Wireless Pers Commun (2007) 43:975–995 DOI 10.1007/s11277-007-9257-4

Hierarchical mobile network binding scheme for route optimization in NEMO Moon Sang Jeong · Yeong Hun Cho · Jong Tae Park

Received: 15 May 2006 / Accepted: 20 January 2007 / Published online: 21 February 2007 © Springer Science+Business Media B.V. 2007

Abstract Recently, there has been a great deal of research on network mobility management that can support the movement of a mobile network consisting of several mobile nodes. The IETF NEMO working group proposed a basic support protocol, which defines methodology for supporting network mobility by using bi-directional tunneling between the home agent and the mobile router. This protocol, however, suffers from the ‘pinball routing problem,’ and most of the research attempts to solve this problem still have limitations in the efficiency of intra-domain communication. Moreover, these methods require additional binding procedures in case of the root mobile router handover. In this paper, we propose new route optimization methodology that can remedy these limitations by using asymmetric tunneling and a hierarchical local binding mechanism, which can provide faster signaling and data transmission. It can also be easily extended to support micro-mobility without the need for additional extensions. The performance is evaluated by simulation which can M. S. Jeong (B)· Y. H. Cho · J. T. Park School of Electrical Engineering and Computer Science, Kyungpook National University, 1370, Sankyuk-Dong, Buk-Gu, Daegu 702-701, South Korea e-mail:[email protected] Y. H. Cho e-mail:[email protected] J. T. Park e-mail:[email protected]

show the efficiency of the approach, compared with several previous route optimization methods. Keywords Mobile network binding · Route optimization · Network mobility management · Mobile IPv6 · WPAN management · Ad-Hoc & ubiquitous network

1 Introduction With the rapid growth of wireless network technology, various wireless and mobile services have emerged. These services are being deployed and extended from personal wireless networks to vehicular and traveler network services, and sensor networks and their applications [8, 10]. For the efficient support of these applications and services, there has been considerable research on network mobility management such as Mobile IP in wireless and mobile environments [8]. Emerging new mobile technology including wireless personal area network, ubiquitous computing, telematics, vehicular network environment, and sensor network require a new paradigm for the management of network mobility. As technology related to wireless and mobile network environments is rapidly being developed, it increases the necessity for research about network mobility that could support the mobility of not only a single mobile node, but also the

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movement of a mobile network which consists of several mobile nodes [3, 10]. This idea is most represented by that of the Internet Engineering Task Force (IETF) Network Mobility (NEMO) working group. The IETF NEMO working group has proposed several Internet drafts [2, 4, 5, 17]. The NEMO basic support protocol defines methodology that supports network mobility by using bidirectional tunneling between the home agent and the mobile router (MR) [2]. It extends the binding mechanism of Mobile IPv6 [8] and the data transmission of a mobile network can be achieved by using the MR, which is the egress interface of a mobile network. In other words, only the MR is involved in the acquisition of care-of-address (CoA) for the handover of an entire mobile network. Mobile network nodes (MNN), which are connected to the MR, can use their home address even if the mobile network has migrated to another network. The NEMO basic support protocol defines basic procedures that support the network mobility of a mobile network, but it does not take into account route optimization, multi-homing, or other issues. These issues will be examined with regard to the extended network mobility support, but this not completed yet [11]. In particular, the basic support protocol has a serious disadvantage called ‘pinball routing problem’; that is, all traffic to or from the MNN in the nested mobile network should pass through the home agents (HAs) of all preceding MR [16, 20]. In order to solve this problem, various methods have been proposed [1, 9, 12, 14, 18, 19]. Most of these methods use direct tunneling between the root-MR and the HA of a nested MR, which is subordinate to the root-MR. The direct tunneling mechanism, however, requires an additional handover procedure, such that the binding address of the nested mobile network should be updated when the mobile network moves along with the root-MR. This is because the CoA of the root-MR, which is used for the binding procedure, is changed even though the nested MRs do not change their point of attachment. In a vehicular environment, this root-MR handover usually generates mass signaling for all nested mobile networks, and network services could become disconnected until the handover procedure is finished.

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In addition, the root-MR experiences a very heavy load because it must maintain full paths for all nested MRs [1, 6, 9, 12, 15]. The root-MR suffers from a large processing load and this can cause a communication bottleneck. Furthermore, the exchange of direct messages, between the mobile network nodes under the same root-MR, which is called intra-domain communication, is not supported. If an MR or MNN which has a mobile-HA, that is an MR playing the role of HA, moves into a foreign network, the node also suffers from the pinball routing problem because the packet, to or from the nodes, must pass through many HAs, such as its own HA, the HA of the mobile-HA, and the HA of the visited MR. Thus, most previous route optimization methods have serious limitations with regard to signaling overhead, additional pinball routing problem for the mobile-HA, and concentrated traffic and load isuues in the rootMR [7]. In order to solve the aforementioned problems, we propose a new route optimization methodology, called a hierarchical mobile network binding (HMNB) scheme, for the efficient support of network mobility. Our proposed scheme uses a home address (HoA) of the root-MR and a destination routing header (DRH), in order to provide asymmetric tunneling and intra-domain communication. A hierarchical local binding scheme and local binding cache management are used for DRH manipulation and intra-domain packet forwarding. The HA to the MR tunnel should be used to transmit data from the correspondent node (CN) to the MNN, but traffic from the MNN to the CN does not have to pass through the tunnel for route optimization. Asymmetric tunneling, which consists of downward tunneling from the HA to the MR and upward tunneling from the MR to the CN, results in shorter paths for route optimization. Using tree-based routing for intra-domain communication and binding procedures, hierarchical mobile network binding is more efficient and faster than previous tunneling mechanisms in the signaling and transmission of data. In addition, our proposed scheme can support intra-domain communication among mobile networks, which is not supported in other route optimization methods such as basic support protocol

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(BSP) [2], everse routing header (RRH) [19], and top level mobile router (TLMR) scheme [9]. Although the proposed HMNB scheme passes through a two-hop path, it has smaller signaling complexity and service discontinuity time than those of other one-hop path route optimization techniques such as RRH and TLMR. In a mobile environment such as a vehicular network, where root-MR handovers frequently occur, the large signaling and processing overhead of the RRH and TLMR may not be acceptable to important business services. We have conducted extensive experiments to show the reduction in signaling complexity and in service discontinuity time. We have compared the performance of the proposed route optimization scheme with that of the IETF’s basic support protocol (BSP), RRH, and TLMR schemes. The simulation results show that the proposed scheme demonstrates a higher level of performance. The rest of the paper is organized as follows: In Sect. 2, the basic concept of network mobility is introduced, and other related works are described. In Sect. 3, a new route optimization scheme is proposed for the efficient support of network mobility. In Sect. 4, performances of the network mobility methods are compared by simulation. Finally, the conclusion presented in Sect. 5.

