SURVEY ON MOBILITY MANAGEMENT PROTOCOLS FOR IPv6

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1 SURVEY ON MOBILITY MANAGEMENT PROTOCOLS FOR IPv6 BASED NETWORK 1 Nitul Dutta, 2 Iti Saha Misra, 3 Kushal Pokhrel and 4 Md. Abu Safi 1 Department of Computer Science & Engineering, Sikkim Manipal Institute of Technology, East Sikkim , India 2,4 Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata , India 3 Department of Electronics and Communication Engineering, Sikkim Manipal Institute of Technology, East Sikkim , India Abstract The mobility management in IP based network in general and IPv6 network in particular has under gone lots of changes in the last few years. Many mobility management schemes for IPv6 have been proposed and successfully implemented so far. In this paper, a brief survey of existing protocols for providing seamless mobility in IP based network is carried out with an emphasis on mobility management in IPv6. The discussion of this paper includes few well-established protocols like Mobile IPv6, Hierarchical Mobile IPv6, Fast handover in MIPv6. We have also included few latest proposals in the area of IPv6 mobility management at the end of the paper. This discussion will help new researchers in this field to give a direction in their work. At the beginning of the paper we have also discussed Mobile IPv4 as the first protocol for IP mobility support. Keywords: MIPv4, MIPv6, Hierarchical MIPv6, Fast Handover for MIPV6, Survey. I. INTRODUCTION Mobile nodes are those nodes in the network that changes their IP subnets due to change of its location within the Internet topology. Such mobile nodes, despite of changing their subnet, want to have uninterrupted connectivity using the same IP address. Mobility management protocols facilitate uninterrupted communication to mobile nodes without changing their IP address. Mobile IP or MIP is the first mobility management protocol for IPv4 based networks standardized by Internet Engineering Task Force (IETF) that supports communication on the move. The mobility management mechanism in IP protocol allows location-independent routing and efficient scalable mechanism for roaming users on the Internet. The features of Mobile IP allow mobile nodes to change their point-of-attachment without changing their permanent home IP address. It is most often found in wired and wireless environments where users need to carry their mobile devices across multiple Local Area Network (LAN) [1, 2] segments. It may also be used in roaming between heterogeneous wireless network systems, such as Wireless LAN (WLAN) [3], WiMAX [4], IP over Digital Video Broadcasting (DVB) [5] and Broadband Wireless Access (BWA). Currently, Mobile IP is not required within cellular systems such as 3G [6] in order to provide transparency when Internet users migrate between cellular base stations as these systems provide their own data link layer handover and roaming mechanisms. However, it is often used in 3G systems to allow seamless IP mobility between different Packet Data Serving Node (PDSN) domains. II. MOBILITY MANAGEMENT IN IP NETWORK The mobility management protocols in wireless networks are divided in to two classes location management protocols and handover management protocols. The former deals with the tracking of the location of mobile users between consecutive communications and the latter refers to the process by which the network maintains an active connection for a mobile user as they move from one access point to geographically adjacent another access point. The efficiency of mobility management protocols depends on the level of intelligence and the mechanisms by which location information or other control information are conveyed to the appropriate network. The location management and handover management techniques used in packet switched based wireless data Advanced in Network and Communications (ANC) Volume1, Number2,July 2013 doi: /anc.vol1.issue2.2

2 networks (e.g. Internet) and circuit switched based cellular networks (e.g. PCS and GSM) are significantly different. The notion of mobility of nodes in the Internet is hidden from the network in IP based architecture. All the functionalities required to facilitate mobility in IP based architecture, is restricted either to end-users such as Mobile Nodes (MN) and Correspondent Nodes (CN) or to some certain specialized agents such as Home Agent (HA) and Foreign Agents (FA). Both location management and handoff management have equal importance in mobility management and thus gaining research interest worldwide. This paper addresses only the handover management related issues not the location management issues. However, in this section a brief introduction to the location management mechanism is given along with a discussion about the handoff management. A. Location Management Location management is an important aspect for a wireless network in order to provide continuous connectivity to roaming nodes. Uninterrupted packet delivery to a mobile node (MN) is only possible if its location information is properly maintained by the concerned network. The location management schemes maintain the location information of mobile users not only when it gets connected to the network, but also when they move within the network and when they get detached from the network. Location management is handled in two different phases, location tracking and location information storage. Location management schemes used in cellular networks like Personal Communication Systems (PCS) [7] and Global Systems for Mobile Communications (GSM) [8] are well established so far. However, with increased mobility levels, high traffic conditions and emerging sophisticated applications, the present location management schemes become insufficient for delay sensitive applications. There are many algorithms proposed for location management [9, 10, 11, 12, and 13]. They divide the movement area of a node into smallest region called cell and number of cells that are grouped into the so called Location Areas (LAs) [14]. Users can move within these LAs, updating their location with the network, based on some predefined standards. The network can page the cells within the LA to find any user as quickly as possible. For more accurate and consistent location information of mobile nodes, the network may need frequent Location Updates (LUs). Frequent update of location information reduces polling costs, but increases cost of location update [13, 14]. Conversely, the network could only require less LUs, storing less information about users to reduce computational overhead, but at a higher polling cost. Additionally, LAs themselves can be optimized in order to create regions that require less handoff and faster location of users. The goal of location management protocols is to find a proper balance between these important parameters. Based on the method of updating location information, these protocols are divided into two types: static and dynamic location management schemes. In the static algorithms, cells are assumed to be of constant size, uniform, and identical to each other. In this scheme, location updates of mobile nodes occur on either periodic intervals or upon every cell change. Therefore this method incurs larger costs when users movement is limited between any two LAs, as updates are continuously performed unnecessarily. Dynamic location management schemes on the other hand are an advanced form of location management where, the parameters of location management are modified to best fit individual user s mobility and traffic conditions. Theories are continually being proposed to improve the efficiency of dynamic location updates solutions. Few of the available location management protocols are: Location Areas [11], Reporting Cells [15], Time-Based Location Update Strategies [16], Movement-Based Location Update Strategies [17], and Profile-Based Location Management Strategies [18]. B. Handoff Management In a mobile wireless environment, the term handoff is used to describe the movement of a user from one cell to another during a conversation. The handoff management deals with the process of transferring the ongoing conversation during the handover of cell, without interruption to end users. In IP based networks, the smallest service areas (or wireless subnet) are managed by Access Points (APs) and in cellular telephone network (a cell in such case) the Base Stations (BSs) take care of them. The size and shape of each coverage area (subnet or cell) in a network depends on the nature of the terrain in the region, the number of APs or BSs, and their coverage range. In theory, the cells in a network overlap and user may be within the range of more than one AP (or BS) at a time. The network must decide, from time to time, which AP will handle the user in presence of more than one AP for the same

