Mobile Netw Appl

DOI 10.1007/s11036-009-0185-2

A Proxy Mobile IPv6 Based Global Mobility Management

Architecture and Protocol
Huachun Zhou & Hongke Zhang & Yajuan Qin &
Hwang-Cheng Wang & Han-Chieh Chao

# Springer Science + Business Media, LLC 2009

Abstract This paper specifies a global mobility management Keywords global mobility management . proxy mobile
architecture and protocol procedure called GPMIP, which is IPv6 . hierarchical mobile IPv6 . fluid flow mobility model .
based on Proxy Mobile IPv6. In GPMIP, mobility manage- cost function
ment is performed by the network entity rather than individual
mobile nodes. The benefit is the elimination of the wireless
link data delivery tunnel overhead between a mobile node and 1 Introduction
the access router. To compare with the well known Hierar-
chical Mobile IPv6 mobility management protocol, the Mobile IPv6 (MIPv6) [1] enables a mobile node (MN) to
location update, packet delivery, and total cost functions maintain its connectivity to the Internet during handover. In
generated by a mobile node during its average domain order to reduce the amount of signaling between the mobile
residence time are formulated for each protocol based on node, its correspondent nodes and its home agent, the
fluid flow mobility model. Then, the impacts of various Hierarchical Mobile IPv6 Mobility Management (HMIPv6)
system parameters on the cost functions are analyzed. The [2] protocol was established. HMIPv6 is an extension of
analytical results indicate that the proposed global mobility Mobile IPv6 and IPv6 neighbor discovery to allow for local
management protocol can guarantee lower total costs. mobility handling. However, mobile IP protocols are
Furthermore, a qualitative comparison between GPMIP and mobile node-centric in that the handover related decision
some other global management protocols is also investigated. making is mostly performed by the mobile node.
Recently, IETF proposed the Network-based Localized
Mobility Management (NETLMM) [3, 4] protocol, which
requires no localized mobility management support on the
H. Zhou : H. Zhang : Y. Qin : H.-C. Chao
School of Electronic and Information Engineering,
mobile node. Instead, the network is responsible for
Beijing Jiaotong University, managing IP mobility on behalf of the mobile node. In
Beijing 100044, China previous NETLMM discussions, HMIPv6 was presented as
H. Zhou a candidate solution but was ruled out because of host
e-mail: hchzhou@bjtu.edu.cn involvement. Proxy Mobile IPv6 (PMIPv6) [5] enables IP
H. Zhang mobility for mobile nodes without inducing any mobility-
e-mail: hkzhang@bjtu.edu.cn related signaling. The PMIPv6 protocol was finally adopted
Y. Qin by NETLMM since standards development organizations
e-mail: yjqin@bjtu.edu.cn have identified requirements needed to support PMIPv6
solution. Note that although PMIPv6 was derived from
H. Zhou : H. Zhang : Y. Qin : H.-C. Wang : H.-C. Chao (*)
MIPv6, it is different from HMIPv6.
Department of Electronic Engineering, National Ilan University,
I-Lan, Taiwan One limitation of PMIPv6 is that it is restricted to
e-mail: hcc@niu.edu.tw providing IP connectivity and reachability for mobile nodes
H.-C. Wang within an access network. On the other hand, mobile nodes
e-mail: hcwang@niu.edu.tw require global mobility management protocols in order to
 Mobile Netw Appl

