whenever the Ad hoc host say “A” joins the ad hoc network, the host A broadcasts DSDV advertisements to its neighbors with sequence number of ‘0’. Each host takes a note of it and makes an entry about host “A” in their routing tables. Later they broadcast with increased sequence number to their neighbors. This broadcasting process continues until the advertisements reach all the destinations i.e. the diameter of the network. The CH also comes to know about the host “A” and makes an entry in its routing table. The host “A” also gets routing updates from its neighbors and thereby creates its routing table, including the route to CH. After this, the host “A” sends its registration information to the CH like its Home Address. Based on this information CH acts as a mobile IP proxy for “A”. The CH sends the registration request to the host’s Home Agent. After successful registration, a registration reply is returned to the CH from the HA. The CH then informs the host “A” about the registration status. The CH keeps the registration information of all the ad hoc hosts and uses it during re-registration. The CH uses its address as the COA to register with the HA. The mobile IP registration lifetime is taken as 3 times that of DSDV periodic route update interval.

C. Communication Scenarios The proposed framework provides the following three modes of communication in order to provide bi-directional communication: 1). Intra-MANET routing (Communication within the MANET): This form of communication is the conventional communication within the ad hoc network by means of CGSR which is the local Protocol within the Cluster. 2) Communication between an ad hoc Host and a Correspondent Node (CN): This type of communication is initiated by the Mobile Node (MN) in the MANET. The MN wishing to send data to the Correspondent Host, first checks its routing table. If the destination is not found in the routing table, then it sends the packet to its Cluster Head. If the Cluster Head is registered with the FA, forwards the packet to the CN through the FA. This communication scenario is illustrated in Figure 2. In case if the CH is not registered with the FA, then it forwards the packet to the CG. The CG shall forward the packet to another CH which is within the overlapping zone of the CG. If that CH is registered with the FA , then the packet will be forwarded to the CN via this CH. This communication scenario is illustrated in Figure 3. In case if this CH is as well not registered with the FA then the packet will be discarded. 3) Communication between Correspondent Node and an ad hoc Host: This type of communication is initiated by the CN. The CN, when wishing to send packets to the ad hoc host, delivers the packet to the HA. If the ad hoc host had registered with the HA, then it will forward the packet to the ad hoc host in consultation with its routing table. If the ad hoc host has roamed away from it’s HA domain, then the HA will have the COA of the CH, if it has registered. Using the CAO the packet will be tunneled to the CH by the HA. The CH checks its routing table, and delivers the packets to the requested destination ad hoc host using the CGSR routing protocol.

Figure 2. Mobile Node MN1 communicating with Correspondent Host in the

Internet via Cluster Head

Figure 3. Mobile Node MN1 communicating with Correspondent host in the Internet via Cluster Gateway.

IV. SIMULATION RESULTS

A. Simulation Environment To evaluate the proposed architecture, the simulation experiments were carried out using the ns 2.31[12] network simulator. The details of the simulation are as given. Number of MANET hosts used are 10. Two traffic sources were used. Two cluster heads and one cluster gateway were employed. Two FA’s and two wired hosts were taken. The size of the topology is 800x700m. Radio range of hosts is 250m. The traffic type is CBR with packet size of 512B and sending rate of 5 Packets/s. The mobility model is random waypoint. The pause time is 5 sec. The wireless bandwidth is 2 Mbps and wired bandwidth is 10 Mbps. The simulation time is 600 sec. Beacon time of FA is 5 Sec. Agent Advt. lifetime is 15 sec. MANET node registration lifetime is 15 sec.

B. Simulation Results The performance of the proposed framework is evaluated with respect to packet delivery ratio, control overhead, end- end delay, and gateway connectivity ratio. The performance of the strategy is first evaluated by varying the speed of the CH and CG from 2 to 10 m/s. Figures 4 to 7 shows the performance with respect to the metrics of packet delivery ratio, end-end delay and routing control overhead and the connectivity ratio. Figure 4 shows that the packet delivery ratio decreases as the

speed increases. However, it is always over and above the 90% for the proposed strategy. Figure 5 shows the impact of the speed on the end-end delay. As the speed increases the delay also increases due to the fact that the routes becomes stale and it takes some time for the routing tables to get stabilized. Figure 6 shows the overhead of the MIP and the routing

protocol in terms of the number of packets. Figure 7 shows the impact of speed on the gateway connectivity ratio. It can be seen that the connectivity ratio decreases with the increase in the speed. The mobile nodes don’t have to register with the CH. Rather the CH knows about all the nodes. Figures 8 to 10 show the impact of the beacon interval or the advertisement interval of the FA on the performance of the proposed strategy. Figure 8 shows that the packet delivery ratio reduces due to the fact that the mobility in the Cluster Heads may require re-registrations with the FA and hence the

decrease in the packet delivery ratio. Figure 9 shows that as the beacon interval increases, the end-end delay increases as expected. Finally Figure 10 shows that, the control overhead decreases as the beacon interval increases.

Figure 4. Packet delivery ratio versus Speed of the CH & CG

Figure 5. End-End delay versus Speed of the CH and CG

Figure 6. Control Overhead versus Speed of the CH and CG

Figure 7. Gateway Connectivity ratio versus Speed of the CH and CG

Figure 8. Packet Delivery Ratio versus Beacon Intervals

Figure 9. End-End delay versus Beacon Intervals

Figure 10. Control Overhead versus Beacon Intervals

V. CONCLUSION

In this paper a way to provide Internet access for MANETs by using a Hierarchical Routing Protocol is described. One of the notable feature of this integration strategy is that, it provides an alternate route to the mobile node through Cluster Gateway, incase if any Cluster Head fails to provide the

Internet access. The Integrated protocol uses proactive approach of agent advertisements for the registration of the Cluster Heads with the Foreign Agents. We have observed that the proposed strategy provides better packet delivery, end-end delay and the gateway connectivity in comparison with the Integration strategies [10] and [11]. However the control overhead is slightly on the higher side in comparison with the strategy [11].

REFERENCES

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