3 user. During movement, a mobile user passes from one cell to another and the network automatically switches controlling responsibility of the user from one cell to another. In a properly functioning network, handoff occurs smoothly, without gaps in communication and without confusion about which AP should be dealing with the subscriber. Although the handover management algorithms are matured enough in cellular telephone network, it is still in the growing stage for IP based network. Designing an efficient handover mechanism is an upcoming area of research to make it suitable for Next Generation Networks. In this subsection, few mobility management schemes for IP based network are discussed. In the context of these literatures, some parameters to judge the performance and their significance on mobility management are discussed below. Location update frequency: It is measured as the rate at which a mobile user updates its location information with a centrally available database. This database is the home agent for mobile IP supported networks. It depends on the rate at which the MN changes its coverage area. This parameter is influenced by various factors like speed of mobile users, movement pattern, shape and size of the subnet (or cell). If a user moves in a fixed direction with high speed, the handoff frequency increases. On the other hand if user moves in a random direction, even for higher speed the frequency may be less. This parameter has significant importance on the performance of the mobility management algorithms. For a mobile scenario with high location update frequency, the protocol must be robust enough to cope up with failure due to densely populated mobile users with frequent handoffs. Handoff latency: In a network, latency also called delay is an expression of how much time a packet takes to get from one designated point to the other. In a wireless environment where mobile nodes change their location over time, the term handoff latency is defined as the time taken by a mobile node to re-establish its connection under the coverage of new service area or cell after handover. It is measured as the difference in time between the reception of the last packet in the old service area and the first packet in the new service area in an ongoing session during handover. Lower handoff latency is always a desirable property of handoff management protocols. During the period of handoff, the mobile user gets detached from the network until the connection is re-established. So, ongoing connections to mobile nodes during this period will be lost. User is never satisfied with a service if the connection reestablishment time (i.e. handoff latency) is high. All protocols for mobility management proposed so far have tried to minimize the handoff latency suffered by end users in a mobile environment using different methods. Signaling overhead: For mobility support in an IP based network, the home network needs to maintain a database, wherein, the location information of all the mobile nodes that are away from the home network, are recorded from time to time. A special agent maintains this location information. During the visit of a node into a foreign network, every mobile node has to inform its current location information to its home network; otherwise, the packets transmitted to a mobile node cannot be delivered to its actual destination. To inform the home network about its new location, mobile nodes use some managerial packets. These packets (or messages) are called binding related packets. Once the location information is delivered to the home network of the visitor node, the same should be acknowledged by the home network to make the mobile node aware that its location information is successfully updated. The signaling overhead for mobility management or signaling overhead is the cost of exchanging these managerial packets over the network to complete the location update process of mobile node with the home network. This cost is basically the bandwidth consumed by these packets during handoff. It can be measured as the product of size of the binding related packets and distance (in terms of hop count) traversed by them. In a highly mobile scenario with large handoff frequency, the signaling load may overwhelm the network and may lead to congestion. So, producing less signaling overhead is another desirable property of the mobility management solutions. Packet tunneling cost: When a mobile user stays in the home network, the packets are delivered to them using normal routing mechanism adopted in IP network. The sender communicates to the default router of the home network of the receiver node to deliver a packet. But if a mobile node is not located in its home network then the packets cannot be delivered to them using normal IP protocol. Here arises the need of mobility aware IP protocol. In mobility aware IP, a special agent that is located in the home network not only keeps track of mobile nodes location but also take care of these packets. Basically, a mechanism called tunneling is adopted by the agent to deliver the packet to actual location of the mobile node (more about tunneling is found with the discussion of MIPv6 in

