Implementation and Analysis of a Testbed for IP-Based Heterogeneous Wireless Networks

Transcription

1 Implementation and Analysis of a Testbed for IP-Based Heterogeneous Wireless Networks JYH-CHENG CHEN, CHING-YANG HUANG, SHUN-CHAO HUANG, MING-CHIA JIANG, CHIA-FENG KANG, HONG-WEI LIN, LIAN-DONG LIU,YI-WEN LIU, JUI-HUNG YEH National Tsing Hua University Hsinchu, Taiwan Abstract: - This paper presents a generic testbed for IP-based heterogeneous wireless networks. The testbed comprises GPRS, wireless LANs, VoIP system, and PSTN. The interworking between GPRS and WLAN is achieved by a GPRS-WLAN Mobility Gateway (GWMG) that resides on the border of GPRS system. A WLAN-centric authentication is proposed and implemented to authenticate users in the testbed. The Mobile IP messages are capable of traversing NAT. A simplified SIP user agent is implemented to execute IP signaling for real-time sessions. The testbed also incorporates a traffic conditioner such that QoS control mechanism can be enforced. Furthermore, by connecting to the public Internet and PSTN, any user in the world can make a real circuit-switched or packet-switched phone call to any user in our testbed. In addition, a privacy network architecture is proposed to protect the location privacy of Internet users. Performance analysis in terms of handoff latency, packet delay, and packet loss is achieved by empirical experiments. Key-Words: All-IP wireless networks, mobility management, authentication, NAT, VoIP, privacy network, QoS, and signaling. 1 Introduction Today, many different wireless systems exist, ranging from wireless PANs (Personal Area Networks), wireless LANs (Local Area Networks) to outdoors cellular systems. They are typically not compatible with each other, making it difficult to roam from one system to another. Wireless PANs, LANs, and cellular systems are also being developed and are evolving independently. Although ITU IMT-2000 has been trying to unify third-generation (3G) wireless systems, incompatible systems are expected to co-exist in the future. No wireless technology has emerged as a common and long-term universal solution. IP (Internet Protocol), which is already a universal network-layer protocol for wireline packet networks, is becoming a promising universal network-layer protocol over all wireless systems. An IP device, with multiple radio interfaces or software-defined radio, could roam between heterogeneous wireless systems if they all support IP as a common network layer. Unlike today's radio systems that depend heavily on proprietary technologies, IP provides a globally successful open infrastructure for services and applications. Such an all-ip wireless and wireline network could also make wireless networks more scalable and cost effective. Although IP is a promising technology for future generation wireless networks, there are still many challenges for realizing IP-based heterogeneous wireless networks. Constructing a testbed is one of the effective ways to inspect and experiment various design alternatives. This paper illustrates a testbed being building at the WIRE Lab (Wireless Internet Research & Engineering Laboratory) for future generation wireless networks. The testbed, which comprises numerous IP-based protocols and applications, is capable of demonstrating wireless multimedia communications in heterogeneous networks. Major technologies of a completed system, including mobility management, security, NAT (Network Address Translation, IETF RFC 2663), VoIP (Voice over IP), signaling, QoS (quality-of-service), and location privacy are implemented. Empirical experiments are conducted to analyze the testbed performance. Section 2 defines the testbed architecture. It also describes the realization of network components and protocols. Section 3 depicts the testbed implementation. Section 4 illustrates the experimental results. Section 5 concludes the paper. 2 Architecture and Protocols With a view to realizing different network components, protocols, and applications in future IP-based heterogeneous networks, a testbed has been implemented to examine design alternatives and to perform various experiments.