2 Background 2.1 IETF NEMO basic support protocol Network mobility is defined as the capability to support the mobility of a whole network, which is transparent to the nodes inside the mobile network [2, 10]. The IETF NEMO working group has defined a basic protocol operation that supports network mobility of a mobile network based on Mobile IPv6. There are several Internet drafts regarding goals and requirements [4], terminology [5], and basic support protocol for network mobility [2]. The IETF defines that the mobile network can be consisted by the Personal Area Network (PAN), Sensor network, vehicular network, public transportation network and mobile adhoc network.

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In the IETF, network mobility standards are defined in two parts; NEMO basic support and NEMO extended support parts. NEMO basic support provides a solution that maintains session continuity for a mobile network by using bi-directional tunneling between the HA and the MR. NEMO extended support provides route optimization for a nested mobile network and other issues such as multi-homing, but this has not been completed [4, 11]. The IETF also defines terminology that is used in a mobile network [5]. A mobile network consists of one or more MR and several MNN. An MR is one of mobile node which plays the role of a router within a mobile network. A MR performs internal routing and the transmission of data to or from the external network, for the MNN behind the MR. MNNs are subordinate to the MR, and they can be fixed to the MR (LFN: local fixed node) or they can be mobile nodes (LMN: local mobile node). If a local mobile node moves into a foreign network, the node is referred to as a visited mobile node (VMN) with regard to the foreign mobile network. The MR communicates with the external network by accessing the access router (AR), which is the edge router of an external network. The goal of the NEMO basic support protocol is to support network mobility and backward compatibility with Mobile IPv6. In the NEMO basic support protocol, only the MR of a mobile network is involved in handover procedures for the whole mobile network movement. The transmission of data between the MNN and CN is accomplished over a bi-directional tunnel between the HA and the MR of the mobile network, to which the MNN belongs. All traffic passes through the HA, and IPSec is used to secure signaling between the MR and the HA [2]. Figure 1 shows the components of the mobile network and its handover scenarios. In Fig. 1, mobile network handovers can be divided into several cases; Inter-domain, intra-domain, and root-MR. The inter-domain handover is defined as a mobile network’s movement into a foreign network with a different root-MR domain, and the intra-domain handover is defined as a mobile network’s movement within the same root-MR domain. When a mobile network moves along with the root-MR,

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the root-MR handover occurs. The NEMO basic support protocol only considers the inter-domain handover procedure. When a mobile network moves into a foreign network, a bi-directional tunnel for data transmission is established between the HA and the MR of the mobile network. The MR of the mobile network is only involved in the acquisition of a CoA for the handover of the mobile network, and all MNNs in the mobile network can keep their home network addresses. The MR operates both as a router for the data transmission of MNNs and as a mobile node itself. If a mobile node is attached to an MR on a visited foreign network, signaling, and data transmission can be achieved by using the Mobile IPv6 protocol. For the construction of a bi-directional tunnel, the basic support protocol extends the binding message of Mobile IPv6. The extended binding update (BU) message contains a network prefix instead of a home address, and an egress interface address of the MR for CoA. By using these extensions, network mobility can be supported without changing the addresses of MNNs in a mobile network.

2.2 Other related research The NEMO basic support protocol defines the minimal procedures and extensions that support network mobility, and it excludes issues in route optimization and multi-homing. These issues are being investigated as NEMO extended support, but the work is on-going. In the cases of the PAN, mobile adhoc network, and converged network, the mobile networks can form the hierarchy for each mobile router, and a MR which can access to the public Internet can be the root-MR. Especially, the mobile adhoc network and the wireless sensor network can be easily composed the hierarchy, and they may have several nesting depth for constructing hierarchy of the mobile networks. In a basic support protocol, the tunnel of a nested mobile network is constructed through all preceding mobile network tunnels. All the traffic of the nested mobile network passes through the HAs of all preceding mobile networks. This causes a serious problem that is called the ‘pinball routing’ [16, 20]. Figure 2 shows an example of ‘pinball routing’ problem in a basic support protocol.

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Fig. 2 Pinball routing problem in the NEMO basic support protocol

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Recently, a great deal of research has been conducted in order to solve the pinball routing problem, which includes the route optimization of the basic support protocol [1, 6, 7, 9, 12–15, 18–20]. Most of the previous research on route optimization has used bi-directional tunneling between the HA of the nested mobile network and the root-MR [7, 9, 3, 14, 19]. Two bi-directional tunnels were made between the HA of the nested mobile network and the root-MR, and between the root-MR and the nested MR. By using direct tunneling between the HA of the nested mobile network and the root-MR, ‘pinball routing’ can be solved. For this, an extended router advertisement (RA) message that includes an address of the root-MR egress interface is defined in order to discover the rootMR address and to notify the nested MRs. The recursive binding update method [1] and path control header based route optimization mechanism [12] perform route optimization by using the binding procedures between the MR and the correspondent node or router. These mechanisms, however, require modifying the correspondent nodes or routers which are not NEMO-related nodes, in order to support the extended binding procedures and the extended header manipulation. Furthermore, if the handover does occur fre-

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quently and the mobile network has large data connections, the amount of additional signaling overhead can be very huge. In most previous research regarding route optimization, direct tunneling between the root-MR and the HA of a nested MR is established to solve the route optimization problem [7, 9, 13, 14, 19]. In the direct tunneling mechanism, the HAs of every nested MR are tunneled with their root-MR. Therefore, the packets can be transmitted to the CN by just passing through only one HA of the nested MR. The direct tunneling mechanism, however, requires an additional handover procedure when the mobile network moves along with the rootMR. In this case, when the CoA of the root-MR is changed, the binding addresses of all nested MRs should also chang accordingly. In a vehicular environment where this kind of root-MR handover often occurs, the amount of additional signaling overhead, due to the MRs’ binding updates, can be very large. The root-MR also suffers from a large processing load, thus becoming a communication bottleneck, and non-negligible service discontinuity may occur because the signaling delay of the nested MR becomes larger as the depth of the MR increases. Furthermore, direct message exchange between the mobile network nodes under the same

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root-MR, which is called intra-domain communication, is not supported. If an MR or MNN which has a mobile-HA, that is an MR playing the role of HA, moves into a foreign network, the node also suffers from ‘pinball routing’ because the packet, to or from the nodes, must pass through several Has. This includs its own HA, the HA of the mobile-HA, and the HA of the visited MR. In Ref. [9], the root-MR experiences a very heavy load because it must maintain full paths for all nested MRs. In conclusion, most previous route optimization methods could provide the shortest routing path, since they use the CoA of root-MR as a binding address. All the MR which are subordinate to the root-MR, however, must execute additional binding procedures whenever a root-MR handover occurs. Therefore, if a rootMR handover occurs frequently, these accompanying signaling overhead may lead to unacceptable service discontinuity. Therefore, a new route optimization methodology, which can solve the signaling overhead problem and supports intra-domain communication, is necessary.