4 forthcoming sections). In tunneling, the sender (i.e. the agent that tunnels the packet) encapsulates the packet within another IP packet and sends it to the new location of the mobile node. In the receiver end the packet is decapsulated from the tunneled packet and delivered to the actual recipient (i.e. visitor mobile node in foreign network). So, tunneling cost is also referred as encapsulation and decapsulation cost. It is measured in terms of bytes added to encapsulate the packet to the destination or the time required to encapsulate and decapsulate the packets. In case of layered architecture, the cost increases with the increase of layers. Because, the packets destined to visitor mobile node located in a foreign network must be tunneled by every layer before delivering it to the final destination. The packet tunneling cost or encapsulation decapsulation cost or packet delivery cost is an important parameter to consider in designing hierarchical architecture. III. MOBILE IPV4 (OR MOBILE IP OR MIP) In IP network, the IP address is assigned to the node that uniquely identifies its point of attachment to the Internet [19]. Therefore, a node must be located on the subnet indicated by its IP address in order to receive datagram destined to it; otherwise the datagram destined to the node would be undeliverable. Mobile IP is first protocol to support mobile uses in IP based network. It is intended to enable nodes to move from one IP subnet to another maintaining connectivity with the internet. This protocol facilitates node movement from one Ethernet network segment to another as well from an Ethernet segment to a wireless network segment. It allows mobile nodes to use the same IP address across the globe. Protocol enhancement allows transparent routing of IP datagram to mobile node in the Internet. Each mobile node is always identified by its home address, regardless of its current point of attachment. While the mobile node visits a network or subnet other than its home network, it also assigns a care-of address by an agent in the foreign network, which signifies its temporary current point of attachment to the Internet. The functional elements and operational architecture of MIPv4 [20] is discussed separately in next subsections. A. Mobile IP Functional Entities To enable mobility in IPv4, few new functional elements are introduced. These elements have their own responsibilities to make MIPv4 a successful architecture for mobility management. These functional elements are briefly discussed next. Mobile Node (MN): A host equipped with a wireless interface and changes its point of attachment from one network to another. An MN is given a permanent IP address (called home address) on a home network and may change its location without changing its IP address. It may continue to receive data with other Internet nodes at any location using its permanent IP address. The home address of MN is administered in the same way as an IP address provided to a stationary node in the home network. When away from its home network, a care-of address (CoA) is associated with the MN in the foreign network and it is used as the MN s current temporary point-of attachment. The MN receives data with temporary care-of address and uses its home address as the source address of all IP datagram that it sends to other peer nodes. Home Network (HN): The HN is the network under which a mobile node gets registered permanently. The home network has a subnet address (also called network prefix) same as that of an MN s home address. When a MN resides in its home network, data is delivered using normal IP routing mechanism through the default gateway of the HN. The default gateway of the home subnet is responsible for sending and receiving of data packets from and to the mobile node. The mobile IP has nothing to do when the mobile node stays in its home network. Home Agent (HA): The HA is a special server maintained in a network segment to support mobility in IP. All MNs that wishes to make use of MIPv4 must register with the HA before it moves to another subnet. HA keeps track of all MNs under its coverage that currently visiting different subnets or Foreign Networks (FN). Mobile nodes when visiting a foreign network must inform their CoAs to their home agent by some managerial messages. Any packet sent to MN s home network during its absence is tunneled to its CoA by the home agent. Foreign Network (FN): Any network other than the MN s Home Network. FN has a different subnet address than the MN s HN. The MN cannot use their permanent home address in an FN and

5 must acquire some CoA in order to connect the FN. There is a special server available in the FN that provides a temporary address to the visitor MN. Foreign Agent (FA): A special server similar to HA but located in a foreign network. Every foreign network that wants to support mobile users via MIP, must maintain a foreign agent. All nodes visiting a foreign network acquire a CoA for the visiting subnet by exchanging some managerial messages with the FA. On receipt of a CoA, the receiving node registers itself with the foreign agent of that subnet and sends the new location information to its home agent. The FA keeps track of visitor nodes located under its coverage. The HA delivers all packets sent to a visitor node to MN s CoA. For datagram sent by a visitor MN, the foreign agent serves as a default router. Correspondent Node (CN): A peer node either stationary or mobile that sends data to a mobile node. There are no special functionalities incorporated in a correspondent node. It is considered as an ordinary node in IP based network with the mobility support and capable of communicating to any other node in the Internet. The normal IP routing is enabled in such correspondent nodes. B. Mobile IP Architecture Figure 1 is an example network to show different functional entities and control messages exchanged among the elements to enable MIP. To understand the MIP architecture, the diagram is made simple and only those components relevant to MIPv4 architecture are shown in the figure. Three network segments N 1, N 2 and N 3 are shown, all of which are connected to the Internet through their default routers. Within a network segment all nodes have the same subnet address. Nodes (also called host) may be categorized as stationary, migratory and roaming. Stationary nodes never move and are connected to the network via fixed wired link. Migratory nodes are those who change their location from one site to another but use the network when they are physically connected. Roaming nodes want to maintain connectivity on the move. The concept of mobile IP is to enable the nodes to communicate on the move. All nodes are assumed to have a permanent IP address [19, 21, and 22] that never changes. The permanent IP address is assigned to each of the nodes, which is determined by the home network address and this address can be used to determine the home location of a specific node. All nodes wanting to receive packets when they are away from home, must register with the home agent. Home agent keeps track of location information of all nodes visiting a foreign network. Each area or subnet must also have one or more FAs. They periodically broadcast Router Advertisement (RA) message containing subnet information. When an MN visits a foreign network it performs the following steps: Step 1: The visitor MN waits for RA message from the foreign agent. On receipt of RA, the node constructs CoA from the control information contained in the advertisement. Step 2: The visitor node after constructing the CoA, must register with the FA giving its permanent home address and link layer address. Step 3: The FA stores location information of the visitor node and sends back an acknowledgement. Step 4: On receipt of the acknowledgement from the FA, the visitor node sends a Binding Update (BU) message to it s HA. The BU message contains the information of the newly acquired CoA and a tentative lifetime of the CoA. Step 5: When the HA receives a BU from its MN from a foreign network, it stores the location information of the node in its database and acknowledges the receipt of BU using a Binding Acknowledgement (BACK) message. Step 6: Reception of BACK by a visitor node is considered as the completion of the handover process and the MN starts receiving packets in its new location. In a normal situation when MNs reside in their home network, MIPv4 is not used. All packets from a CN are sent to the default router of the MN as it is done in IPv4. If during the arrival of a packet to the home network, the destination MN is not present in its home location, then only the MIPv4 is invoked. In such a case, the home agent finds the temporary location of the MN from its database and then it encapsulates the received packet within another IP packet [23,24] and then sends it to the FA under whom the MN is currently residing in the foreign network. In the original version of MIPv4, every packet from the CN to MN is tunneled by the HA. It introduces extra packet delivery cost due to triangular routing from CN to HA and then HA to MN. Therefore, an enhanced version of