2 Fig. 1. Testbed architecture Fig. 1 presents the testbed architecture. There are four major components in the testbed including GPRS, public WLAN, private WLAN, and VoIP networks. The testbed is connected to the public Internet by a router. In addition, it connects to the Public Switched Telephone Network (PSTN) by a PSTN gateway. The critical integration issues and solutions implemented in the testbed are discussed in next sessions. 2.1 GPRS-WLAN Mobility Gateway (GWMG) General Packet Radio Service (GPRS), a wireless packet system based on the GSM architecture, is designed to serve highly mobile subscribers with sophisticated high-power radio. Cell diameters generally can exceed 10 Km. Current available data rate is limited on the range of Kbps. On the other hand, by utilizing short range and low power radio, wireless LANs (WLANs) are mainly deployed in indoor environment for low mobility and high speed applications. The bit rates of WLANs range from 11 Mbps (e.g. IEEE b) to 54 Mbps (e.g. IEEE a). Therefore, users might want to use GPRS virtually anywhere to access to the Internet. They nevertheless would like to leverage the high-speed access of WLANs whenever it is possible. However GPRS and WLANs are based on different networking technologies. The integration of them, especially seamless roaming, thus becomes a critical issue. Mobile IP (IETF RFC 3220) is the mobility management protocol developed by the Internet Engineering Task Force (IETF). It is a natural choice that the testbed employs Mobile IP as the mobility management protocol in WLANs. To integrate Mobile IP with the mobility management defined in GPRS, we design a GPRS-WLAN Mobility Gateway (GWMG) [1]. By simply deploying the GWMG on the border of GPRS and WLANs, users could seamlessly roam among these two systems without changing the existing infrastructure. The GWMG is a logical entity that could be implemented stand-alone or as an addition to the gateway GGSN which connects GPRS to external IP networks. Because a user might have his/her home network in either GPRS or WLAN networks, the gateway should be able to function like a Home Agent (HA) and Foreign Agent (FA). The two cases when a user has home network in WLANs and GPRS, respectively, are described as follows: Home in WLANs - When the home network of a user is in WLANs, the correspondent node 2

3 (CN) sends its traffic to the WLAN system regardless of the mobile station's (MS) anchor point. The home network should be able to tunnel traffic to the MS's current location. In this scenario, the gateway should function like a FA. To identify a MIP (Mobile IP) request, the Access Point Name (APN) in PDP context is utilized to select the specific network service. Home in GPRS In this case, the GWMG plays a role as HA and connects to GGSN through the standard G i interface. When both MS and CN are inside GPRS, packets from CN to MS will pass through BSS, SGSN and finally arrive at GGSN. GGSN will route them to the suitable SGSN by looking at the PDP context of the MS. Once a MS moves to WLANs, the MS will send MIP registration message to its HA (the GWMG). The GWMG then will send a message to inform the GGSN that the MS is out of the GPRS network. GGSN, thus, needs to initiate PDP context deactivation to delete the PDP context in GGSN, SGSN and the MS. If there are packets from GPRS network to the MS, GGSN will forward them to the GWMG rather than SGSN due to lack of PDP context of the MS. When MS is in GPRS network and CN is in WLANs, it works as what defined in the standards. Once a MS roams to WLANs, packets from CN to MS will be intercepted and tunneled by HA (the GWMG) to WLANs once the MIP registration is completed. 2.2 Authentication A SIM-based authentication is preferable for GPRS operators for the integrated GPRS and WLAN networks. It requires WLAN system processes the GPRS-based authentication and transports the GPRS authentication messages back to the GPRS networks. In real world, however, the WLAN users may not be subscribers of the GPRS system. There is no SIM card in WLAN users. In addition, the WLAN operators may not want to reconstruct their WLANs for SIM-based authentication. We propose an alternative WLAN-centric approach based on the perspective of WLAN providers. By deploying WLAN-based Authentication, Authorization, Accounting (AAA) server in both GPRS and WLAN networks as shown in Fig. 2, WLAN users could be authenticated between GPRS and WLAN systems without using a SIM card. Fig. 2. Architecture for WLAN-centric authentication The proposed architecture is based on the loose coupling architecture. In addition, GPRS and WLAN are two parallel systems and work independently. That is, GPRS and WLAN systems could keep existing authentication mechanisms. In GPRS, the authentication process is based on the Authentication and Key Agreement (AKA) developed in GSM. For WLANs, we assume IEEE 802.1X [2], which is now widely deployed in many 802 series standards, is adopted. Because both GPRS and WLANs are widely deployed already, an efficient way to integrate them should reduce the impact on the existing systems as much