3 Hierarchical mobile network binding scheme for network mobility 3.1 The design principles of the hierarchical mobile network binding scheme In the hierarchical mobile network binding (HMNB) scheme, several assumptions are made. First, an MR has one home agent and one home address; it has also one uplink interface, that is, single homed mobile network. Second, the HA of an MR is can be a fixed node or a mobile node. Third, the MR can play the role of a home agent for the local MNN, such as LMN, behind the MR. As previously stated, a great deal of research has been conducted for efficient route optimization, but there are still several on-going problems regarding signaling overhead and intra-domain communication. Therefore, new methodology for route optimization is needed that meets the following requirements: Route optimization for a mobile network, intra-domain handover support, efficient intra-domain communication support and fast

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signaling. The design principles of the HMNB scheme are as follows: •

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Network mobility support: MNNs behind the MRs do not change their own physical point of attachment as a result of the mobile network movement, and can maintain their home addresses. Route optimization for the nested mobile network: The path for the nested mobile network may have minimal intermediate points which can be passed through, and the route optimization of the MNNs, behind the MR, can be achieved by using their MR’s optimized route. Signaling efficiency: Route optimization methods should provide minimal signaling overhead, and should efficiently support the root-MR handover. Intra-domain communication support: Data transmission, within the same root-MR domain, can be achieved without passing through the external network. Local mobility support: The MR or MNN movement, within the same root-MR domain, can be achieved by an intra-domain handover procedure, without binding to the external home agent. Processing scalability: The signaling and processing load of the MR must be minimized without additional procedures in the MR.

3.2 The basic concept of the hierarchical mobile network binding scheme To satisfy the requirements and design principles in Sect. 3.1, we propose a hierarchical mobile network binding (HMNB) scheme. As a mobile network moves into a new foreign network, an MNN behind the MR cannot receive data directly from the CN, since it uses its HoA still in the visited foreign network. Data from an MNN, however, can be directly transmitted to the CN by using a normal Internet routing scheme. In other words, a tunnel from the HA to the MR is required for data transmission, but the other tunnel from the MR to the HA does not have to be established for route optimization. In this way, the HMNB scheme uses different routing paths between the inward and outward packets for efficient route optimization. It

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is said to use an asymmetric tunneling technique. In the HMNB scheme, a hierarchical local binding scheme is employed between the HA of the nested mobile network and the root-MR in order to reduce the signaling overhead of the nested mobile network. The root-MR can only de-capsulate the packets from the CN. Figure 3 shows a configuration of the HMNB scheme for route optimization. In the HMNB scheme, the home address (HoA) of the root-MR is used as a binding address that supports the route optimization of the nested mobile network. The root-MR binds its CoA to its HoA and advertises the HoA to the nested mobile networks. The nested MR binds its network prefix to the HoA of the root-MR; thus, the data from the CN to the MNN passes through the HA of the MNN and the HA of the root-MR. By using this mechanism, the nested mobile networks can be independent of the root-MR handover because the binding address of the nested mobile networks, which is the HoA of the root-MR, does not change. Moreover, the route between the MR and its HA is shorter than that of the BSP with the same signaling complexity. This is because the HMNB scheme only has two intermediate HAs, regardless of the nested level of the mobile network. On the other hand, the outward packet from the MNN can be directly tunneled to the CN by using an asymmetric tunneling mechanism, without passing through any HAs. 3.3 Destination routing header and hierarchical local binding procedure In order to support asymmetric tunneling and intradomain routing, the HMNB scheme defines the destination routing header (DRH) by extending the IPv6 routing header option. The destination routing header, in the encapsulated header, has only the destination address of the original packet as a routing option. The address is used to check whether the packet reaches the destination or not. If the packet does not reach the destination, the MR changes the address of the encapsulated packet to the next-hop address in the local binding cache entry. If there is no local binding cache entry to the destination, the MR changes the address to the default routing entry, which is the address of the parent MR. The root-MR, which has received the packet without

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reaching the destination, changes the destination address of an encapsulated header as the destination address in the destination routing header, and the packet is forwarded to the CN by using a normal IP routing mechanism. By using this mechanism, intra-domain communication can be efficiently supported without passing through any HAs. Figure 4 shows the inter-domain and intradomain data transmission procedures of the HMNB scheme, with the destination routing header manipulation and asymmetric tunneling. The local binding cache of the MR is updated by using a hierarchical local binding procedure. Mobile networks take the form of tree topology, where only the root-MR has an egress interface to transmit data to or from the external network. If the nested mobile network acquires a new CoA, the MR sends the local binding update (LBU) message to the parent-MR in order to update the local binding cache information. The local binding update message contains the mobile network prefix and the new CoA of the mobile network pairs. Then, the parent-MR updates its routing entry and resends the local binding update message to its parent-MR recursively. At this time, the local binding update message of the parent-MR gets the CoA of the parent-MR as a new binding address. When a local binding update message arrives at the rootMR or a crossover MR, which contains the same routing entry in the local binding update message, the local binding procedure is finished. By using the local binding procedure, all MRs can maintain the next hop address of their nested mobile networks. In the intra-domain communication of the HMNB scheme, traffic can also be transmitted to its destination without passing through the root-MR, as long as an MR exists which contains a routing entry to the destination. To support the binding and routing of the HMNB scheme, a router advertisement message extension is required to discover the root-MR and to advertise its information. The HMNB also requires a root-MR option, which contains the HoA of the root-MR. A routing advertisement message, with the root-MR option, is used to advertise the HoA of the root-MR. Figure 5 shows the packet head structure of the root-MR option which is delivered with the extended RA message in the HMNB scheme.