6 MIPv4 was proposed that uses the concept of route optimization. In this mechanism, the CN sends the first packet (or first few packets) to the HA. The HA tunnels the first packet to the MN via FA and simultaneously sends the CoA of the MN to the CN. On receipt of the CoA, the CN sends rest of the packets directly to the MN via FA without intervention of HA. This route optimization significantly reduces the packet delivery cost of MIPv4. Flow of mobility management messages and data transfer with and without route optimization in mobile IPv4 network is shown in Fig. 2. IV. MOBILE IPV6 The Mobile IPv6 protocol is designed by incorporating mobility in IPv6 [25]. As in MIPv4, MIPv6 enables mobile devices to be reachable and maintain ongoing connections while moving within the Internet topology. As in MIPv4, to be reachable, MNs are provided with a permanent IP address called home address. To maintain ongoing connections while moving, the HA which is defined in MIPv6 uses a redirection function to deliver packets to the temporary location of MN. The HA redirects the packets destined to any mobile node which is away from its home network and acquired a temporary address in its visiting network. Mobile node always updates its location information with the home agent in order to receive packets from the HA in its current temporary location. In addition to be reachable and to be able to maintain ongoing connections, the protocol allows for optimal routing between mobile nodes and other nodes they are communicating with. That is, MIPv6 allows a mobile node to communicate with another peer using shortest possible path provided by IPv6 [26] routing. 3. Data for MN is first sent to HA Home Network N 1 HA 4. MN s data is tunneled by HA to new location of MN via FA CN 2. BACK IP Network N 2 1. BU MN FA Foreign Network N 3 FA Foreign Network Figure 1. Mobile IPv4 Architecture without route optimization

7 MN 1. Process RA and FA HA CN acquire CoA Data Transfer without route optimization Data Transfer with route optimization Handoff 2. Send BU to HA (CoA and lifetime) 3. Send BACK to MN by HA 2. Tunnel Data to MN by HA via FA 2. HA tunnels received data to MN via FA 4. CN sends data directly to MN via FA 1. Data sent to MN s Home Network 1. First data packet sent to MN s Home Network 3. Send MN s Location to CN Figure 2. Mobile IPv4 messages A. Architectural Entities for Mobile IPv6 The architectural entities of MIPv6 are similar to MIPv4 except few new entities introduced in MIPv6 to get the benefits of IPv6 in mobility management. These new functional entities are discussed in this subsection. The descriptions of entities that are discussed with respect to MIP are not discussed again here, as their functionalities and behaviors are same as in MIP. Access Router (AR): This functional element is located in every IPv6 based network segment that supports mobility management.the functional entity AR is similar to foreign agent of MIPv4 and provides CoA to visitor mobile nodes in a foreign network. An AR may serve a group of MNs under its coverage and maintain a database of all such mobile nodes. B. Mobile IPv6 Architecture Figure 3 shows the MIPv6 architecture and control message flow in order to provide mobility to roaming devices. The permanent address assigned to different devices in MIPv6 based network serve two purposes. First, it allows a MN to be reachable by having a stable entry in the Domain Name Server (DNS) [27] and second, to hide the IP layer mobility from upper layers. A consequence of keeping a stable address independent of the MN s location is that all the correspondent nodes try to reach the MN at that address, without knowing the exact location of the mobile node. That is, whether the MN is physically located on the home link or not, packets are forwarded to the home link. If the MN is not at its home link, it s HA is responsible for tunneling packets to the MN s Care-of-address (CoA) (i.e., its real location). Since correspondent nodes attempt to connect to the MN s home address, hence sockets use the home address to record such connections. Therefore, it is necessary that applications see only the home address for the MN. Therefore, the IP layer is responsible for presenting the home address to applications running on the MN as a source address regardless of the MN s actual location. The IP layer hides the mobility from upper layers to maintain ongoing connections while the MN changes its address. The home address is formed by appending an interface identifier to the prefix advertised on the active link. Like any IPv6 node, an MN can be assigned several addresses of different scopes. This applies to both the home address and CoA. While at home, a MN operates like any other IPv6 node. It receives packets addressed to any of its home addresses and delivers via normal routing. Mobile IPv6 is only invoked when the MN is located on a FN. When an MN moves from its home to a foreign network, it first forms a CoA based on the prefix of the FN. The CoA can be formed based on stateless or stateful mechanisms. However, in this paper, a stateless address auto configuration [28] is adopted as a mechanism to form CoA by the visiting MNs. After address configuration, the MN informs it s

8 HA of such movement by sending a binding update message. The binding update message is one of several MIPv6 messages that are encoded as options in a new header called the mobility header. The binding update message contains the MN s home address and it s CoA. The home address is included in a new option called the home address option, and the CoA is included either in the source address in the IP header or in a new option called the alternate-care-of address option. The home address option is part of the destination options extensions header, while the alternate care of address option is included in the mobility header. The purpose of the binding update is to inform the HA of the MN s current address. The HA needs to store the information contained in the binding update message in order to forward packets to the MN s current location. The HA also contains a binding cache, where it keeps binding information of all nodes that it serves. Each entry in the binding cache stores a binding update message for one home address. When the HA receives the binding update, it performs number of actions to validate the message; if the binding update is accepted, the HA searches its binding cache to see if an entry already exists for the MN s home address. If an entry is found, the HA updates that entry with the new information received in the binding update message. Otherwise, if no entry is found, a new one is created. On completion of the location information update with the HA, the MN can receive data in its new location. In that case, the HA behaves like a proxy gateway for the MN on the home network. Hence, the home agent ensures that any IP packet addressed to the MN is forwarded to the HA s link-layer address. Home agent also defends the MN s home address. That means, if another node tentatively configures one of the MN s addresses and attempts to test it using Duplicate Address Detection (DAD) [29], the home agent replies to the message, indicating that the address is already assigned to another node. At this stage, the HA starts receiving all packets addressed to the MN. Upon receiving a packet addressed to the MN s home address, the HA checks its binding cache by using the MN s home address as a key to identify each entry. When an entry is found, the packet is tunneled to the MN s CoA, which is included in the MN s binding cache entry. The tunnel entry point is the HA and the exit point is the mobile node s CoA. The diagram given in Figure 4 illustrates the binding updates messages and data flow in MIPv6 between a visitor MN and HA. V. HIERARCHICAL MIPV6 In MIPv6, a mobile host sends binding update messages to it s HA and associated CNs each time it changes its point-of-attachment regardless of whether the MN moves to an adjacent cell or to another cell distance apart. As a consequence the signaling load introduced in the Internet is same for both local and global movement of the mobile nodes. So, MIPv6 is considered less scalable since the generated signaling load may overwhelm the network as the number of MN increases. Hierarchical Mobile IPv6 (HMIPv6) [30] on the other hand differentiate movement of MNs as local and global mobility and handles both the movement separately and introduces both the mobility by different hierarchically arranged agents. 3. Data for MN is first sent to HA Home Network N 1 2. BACK HA 4. MN s data is tunneled by HA to new location of MN via AR CN 5. MN s CoA sent to 6. MN s data sent directly by CN in FN IP Network 1. BU MN N 2 AR AR Foreign Network Foreign Network Figure 3. Mobile IPv6 Architecture N 3