support global mobility across different NETLMM access The second consideration is that future mobile network
networks [6]. To the best of our knowledge, no study has will introduce the separation between network address and
been conducted in the area of PMIPv6-based global identity of a mobile node entity. Ambient Networks have
mobility management schemes. developed a framework of naming, addressing and identity
In this paper, PMIPv6 is extended and the design of a mechanisms that enable dynamic bindings for supporting
PMIPv6-based global mobility management architecture connectivity across heterogeneous network domains [10].
and protocol support is described. The resulting scheme is Furthermore, node-identity-based internetworking architec-
called GPMIP. One distinguishing feature of GPMIP is that ture is proposed in paper [11]. The Mobility Management
the mobility management is actually performed by the framework [12] describes an IP-based Mobility Manage-
network entity instead of mobile nodes. Another feature is ment framework. Some design considerations include
the separation of network address and identity of the mobile separation of user identifier and location identifier, and
node. To assess the efficiency of the proposed scheme, the location and handover management information flows.
location update and packet delivery costs are compared Recently, many architectural discussions show that the split
against the well-known HMIPv6. of address and identity of a mobile node entity may help
The remainder of the paper is organized as follows. issues such as routing scalability, mobility, and identity
Section 2 gives the design motivations and provides an authentication in the Internet architecture [13, 14]. In a
overview of related work. Section 3 describes the GPMIP, PMIPv6 access network, the mobile node has a stable
including the mobility management architecture and proto- identifier. After the mobility management entities in a
col. HMIPv6-based global mobility management architecture PMIPv6 access network identify the mobile node and
and protocol are described in section 4. In section 5, the acquire the mobile node's identity, the mobile node can be
analytical network and user mobility models are described, authorized for the network-based mobility management
followed by the derivation of location update, packet delivery service, i.e., permitted by the network to obtain an access
and total cost functions for GPMIP and HMIPv6-based address. The proposed PMIPv6-based global mobility
method. Subsequently, the numeric results of cost compari- management architecture and protocol exploit this feature.
son are analyzed in section 6. Section 7 gives a qualitative
comparison between GPMIP and other global management 2.2 Related work
protocols. Finally, in section 8, conclusion is drawn.
There are two classes of mobility management methods.
The first is tunnel based approach, as exemplified by
2 Design motivations and related work Mobile IPv6, in which mobility agents establish tunnels to
forward packets whose destination address does not belong
2.1 Design motivations to the network. As long as the tunnel endpoints can support
the protocol, intermediate nodes need not be aware of the
This paper specifies a PMIPv6-based global mobility protocol and their routing tables are not affected. The
management architecture and protocol. There are two second is host-routing based approach, such as Cellular IP
design considerations. The first is that future mobile and HAWAII [15], in which mobility agents maintain the
network requires network-based mobility management, next hop for the mobile node and packets destined for the
shifting the mobility management function from mobile mobile node are relayed by these agents. Although there is
nodes to access network by using existing mobile IP no tunnel overhead, all the nodes need to be aware of the
protocols [7]. Recent developments in network architec- protocol and their routing tables are influenced. A detailed
tures in standards development organizations, such as description of these mobility support protocols is provided
WiMAX Forum [8] and 3GPP [9] have identified a need in [15]. It should be noted Mobile IPv6, Cellular IP and
to support proxy mobile solution. The WiMAX network HAWAII are host-based solution. In contrast, GPMIP is a
architecture [8] currently supports proxy mobile IPv4 for network-based solution, i.e., a network entity, the Mobile
enabling mobility for mobile nodes that may not have a Access Gateway, sends Proxy Binding Update messages for
mobile IPv4 client. PMIPv6 is a solution that is aligned location registration. The Local Mobility Anchor advertises
with the architectural direction of WiMAX. In 3GPP, there the mobile node's home network prefix or an aggregated
has been some degree of interest in PMIPv6 as well, prefix with a larger scope to the Routing Infrastructure.
primarily in the SAE (System Architecture Evolution) [9] Mobile IPv6 is a host-based solution for handling the
work item. The possible solution is the use of a hierarchical global mobility of hosts in IPv6 networks. This means that
mobility concept including a global mobility protocol and a a host is involved in mobility-related signaling and a
local mobility protocol. This paper extends PMIPv6 to modification of the host protocol stack is required for
support global mobility management. operating Mobile IPv6 [16]. In contrast, GPMIP provides a
Mobile Netw Appl