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Fig. 3 Route optimization for the NEMO by using asymmetric tunneling of the HMNB scheme

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The root-MR option has the address of the rootMR for the binding of nested MRs, and it also has a local update sequence which can be used to request a local binding procedure to subordinate MRs. When the mobile network, which includes nested mobile networks, does handover within an intradomain, the highest level MR can only acquire the CoA, and the other subordinate MRs are not able to update their changed addresses. In this case, by using a local update sequence, an MR can inform its subordinate MRs of the change of its address. Subordinate MRs compare the new incoming LUSeq of the RA message and the root-MR option with the existing ones. If the new LUSeq is different form the existing LUSeq, the subordinate MRs perform the local binding update procedure and they can deliver their route information to their superior MR.

and a root-MR option. Therefore, the handover procedures in the HMNB scheme can be decided by using a routing advertisement message. In other words, an MR may perform handover procedures by using a network prefix and a root-MR address, which are delivered by the routing advertisement message. Figure 6 shows a routing advertisement message handling procedure that supports interdomain and intra-domain handovers. In the inter-domain handover, 1.

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3. 3.4 Handover procedures of hierarchical mobile network binding 4. A HMNB scheme supports both inter-domain and intra-domain handovers regarding the movement of a mobile network. When a mobile network detects movement, the MR sends a router solicitation (RS) message in order to acquire a network prefix for the foreign network. If an RS message arrives, the parent-MR or access router responds to the MR with a routing advertisement message

If the MR receives a routing advertisement message with a root-MR option, the MR processes a binding procedure between its HA and the root-MR, by using the HoA of the root-MR. The MR sends a local binding update message to the parent-MR for intra-domain communication. Finally, the MR advertises the root-MR address to its nested mobile network by using a routing advertisement message with a rootMR option. On the other hand, if the MR receives a routing advertisement message without a root-MR option, the MR sets itself up as the root-MR and sends the BU message to its HA. Then, the MR advertises a routing advertisement message with its HoA to the nested mobile network.

An intra-domain handover occurs when a mobile network moves within the root-MR domain.

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(b) Intra-domain data transmission by using destination routing header Fig. 4 Data transmission of the HMNB scheme by using the destination routing header. (a) Inter-domain data transmission by using the destination routing header. (b) Intra-domain data transmission by using the destination routing header

In this case, the MR does not need to update the binding to its HA and it only performs a local binding procedure. If an MR, which plays the role of the HA, receives a binding message, the MR forwards this message to its own HA after updating its local binding cache information. By using this mechanism, the packet from the CN is transmitted to the HA of the foreign root-MR without passing through additional intermediate HAs, including its own HA. Therefore, the traffic to the MR is always passed through only two HAs.

When a handover of mobile network occurs, the MRs in the previous domain still have the local binding information of the MR which has already moved. Therefore, data from the previous domain cannot be delivered to the moved MR. Therefore, the LBC deregistration procedure is needed in order to prevent data loss. The deregistration procedure of the MR’s local binding cache (LBC) is different whether an intra-domain handover or inter-domain handover is occurred. In the case of an intra-domain handover, the LBU is delivered

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Fig. 5 The packet head structure of the root-MR option

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a crossover MR or a root-MR, then the crossover MR or root-MR sends the deregistration message to its subordinate MR by using the old path to the moved MR before updating its LBC. The MR which receives the deregistration message, sends the message to its old path to the moved MR and updates the LBC recursively. Then, all MRs in the previous domain can update their local binding information. In the case of an inter-domain handover, the MR send the deregistration message to its previous root-MR and the previous root-MR delivers the de-registration message recursively to its subordinate MRs by using its old path information. Then, the de-registration procedure can be completed similar to that of the intra-domain handover. If an MR, which plays the role of the HA, receives a binding message, the MR forwards this message to its own HA after updating its local binding cache information. By using this mechanism, the packet from the CN is transmitted to the HA of the foreign root-MR without passing through additional intermediate HAs, including its own HA. Therefore, the traffic to the MR is always passed through only two HAs. In a mobile-HA scenario, which means that the HA of an MR is a mobile node, the node also suffers from the pinball routing problem because the packet, to or from the nodes, must pass through many HAs, such as its own HA, the HA of the mobile-HA, and the HA of the visited MR. In the HMNB scheme, if the mobile-HA moves into a foreign network, the packet to the mobile node, which has mobile-HA, is passed through the several HA. However, the packet from the mobile node is delivered to the CN directly by using the asymmetric tunneling. Moreover, if the mobileHA moves into the same root-MR domain with its MR, the packet to or from the MNN behind the MR is passed directly to the mobile-HA by using the DRH scheme, In the mobile-HA scenario, the HMNB scheme has more optimal paths compared with other route optimization methods. In the proposed HMNB scheme, if the MIPv6enabled VMN prefers the MIPv6 route optimization scheme, it can choose the MIP6 procedure, independently. If a VMN chooses the MIPv6 route optimization procedure, the VMN can acquire a CoA from the RA message and prefix of its parent-MR without accessing the HA of the VMN.

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Data to or from a mobile node can be delivered directly via the route which is determined by the MIPv6 route optimization procedure.

3.5 The extension of the hierarchical mobile network binding scheme The HMNB scheme can provide more optimal route than the BSP, and can reduce the number of additional handovers and the signaling complexity in a vehicular network environment. Moreover, the HMNB scheme can be easily extended in order to support more optimal routing. In the HMNB scheme, if the root-MR handover does not occur frequently, the CoA of the root-MR, instead of HoA, is chosen as the binding address of the nested MR. If the CoA of the root-MR is used as the binding address of the nested MR, the HMNB scheme can provide the shortest path without changing architecture. In this case, similar to the TLMR method, data that is transmitted from the CN to the MNN only has to pass through one tunnel, between the nested MR and its HA, via the root-MR. As shown in the root-MR option in Fig. 5, both the HoA and CoA of the root-MR can be delivered together by an extended RA message. According to the mobility pattern of a nested MR or policy of a mobile network, the nested MR can be selective in choosing the route optimization methods. Moreover, according to the dynamic alteration of the mobility pattern and network environment, the nested MR can choose the HoA or CoA of the root-MR spontaneously, by delivering the binding update message to the HA of the nested MR. These can support the dynamic conversion between a basic mode and an extended mode. The dynamic conversion mechanism, however, remains as an area of further study. In the HMNB scheme, the packets are transmitted securely, because packets are delivered through tunnels by using local binding and binding cache. The objective of this paper, however, is to improve performance with regard to route optimization. Therefore, details concerning the security analysis are not within the scope of this work and these are an area of further study.