9 MN AR HA CN 1. Process RA and acquire CoA Handoff 2. Send BU to HA (CoA and lifetime) 3. Send BACK to MN by HA Data Transfer 2. Tunnel data to MN by HA via AR 4. Data sent directly to MN by CN via AR 1. Data sent to MN s Home Network 3. MN s location information to CN Figure 4. Mobile IPv6 Message Such division of movement has two main advantages. First, it improves handoff latency since local handoffs are managed locally. Second, it significantly minimizes the signaling load due to handoff management because signaling messages corresponding to movement within the local site do not cross the whole Internet but stay confined to the site. With hierarchical arrangement the intra site mobility of MNs are completely hidden to CN. A. Hierarchical Mobile IPv6 Architectural Entities Figure 5, illustrates a three network segment in a HMIPv6 enabled network. The architectural entities and functional model with respect to Figure 5 are discussed in this subsection. HMIPv6 is the extension of MIPv6 by introducing new entity called Mobile Anchor Point (MAP). All the architectural entities of MIPv6 are also available in HMIPv6. The description of MAP is given below. Mobile Anchor Point (MAP): The MAP is basically a server maintained in the network that keeps track of all the MN that currently visiting that site. The MAP limits the amount of MIPv6 signaling outside the local domain. The MAP provides a solution to various issues associated with MIPv6. The MN sends binding update related messages to MAP rather than sending it to HA and CNs. The aim of introducing the hierarchical mobility management model in MIPv6 is to enhance its performance. Furthermore, HMIPv6 through MAP allows MN to hide their location from CN and HA, while it uses the benefits of route optimization mechanism of MIPv6. B. Hierarchical Mobile IPv6 Architecture The main operations of HMIPv6 are divided into two categories, Inter-site mobility and Intrasite mobility, which are discussed in this subsection. Inter-site mobility: Inter site mobility in HMIPv6 is defined as the movement of nodes from one foreign network to another foreign network. When a mobile host enters into a new site, it gets two CoAs one is called link CoA (LCoA) acquired from the subnet that the visitor MN attached to and the other is the regional CoA (RCoA) acquired from the MAP within the site. The visitor MN then sends binding update message to its MAP, which specifies the mapping of LCoA and RCoA along with some other information related to binding. On receipt of the BU, MAP performs admission control such as authentication and sends an acknowledgement to the MN. Mobile node then sends another binding update to its home agent with a mapping of RCoA and its home address. The home agent sends an acknowledgement to the concerned MAP and maintains a binding of the mobile node s home address

10 with RCoA communicated to it. Now any packet sent to the MN s home address is tunneled to the RCoA by the HA. The message flow for inter site mobility is shown in Figure 6. Intra-site mobility: The intra-site mobility in HMIPv6 is defined as the movement of the nodes from one cell to another in the same foreign network. In a situation of changing cell within the same site, the mobile node gets a new LCoA for the new cell but the RCoA remains the same. Since, the RCoA is not changed, so the MN need not update its location information with the HA or associated CN. The MN sends a binding update message only to the MAP informing the new LCoA. The binding update message is acknowledged accordingly. As long as the MN resides in that site the binding update messages are not sent over the Internet. Hence, the introduction of MAP significantly reduces handoff latency and signaling overhead for intra-site movement of nodes in HMIPv6 architecture. Figure 7 shows the message flow for intra site mobility of nodes in HMIPv6 based network. The Inter-site mobility and Intra-site mobility are different only in the binding registration process in HMIPv6 architecture. The packet routing process is same for both the cases. CN N 1 3. Data to HA HA 6. MN s location to CN IP Network Home Network 4. Tunneled data to MAP 7. Data directly sent to MAP by CN N 2 MAP MAP 1. BU 5. Tunneled data to MN via AR MN AR Access Network Router 2. BACK Router N 3 AR Figure.5 Hierarchical Mobile IPv6 Architecture VI. FAST HANDOVER FOR MIPV6 The goal of the Fast Handover in MIPv6 (FMIPv6) [31] is to allow a MN to configure a new CoA before it moves under the coverage of new cell or an access area. This mechanism is popularly known as make before break. The principle is to construct a new temporary address to MN and establish a new connection before the break down of the MN s ongoing connection with its old Access Router (OAR). In such a case, when the MN is attached to the new Access Router (NAR), it can continue its communications with its new already assigned address. While constructing the new CoA before the actual handover, the protocol takes help of the signal strength of the used signal and newly received signal during the movement of MN.

11 MN AR MAP HA CN 1. Process RA and acquire CoA Inter site Handoff 2. Sends BU to HA (CoA and lifetime) 3. Sends BACK to MN by HA Data Transfer 4. Tunnel data to MN by MAP 6. Tunnel data to MN by MAP 2. Tunnel Data to MAP by HA 1. Data sends to MN s Home Network 3. MN s MAP information to CN 5. Data sent to MAP by CN Figure 6. Inter-site mobility in Hierarchical Mobile IPv6 MN 1. Process RA and AR MAP HA CN acquire CoA Intra site Handoff Data Transfer 2. Sends BU to MAP (CoA and lifetime) 3. Sends BACK to MN by MAP 4. Tunnel data to MN by MAP 6. Tunnel data to MN by MAP 2. Tunnel data to MAP by HA 1. Data sends to MN s Home Network 3. MN s MAP information to CN 5. Data sent to MAP by CN Figure 7. Intra-site mobility in Hierarchical Mobile IPv6 If due to some unavoidable circumstances, the temporary address constructed in advance cannot be used, which may be termed as anticipated registration failed, MN can always carry out a normal handoff initiation. Moreover, the Fast Handover sets up a packet forwarding mechanism between the OAR and the NAR. The establishment of the new CoA before the MNs actual changeover involves anticipation on the network. This anticipation can be made from the exchanged messages at the physical level or simply by relevant information from MAC layer (level or layer 2) messages in the network. Fast handover is accomplished by means of exchanging few messages among adjacent ARs in the network as well as between AR and the MN. The FMIPv6 architecture and different messages used in the mechanism are shown in Figure 8.