network-based solution for handling the mobility of IPv6 The roaming mechanisms between PMIPv6 domains
hosts. Therefore, no requirement on the hosts is needed. have been discussed in NETLMM working group. In [18],
3GPP General Packet Radio Service (GPRS) has devised Local Mobility Anchors and Mobile Access Gateways in
its own protocol, the GPRS Tunneling Protocol (GTP) as two domains perform exchange of mobility signaling
documented in 3GPP TS 23.060, to handle mobility. In the messages on behalf of mobile nodes. All scenarios that
GTP protocol, a tunnel is established from Serving GPRS require direct interaction between MIPv6 and PMIPv6 are
Support Node (SGSN) to Gateway GPRS Support Node analyzed in [19]. One of the scenarios uses MIPv6 to
(GGSN) for the User Equipments data packets. GTP manage mobility among different access networks and uses
provides a kind of IP localized mobility management that PMIPv6 to implement mobility within an access network.
requires minimal host involvement. From the IP perspective This interaction is very similar to the HMIPv6-MIPv6
of the mobile node, the mobile node is attached to a single interaction. However, based on the design considerations
subnet while it moves around a particular GPRS domain. mentioned in subsection 2.1, the proposed GPMIP is a
When the MN roams outside its home network, GPRS centralized architecture. It introduces a global location
Roaming eXchange (GRX) as prescribed in GSM Oper- database server and a global AAA server. In this paper,
ators' Association Permanent Reference Document IR.33 is the proposed GPMIP is compared with the distributed
used as a global mobility management protocol. GRX is a HMIPv6-MIPv6 protocol.
network-based protocol that enables the serving network
GGSN to manage an address in the home network in a way
similar to Mobile IP. To support the mechanism, Mobile 3 GPMIP global mobility management architecture
Switching Center/Visitor Location Register (MSC/VLR) and protocol
and Home Location Register (HLR) in the existing GSM
network are also modified [17]. This section describes the proposed PMIPv6-based global
Recently, 3GPP is working on the new SAE Evolved mobility management architecture and the protocol procedure.
Packet System (EPS) for Release 8. The target is a low-
latency, higher data-rate, all-IP core network capable of 3.1 PMIPv6 overview
supporting real-time packet services over multiple access
technologies. Two network architecture solutions are GTP- PMIPv6 [5] is a network-based mobility management
based solution described in 3GPP TS 23.401 and PMIP- protocol reusing MIPv6 entities and concepts as much as
based solution outlined in 3GPP TS 23.402. 3GPP does not possible. PMIPv6 Domain is a localized mobility manage-
require PMIP for different technology handover (that is ment domain where the mobility management of a mobile
done by LTE, WIMAX or UMTS specific L2 mobility), but
wants to deploy PMIP for the integration of these
technologies in an SAE architecture.
In contrast, GPMIP has some resemblance to GPRS in
that they are both network-based mobility management PMIPv6
protocols and have similar functionalities. The bi-
AAA Domain
directional tunnel in GPMIP is established between the
Local Mobility Anchor and Mobile Access Gateway and is
LMA
typically a shared tunnel, and can be employed to route
traffic streams for different mobile nodes attached to the
same Mobile Access Gateway. From the perspective of the
mobile node, the PMIPv6 access network appears as its
home link or a single link. Furthermore, there exist a PBU

location database server for maintaining global and visitor

MAG2
locations and an Authentication, Authorization, and Ac- MAG1
counting server for global AAA and AAA in the GPMIP
core and access network, respectively.
GPMIP is an Internet protocol which is not dependent on
any access-technology-specific protocol. Therefore, it can movement
be used in any IP-based network. On the other hand, GPRS
is an access-technology-specific protocol closely coupled
MN
with the signaling protocols used in legacy cellular
systems. Fig. 1 PMIPv6 domain architecture
 Mobile Netw Appl