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4 Performance evaluation

DSIG_TLMR = 2

4.1 An analysis of signaling and data transmission delays For performance evaluation, we compare the signaling delays and the data transmission delays of the HMNB scheme with several network mobility support protocols, such as, basic support protocol, TLMR scheme and RRH scheme. The TLMR and RRH schemes have similar signaling and data transmission paths. Therefore, we analyze the signaling and data transmission delays of the TLMR scheme as representative of them. The signaling delay, DSig_BSP , and the data transmission time of the basic support protocol, DBSP , can be obtained as the sum of the mobile network delay, DMRs , the tunnel delay, DHAs , and the endhost transmission delays, DMNN,MRn and DHAn,CN , such that DSIG_BSP = 2(DMRs + DHAs ) n
 =2 DMR(i,i+1)

n 

 DMR (i, i+1)+ DMR1,HAn ,

i=1

(3) DTLMR = 2(DMNN,MRn +

n 

+ DMR1,HAn + DHAn,CN ).

+ DMR1,HA1 +

n
 DSIG_HMNB = 2 DMR (i, i + 1) + DMR1,HA1 i=1

 + DHA1,HAn ,  DHA(i,i+1) ,

(1)

i=1

DBSP = 2(DMNN,MRn +DMRs +DHAs +DHAn,CN ) n  = 2(DMNN,MRn + DMR (i, i + 1) i=1 (2) n−1  DHA (i, i+1) + DMR1,HA1 + + DHAn,CN ),

(4)

In the HMNB scheme, DHAs becomes the sum of DMR1,HA1 , which is the transmission delay between the root-MR and its HA, and DHA1,HAn , which is the transmission delay between the HA of the root-MR and the HA of the MNN. The path from the root-MR to the correspondent node is directly connected with the transmission delay DMR1,CN , so that the signaling delay and the data transmission time of the HMNB scheme, DSig_HMNB and DHMNB , are

i=1 n−1 

DMR (i, i + 1)

i=1

i=1

where DMR (i, i + 1) is the transmission delay between the adjacent MRs, and n is the level of the mobile network. Here, DMR1,HA1 is the delay between the root-MR and its HA, and DHA (i, i + 1) is the transmission delay between the HAs of the adjacent MRs. In the TLMR and RRH schemes, DHAs becomes DMR1,HAn , which is the transmission delay between the root-MR and the HA of the MNN. The top-level MR tunneling scheme uses the symmetric tunneling, so that the signaling delay and the data transmission time of the TLMR scheme, DSig_TLMR and DTLMR , are

DHMNB = 2(DMNN,MRn +

(5)

n 

DMR (i, i + 1))

i=1

+ DMR1,CN + DCN,HAn + DHAn,HA1 + DHA1,MR1 .

(6)

In the extended HMNB scheme, DHAs becomes DMR1,HAn , which is the transmission delay between the root-MR and the HA of the MNN. The path from the root-MR to the correspondent node is directly connected with the transmission delay DMR1,CN , so that the signaling delay and the data transmission time of the extended hierarchical mobile network binding scheme, DSig_HMNB−E and DHMNB−E , are n 
 DMR (i, i+1)+DMR1,HAn DSIG_HMNB−E = 2 i=1

(7) DHMNB−E = 2(DMNN,MRn +

n 

DMR (i, i + 1))

i=1

+ DMR1,CN + DCN,HAn + DHAn,MR1 .

(8)

Hierarchical mobile network binding scheme

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Assuming that the mobile network link delay is a constant number Kmnet and the wired link delay is constant, K; Eqs. 1–8 are calculated as follows. In the NEMO basic support protocol, the signaling and the transmission delays are denoted as Eq. 9 and 10, DSIG_BSP = 2 · n · (Kmnet + K),

(9)

DBSP = 2 · (n + 1) · (Kmnet + K).

(10)

In the TLMR and RRH schemes, the signaling and the transmission delays are denoted as Eqs. 11 and 12, DSIG_TLMR = 2 · (n · Kmnet + K),

(11)

DTLMR = 2 · ((n + 1) · Kmnet + 2 · K).

(12)

In the proposed hierarchical HMNB and extended HMNB schemes, the signaling and the transmission delays are denoted as Eqs. 13 and 14, and Eqs. 15 and 16, respectively,  if n = 1, 2 · (Kmnet +K) DSig_HMNB = 2·(n ·Kmnet +2·K) otherwise, (13)  DHMNB =

4·Kmnet +3·K 2·(n+1)·Kmnet +4 ·K

if n = 1, otherwise, (14)

DSIG_HMNB−E = 2 · (n · Kmnet + K),

(15)

DHMNB−E = 2 · (n + 1) · Kmnet + 3 · K.

(16)

As a result, the signaling delay and the data transmission delay of the HMNB scheme are smaller than those of the IETF’s basic support protocol.

4.2 Simulation results Table 1 shows the characteristics of the network mobility protocols which are used for performance evaluation. The Nemo basic support protocol and the HMNB Scheme have the least amount of signaling overhead, as they do not need to perform binding procedures when a root-MR handover occurs. Therefore, they have advantages in terms of both signaling complexity which represents the

procedures of various handover scenarios and scalability. The basic support protocol, however, has drawbacks in terms of signaling latency, handover delays, and data transmission delays due to the dogleg problem. In particular, the proposed scheme has several advantages compared with previous methodologies. It has the smallest delay in both data transmission and signaling. Moreover, intradomain handover and communication are well supported, and micro-mobility can be well supported without the need for additional extensions. Both the TLMR and HMNB schemes need an additional routing repository in order to support intra-domain communication. In the TLMR method, only the root-MR has the full path information of all nested MRs. On the contrary, in the HMNB scheme, all MRs have the next hop address and the local binding cache which contains mapping information. The BSP always uses the same number of tunnels as nesting levels. The TLMR method uses only one tunnel from the root-MR and the HA of the nested MR. In the case of intradomain communication, however, the TLMR uses the same number of tunnels as nesting levels. The RRH and HMNB schemes can only have one or two tunnels, which contain an extended routing header. Therefore, the RRH and HMNB schemes have the minimum packet overhead which is caused by tunneling. On the other hand, the BSP has the minimum processing load of the root-MR. This is because the BSP can deliver data by encapsulating and de-capsulating header information. In the RRH scheme, because the HA can provide the RRH of full path, each MR can deliver data to the next hop by using the path information of the RRH. Therefore, the RRH scheme also has the minimum processing load. The HMNB scheme handles next hop routing by searching the LBC entry, so that it has a greater processing load than those of the BSP and the RRH. The nested MR of the TLMR method performs processing, similar to the nested MR of the BSP. The root-MR of the TLMR method which keeps the whole routing path, however, performs multiple encapsulation and de-capsulation procedures for all packets. Therefore, it has the largest processing load. We evaluated the performance of the proposed HMNB scheme by using discrete event simulation