12 Internet Cloud Old AR Data forwarded to NAR HA 2.PrRtAdv 1.RtSolPr 5.F-BU 6. FBACK 3. HI 4. HACK 9. Packet delivered to MN Movement of MN 8.F-NA New AR Figure 8. Fast Handover in Mobile IPv6 L2 Trigger Disconnect MN OAR NAR 1. RtSolPr 2. PrRtAdv 3. HI 4. HACK 5. F-BU 6. F-BACK 6. F-BACK Connect 8. F-NA 9. Deliver packets 7. Forward packets Figure 9. Message passing in fast handover The message flow diagram for FMIPv6 is also depicted in Figure 9. Based on the link layer information, either the MN or the OAR may initiate the fast handover. The MN initiates the handover by sending a Router Solicitation for Proxy (RtSolPr) message to the OAR. The OAR then transmits a Proxy Router Advertisement (PrRtAdv) message to the MN. The MN obtains a new CoA (NCoA), while being connected to the OAR. The OAR will validate the MN s new CoA and initiate the process of establishing a bidirectional tunnel between the OAR and the NAR, by sending a Handover Initiation (HI) message to the NAR. In response to the HI 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 sends a Fast Binding Update (FBU) message. When the OAR receives an FBU message, it must verify that the requested handover is accepted by the NAR as indicated in the HACK message. Then, it begins forwarding packets intended for old CoA to the NAR and sends a Fast Binding Acknowledgement (F-BACK) message to the MN. The NAR stores all the packets received from the OAR till the actual arrival of the new MN in its coverage area. On arrival of the MN under the coverage of the NAR, it initiates a Fast Neighbor Advertisement (F-NA) to inform its arrival in the new cell. When the NAR receives the F-NA message it forwards all the packets which are being waiting for the visitor MN.

13 VII. SURVEY OF SOME MORE MOBILITY MANAGEMENT RELATED RESEARCH Apart from the mobility management schemes described in previous sections, there are several other methods that provide seamless mobility to end users [32, 33, and 34]. These methods are based on either hierarchical arrangement of anchor agent or incorporating new features over existing mobility protocols in order to reduce handoff latency and signaling load. In this section few such techniques are selected to study which are closer to the topic of this paper either from improved mobility management point of view or from hierarchical arrangement of anchor agent. These papers adopted either analytical or simulated approach for establishing their protocols. The work, ES-FHMIPv6: An Efficient Scheme for Fast Handover over MIPv6 Networks [35] proposed by Hwan Souk Yoo et. al. is a recent publication on mobility management in IPv6 based network. This scheme is the enhanced mechanism of handover in IPv6 network and based on functionalities of HMIPv6 handover procedure. It states that the HMIPv6 uses MAP to assist handoff by deploying them in the border of a domain. But most of the handoffs occur at the lowest level and if the signaling load is handled near the bottom of the hierarchy then, a significant reduction in latency may be achieved. Furthermore, in HMIPv6, as soon as a MN enters into a foreign network, it configures the LCoA by taking information from RA message that the AR periodically broadcasts. The MN then sends a local BU message to the MAP. The MAP on receipt of the BU performs a so called DAD (Detect Address Duplication) and returns a BACK message to the MN. The proposal of Hwan- Souk Yoo et. al. states that, DAD takes at least 1000 ms to detect address duplication and hence overall handover delay increases. So, to reduce handover latency, a new method of address configuration is proposed in connection with HMIPv6. It is assumed that Access Point (AP) are located under ARs. Any AR is equipped to know the subnet information of all APs under its coverage. When a MN is supposed to move from an OAR to NAR, the OAR sends an RA packet in advance to the NAR. The NAR then sends it to the respective new AP (NAP) to store it in the buffer available in the AP. On actual movement of the MN to the NAP, it receives the stored RA immediately in the new location. This process reduces the waiting time of the MN for new RA to arrive. Furthermore, the authors have stated that the process also reduces the time to verify the LCoA and RCoA through DAD because the CoAs acquired from the stored RA is unique. This paper also utilizes the concept of L2 handover and configures the MN to initiate L2 handover when it detects change in subnet. The implementation of L2 handover further reduces the handoff latency. The proposal made by Deeya et. al. [36] is an integrated mobility scheme that combines the procedures of Fast Handover for MIPv6 (FMIPv6) [11] and Session Initiation Protocol (SIP) [13] mobility for real-time communications. Authors have used functionalities of FMIPv6 and SIP in order to reduce signaling load [32, 33] due to handover. The proposed scheme also reduces packet loss for an ongoing real-time data transfer during handoff. In this scheme, end-to-end negotiation is implemented within the SIP proxy for quality of service provisioning. The session re-establishment process enables CN to redirect all its ongoing streams to the MN s CoA. The Re-INVITE message introduced in the model contains updated contact field where the MN would receive SIP messages in future. If the CN responds with a SIP OK message, agrees to INVITE response, the MN will in turn respond with an ACK to complete the SIP. The proposed integrated scheme aims at avoiding triangular routing and any kind of encapsulation mechanism during the ongoing calls to reduce extra delays. It also reduces the signaling loads by integrating the redundant messages from both FMIPv6 and SIP for ongoing calls. The hierarchical arrangement of anchor agents reduces handoff latency and signaling cost but increases tunneling cost. In the work, A Study on Optimal Hierarchy in Multi-Level Hierarchical Mobile IPv6 Networks [37], Sangheon Pack et. al. performed a mathematical analysis on hierarchical MIPv6 network. They formulated the location update cost and the packet delivery cost in a multi-level HMIPv6. Based on the formulated cost functions, the authors have presented a hierarchical solution to minimize the total cost of handoff management in IPv6 network. The numerical results stated in the paper figures out the various relationships among network size, optimal hierarchy, and signal to mobility ratio, etc. They have suggested that their findings may be utilized to design the optimal HMIPv6 network. The proposal made in the paper, [38] by Zheng Wan et. al. is a three-level hierarchical architecture for HMIPv6 networks. According to this scheme an MN may register with either a higher

14 or lower MAP or it s HA. By analyzing the inter-domain registration cost function, a parameter for MAP selection is suggested which takes both the mobility parameter and the traffic parameter of an MN into account to minimize the overall registration cost by selecting appropriate agent for the registration process. This adaptive agent selection protocol reduces signaling cost considerably. Simulation results shown in the paper suggests that normally the MAP selection procedure adopted in the research achieves 25% reduction of registration cost over the traditional mobility management algorithms. The algorithm obtains better performance for varying mobility and traffic parameter of MN. T. Kato et. al.[38] presented a new protocol based on their study on Mobile IPv6 Based Mobility Management Architecture. Unlike other mobility management protocols this approach suggests a method which provides fast handover along with route optimization. In order to implement their scheme, only minor modifications are required in MIPv6. In their version of hierarchical architecture, the functions of HA and CN are not required to change. To realize their architecture they have introduced two agents: Gateway Edge Nodes (G-ENs) and Temporary Home Agents (THAs). These two agents are organized hierarchically in the architecture. When an MN enters in a coverage area of THA, it gets a Temporary CoA (TCoA) and an LCoA from the AR of that area. With these acquired CoAs the MN sends a BU message to THA to perform binding on the THA. This scheme reduces BU messages communicated to HA and CN by 20 and 60 percentage respectively compared to original MIPv6. It also reduces the occupied backbone load by 50% compared to HMIPv6. They have considered their protocol suitable for large-scale network for seamless mobility. The focus of the work, An approach for Optimal Hierarchical Mobility Management Network Architecture [39] is to provide hierarchical mobility management solution for MIPv4 network. For this purpose very preliminary mathematical analysis and simulation study is done on a hierarchical model. The Foreign Agents (FA) defined in MIPv4 is organized in a pyramid like structure to form a layered architecture. There is a single FA at the root (RFA) and multiple FAs are present in the lower layers. To see the performance of the proposed architecture, the multi layered architecture is examined under various network conditions. A number of network parameters like location update frequency, handoff latency and signaling overhead are evaluated in this research from very simple mathematical analysis and ns-2 simulation results. Results indicate that three level of hierarchy in the pyramid structure shows optimal tendency in performance. Unlike this work, our research involved IPv6 based hierarchical mobility modeling architecture in which extensive mathematical formulation is done based on Markov process considering proper mobility models for the mobile nodes. Apart from analytical and simulation model, real test bed is also designed for the verification of the results obtained in analytical model. In their paper, The Research of Mobile IPv6 Optimized Hierarchical Mobile Routing Protocol Yong Gan, Baohua Jin et. al. [40] propose an optimized hierarchical mobile routing management model based on HMIPv6. The messages used in the model are extensions of HMIPv6 and in FMIPv6 messages. They make use of hierarchical anchor agents to reduce signaling load by introducing the border router to realize route optimization. Fast handover in the intra-domain and interdomain is achieved in the proposed model by combining the advantages of HMIPv6 and FMIPv6. The concept of multicasting is also used in the model to reduce packet loss. The model is simulated in ns-2 network simulator. The simulation results show that the new model can reduce the handover delay and packet loss rate much more compared with the standard MIPv6 protocol. In the work, Multilevel Hierarchical Mobility management scheme in complicated structured networks, [41], K. Kawano et. al. suggest a scheme for MAP selection in a simple tree-based hierarchical network. According to the proposed scheme, actual networks have some redundancy in structure. This type of network is considered as a complicated structured network. In such a complicated structured network, the MAP domains intricately overlap each other. This causes difficulty in selecting the MAP suitable for managing the mobility of the mobile nodes. They have proposed a method to allow an MN to select the suitable MAP in such a network by adjusting the selection criteria individually configured for use at a particular place. The performance of the proposed scheme is evaluated using simulation experiments. The simulation results show that the new scheme works well in complicated structured networks.