node is handled using PMIPv6 protocol. The architecture of ters, such as the mobile node's home network prefix (HNP),
a PMIPv6 domain is shown in Fig. 1. permitted address configuration modes, roaming policy, and
In this protocol, the mobile nodes are differentiated by a other parameters that are essential for providing network-
Network Access Identifier (NAI) [20], which has an based mobility service.
associated set of information stored on the network, The GPMIP access network is a PMIPv6 Domain (PMIPv6
including a profile containing the home prefix. The Mobile Domain). There are a Dynamic Host Configuration Protocol
Access Gateway (MAG), located in the access router, (DHCP) server, an AAAA server, and a Visitor Location
retrieves the MN profile information from AAA server and Database (VDB) server in a PMIPv6 Domain. PMIPv6
sends the customized Router Advertisements (RAs) to the Domains are interconnected by core routers (CRs).
MN, emulating the home network behavior. The MN In a PMIPv6 Domain, LMA is the Home Agent for the
configures its Home Address (MN-HoA) on the network mobile node. It has the functional capabilities of a Home
interface. Because the MN always receives the same home Agent as defined in Mobile IPv6 base specification. It is
prefix, it believes that it is in the Home Domain. Furthermore, also the entity that manages the mobile node's reachability
the Mobile Access Gateway performs Proxy Binding state. MAG is the entity that performs the mobility
Updates (PBU) signaling on behalf of the MN to the MN's management on behalf of a mobile node and resides on
Local Mobility Anchor (LMA), informing the LMA that the the access link where the mobile node is anchored. MAG is
current Proxy Care-of Address of the registered MN is the responsible for detecting the mobile node's movements on
MAG's address. These procedures also lead to the estab- its access link and for sending binding registrations to the
lishment of tunnels between LMA and MAG. mobile node's LMA for updating the route to the mobile
node's home address.
3.2 PMIPv6 based global mobility management Once the mobile node enters its PMIPv6 domain, the
architecture link layer Link Up trigger occurs when the link layer link
between the MN and the MAG is established. The mobile
The proposed GPMIP extends PMIPv6 to support global node sends the Link Up trigger message to the MAG.
mobility management. The proposed GPMIP is shown in When the mobile node attaches to an access link
Fig. 2. The GPMIP administration domain is composed of a connected to the MAG, it presents its identity (e.g., NAI)
core network and several access networks. as part of the access authentication procedure. If the mobile
There exist a global location database server (GDB) and node enters a PMIPv6 domain for the first time, the AAA
a global Authentication, Authorization, and Accounting server does not have its policy profile, and the AAA server
(GAAA) server in the GPMIP core network. GDB is used in the PMIPv6 domain will relay the AAA request to
to store up-to-date location information and controls the GAAA. After a successful access authentication using that
location management for all mobile nodes. GAAA server identifier, the MAG will obtain the mobile nodes policy
stores the policy profile of all mobile nodes. The policy profile from GAAA server.
profile typically contains the provisioned network-based The current PMIPv6 specification supports the per-
mobility service characteristics and other related parame- MN's interface prefix addressing model. In this addressing

Fig. 2 GPMIP architecture

core network
GAAA GDB

access network 2
access network 1 VDB2
DHCP2 AAA2
DHCP1 VDB1
AAA1

CR CR PMIPv6
LMA 1 LMA2 Domain 2
PMIPv6
Domain 1
MAG3 MAG 4
MAG2
MAG1
movement

MN CN
Mobile Netw Appl

model, each interface of a mobile node is allocated an location registration or update message to the GDB server of
exclusively unique home network prefix and the prefix is the core network. When the GDB server receives the location
not hosted on the home link. In this addressing model, the update message from the VDB server, it will update the
LMA is just a topological anchor point and the prefix is associated entry in the mapping table for the mobile node.
physically hosted on the access link to which the mobile When a LMA is serving a mobile node, it must attempt
node is attached. The home network prefix of the mobile to intercept correspondent nodes (CNs) packets that are
node may have been statically configured in the GAAA's sent to any address that is in the mobile node's home
policy profile, or, it may have been dynamically allocated network prefix address range. The LMA advertises a
by the LMA. connected route to the Routing Infrastructure for that
For updating the LMA about the current location of the mobile node's home network prefix or for an aggregated
mobile node, the MAG sends a PBU message to the mobile prefix with a larger scope. This enables routers in the IPv6
node's LMA. The message will have the mobile node's NAI core network to detect the LMA as the last-hop router for
option and Home Network Prefix option. The source that prefix.
address of that message will be the address of the MAG
on its egress interface. Upon accepting the PBU request, the 3.3 PMIPv6-based global mobility management protocol
LMA allocates a prefix for the mobile node. procedure
As DHCP for IPv6 (DHCPv6) [21] servers can manage
prefixes [22], GPMIP releases the prefix allocation tasks In GPMIP architecture, the stateful address configuration is
from LMA to the DHCPv6 server in a PMIPv6 domain. used in PMIPv6 access links and prefix allocation using
The procedure for prefix delegation with DHCP has been DHCPv6. The GPMIP protocol procedure is shown in
defined in [23] which is independent of address assignment Fig. 3. Here it is assumed that MAG has established a
with DHCP. secure association with LMA, VDB, DHCP and AAA,
After allocating a prefix for the mobile node, the LMA respectively. Also it is assumed that all the AAA and VDB
sends a Proxy Binding Acknowledgement (PBA) message in a PMIPv6 domain have already established secure
which includes the Home Network Prefix option containing associations with GAAA and GDB, respectively.
the allocated prefix value. It creates a Binding Cache entry The procedure involves the following steps:
and establishes a bi-directional tunnel to the mobile access
1-3) MN enters the network and MAG receives the
gateway. It also sets up a route to the mobile node's home
authorization profile from AAA server after success-
network over the tunnel.
ful AAA exchanges.
Upon receiving PBA message, the MAG sets up a bi-
4) MAG sends a PBU to LMA. When a MN first enters
directional tunnel to the LMA and adds a default route over
a PMIPv6 domain, the HNP field is set to zero, and
the tunnel to the LMA All traffic from the mobile node gets
then the LMA will allocate a prefix for the MN. If the
routed to the mobile node's LMA over the tunnel. Now the
MN moves to a different access link and a new MAG
MAG has all the information for it to emulate the mobile
learns the MNs HNP, the MAG will specify the same
node's home network on the access link. The MAG also
in the HNP option to request the LMA to allocate that
starts sending periodic Router Advertisements to the mobile
prefix.
node advertising its home network prefix.
After receiving the Router Advertisement messages on
the access link, the mobile node will configure its interface MN MAG1 LMA1 AAA1 GAAA
1.MN Attached
using stateful address configuration modes. At this point, 2.Access Authentication
3.Authentication success
the mobile node has a valid home address from its home DHCP1
network prefix at the current point of attachment. The 4.PBU (HNP=0)
5.DHCP Solicit
serving MAG and LMA have proper routing states for 6.DHCP Advertise
7.DHCP Request (HNP)
handling the traffic sent to and from the mobile node. From 8.DHCP Reply (HNP)
the perspective of the mobile node, the entire PMIPv6 9.PBA (HNP)
10.Bi-directional Tunnel
domain appears as its home link or a single link. Profile Complete
The serving MAG sends location registration or update AAA1 VDB1 GDB
11.DHCP Request
message to the PMIPv6 domains VDB server. The VDB 12.DHCP Reply
13.Access-Request
server will add (for an MN first entering a PMIPv6 domain) or 14.Location Update
15.Access-Accept
update (for MAG handover in a PMIPv6 domain) the 16.Location query
mapping table that contains the mapping relationship between 17.Location Reply
Deliver packets
the mobile nodes NAI and MN-HoA. For an MN first
entering a PMIPv6 domain, the VDB server will then send a Fig. 3 GPMIP protocol procedure
 Mobile Netw Appl

5) LMA as the requesting router initiates DHCP Solicit 4 HMIPv6-based global mobility management
procedure to request a prefix for the MN. LMA architecture and protocol
creates and transmits a Solicit message. The Solicit
message should include an Identity Association for As the architecture and functionality of GPMIP are similar
Prefix Delegation option [23]. to HMIPv6 [2], HMIPv6 is chosen for comparison with the
6) The DHCP server acts as the delegating router and proposed GPMIP.
sends an Advertise message to LMA.
7) LMA uses the DHCP Request message to obtain or 4.1 HMIPv6-based global mobility management
update the prefix from a DHCP server. architecture
8) LMA stores the prefix information it received in the
Reply message. According to Mobile IPv6 definition, a MN must send
9) LMA replies with PBA and sets its HNP parameter. Binding Updates (BUs) to its Home Agent and all Corre-
10) Bi-directional tunnel is established. Access authenti- spondent Nodes to keep session continuity while moving
cation and profile acquisition are completed. across different subnets. A return routability procedure before
11) MN requests an address from the local DHCP proxy a correspondent registration must be executed between the
collocated in MAG. MN and each CN. Four messages, including Home and Care-
12) DHCP Proxy assigns MN-HoA from this prefix and of Test Init and Home and Care-of Test, form the return
sends it to MN in DHCP Reply message. routability procedure. Since Home Agent is usually far away
13) Once address configuration finishes, the MAG sends from mobile node and the Binding Updates latency is very
Access-Request with MIP6-DNS-MO Attribute de- large, HMIPv6 [2] is proposed.
fined in [24] to instruct AAA server to perform a The Mobile IPv6 administration domain is also com-
dynamic DNS update. posed of a core network and several HMIPv6 access
14) The AAA server performs DNS update according to networks. HMIPv6 access network is a localized mobility
[25]. management domain in which the mobility management of
15) The AAA server sends Access-Accept message a MN is handled using HMIPv6 protocol. In order to
including MIP6-DNS-MO attribute to confirm the implement global mobility management, HMIPv6 must
DNS update. interact with Mobile IPv6. For simplicity, HMIPv6 means
16-17) When a MN wants to communication with a HMIPv6-MIPv6 interactive protocol in this paper. The
CN, the MN sends a location query message architecture of HMIPv6 is shown in Fig. 4.
including the CNs NAI to VDB server. If there HMIPv6 defines a local Mobile Anchor Point (MAP)
is no location entry of the CN, VDB server will which acts as a local Home Agent. HMIPv6 domain is the
forward the location query message to GDB same as MAP domain. A HMIPv6-compliant MN can send
server. GDB server will return the CNs address BUs to the local MAP rather than the Home Agent and
to the MN through location reply message. In CNs. This can reduce the amount of Mobile IPv6 signaling
this paper, it is assumed that the CN has outside the local MAP domain. When a MN moves into a
performed steps 1-15. new MAP domain, thus inducing an inter-domain hand-

Fig. 4 HMIPv6 architecture

Core network access network 2

access network 1
DHCP2 HAAA
DHCP1
AAA

CR CR HMIPv6
HMIPv6 MAP1 MA P Domain 2
Domain 1
AR3 AR4
AR2
AR1
movement

MN CN
Mobile Netw Appl

MN AR1 MAP1 AAA1 HAAA

1.MN Attached 5 Analytical models
2.Access Authentication
3.Authentication Success
4.Prefix Advertisement In this section, the analytical network and user mobility
DHCP1
5.DHCP Solicit
models are described. Based on these models, this section
6.DHCP Advertise derives analytically the location update, packet delivery,
7.DHCP Request
8.DHCP Reply and total cost functions generated by a MN during its
9.Binding Update average domain residence time in a PMIPv6 or MAP
10.Binding Acknowledgement
HA CN domain. For simplicity, the periodic binding refresh costs
11.Binding Update
12.Binding Acknowledgement are not considered. The costs of GPMIP and HMIPv6 are
13.Bi-directional Tunnel compared in section 6.
14.Home Test Init
15.Care-of Test Init
16.Home Test
17.Care-of Test
5.1 Network model
18.Binding Update
19.Binding Acknowledgement
20.Deliver packets The GPMIP architecture given in Fig. 2 can be viewed as a
three-tier hierarchical network model as shown in Fig. 6.
Fig. 5 HMIPv6 protocol procedure in integrated scenario
The first tier comprises the GDB server and the GAAA
server. The second tier has a mesh topology, which consists
of M mesh nodes, i.e., LMAs. It is assumed that DHCP
over, it needs to configure two Care-of Addresses (CoAs): a server, VDB server and AAA server in a PMIPv6 domain
Regional CoA (RCoA) on the MAP's link and an on-link co-locate with the LMA node. It is also assumed that each
CoA (LCoA) based on the prefix advertised by current second tier node is the root of an N-ary tree of depth 1. The
Access Router (AR). The RCoA can be formed in a third tier nodes are MAGs. Each PMIPv6 domain is
stateless or stateful manner. After forming the RCoA, the composed of all the third tier nodes under the same second
MN sends a local BU to the MAP, which returns a Binding tier node. The domain size, i.e., N, is defined as the number
Acknowledgement (BA) to the MN. After successfully of the third tier nodes in a PMIPv6 domain.
registering with the MAP, a bi-directional tunnel between In this paper, it is assumed that the link hop count
the MN and the MAP is established. Next, the MN must between the first tier and second tier nodes is a, the hop
register its new RCoA with its Home Agent and CNs by count among the second tier nodes is b, the hop count
sending each a BU that specifies the binding (RCoA, Home between the second and third tier nodes in the same domain
Address). Packets from the Home Agent or CNs will be is c, and the hop count between the third tier nodes and an
tunneled from the MAP to the MN's LCoA. If the MN MN or CN in the same domain is 1, respectively.
change its LCoA within a MAP domain (i.e., an intra- Obviously, the hop counts a, b, and c are for wired links,
domain handover), it only needs to register the new LCoA only the last hop is wireless.
with the MAP. In HMIPv6, the MAP performs the function For the performance analysis of the two protocols under
of a "local" Home Agent that binds the MN's RCoA to an the same network architecture, the functionality of MAP is
LCoA. The Home Agent and CNs are unchanged. HMIPv6 assumed to be resident on the second-tier node. There exists
requires updating the implementation of mobile nodes a DHCP server located in a MAP domain. The AAA server,
only. HAAA server, and DHCP server are assumed to exist on

4.2 HMIPv6-based global mobility management protocol GAAA,GDB

procedure
LMA,DHCP,VDB,AAA
MAP,DHCP,HAAA a
or MAP,DHCP,AAA
Because of the similarities between GPMIP and Mobile
IPv6 for integrated scenario, Mobile IPv6 for integrated MAG or AR
scenario [26] is chosen for comparison. In an integrated HA First tier nodes
scenario, the same Home AAA (HAAA) server can
authorize the MN for network access and mobility service b Second tier nodes
at the same time. In Fig. 4, there is an AAA and a Home c Third tier nodes
AAA (HAAA) server in a visited MAP domain and the
MNs home domain, respectively. There exists a DHCP
server located in a MAP domain. Figure 5 shows the
CN MN
HMIPv6 protocol procedure in an integrated scenario. The
details are described in [26, 27]. Fig. 6 Network model
 Mobile Netw Appl

the second tier node, too. The access routers and the MNs respectively, and denotes the additional weight of packet
Home Agent (HA) form the third tier. It is also assumed tunneling.
that the CN, MN, and HA are located in different domains, