《信息网络协议基础》课程教学资源（学习资料）MOBILITY MANAGEMENT FOR ALL-IP MOBILE NETWORKS：MOBILE IPV6 VS. PROXY MOBILE IPV6

ARCHITECTURES AND PROTOCOLS FOR MOBILITY MANAGEMENT IN ALL-IP MOBILE NETWORKS MOBILITY MANAGEMENT FOR ALL-IP MOBILE NETWORKS: MOBILE IPV6 VS.PROXY MOBILE IPV6 KI-SIK KONG AND WONJUN LEE,KOREA UNIVERSITY YOUN-HEE HAN,KOREA UNIVERSITY OF TECHNOLOGY AND EDUCATION MYUNG-KI SHIN,ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE(ETRI) HEUNGRYEOL YOU,KOREA TELECOMMUNICATION(KT) MAG ABSTRACT Force (IETF),Third Generation Partnership Project (3GPP),and International Telecommu Recently,a network-based mobility manage- nication Union-Telecommunication Standard- ment protocol called Proxy Mobile IPv6 ization Sector (ITU-T)appear to increase the (PMIPv6)is being actively standardized by the possibility of realizing mobile and ubiquitous IETF NETLMM working group,and is starting computing environments.However,many chal- MAG to attract considerable attention among the lenges still remain to be solved for achieving telecommunication and Internet communities. such a goal. Unlike the various existing protocols for IP The recent fundamental networking trend has mobility management such as Mobile IPv6 been focused mostly on realizing all-IP mobile (MIPv6),which are host-based approaches,a networks.All-IP mobile networks,which are IN-HoA) network-based approach such as PMIPv6 has expected to combine the Internet and telecom- s long as salient features and is expected to expedite the munication networks tightly together,are net- e domain Proxy care-of addre real deployment of IP mobility management.In works in which IP is employed from a mobile The address c this article,starting by showing the validity of a subscriber to the access points (APs)that con- This will be the tur network-based approach,we present qualitative nect the wireless networks to the Internet.One and quantitative analyses of the representative of the most important and challenging issues for The authors present host-based and network-based mobility manage- next-generation all-IP mobile networks is mobili- ment approaches (i.e.,MIPv6 and PMIPv6), ty management.Mobility management enables the qualitative and which highlight the main desirable features and the serving networks to locate a mobile sub- key strengths of PMIPv6.Furthermore,a com- scriber's point of attachment for delivering data quantitative analyses prehensive comparison among the various exist- packets (i.e.,location management)and main- of the representative ing well-known mobility support protocols is tain a mobile subscriber's connection as it con- investigated.Although the development of tinues to change its point of attachment (i.e.. host-based and the PMIPv6 is at an early stage yet,it is strongly handover management). expected that PMIPv6 will be a promising candi- Mobile IPv6(MIPv6)[1]is one of the most representative net- date solution for realizing the next-generation representative efforts on the way toward next- work-based mobility all-IP mobile networks. generation all-IP mobile networks.However, although MIPv6 is a well-known mature stan- management INTRODUCTION dard for IPv6 mobility support and solves many problems seen in Mobile IPv4(MIPv4)[2],it has approaches. With the rapid growth in the number of mobile still revealed some problems such as handover subscribers and mobile devices such as cellular latency,packet loss,and signaling overhead.Fur- phones,personal digital assistants(PDAs),and thermore,despite the reputation of this proto- laptop computers,the demand for "anywhere, col,it has been slowly deployed in real anytime,and any way"high-speed Internet implementations over the past years,and does access is becoming a primary concern in our not appear to receive widespread acceptance in lives.Recent advances in various wireless access the market [3,4].Recently,a network-based technologies such as IEEE 802.16d/e and wide- mobility management protocol called Proxy band code-division multiple access(WCDMA) Mobile IPv6(PMIPv6)[5]is being actively stan- and the incessant efforts of several standards dardized by the IETF NETLMM working group, bodies such as the Internet Engineering Task and is starting to attract considerable attention 36 1536-1284/08/$25.00©2008IEEE EEE Wireless Communications.April 2008

36 1536-1284/08/$25.00 © 2008 IEEE IEEE Wireless Communications • April 2008 MAG MAG Proxy care-of addre The address o This will be the tunne (MN-HoA) as long as me domain ARCHITECTURES AND PROTOCOLS FOR MOBILITY MANAGEMENT IN ALL-IP MOBILE NETWORKS INTRODUCTION With the rapid growth in the number of mobile subscribers and mobile devices such as cellular phones, personal digital assistants (PDAs), and laptop computers, the demand for “anywhere, anytime, and any way” high-speed Internet access is becoming a primary concern in our lives. Recent advances in various wireless access technologies such as IEEE 802.16d/e and wide￾band code-division multiple access (WCDMA) and the incessant efforts of several standards bodies such as the Internet Engineering Task Force (IETF), Third Generation Partnership Project (3GPP), and International Telecommu￾nication Union — Telecommunication Standard￾ization Sector (ITU-T) appear to increase the possibility of realizing mobile and ubiquitous computing environments. However, many chal￾lenges still remain to be solved for achieving such a goal. The recent fundamental networking trend has been focused mostly on realizing all-IP mobile networks. All-IP mobile networks, which are expected to combine the Internet and telecom￾munication networks tightly together, are net￾works in which IP is employed from a mobile subscriber to the access points (APs) that con￾nect the wireless networks to the Internet. One of the most important and challenging issues for next-generation all-IP mobile networks is mobili￾ty management. Mobility management enables the serving networks to locate a mobile sub￾scriber’s point of attachment for delivering data packets (i.e., location management) and main￾tain a mobile subscriber’s connection as it con￾tinues to change its point of attachment (i.e., handover management). Mobile IPv6 (MIPv6) [1] is one of the most representative efforts on the way toward next￾generation all-IP mobile networks. However, although MIPv6 is a well-known mature stan￾dard for IPv6 mobility support and solves many problems seen in Mobile IPv4 (MIPv4) [2], it has still revealed some problems such as handover latency, packet loss, and signaling overhead. Fur￾thermore, despite the reputation of this proto￾col, it has been slowly deployed in real implementations over the past years, and does not appear to receive widespread acceptance in the market [3, 4]. Recently, a network-based mobility management protocol called Proxy Mobile IPv6 (PMIPv6) [5] is being actively stan￾dardized by the IETF NETLMM working group, and is starting to attract considerable attention KI-SIK KONG AND WONJUN LEE, KOREA UNIVERSITY YOUN-HEE HAN, KOREA UNIVERSITY OF TECHNOLOGY AND EDUCATION MYUNG-KI SHIN, ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE (ETRI) HEUNGRYEOL YOU, KOREA TELECOMMUNICATION (KT) ABSTRACT Recently, a network-based mobility manage￾ment protocol called Proxy Mobile IPv6 (PMIPv6) is being actively standardized by the IETF NETLMM working group, and is starting to attract considerable attention among the telecommunication and Internet communities. Unlike the various existing protocols for IP mobility management such as Mobile IPv6 (MIPv6), which are host-based approaches, a network-based approach such as PMIPv6 has salient features and is expected to expedite the real deployment of IP mobility management. In this article, starting by showing the validity of a network-based approach, we present qualitative and quantitative analyses of the representative host-based and network-based mobility manage￾ment approaches (i.e., MIPv6 and PMIPv6), which highlight the main desirable features and key strengths of PMIPv6. Furthermore, a com￾prehensive comparison among the various exist￾ing well-known mobility support protocols is investigated. Although the development of PMIPv6 is at an early stage yet, it is strongly expected that PMIPv6 will be a promising candi￾date solution for realizing the next-generation all-IP mobile networks. MOBILITY MANAGEMENT FOR ALL-IP MOBILE NETWORKS: MOBILE IPV6 VS. PROXY MOBILE IPV6 The authors present the qualitative and quantitative analyses of the representative host-based and the representative net￾work-based mobility management approaches. KONG LAYOUT 4/9/08 11:02 AM Page 36

among the telecommunication and Internet com- mance improvement in MIPv6.However,MIPv6 Compared to munities.Unlike the various existing protocols and its various enhancements basically require for IP mobility management such as MIPv6, protocol stack modification of the MN in order host-based mobility which are host-based approaches,a network- to support them.In addition,the requirement based approach such as PMIPv6 has salient fea- for modification of MNs may cause increased management tures and is expected to expedite the real complexity on them.On the other hand,in a approaches such as deployment of IP mobility management.To the network-based mobility management approach best of our knowledge,this article is the first to such as PMIPv6,the serving network handles the MIPv6 and its present qualitative and quantitative analyses on mobility management on behalf of the MN:thus. MIPv6 and PMIPv6.In addition,this article pro- the MN is not required to participate in any enhancements,a vides a comprehensive comparison and summary mobility-related signaling.Compared to host- network-based that addresses the main strong and weak points based mobility management approaches such as of PMIPv6 against various existing well-known MIPv6 and its enhancements,a network-based mobility management mobility support protocols. mobility management approach such as PMIPv6 The remainder of this article is organized as has the following salient features and advan- approach such as follows.First,we briefly present overviews and tages discuss problems of host-based mobility manage- Deployment perspective:Unlike host-based PMIPv6 has several ment approaches and then identify several key mobility management,network-based mobility advantages. strengths of the network-based mobility manage- management does not require any modification ment approach.Then we present an overview of of MNs.The requirement for modification of the network-based mobility management MNs can be considered one of the primary rea- approach(i.e.,PMIPv6)to providing IP mobility sons MIPv6 has not been widely deployed in support.Qualitative and quantitative compar- practice,although several commendable MIPv6 isons of PMIPv6 against various existing mobility enhancements have been reported over the past support protocols are thoroughly investigated. years [3,4.Therefore,no requirement for modi- highlighting the main desirable features and key fication of MNs is expected to accelerate the strengths of PMIPv6.Finally,concluding remarks practical deployment of PMIPv6.Such an expec- are given. tation can easily be demonstrated by the fact that in the WLAN switching market,no modifi- WHY NETWORK-BASED cation of the software on MNs has been required to support IP mobility,so these unmodified MNs MOBILITY MANAGEMENT? have enabled network service providers to offer services to as many customers as possible [8. Mobile IP is probably the most widely known IP Performance perspective:Generally,wireless mobility support protocol.Two versions of resources are very scarce.In terms of scalability Mobile IP have been standardized for support- efficient use of wireless resources can result in ing host-based mobility on the Internet:MIPv4 enhancement of network scalability.In host- and MIPv6.They support the mobility of IP based network layer approaches such as MIPv6, hosts by allowing them to utilize two IP address- the MN is required to participate in mobility- es:a home address(HoA)that represents the related signaling.Thus,a lot of tunneled mes- fixed address of a mobile node (MN)and a care- sages as well as mobility-related signaling of-address (CoA)that changes with the IP sub- messages are exchanged via the wireless links. net to which an MN is currently attached.In Considering the explosively increasing number terms of the fundamental architectural aspects, of mobile subscribers,such a problem would these two mobility support standards follow the cause serious performance degradation.On the same concept.However,there are slight differ- contrary,in a network-based network layer ences with regard to some important details approach such as PMIPv6,the serving network MIPv6 comprises three components:the MN, controls the mobility management on behalf of the home agent (HA),and the correspondent the MN,so the tunneling overhead as well as a node (CN).The role of the foreign agent (FA) significant number of mobility-related signaling in MIPv4 was replaced by the access router message exchanges via wireless links can be (AR)in MIPv6.In addition,although route opti- reduced.Generally,the signaling latency intro- mization extensions were proposed for both duced by an MN can be significantly affected by MIPv4 and MIPv6,they were only standardized the performance parameters such as wireless for MIPv6.A detailed description of MIPv6 channel access delay and wireless transmission route optimization as well as details of MIPv4 delay.The latencies incurred by such perfor- and MIPv6 can be found in [1,2]. mance parameters can be considerable com- Although MIPv6 is a mature standard for IP pared to those of the wired link;thus,the mobility support and solves many problems,such signaling latency introduced by the MN could as triangle routing,security,and limited IP result in increasing handover failures as wireless address space,addressed in MIPv4,it still has channel access and wireless transmission delays some problems such as handover latency,packet get larger (more details on handover latency can loss,and signaling overhead.Besides,the hand- be found later in this article). over latencies associated with MIPv4/v6 do not Network service provider perspective:From provide the quality of service (QoS)guarantees the perspective of a network service provider,it required for real-time applications.Therefore, is expected that network-based mobility manage various MIPv6 enhancements such as hierarchi- ment would enhance manageability and flexibili- cal Mobile IPv6 (HMIPv6)[6]and fast handover ty by enabling network service providers to for Mobile IPv6(FMIPv6)[7]have been report- control network traffic and provide differentiat- ed over the past years,mainly focused on perfor- ed services and so on.Such a possibility can easi- EEE Wireless Communications.April 2008

IEEE Wireless Communications • April 2008 37 among the telecommunication and Internet com￾munities. Unlike the various existing protocols for IP mobility management such as MIPv6, which are host-based approaches, a network￾based approach such as PMIPv6 has salient fea￾tures and is expected to expedite the real deployment of IP mobility management. To the best of our knowledge, this article is the first to present qualitative and quantitative analyses on MIPv6 and PMIPv6. In addition, this article pro￾vides a comprehensive comparison and summary that addresses the main strong and weak points of PMIPv6 against various existing well-known mobility support protocols. The remainder of this article is organized as follows. First, we briefly present overviews and discuss problems of host-based mobility manage￾ment approaches and then identify several key strengths of the network-based mobility manage￾ment approach. Then we present an overview of the network-based mobility management approach (i.e., PMIPv6) to providing IP mobility support. Qualitative and quantitative compar￾isons of PMIPv6 against various existing mobility support protocols are thoroughly investigated, highlighting the main desirable features and key strengths of PMIPv6. Finally, concluding remarks are given. WHY NETWORK-BASED MOBILITY MANAGEMENT? Mobile IP is probably the most widely known IP mobility support protocol. Two versions of Mobile IP have been standardized for support￾ing host-based mobility on the Internet: MIPv4 and MIPv6. They support the mobility of IP hosts by allowing them to utilize two IP address￾es: a home address (HoA) that represents the fixed address of a mobile node (MN) and a care￾of-address (CoA) that changes with the IP sub￾net to which an MN is currently attached. In terms of the fundamental architectural aspects, these two mobility support standards follow the same concept. However, there are slight differ￾ences with regard to some important details. MIPv6 comprises three components: the MN, the home agent (HA), and the correspondent node (CN). The role of the foreign agent (FA) in MIPv4 was replaced by the access router (AR) in MIPv6. In addition, although route opti￾mization extensions were proposed for both MIPv4 and MIPv6, they were only standardized for MIPv6. A detailed description of MIPv6 route optimization as well as details of MIPv4 and MIPv6 can be found in [1, 2]. Although MIPv6 is a mature standard for IP mobility support and solves many problems, such as triangle routing, security, and limited IP address space, addressed in MIPv4, it still has some problems such as handover latency, packet loss, and signaling overhead. Besides, the hand￾over latencies associated with MIPv4/v6 do not provide the quality of service (QoS) guarantees required for real-time applications. Therefore, various MIPv6 enhancements such as hierarchi￾cal Mobile IPv6 (HMIPv6) [6] and fast handover for Mobile IPv6 (FMIPv6) [7] have been report￾ed over the past years, mainly focused on perfor￾mance improvement in MIPv6. However, MIPv6 and its various enhancements basically require protocol stack modification of the MN in order to support them. In addition, the requirement for modification of MNs may cause increased complexity on them. On the other hand, in a network-based mobility management approach such as PMIPv6, the serving network handles the mobility management on behalf of the MN; thus, the MN is not required to participate in any mobility-related signaling. Compared to host￾based mobility management approaches such as MIPv6 and its enhancements, a network-based mobility management approach such as PMIPv6 has the following salient features and advan￾tages. Deployment perspective: Unlike host-based mobility management, network-based mobility management does not require any modification of MNs. The requirement for modification of MNs can be considered one of the primary rea￾sons MIPv6 has not been widely deployed in practice, although several commendable MIPv6 enhancements have been reported over the past years [3, 4]. Therefore, no requirement for modi￾fication of MNs is expected to accelerate the practical deployment of PMIPv6. Such an expec￾tation can easily be demonstrated by the fact that in the WLAN switching market, no modifi￾cation of the software on MNs has been required to support IP mobility, so these unmodified MNs have enabled network service providers to offer services to as many customers as possible [8]. Performance perspective: Generally, wireless resources are very scarce. In terms of scalability, efficient use of wireless resources can result in enhancement of network scalability. In host￾based network layer approaches such as MIPv6, the MN is required to participate in mobility￾related signaling. Thus, a lot of tunneled mes￾sages as well as mobility-related signaling messages are exchanged via the wireless links. Considering the explosively increasing number of mobile subscribers, such a problem would cause serious performance degradation. On the contrary, in a network-based network layer approach such as PMIPv6, the serving network controls the mobility management on behalf of the MN, so the tunneling overhead as well as a significant number of mobility-related signaling message exchanges via wireless links can be reduced. Generally, the signaling latency intro￾duced by an MN can be significantly affected by the performance parameters such as wireless channel access delay and wireless transmission delay. The latencies incurred by such perfor￾mance parameters can be considerable com￾pared to those of the wired link; thus, the signaling latency introduced by the MN could result in increasing handover failures as wireless channel access and wireless transmission delays get larger (more details on handover latency can be found later in this article). Network service provider perspective: From the perspective of a network service provider, it is expected that network-based mobility manage￾ment would enhance manageability and flexibili￾ty by enabling network service providers to control network traffic and provide differentiat￾ed services and so on. Such a possibility can easi￾Compared to host-based mobility management approaches such as MIPv6 and its enhancements, a network-based mobility management approach such as PMIPv6 has several advantages. KONG LAYOUT 4/9/08 11:02 AM Page 37

The fundamental IP tunnel LMA:Local mobility anchor foundation of PMIPy6 IP-in-IP tunnel between LMA and MAG MAG:Mobile access gateway is based on MIPv6 in the sense that it LMA Home network MN's home network extends MIPv6 (topological anchor point) MAG signaling and re-uses many concepts such &、LMA address(LMAA) That will be the tunnel entry point as the HA functionality. NETLMM domain- However,PMIPv6 is Proxy binding acknowledgment(PBA) MAG Movement management domain)The control message sent by LMA to MAG designed to provide network-based Proxy binding update(PBU) The control messag e sent by MAG to LMA mobility management MN's home address (MN-HoA) to establish a binding to use it as long as between MN-HoA and Proxy-CoA support to an MN in it roams within the same domain Proxy care-of address (Proxy-CoA) atopologicaly The address of MAG. This will be the tunnel end point localized domain. Figure 1.Overview of PMIPv6. ly be expected from legacy cellular systems such ment,and should support any type of wireless as IS-41 and Global System for Mobile Commu- link technology nications (GSM),which can be considered net- Handover performance improvement:A net- work-based (i.e.,network-controlled)systems. work-based approach should minimize the Note that PMIPv6 has some resemblance to time required for handover. General Packet Radio Service (GPRS)in that they are both network-based mobility manage- OVERVIEW OF PMIPV6 ment protocols and have similar functionalities. The fundamental foundation of PMIPv6 is based However,PMIPv6 is an Internet protocol that is on MIPv6 in the sense that it extends MIPv6 sig- not dependent on any access-technology-specific naling and reuses many concepts such as the HA protocol,so it could be used in any IP-based net- functionality.However,PMIPv6 is designed to work,while GPRS is an access-technology-spe- provide network-based mobility management cific protocol closely coupled with the signaling support to an MN in a topologically localized protocols used in legacy cellular systems. domain.Therefore,an MN is exempt from par- ticipation in any mobility-related signaling,and NETWORK-BASED MOBILITY the proxy mobility agent in the serving network performs mobility-related signaling on behalf of MANAGEMENT:PMIPV6 the MN.Once an MN enters its PMIPv6 domain and performs access authentication,the serving In a network-based approach such as PMIPv6, network ensures that the MN is always on its the serving network controls mobility manage- home network and can obtain its HoA on any ment on behalf of the MN:thus,the MN is not access network.That is,the serving network required to participate in any mobility-related assigns a unique home network prefix to each signaling.The design goals the IETF NETLMM MN,and conceptually this prefix always follows working group aims to cover are very extensive. the MN wherever it moves within a PMIPv6 The primary features of such goals are as follows domain.From the perspective of the MN,the (more details are provided in [4,8): entire PMIPv6 domain appears as its home net- .Support for unmodified MNs:Unlike a host- work.Accordingly,it is needless (or impossible) based approach,a network-based approach to configure the CoA at the MN. should not require any software update for IP The new principal functional entities of mobility support on MNs. PMIPv6 are the mobile access gateway (MAG) I Typically,there are vari- Support for IPv4 and IPv6:Although the ini- and local mobility anchor (LMA).The MAG ous link-layer-specific tial design of a network-based approach uses typically runs on the AR.The main role of the events on which the MAG an IPv6 host,it is intended to work with IPv4 MAG is to detect the MN's movements!and ini- can depend for detecting or dual-stack hosts as well. tiate mobility-related signaling with the MN's the MN's attachment and Efficient use of wireless resources:A network- LMA on behalf of the MN.In addition,the detachment within a based approach should avoid tunneling over- MAG establishes a tunnel with the LMA for PMIPv6 domain.For head over a wireless link;hence,it should enabling the MN to use an address from its example,the help of layer minimize overhead within the radio access home network prefix and emulates the MN's 2 triggers such as network. home network on the access network for each MN ATTACH and Link technology agnostic:A network-based MN.On the other hand,the LMA is similar to MN DETACH may be approach should not use any wireless-link-spe- the HA in MIPv6.However,it has additional needed [91. cific information for basic routing manage- capabilities required to support PMIPv6.The 38 EEE Wireless Communications.April 2008

38 IEEE Wireless Communications • April 2008 ly be expected from legacy cellular systems such as IS-41 and Global System for Mobile Commu￾nications (GSM), which can be considered net￾work-based (i.e., network-controlled) systems. Note that PMIPv6 has some resemblance to General Packet Radio Service (GPRS) in that they are both network-based mobility manage￾ment protocols and have similar functionalities. However, PMIPv6 is an Internet protocol that is not dependent on any access-technology-specific protocol, so it could be used in any IP-based net￾work, while GPRS is an access-technology-spe￾cific protocol closely coupled with the signaling protocols used in legacy cellular systems. NETWORK-BASED MOBILITY MANAGEMENT: PMIPV6 In a network-based approach such as PMIPv6, the serving network controls mobility manage￾ment on behalf of the MN; thus, the MN is not required to participate in any mobility-related signaling. The design goals the IETF NETLMM working group aims to cover are very extensive. The primary features of such goals are as follows (more details are provided in [4, 8]): • Support for unmodified MNs: Unlike a host￾based approach, a network-based approach should not require any software update for IP mobility support on MNs. • Support for IPv4 and IPv6: Although the ini￾tial design of a network-based approach uses an IPv6 host, it is intended to work with IPv4 or dual-stack hosts as well. • Efficient use of wireless resources: A network￾based approach should avoid tunneling over￾head over a wireless link; hence, it should minimize overhead within the radio access network. • Link technology agnostic: A network-based approach should not use any wireless-link-spe￾cific information for basic routing manage￾ment, and should support any type of wireless link technology. • Handover performance improvement: A net￾work-based approach should minimize the time required for handover. OVERVIEW OF PMIPV6 The fundamental foundation of PMIPv6 is based on MIPv6 in the sense that it extends MIPv6 sig￾naling and reuses many concepts such as the HA functionality. However, PMIPv6 is designed to provide network-based mobility management support to an MN in a topologically localized domain. Therefore, an MN is exempt from par￾ticipation in any mobility-related signaling, and the proxy mobility agent in the serving network performs mobility-related signaling on behalf of the MN. Once an MN enters its PMIPv6 domain and performs access authentication, the serving network ensures that the MN is always on its home network and can obtain its HoA on any access network. That is, the serving network assigns a unique home network prefix to each MN, and conceptually this prefix always follows the MN wherever it moves within a PMIPv6 domain. From the perspective of the MN, the entire PMIPv6 domain appears as its home net￾work. Accordingly, it is needless (or impossible) to configure the CoA at the MN. The new principal functional entities of PMIPv6 are the mobile access gateway (MAG) and local mobility anchor (LMA). The MAG typically runs on the AR. The main role of the MAG is to detect the MN’s movements1 and ini￾tiate mobility-related signaling with the MN’s LMA on behalf of the MN. In addition, the MAG establishes a tunnel with the LMA for enabling the MN to use an address from its home network prefix and emulates the MN’s home network on the access network for each MN. On the other hand, the LMA is similar to the HA in MIPv6. However, it has additional capabilities required to support PMIPv6. The ■ Figure 1. Overview of PMIPv6. Movement MAG IP tunnel IP-in-IP tunnel between LMA and MAG MAG LMA LMA: Local mobility anchor MAG: Mobile access gateway NETLMM domain (network-based localized mobility management domain) Home network MN’s home network (topological anchor point) LMA address (LMAA) That will be the tunnel entry point Proxy binding acknowledgment (PBA) The control message sent by LMA to MAG Proxy binding update (PBU) The control message sent by MAG to LMA to establish a binding between MN-HoA and Proxy-CoA Proxy care-of address (Proxy-CoA) The address of MAG. This will be the tunnel end point MN’s home address (MN-HoA) MN continues to use it as long as it roams within the same domain 1 Typically, there are vari￾ous link-layer-specific events on which the MAG can depend for detecting the MN’s attachment and detachment within a PMIPv6 domain. For example, the help of layer 2 triggers such as MN_ATTACH and MN_DETACH may be needed [9]. The fundamental foundation of PMIPv6 is based on MIPv6 in the sense that it extends MIPv6 signaling and re-uses many concepts such as the HA functionality. However, PMIPv6 is designed to provide network-based mobility management support to an MN in a topologically localized domain. KONG LAYOUT 4/9/08 11:28 AM Page 38

PBU:Proxy binding update Unlike MIPv6, PBA:Proxy binding acknowledgment a tunnel in PMIPv6 is MN MAG AAA server LMA CN established between (1)MN attachment the LMA and the (2)AAA query with MN-ID MAG,and not an (3)AAA reply with profile MN.This could be (4)PBU with MN-ID desirable because the (5)AAA query with MN-ID tunneling increases the bandwidth (6)AAA reply constraints on the (7)PBA with MN-ID,homhe network prefix option wireless link and Bidirectional tunnel setup Router advertisement the processing burden Data packets. Tunneled data packets on the MN. Data packets Figure 2.Message flow in PMIPv6. main role of the LMA is to maintain reachability message.If the sender is a trusted MAG.the to the MN's address while it moves around with- LMA accepts the PBU message. in a PMIPv6 domain,and the LMA includes a Step 7:Then the LMA sends a proxy binding binding cache entry for each currently registered acknowledgment(PBA)message including the MN.The binding cache entry maintained at the MN's home network prefix option,and sets up LMA is more extended than that of the HA in a route for the MN's home network prefix MIPv6 with some additional fields such as the over the tunnel to the MAG. MN-Identifier,the MN's home network prefix,a Unlike MIPv6.a tunnel in PMIPv6 is estab flag indicating a proxy registration,and the lished between the LMA and the MAG,and interface identifier of the bidirectional tunnel not an MN.This could be desirable because the between the LMA and MAG.Such information tunneling increases the bandwidth constraints associates an MN with its serving MAG.and on the wireless link and the processing burden enables the relationship between the MAG and on the MN.Once the MAG receives the PBA LMA to be maintained. message from the LMA,it has obtained all the Figure 1 illustrates an overview of how required information to emulate the MN's PMIPv6 works within a localized domain.The home network on the access network,and it brief descriptions of the basic terminology are then starts to send a router advertisement (RA) also shown in this figure. message to the MN.It is noted that the RA MESSAGE FLOW OF PMIPV6 message contains the MN's home network pre- fix.After receiving the RA message,the MN Figure 2 shows the message flow of the overall configures its home address by combining the operations in PMIPv6.Each step shown in Fig.2 home network prefix included in the RA mes- is described as follows: sage and its interface address,which is based Steps 1 and 2:When an MN first attaches to an on the supported address configuration mode access network connected to the MAG.the (e.g.,stateless or stateful address configuration access authentication procedure is performed mode)from the policy store.It must be noted using an MN's identity (i.e.,MN-Identifier) that since PMIPv6 only supports the per-MN- via the deployed access security protocols on prefix model and not the shared-prefix model,a the access network. unique home network prefix is assigned to each Step 3:After successful access authentication. MN.Therefore,unlike MIPv6 and its various the MAG obtains the MN's profile.which enhancements,the MN always obtains its contains the MN-Identifier,LMA address, unique home address while it moves within a supported address configuration mode,and so PMIPv6 domain. on from the policy store (e.g.,authentication, After the bidirectional tunnel is successfully authorization,and accounting [AAA]server). set up,all traffic sent from the MN gets routed Step 4:Then the MAG sends a proxy binding to its LMA through the tunnel.The LMA update (PBU)message including the MN- receives any data packets sent by the CN to the Identifier to the MN's LMA on behalf of the MN.The LMA forwards the received packet to MN. the MAG through the tunnel.After receiving Steps 5 and 6:Once the LMA receives the PBU the packets,the MAG on the other end of the message,it checks the policy store to ensure tunnel removes the outer header and forwards that the sender is authorized to send the PBU the packets to the MN. IEEE Wireless Communications.April 2008 39

IEEE Wireless Communications • April 2008 39 main role of the LMA is to maintain reachability to the MN’s address while it moves around with￾in a PMIPv6 domain, and the LMA includes a binding cache entry for each currently registered MN. The binding cache entry maintained at the LMA is more extended than that of the HA in MIPv6 with some additional fields such as the MN-Identifier, the MN’s home network prefix, a flag indicating a proxy registration, and the interface identifier of the bidirectional tunnel between the LMA and MAG. Such information associates an MN with its serving MAG, and enables the relationship between the MAG and LMA to be maintained. Figure 1 illustrates an overview of how PMIPv6 works within a localized domain. The brief descriptions of the basic terminology are also shown in this figure. MESSAGE FLOW OF PMIPV6 Figure 2 shows the message flow of the overall operations in PMIPv6. Each step shown in Fig. 2 is described as follows: Steps 1 and 2: When an MN first attaches to an access network connected to the MAG, the access authentication procedure is performed using an MN’s identity (i.e., MN-Identifier) via the deployed access security protocols on the access network. Step 3: After successful access authentication, the MAG obtains the MN’s profile, which contains the MN-Identifier, LMA address, supported address configuration mode, and so on from the policy store (e.g., authentication, authorization, and accounting [AAA] server). Step 4: Then the MAG sends a proxy binding update (PBU) message including the MN￾Identifier to the MN’s LMA on behalf of the MN. Steps 5 and 6: Once the LMA receives the PBU message, it checks the policy store to ensure that the sender is authorized to send the PBU message. If the sender is a trusted MAG, the LMA accepts the PBU message. Step 7: Then the LMA sends a proxy binding acknowledgment (PBA) message including the MN’s home network prefix option, and sets up a route for the MN’s home network prefix over the tunnel to the MAG. Unlike MIPv6, a tunnel in PMIPv6 is estab￾lished between the LMA and the MAG, and not an MN. This could be desirable because the tunneling increases the bandwidth constraints on the wireless link and the processing burden on the MN. Once the MAG receives the PBA message from the LMA, it has obtained all the required information to emulate the MN’s home network on the access network, and it then starts to send a router advertisement (RA) message to the MN. It is noted that the RA message contains the MN’s home network pre￾fix. After receiving the RA message, the MN configures its home address by combining the home network prefix included in the RA mes￾sage and its interface address, which is based on the supported address configuration mode (e.g., stateless or stateful address configuration mode) from the policy store. It must be noted that since PMIPv6 only supports the per-MN￾prefix model and not the shared-prefix model, a unique home network prefix is assigned to each MN. Therefore, unlike MIPv6 and its various enhancements, the MN always obtains its unique home address while it moves within a PMIPv6 domain. After the bidirectional tunnel is successfully set up, all traffic sent from the MN gets routed to its LMA through the tunnel. The LMA receives any data packets sent by the CN to the MN. The LMA forwards the received packet to the MAG through the tunnel. After receiving the packets, the MAG on the other end of the tunnel removes the outer header and forwards the packets to the MN. ■ Figure 2. Message flow in PMIPv6. PBU: Proxy binding update PBA: Proxy binding acknowledgment (1) MN attachment MN MAG AAA server LMA CN Router advertisement Data packets Data packets Tunneled data packets (2) AAA query with MN-ID (4) PBU with MN-ID (7) PBA with MN-ID, home network prefix option (3) AAA reply with profile (5) AAA query with MN-ID (6) AAA reply Bidirectional tunnel setup Unlike MIPv6, a tunnel in PMIPv6 is established between the LMA and the MAG, and not an MN. This could be desirable because the tunneling increases the bandwidth constraints on the wireless link and the processing burden on the MN. KONG LAYOUT 4/9/08 11:02 AM Page 39

Category MIPv6 PMIPv6 Mobility management type Host-based mobility management Network-based mobility management Mobility scope Global mobility Localized mobility Functionally correspondent entity HA LMA(i.e.,HA functionality with additional capabilities) Topologically correspondent entity AR MAG MN modification Yes No Location registration message Binding update message Proxy binding update message MN address HoA or CoA HoA(always) Relation between tunnel and binding cache entry 1:1 relation (i.e.,HA-MN tunnel) 1:m relation (i.e.,LMA-MAG tunnel) Tunneling over wireless link Required Not required Router advertisement type Broadcast Unicast Lookup key in binding cache HoA MN identifier Addressing model Shared-prefix model Per-MN-prefix model Supported link type Any type of link Point-to-point link Route optimization Supported Not supported Movement detection Required(performed by RS/RA) Not required(performed by layer 2) Duplicate address detection(DAD) Performed at every subnet move Performed only one time(at initial movement into the ment domain) Return routability Required Not required Table 1.Comparison between MIPv6 and PMIPv6. QUALITATIVE ANALYSIS ing some extensions for supporting the IPv4 tun- In this section we qualitatively investigate neling mechanism and specific encapsulation PMIPv6 based on various evaluation criteria and modes. compare it with various existing well-known Basically,PMIPv6 attempts to reuse MIPv6 mobility support protocols as well as MIPv6.A because MIPv6 is a considerably mature proto- synopsis of the main characteristics,including col with several implementations that have the strong and weak points of PMIPv6 compared been realized through interoperability testing. to the various existing well-known mobility sup- Thus,the functionality of the LMA in PMIPv6 port protocols,is provided in Tables 1 and 2. can be considered as an enhanced HA with additional capabilities.In MIPv6 a bidirectional COMPARISON BETWEEN MIPV6 AND PMIPV6 tunnel is established between the HA and each We first compare MIPv6 and PMIPv6 in terms MN,whereas a bidirectional tunnel in PMIPv6 of some high-level characteristics and perfor- is established between the LMA and MAG,not mance aspects,which are shown in Table 1. each MN.This is because the MN is not MIPv6 is a host-based solution for handling the involved in any type of mobility-related signal- global mobility of hosts in IPv6 networks.This ing.As in MIPv4 [2],the bidirectional tunnel means that a host is involved in mobility-related between the LMA and MAG is typically a signaling;thus,a modification of the host proto- shared tunnel,and can be employed for routing col stack is required for operating MIPv6(i.e., traffic streams for different MNs attached to an MN sends the BU message for location regis- the same MAG.It extends the 1:1 relation tration).In contrast,PMIPv6 provides a net- between a tunnel and an MN's binding cache work-based solution for handling the localized entry to a 1:m relation,reflecting the shared mobility of hosts in IPv6 networks (i.e.,a net- nature of the tunnel. work entity,the MAG,sends the PBU message MIPv6 employs the shared-prefix model in for location registration).Therefore,no require- which multiple MNs in the same subnet are ment of the hosts is needed.Moreover,PMIPv6 configured with a common IPv6 network prefix. can also support IPv4 as well as IPv6 by specify- In contrast,PMIPv6 employs the per-MN-prefix 40 EEE Wireless Communications.April 2008

40 IEEE Wireless Communications • April 2008 QUALITATIVE ANALYSIS In this section we qualitatively investigate PMIPv6 based on various evaluation criteria and compare it with various existing well-known mobility support protocols as well as MIPv6. A synopsis of the main characteristics, including the strong and weak points of PMIPv6 compared to the various existing well-known mobility sup￾port protocols, is provided in Tables 1 and 2. COMPARISON BETWEEN MIPV6 AND PMIPV6 We first compare MIPv6 and PMIPv6 in terms of some high-level characteristics and perfor￾mance aspects, which are shown in Table 1. MIPv6 is a host-based solution for handling the global mobility of hosts in IPv6 networks. This means that a host is involved in mobility-related signaling; thus, a modification of the host proto￾col stack is required for operating MIPv6 (i.e., an MN sends the BU message for location regis￾tration). In contrast, PMIPv6 provides a net￾work-based solution for handling the localized mobility of hosts in IPv6 networks (i.e., a net￾work entity, the MAG, sends the PBU message for location registration). Therefore, no require￾ment of the hosts is needed. Moreover, PMIPv6 can also support IPv4 as well as IPv6 by specify￾ing some extensions for supporting the IPv4 tun￾neling mechanism and specific encapsulation modes. Basically, PMIPv6 attempts to reuse MIPv6 because MIPv6 is a considerably mature proto￾col with several implementations that have been realized through interoperability testing. Thus, the functionality of the LMA in PMIPv6 can be considered as an enhanced HA with additional capabilities. In MIPv6 a bidirectional tunnel is established between the HA and each MN, whereas a bidirectional tunnel in PMIPv6 is established between the LMA and MAG, not each MN. This is because the MN is not involved in any type of mobility-related signal￾ing. As in MIPv4 [2], the bidirectional tunnel between the LMA and MAG is typically a shared tunnel, and can be employed for routing traffic streams for different MNs attached to the same MAG. It extends the 1:1 relation between a tunnel and an MN’s binding cache entry to a 1:m relation, reflecting the shared nature of the tunnel. MIPv6 employs the shared-prefix model in which multiple MNs in the same subnet are configured with a common IPv6 network prefix. In contrast, PMIPv6 employs the per-MN-prefix ■ Table 1. Comparison between MIPv6 and PMIPv6. Category MIPv6 PMIPv6 Mobility management type Host-based mobility management Network-based mobility management Mobility scope Global mobility Localized mobility Functionally correspondent entity HA LMA (i.e., HA functionality with additional capabilities) Topologically correspondent entity AR MAG MN modification Yes No Location registration message Binding update message Proxy binding update message MN address HoA or CoA HoA (always) Relation between tunnel and binding cache entry 1:1 relation (i.e., HA-MN tunnel) 1:m relation (i.e., LMA-MAG tunnel) Tunneling over wireless link Required Not required Router advertisement type Broadcast Unicast Lookup key in binding cache HoA MN identifier Addressing model Shared-prefix model Per-MN-prefix model Supported link type Any type of link Point-to-point link Route optimization Supported Not supported Movement detection Required (performed by RS/RA) Not required (performed by layer 2) Duplicate address detection (DAD) Performed at every subnet move￾ment Performed only one time (at initial movement into the domain) Return routability Required Not required KONG LAYOUT 4/9/08 11:02 AM Page 40