15 S. Wang et. al. [42] proposes a mobility management model to analyze the application scopes of MIPv6 and HMIPv6. Through the proposed model, an Optimal Choice of Mobility Management (OCMM) scheme is designed. The objective of the OCMM is to choose the better alternative between MIPv6 and HMIPv6 according to the mobility profile of the MN and service characteristics of users. Based on the profile and traffic pattern, the scheme also decides whether to use hierarchical MAP in the network or not. The research also suggests selecting the best mobility anchor point when HMIPv6 is adopted. Simulation results demonstrate the impact of key parameters on the application scopes of MIPv6 and HMIPv6 as well as the optimal regional size of HMIPv6. The results also show that the OCMM outperforms MIPv6 and HMIPv6 in terms of total cost including registration and packet delivery. In another paper THMIP-A Novel Mobility Management Scheme using Fluid Flow Model, the authors S. Saha and A.K. Mukhopadhyay [43] propose an improved hierarchy based mobility management scheme called Three-level Hierarchical Mobile IP (THMIP). They have used fluid flow mobility model to sketch the movement pattern of users in their model. The signaling overhead for frequently moving MNs within its hierarchical domain is studied. In this scheme, the MN sends the binding update to the HA only for the first time when the CoA gets changed. From the next movement onwards, it sends binding update to the previous MAP. A mathematical analysis of the signaling load and the packet delivery cost is carried out in the work. The performance of the proposed protocol is compared with other existing mobility management protocols and the THMIP shows a considerable improvement over the others in the context of location update and packet delivery cost. Unlike the various existing protocols for IP mobility management such as MIPv6, which are host-based approaches, Proxy Mobile IPv6 (PMIPv6) [44] is a network based mobility management protocol. The host based protocols require protocol stack modification of the MN in order to support mobility. As a result, these modifications may cause increased complexity on them. On the other hand, in a network-based mobility management approach, the serving network handles the mobility management on behalf of the MN. So, the MN is not required to participate in any mobility-related signaling. The article, Mobility management for all-ip mobile networks: mobile IPv6 vs. proxy mobile IPv6, [45] presents a qualitative and quantitative analysis of the host-based and network-based mobility management approaches. Their discussion mainly includes MIPv6 and PMIPv6. For the validation of a network-based approach they have highlighted the main features and key strengths of PMIPv6. Furthermore, a comprehensive comparison among the various existing well-known mobility support protocols is investigated. In the discussion they have stated that the development of PMIPv6 is at an early stage yet and expected that PMIPv6 will be a promising candidate solution for realizing the next-generation all-ip mobile networks. This paper A Comparative Performance Analysis on Hierarchical Mobile IPv6 and Proxy Mobile IPv6, [46] presents comparative results on HMIPv6 and PMIPv6. A cost based evaluation model is developed and discussed in the paper. They evaluate the location update cost, the packet delivery cost, and the wireless power consumption cost based for both the protocol. Through numerical analysis, the authors have discussed the impact of the various system parameters. The results demonstrate that PMIPv6 always outperforms HMIPv6 due to its ability to avoid the mobility signaling sent by the mobile host and it also generates reduced tunneling overhead during communications with other nodes. The paper, A Comparative Analysis on the Signaling Load of Proxy Mobile IPv6 and Hierarchical Mobile IPv6, [47] investigates the performance of the PMIPv6 and compare with HMIPv6. An analytical mobility model based on the random walk is proposed to examine various mobility conditions. Based on the analytical model, the location management cost and handoff management cost is formulated. The numerical results show that the PMIPv6 has superior performance to HMIPv6 in terms of latencies for location update and handoff.

16 VIII. CONCLUSION The discussion carried out in this paper reveals that the structure of IP address assignment to a particular node in the TCP/IP based network makes it difficult to use the same IP address by mobile users in a new subnet. As a first mobility solution to IP based network, MIPv4 got a large popularity. But due to lack of address space, MIPv4 could not be continued further. MIPv6 has lot of other additional features compared to MIPv4 more than having reduced value of handoff latency. Absence of separate technique to handle global and local mobility of nodes makes MIPv6 less efficient. HMIPv6 on the other hand reduces both handoff latency and signaling overhead by arranging a hierarchical agent at the border of the local domain to handle local movement of nodes in IPv6 network. We foresee a great deal of technological developments in the near future in the quest of providing a seamless and uninterrupted IPv6 based mobile connectivity. This survey work may help the prospective researchers in this field by providing one stop overview about the recent developments in the field of Mobile IP and motivate them towards further design and development of Mobile IP based network. ACKNOWLEDGMENT This work is supported by All India Council for Technical Education (AICTE), New Delhi, India, under Research Promotion Scheme(RPS) F.No.: 8032/BOR/RID/RPS-29(NER)/ for the Financial Year REFERENCES [1] Andrew S. Tanenbaum, Computer Networks, Fourth Edition Prentice Hall PTR, [2] Ira Winston, Two Methods for the Transmission of IP Datagram over IEEE Networks, RFC 948, June [3] R. Housley and T. Moore, Certificate Extensions and Attributes Supporting Authentication in Point-to- Point Protocol (PPP) and Wireless Local Area Networks (WLAN), RFC 3770, May [4] Roger Marks, IEEE Standard : A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access, IEEE Broadband Wireless Access Working Group, June [5] U. Reimers, Digital Video Broadcasting (DVB), A Guideline for the Use of DVB Specifications and Standards, DVB Project, May 2000, online available from [6] H. Inamura et. al., TCP over Second (2.5G) and Third (3G) Generation Wireless Networks, RFC 3481, February [7] P. G. Escalle, V. C. Giner and J. M. Oltra, Reducing Location Update And Paging Costs in A PCS Network, IEEE Transactions on Wireless Communications, vol. 1, no. 1, pp , [8] M. Rahnema, Overview of The GSM System and Protocol Architecture, IEEE Communications Magazine, vol. 31, no. 4, pp , [9] Jingyuan Zhang, Handbook of Wireless Networks and Mobile Computing, Edited by Ivan Stojmenovic, John Wiley & Sons, Inc., USA, ISBNs: , [10] A. Bar-Noy and I. Kessler, Tracking Mobile Users in Wireless Communications Networks, IEEE Transactions on Information Theory, vol. 39, no. 6, pp , [11] A. Bar-Noy, I. Kessler, and M. Sidi, Mobile users: To update or not to update?, Wireless Networks, vol. 1, pp , [12] Vincent W. S. Wong and Victor C. M. Leung, Location Management for Next-Generation Personal Communications Networks, IEEE Network, vol. 14, no. 5, pp , [13] A. Bhattacharya and S. K. Das, LeZi-Update: An Information-Theoretic Approach to Track Mobile Users in PCS Networks, Proc. IEEE MOBICOM, Seattle, USA, pp. 1-12, [14] S. Ramanathan and M. Steenstrup, A Survey of Routing Techniques for Mobile Communication Networks, IEEE Mobile Networks and Applications, vol. 1, pp , [15] A. Bar-Noy and I. Kessler, Tracking Mobile Users in Wireless Communications Networks, IEEE Transactions on Information Theory, vol. 39, no. 6, pp , [16] A. Bar-Noy, I. Kessler and M. Naghshineh, Topology-Based Tracking Strategies for Personal Communication Networks, Mobile Networks and Applications, vol. 1, pp , [17] S. Okasaka, S. Onoe, S. Yasuda, and A. Maebara, A New Location Updating Method for Digital Cellular Systems, Proc. IEEE Vehicular Technology Conference, vol. 41, pp , [18] Yi-Bing Lin, Reducing Location Update Cost in a PCS Network, IEEE/ACM Transactions on Networking, vol. 5, no. 1, pp , 1997.

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