as possible. The key component in our WLAN-centric architecture is an AAA server, which is installed in both GPRS and WLAN networks. Although RADIUS (Remote Authentication Dial in User Service, IETF RFC 2865) or other servers can serve as the AAA server, in the testbed we use Diameter (IETF RFC 3588) to illustrate our design. In order to filter proper messages to the GPRS AAA server, Fig. 2 shows that an additional Registration Filter (Reg-Filter) is deployed between BSS and SGSN in the GPRS network. Based on the architecture and a two-phase authentication, WLAN users can execute WLAN-based authentication in GPRS networks as they are in WLANs. GPRS subscribers are authenticated by the GPRS authentication mechanism in GPRS networks. All users perform WLAN-based authentication in WLAN systems [3]. 2.3 Network Address Translation Mobile IP assumes every mobile node have a globally unique IP address. However, with the explosive growth of Internet, IPv4 address is 3

4 Fig. 3. UDP tunnelling Fig. 4. Privacy network architecture running out. Network address translator (NAT) that translates between private and public addresses allows several hosts to share one public IP address. However, there are some conflicts between Mobile IP and NAT. The use of tunnel in Mobile IP conceals some information that NAT needs. It is also possible that two mobile stations with identical private IP addresses roam into the same foreign network. We propose the following mechanisms to integrate Mobile IP and NAT: UDP tunneling - UDP tunneling [4] [5] is introduced for encapsulated packet to traverse through NAT. UDP tunneling inserts an additional UDP header into the encapsulated packet as shown in Fig. 3. Thus, NAT could obtain enough information to translate encapsulated packets between private realm and public realm. Static port - Port 434 is the default port number that HA receives registration request message. We bind NAT s port 434 to HA s port 434. When NAT receives any packet from port 434, it will simply redirect the packet to HA s port 434. Therefore, HA can get the registration message. Reverse tunneling Because CN may not reside inside same home network as MS, we mandate the reverse tunneling. With reverse tunneling, all packets from MS will be tunneled to home network first, which then is forwarded to CN by HA. Therefore, packets will traverse through NAT. The CN will get packets with source IP address set to the home NAT s public IP address. Thus, the home NAT would translate the reply packets. In UDP tunneling, data packets will always be encapsulated with UDP destination port 434. With the combination of reverse tunneling and static port, packets could be transferred transparently between CN and MS [6]. 2.4 Signaling The testbed comprises a simplified Session Initiation Protocol (SIP, IETF RFC 3261) User Agent (UA) implemented by the WIRE Lab. The SIP UA executes IP signaling so real-time multimedia sessions can be established between two end points. The WIRE SIP UA includes a Graphic User Interface (GUI) for ease of operation. It mimics a video telephone such that a user can make a multimedia communication through the GUI. After the connection is built, users can not only talk to each other but also see each other in real-time. In addition, a whiteboard is also invoked for information exchange. In the testbed, each laptop is equipped with a PC camera to capture real-time video. Although we develop and implement the WIRE SIP user agent, multimedia applications associated with SIP are vic, rat, and wbd which are available in public domain [7]. 2.5 Voice over IP With Voice over IP (VoIP), voice is sampled and encoded into digital data stream. The digital voice data stream is then segmented and capsulated into IP packets. Voice call is then delivered by IP networks. As shown in Fig. 1, the testbed is connected to the PSTN by a PSTN gateway. The signaling between PSTN and the testbed is controlled by a Media Gateway Controller (MGC), which implements the MEGACO protocol (IETF RFC 3051). PSTN phones (including cellular phones) could initiate a real phone call to the SIP phones 4

5 inside our testbed. The MGC controls the signaling between PSTN and IP networks. Circuit-voice and packet-voice are converted by the PSTN gateway. Users within our testbed could roam between GPRS, public and private WLANs while keeping the session uninterrupted. 2.6 QoS Control In WLANs, we deploy a TC (Traffic Conditioner), which is based on the implementation in Linux kernel, in the testbed to limit the maximum traffic going through a specific IP address and port number. Traffic from each Access Point (AP) into the backbone is controlled by a TC. The TCs are controlled by a TC Controller which instructs each TC how to condition user traffic. The TC Controller and TC essentially function like Policy Decision Point (PDP) and Policy Enforcement Point (PEP), respectively, as that defined in the Policy Framework (IETF RFC 2753) and COPS (Common Open Policy Service, IETF RFC 2748). In addition to the implementation of TC and TC Controller, the testbed also incorporates a GUI center in which one can control the maximum bandwidth from each MS. Once the QoS rule (maximum bandwidth) is enforced, traffic from each MS cannot exceed the defined value unless the operator resets it. To preserve the same QoS level after handoff, the HA issues a Conditioning Request to the TC Controller with the MS's new IP address when receiving a Binding Update from a MS. The TC Controller then sends a request to the associated TC in the new subnet to enforce the same QoS rule. Finally, the QoS rule in the TC in old subnet is revoked as that the MS is no longer within that subnet. 2.7 Location Privacy In Today s Internet, an IP address uniquely identifies a host. For two hosts to communicate with each other, the routing decisions are done based on destination IP address if no advanced routing criteria are defined. Because an IP address represents both identity and location of the host, sending and receiving IP packets usually expose where the user is and possibly also show the identity of the user. We call the issue of exposing IP address information as location privacy problem. To solve the problem, we propose to build a core network through which users can connect each other without knowing where the corresponding user is. An architectural is shown in Fig. 4, in which Host X (X stands for A, B, C and D) are users of the privacy network. Privacy Points are the accessing nodes for users which have subscribed to the privacy service. That is, all privacy service connections will be connected to the privacy points first and routed through the privacy network. Packets then are sent to the corresponding hosts through the nearest privacy point. For example, to build a connection between Host A and Host B, Host A finds out its nearest privacy point and sends out its connection request for Host B through its privacy point. The contacted privacy point determines where packets should be sent to and forwards packets to the determined location. In this scenario, packets are forwarded to another privacy point which is the nearest point to Host B. Packets then will be sent to Host B by this privacy point. The reply packets from Host B are forwarded in reverse direction. Because the testbed is a continuous work, it has not incorporated the privacy service. However an independent testbed has been constructed to demonstrate the feasibility of the proposed idea. 3 Testbed Implementation The testbed architecture is shown in Fig. 1. In the testbed, a GPRS system consisting of HLR, BSS, SGSN and GGSN is purchased from the Industrial Technology Research Institute (ITRI). The MSC is not implemented because the experiments focus on packet-switched network. Due to the regulation of spectrum allocation, instead of GPRS BTS (base transceiver station) an emulator using IEEE b radio is used to emulate the GPRS radio. In GPRS core network, the Reg-Filter function we implement is co-located with SGSN. We also implement the additional AAA server of Diameter and the GPRS-WLAN Mobility Gateway (GWMG) which are shown as gateway in Fig. 1. The gateway connects to GGSN through the G i interface. We have constructed two foreign networks in WLANs. One is a private network with a NAT as the border router. The other one is a public WLAN. The VONTEL VoIP system is also purchased from ITRI. The PSTN Gateway connects our testbed to the PSTN through the PBX (Private Branch exchange) of the university. Any user in public Internet or PSTN including public cellular users can make a real phone call to users in our testbed. Any user in the testbed can also make a phone call to any user in the world, including public Internet, PSTN, and cellular users. As mentioned earlier, currently the privacy network is implemented independent to the testbed. 5

6 Fig. 6. Throughput of video application Fig. 5. Handoff latency between GPRS and WLAN The implementation of SIP servers and privacy points is based on partysip [8]. The SIP user agent is modified from kphone 3.0 [9]. Also, we have implemented a Media Gateway (MG). 4 Experimental Analysis Based on the testbed architecture, various experiments were carried out to analyze the performance. The following sections show the quantified results for mobility management, authentication, NAT, and privacy network. To be more precise for analysis, simplified testbeds were constructed based on the integrated testbed for each specific issue. 4.1 Mobility Management To switch between GPRS and WLAN systems, we implement two policies: WLAN-preferred and usertrigger. In WLAN-preferred mode, the link quality is tracked. It changes to WLAN access if WLAN system is available. The link quality is tracked as well in user-trigger mode. On the other hand, the decision for switching systems is based on user command and the availability of radio interface. The coverage of GPRS and a WLAN is overlapped such that MS could be in the range of both GPRS and WLAN systems. In experiments initially the BTS of GPRS is turned on and the AP of the WLAN is off. MS thus attaches to GPRS and data is received and sent via GPRS radio interface. Once the AP of the WLAN is on, the MS changes to WLAN for high bandwidth service by WLAN-preferred mode Fig. 7. Latency for authenticating GPRS subscriber in WLAN because the WLAN radio is now available. MS then moves to the AP within private network. The MS follows the same path back to GPRS. This time the user-trigger mode is enforced to switch back to the GPRS radio. Fig. 5 indicates the handoff latency between GPRS and WLAN systems. In this experiment, CN continuously sends ping packets to MS with an interval of 1 ms. Fig. 5(a) shows that the average delay to detect FA advertisement is 54.7 ms when the MS moves from GPRS to WLAN. The average time for MS to receive ack from the HA after MS sends MIP registration message is 18.1 ms. Finally, it costs an average of 4.5 ms for MS to receive packets from CN again after the binding update in HA is done. The average handoff latency from GPRS to WLAN totally is 77.3 ms. Relatively, Fig. 5(b) presents the handoff latency from WLAN to GPRS. As mentioned above the handoff is triggered by user, and the average delay is 61.6 ms to send out the registration request. The average delay is ms for the MS to receive ack from the HA. After that, the average latency is 18.7 ms for MS to receive packets from CN again. By comparing them, we notice that the handoff latency from WLAN to GPRS is larger then the latency from GPRS to WLAN. This is because GPRS employs much more complex architecture and protocol stacks. As shown in Fig. 1, in GPRS network packets would need to go through several nodes with more protocol stacks to reach the HA. 6

7 Fig. 8. Latency for authenticating WLAN user in GPRS Due to space limitation, in addition to handoff latency this paper presents only the throughput of video application in Fig. 6. Experimental results discussed here are part of the multimedia conference initiated by SIP signaling. The video codec is based on H.263. Initially, MS obtains an averaged throughput of 56 Kbps in GPRS network. After roaming to WLAN, the traffic is conditioned by a TC with 200 Kbps, 400 Kbps and 600 Kbps, respectively. When MS first moves from GPRS to WLAN, the video quality is drastically improved because of high bandwidth of WLANs. The data rate dramatically drops in handoffs which are marked by vertical dotted-line. Even though there is no retransmission of UDP packets, the video coding techniques help recover loss of small amount of packets by other correctly received packets. 4.2 Authentication Fig. 7 illustrates the latency of a GPRS subscriber authenticated in a visiting WLAN. In the proposed WLAN-centric authentication, GPRS subscribers roaming into WLAN system are requested to perform the WLAN-based authentication, which is Diameter EAP application in our implementation. There are three stages as shown in Fig. 7. The total delay is 118 ms. Although details is not shown in this paper, the total delay for a WLAN user authenticating in WLAN system is 91 ms. Fig. 8 depicts the delay for a WLAN user attaching to GPRS system by the proposed twophase authentication. Because the first phase is WLAN-based, it is similar to Fig. 7 except for the additional K i update procedure. The K i update is measured from the time when GPRS AAA sends out an IMSI Used Notification/Ki Update message to HLR up to the time when the GPRS AAA receives the K i Update Ack message. As shown in Fig. 8, Identity Validation requires 1007 ms. Delays for Authentication, K i Update, and Success are 1012 ms, 605 ms, and 212 ms, respectively. Although the first Fig. 9. Mobile IP with NAT phase is also WLAN-based, it takes more time than that shown in Fig. 7. This is because messages are encapsulated in GPRS Mobility Management (GMM) protocol and are transferred to GPRS core network. First, the protocol stacks in GPRS are more complicated than that in WLAN system. Second, the bandwidth in GPRS is less than that in WLAN. Therefore it takes more time for a WLAN user to execute the first phase authentication. The second phase authentication is a standard GPRS attach. It takes 6172 ms.the total delay is 9008 ms. The delay of a normal GPRS authentication in the same testbed is also around 6172 ms. 4.3 Integration of Mobile IP and NAT Fig. 9 shows the testbed for the integration of Mobile IP and NAT. There are two home networks for two different mobile stations. The mobile stations will move into a same foreign network. Both home network and foreign network are private network with a NAT as the border router. Note that the home agents and foreign agent have the same private IP address and so do the two mobile nodes. This represents an extreme case which is used to show that our solution works even in a exaggerated configuration. Mobile nodes move from their home networks to the foreign network and then move back to their home networks. The experiments are compared with those in a Mobile IP system without NAT. Ping is used continuously when mobiles are moving. The handoff can be split into four stages: Advertisement time: The last ping-reply that MS gets until the MS gets a FA s advertisement. The FA advertisement is sent once per second. 7

8 Mobile IP without NAT Mobile IP with NAT Advertisement time ms ms Mobile node ms 1.594ms processing time Registration 10.58ms 10.75ms time Binding time ms ms Table 1. Handoff latency of Mobile IP with and without NAT Fig. 11. Testbed architecture for privacy network Mobile node processing time: The time between MS gets an advertisement to the time sends a registration request to HA. Registration time: The time between MS sends registration request to the time MS gets a registration reply. Binding time: The time between MS gets registration reply to the time MS get a ping reply. Table 1 summarizes the handoff latency. It indicates that our proposed solution would not incur too much overhead. Fig. 10 shows TCP sequence delay. TCP sequence delay is measured as the time between a TCP sequence is sent to the time an acknowledgment of this sequence is received. Sequence delay is around 20 ms in both scenarios and is increased to around one second for handoff. Due to the processing time of NAT, the sequence delay in Mobile IP with NAT is slightly longer than that Mobile IP system without NAT. However, they are very close. 4.4 Location Privacy Fig. 10. TCP sequence delay The network architecture for the experiments of the privacy network is shown in Fig. 11. Router 1, 2, and 3 assign global IPv6 addresses with router advertisements conforming to [10] using radvd [11]. They handle IPv6 prefixes 4004::/64, 4005::/64 and 4006::/64, respectively. Mobile IPv6 will choose one of these IP addresses to form its care of address (CoA). The privacy network includes one registrar and two privacy points. The privacy points connect to the public network with an identical IP address: 4000::1/16, which is used as an anycast IPv6 address. VoIP is used as the application in experiments. The CN initiates a session by sending out SIP INVITE. After the session is established under router 1 and router 2, the RTP (Real-Time Transport Protocol, IETF RFC 1889) packets are sent between these two nodes through the privacy network. The MS then moves to router 3. Based on the RTP sequence numbers, we collect the RTP packets received in the CN and MS. Results are depicted in Fig. 12 and Fig. 13. The discontinued oblique lines of Fig. 12 and Fig. 13 can be connected with a straight line. The lost packets caused by radio quality and mobile IP binding updates are denoted as vertical lines in these two figures. Although mechanisms are implemented to hide IP address, Fig. 12 and Fig. 13 indicate that the privacy network does not cause too much overhead. 8

9 Acknowledgment This work was sponsored in part by MOE Program for Promoting Academic Excellent of Universities under the grant number 89-E-FA04-1-4, National Science Council under the grant numbers E , E and E , and Industrial Technology Research Institute under the contracts of T , T and 2F Fig. 12. Received and lost RTP packets on CN Fig. 13. Received and lost RTP packets on MS 5 Summary Many radio access techniques and wireless systems exist today. They usually are not compatible with each other which make universal roaming not possible. As driven by mass business and market, there is an immediate need to unify wireless systems so that operators can utilize the network more efficient and mobile users can obtain services easily anytime and anywhere. IP, as it is in today's Internet, is a promising technology for future generation wireless networks. This paper presents a testbed of IP-based heterogeneous wireless network. It demonstrates integration of GPRS and WLAN networks. Mobility management, authentication, NAT, VoIP, QoS, signaling and location privacy are implemented and inspected. Experimental analyses are carried out to examine certain critical performance issues. The testbed is a continuous work. We plan to expand the testbed to a more sophisticated architecture with various crucial protocols and network components so that novel ideas related to IP-based heterogeneous wireless networks can be prototyped and experimented in the testbed. References: [1] H.-W. Lin, J.-C. Chen, M.-C. Jiang, and C.-Y. Huang, Integration of GPRS and wireless LANs with multimedia applications, Lecture Notes in Computer Science: Advances in Multimedia Information Processing - PCM 2002, Springer, pp , Dec [2] IEEE Std X-2001, IEEE Standard for Local and metropolitan area networks- Port- Based Network Access Control, Oct [3] M. C. Jiang, J. C. Chen, and Y. W. Liu, "WLAN-Centric Authentication in Integrated GPRS-WLAN Networks," in Proc. of IEEE Semiannual Vehicular Technology Conference, (VTC '03), Orlando FL, Oct [4] H. Levkowetz, Mobile IP Traversal of Network Address Translation (NAT) Devices. IETF RFC 3519, Apr [5] H. Levkowetz, Mobile IP NAT/NAPT Traversal using UDP Tunnelling. IETF Internet-Draft, Nov [6] C. Y. Huang, J. C. Liu, J. C. Chen, M. C. Jiang, and H. W. Lin, "Integration of NAT with Mobile IP," Proc. of Taiwan Area Network Conference (TANET '02), Hsinchu, Taiwan, pp , October [7] UCL network and multimedia research group. are. [8] A. Moizard, Partysip Mar [9] M. Mustikkamaki, kphone Jan [10] T. Narten, E. Nordmark, W. S. Neighbor Discovery for IP Version 6 (IPv6). IETF RFC 2461, Dec [11] L. Fenneberg, et al., radvd Oct