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Table 1 Characteristics of various network mobility support protocols BSP

TLMR

RRH

HMNB

Signaling amount Signaling latency Signaling complexity Additional handover procedure Handover delay Transmission delay Intra-domain data transmission Scalability Micro-mobility Additional routing repository Number of tunnels

Small Large Small No Large Large N/A Large N/A Not necessary Number of nesting level

Large Small Medium Yes Medium Small N/A Medium N/A Not necessary RRH only

Small Small Small No Small Medium Well-supported Medium Support All MRs One or two DRH

Processing load of MR

Small

Large Medium Large Yes Medium Small Possible Medium Possible Root-MR only Number of nesting level (intra-domain) Large at root-MR

Small

Medium

... HAn

...

HA2

MRn'

HA1 ... Internet

AR1

CN (Inter-domain)

MR1 (Root-MR)

MR2

... Crossover MR i

...

AR2 MR2'' MR Level 1 MR Level 2

CN (Intra-domain)

MRn

MNN

... MRi'' MR Level i

MRn'' MR Level n

Fig. 7 The test configuration of mobile networks for simulation purposes

with topology as shown in Fig. 7. All HAs are assumed to have the same wired link with a 10 ms delay, and the mobile nodes also have the same wireless link with a 10 ms delay. The routing advertisement interval of an MR is assumed to be 3 s, and each MR detects movement within 15 ms. The MRs and HAs are built by implementing the following protocols: basic support protocol (BSP) [2], top-level MR tunneling (TLMR) [9] method, reverse routing header (RRH) [19] scheme, and the proposed hierarchical mobile network binding (HMNB) and extended hierarchical mobile network binding (HMNB-E) schemes. Each protocol is implemented to support its handover procedures, tunneling procedures, routing headers, and the roles of nodes which are mobile router, local mobile node, local fixed node, home agent, and access routers, respectively. Figure 8 a and b show the performance results of the inter-domain and intra-domain data

transmission times for TCP traffic, as the depth of the destination MR increases. In the inter-domain communication environment, the data transmission delays of the TLMR, RRH, HMNB and the extended HMNB schemes were smaller than those of the BSP. The delay of the extended HMNB scheme is smaller than the HMNB scheme itself, but the difference between the extended HMNB and the HMNB is negligible. In the intra-domain communication environment, the data transmission delays in the RRH scheme are larger than those of the HMNB and the extended HMNB schemes. This is because the traffic always passes through the HA. Moreover, the intra-domain communication times of the HMNB and the extended HMNB schemes show that the delays decrease more than that of any other schemes, if the crossover MR is located below the root-MR. Figure 9 shows the signaling completion times for inter-domain, intra-domain, and root-MR

Hierarchical mobile network binding scheme

(a) 0.8 En d - t o - e n d d e l a y ( se c)

Fig. 8 Performance analysis in accordance with the increase of the depth of the MR. (a) Inter-domain data transmission time versus nesting depth of the MR. (b) Intra-domain data transmission time versus nesting depth of the MR

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En d - t o - e n d d e l a y ( se c)

(b) 0.8 0.6

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Intra-domain data transmission time vs. nesting depth of the MR

handovers. In the case of an inter-domain handover, the signaling completion times of the hierarchical mobile network binding scheme are larger than those of the reverse routing header and toplevel MR tunneling schemes because the proposed scheme uses two intermediate HAs. On the other hand, the hierarchical mobile network binding scheme and its extended scheme have the minimal handover delaying time in the case of an intra-domain handover, since it can provide fast handover by using local binding update procedure. In the top-level MR tunneling scheme, it does not define any intra-domain handover procedure. However, the top-level MR can maintain the full paths of the nested mobile networks, so it can perform the intra-domain handover by updating the paths of the nested mobile networks to the toplevel MR. The reverse routing header scheme must send the binding update message to the HA of the nested mobile network. Therefore, the proposed scheme has smallest signaling completion times for the intra-domain handover procedure.

In the case of a root-MR handover, the binding procedures of the hierarchical mobile network binding scheme and basic support protocol are performed by only the root-MR, and the nested mobile networks do not perform the binding procedures. On the contrary, other route optimization schemes use the CoA of the root-MR for binding addresses or routing paths of the nested mobile networks, and all nested mobile networks must perform the binding procedures. These can cause the service discontinuity during the data transmission until the binding procedures are completed. Figure 10 shows the service discontinuity time and the signaling overhead of the root-MR handover for each network mobility support protocols. In Figure 10a, both the hierarchical mobile network binding scheme and basic support protocol can conduct handover procedures by only having to access the root-MR, therefore the service discontinuity times of them are uniformed. On the contrary, other route optimization schemes use the CoA of the root-MR for binding addresses or routing paths of the nested mobile networks,

0.8

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(a)

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Nesting depth of the MR

Inter-domain handover signaling completion time vs. nesting depth of the MR Si g n a l i n g Co m p l e t i o n Ti m e ( se c)

Fig. 9 Handover signaling completion time in accordance with the depth of the MR. (a) Inter-domain handover signaling completion time versus nesting depth of the MR. (b) Intra-domain handover signaling completion time versus nesting depth of the MR. (c) Root-MR handover signaling completion time versus nesting depth of the MR

M. S. Jeong et al. Si g n a l i n g Co m p l e t i o n Ti m e ( s e c)

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Nesting depth of the MR

Root-MR handover signaling completion time vs. nesting depth of the MR

and all nested mobile networks must perform the binding procedures. Therefore, the service discontinuity times for the top-level MR tunneling and the reverse routing header schemes become large as the depth of the nesting level is increased. On the other hand, the number of the nested mobile networks can increase the signaling overhead for the root-MR handover apart from the depth of the mobile networks. Figure 10b shows the signaling overheads for the root-MR handover in accordance with increasing the number of the mobile networks. In case of the hierarchical mobile network binding scheme and the basic support protocol, they have no additional handover procedures for the nested mobile networks, so the

signaling overheads are constants regardless of the number of the nested mobile networks. On the contrary, other route optimization schemes have large signaling overhead in accordance with increasing the number of the nested mobile networks. According to these results, the top-level MR tunneling and reverse routing header schemes may not be suitable for a vehicular environment where the root-MR moves frequently. In addition, they may not be appropriate for time-critical real-time multimedia services such as wireless VoIP (Voice over IP) or multimedia broadcasting services. When handover of the mobile network is performed, the signaling completion times for the handover can cause the service discontinuity

Hierarchical mobile network binding scheme

(a) Ser v i c e D i s c o n t i n u i t y Ti m e ( s e c )

Fig. 10 Service discontinuity time and signaling overhead in case of the root-MR handover. (a) Service discontinuity time for root-MR handover versus nesting depth of the MR. (b) Signaling overhead for root-MR handover vs. number of the nested mobile networks

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Service discontinuity time for root-MR handover vs. nesting depth of the MR

Si g n a l i n g o v e r h e a d r a t i o

(b)

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TLMR HMNB

RRH TLMR

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HMNB-E

40 20 HMNB BSP

0 0

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(a)

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Inter-domain HO

Root-MR HO

Intra-domain HO

Sub-tree HO

Service discontinuity times for the CBR traffic Se r v i ce D i sco n t i n u i t y Ti m e ( se c)

Fig. 11 Service discontinuity times for various handover scenarios. (a) Service discontinuity times for the CBR traffic. (b) Service discontinuity times for the TCP data transmission.

Se r v i ce D i sco n t i n u i t y Ti m e ( se c)

Signaling overhead for root-MR handover vs. number of the nested mobile networks

0.6

(b)

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TLMR

HMNB

HMNB-E

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Root-MR HO

Intra-domain HO

Sub-tree HO

Service discontinuity times for the TCP data transmission

992 1.4 En d - t o - e n d d e l a y ( se c)

Fig. 12 Performance analysis for a mobile-HA scenario. (a) TCP data transmission delays for a mobile-HA scenario. (b) Service discontinuity times for a mobile-HA scenario

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BSP

1.2

RRH

HMNB

(a)

HMNB-E

1 0.8 0.6 0.4 0.2 0

1

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5

6

7

8

9

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Nesting depth of the MR

S e r v i c e d i sco n t i n u i t y t i m e ( se c)

TCP data transmission delays for a mobile-HA scenario 0.6 BSP

RRH

HMNB

HMNB-E

(b)

0.4 BSP 0.2

0

RRH HMNB-E HMNB HO with same rootMR (beneath HA)

HO with same rootMR (above HA)

HO to the different domain (Root-MR)

HO to the different domain (Nested-MR)

Service discontinuity times for a mobile-HA scenario

until completing the binding procedures. Figure 11 shows the service discontinuity times for CBR traffic and the TCP data transmission, under various handover scenarios. In the case of the CBR handover scenario in Figure 11a, the service discontinuity times of the hierarchical mobile network binding scheme are smaller than other route optimization schemes in each handover scenarios. In the case of the rootMR handover or whole mobile networks movement from AR1 to AR2, the discontinuity times of the proposed scheme (81 ms) and the basic support protocol (82 ms) are the lowest. In the case of the basic support protocol, the nested depth of the MR is greater, so that the service discontinuity time increases more than other handover scenarios except the root-MR handover scenario. This is because of the pinball routing problem in basic support protocol. In the cases of an intradomain handover (for example, “MR5 moving to the subordinate of MR4”) and sub-tree handover scenarios (for example, “ MR4 and sub-tree moving to the subordinate of MR4”), the hierarchical mobile network binding scheme shows the best

performance in data transmission and it has smallest delay (100 ms) for the intra-domain handover procedure, since it can provide fast handover by using local binding update procedure. In the case of the TCP handover scenario in Fig. 11b, the hierarchical mobile network binding scheme also has a small service discontinuity time similar to that of the CBR. The reverse routing header scheme has a minimum service discontinuity time when the inter-domain handover and the root-MR handover. In the case of CBR transmission, the reverse routing header must perform additional binding update procedures. On the contrary, in the case of TCP transmission, the reverse routing header scheme is more efficient because it can perform binding updates simultaneously with a piggybacked acknowledgement. In the case of the extended hierarchical mobile network binding scheme, service discontinuity time for the root-MR handover is similar to the toplevel MR tunneling scheme. This is because the additional binding procedure for the nested MR must perform similar to the top-level MR tunneling scheme.

Hierarchical mobile network binding scheme

Figure 12 shows the performance results of the data transmission times and the service discontinuity times for the mobile-HA scenario, according to the various handover cases, respectively. The top-level MR tunneling scheme does not define any methods that support the mobile-HA. The basic support protocol has the largest data transmission delays because the movement of mobileHA cause the additional pinball routing problem. In the hierarchical mobile network binding and extended schemes, when an MR, which plays the role of the home agent, receives the binding message, the MR forwards the binding message to its own HA. Thus, the traffic from the correspondent node is transmitted to the HA of the foreign root-MR without passing through additional intermediate HAs, including its own mobile HA. Therefore, the traffic to the MR always passes through only two HAs and the hierarchical mobile network binding and the extended schemes have the smallest delays for data transmission and the service discontinuity.

5 Conclusion In this paper, we have presented a new route optimization technique, called a HMNB scheme, in nested mobile networks. It employs asymmetric tunneling and a hierarchical local binding mechanism to optimize routes in both inter-domain and intra-domain communication. We have investigated the limitations of previous and current approaches to network mobility management. The proposed scheme is different from other route optimization approaches, whereby the home address of the root mobile router (root-MR) is used as the binding address of a mobile network, and the destination routing header (DRH) is used for intradomain communication. Although there are other RO techniques such as TLMR and RRH which require the accessing of only one HA, signaling overhead and service discontinuity of these protocols are not as efficient as those of the HMNM scheme. In the proposed HMNB scheme, the binding procedures of the mobile networks are not necessary, as a result, there is no additional signaling overhead for the handover of the nested MRs. However, in the TLMR and RRH schemes, all mobile routers which are

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subordinate to the root-MR must execute additional binding procedures whenever a root-MR handover occurs. In a mobile environment where handovers of root-MR frequently occur, such as in a vehicular network, the additional signaling overhead, due to the aforementioned binding procedures of the subordinate mobile routers, may result in unacceptable service discontinuity. In conclusion, even though the proposed HMNB scheme does not provide an optimized path, the less amount of signaling overhead of the proposed scheme, in comparison with other RO methods, can be justified with respect to service quality and intracommunication efficiency. We have also proposed an extension of the HMNB scheme, which enables either CoA or HoA of the root-MR to be used as a binding address. This extension scheme overcomes the two-hop path problem of the HMNB scheme, so that the performance can be improved with respect to both signaling delay and data transmission time. Finally, we performed extensive simulations in order to compare the proposed HMNB scheme with the other network mobility support protocols. Future research may include detailed analyses regarding security issues related to the proposed scheme.

References 1. Cho, H. S., Paik, E. K., & Choi, Y. H. (2003). R-BU: Recursive binding update for route optimization in nested mobile networks.In Proceedings of the IEEE vehicular technology conference 2003, Orlando, USA. 2. Devarapalli, V., Wakikawa, R., Petrescu, A., & Thubert, P. (2005). Network mobility (NEMO) basic support protocol. RFC 3963. 3. Ernst, T., Mitsuya, K., & Uehara, K. (2003). Network mobility from the internetcar perspective. In Proceedings of the 17th international conference on advanced information networking and applications, 19–26. 4. Ernst, T. (2005). Network mobility support goals and requirements. IETF, Internet draft . 5. Ernst, T., Lach, H. Y. (2005). Network mobility support terminology. IETF, Internet draft . 6. Gu, Z. J., Yang, D. M., & Kim, C. H. (2004). Mobile IPv6 extensions to support nested mobile networks. In Proceedings of the 18th international conference on advanced information networking and applications, Fukuoka, Japan. 7. Jeong, M. S., & Park, J. T. (2004). Hierarchical mobile network routing: route optimization and

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M. S. Jeong et al. micro-mobility support for a NEMO. In Proceedings of the international conference on embedded and ubiquitous computing 2004, lecture Notes in Computer Science 3207/2004, pp. 571–580. Johnson, D., Perkins, C., & Arkko, J. (2004). Mobility support in IPv6. RFC 3775. Kang, H. S., Kim, K. C., Han, S. Y., Lee, K. J., & Park, J. S. (2003). Route optimization for mobile network by using Bi-directional between home agent and top level mobile router. IETF, Internet draft . Available: http://ietfreport.isoc.org/idref/draft-hkang-nemo-ro-tlmr/. Lach, H. Y., Janneteau, C., & Petrescu, A. (2003). Network mobility in Beyond-3G systems. IEEE Communication Magazine, 41, 54–57. Ng, C., Paik, E., Ernst, T., & Bagnulo, M. (2005). Analysis of multihoming in network mobility support. IETF, Internet draft . Na, J. K., Choi, J. H., Cho, S. H., Kim, C. K., Lee, S. J., Kang, H. J., & Koo, C. H. (2004). A unified route optimization scheme for network mobility. In Proceedings of the International Conference Personal on Wireless Communications 2004, Lecture Notes in Computer Science, Vol. 3260, pp. 29–38. Na, J. K., Cho, S. H., Kim, C. K., & Koo, C. H. (2004). Generic route optimization model for nemo extended support. IETF, Internet draft . Available: http://ietfreport.isoc.org/idref/draft-na-nemo-gen-ro-model/. Ohnishi, H., Sakitani, K., & Takagi, Y. (2003). HMIP based route optimization method in a mobile network. IETF, Internet draft . Available: http://ietfreport.isoc.org/idref/draft-ohnishi-nemo-ro-hmip/. Park, M. H., Park, C. M., Kim, S. H., Hong, S. B., & Choi, J. S. (2004). A novel routing protocol for personal area network mobility (PANEMO) environment. In Proceedings of the International Conference Advanced Communication Technology, Phoenix Park, Korea. Perera, E., Sivaraman, V., & Seneviratne, A. (2004). Survey on network mobility support. Mobile Computing and Communications Review, 8(2), 7–19. Thubert, P., Wakikawa, R., & Devarapalli, V. (2005). NEMO home network models. IETF, Internet draft . Thubert, P., Molteni, M., Ng, C., Ohnishi, H., & Paik, E. (2005). Taxonomy of route optimization models in the Nemo context. IETF, Internet draft . Available: http://ietfreport.isoc.org/idref/draft-thubert-nemo-ro-taxonomy/. Thubert, P., & Molteni, M. (2004). IPv6 reverse routing header and its application to mobile networks. IETF, Internet draft . Availabe: http://ietfreport.isoc.org/idref/draft-thubert-nemo-reverse-routing-header/. Wells, J. D. (2003). A network mobility survey and comparison with a mobile ip multiple home address extension. M.S.Thesis, Virginia Polytechnic Institute and State University,, Virginia, USA.

Moon-Sang Jeong received his B.S. and M.S. degrees in Electronic Engineering from Kyungpook National University, Daegu, Korea, in 2000. He is currently working towards his Ph.D. degree in the School of Electronic and Electrical Engineering, Kyungpook National University. His research interests include mobile networks and mobility management. In particular, he has been working on route optimization in the Nemo environment. Yeong-Hun Cho received his B.S. and M.S. degrees in Electronic Engineering from Kyungpook National University, Daegu, Korea, in 2001. He is currently working towards his Ph.D. degree in the Department of Information and Communication, Kyungpook National University. His research interests include service management using SIP and conference management. In particular he has been working on mobility management and service management via the use of location technologies. Jong-Tae Park is a Professor in the School of Electrical Engineering and Computer Science at Kyungpook National University. He received his Ph.D. degree in Computer Science and Engineering from the University of Michigan and previously worked at AT &T Bell Labs in the United States. He founded the Committee of Korean Network Operations and Management (KNOM) in the Korean Institute of Communication Sciences and was one of the founding members of Asia-Pacific Symposium on Network Operations and Management (APNOMS). He has served as Chair of the Technical Committee of Information Infrastructure of the IEEE Communication Society. He is currently on the Editorial

Hierarchical mobile network binding scheme Board of the International Journal on Network and Systems Management and China Communications. He was General Chair for APNOMS97, General Chair for ICC 2002 Symposium and Co-Chair for the Globecom2002 Symposium on Global Service Portability and Infrastructure. He has also served as a committee member or on the Advisory Board member for IEEE/IFIP NOMS and IM. He has published more than 100 journals and articles in the areas of computer communication networks, network management, and

995 distributed systems. His current research interests are related to the control and management of next generation information networks, which includes Ad-Hoc Network, MPLS/GMPLS, B3G/4G, IPv6, home network, and ubiquitous sensor networks. He is also interested in the development of the SIP-based mobile multimedia platform, mobile RFID middleware, and dependable software systems.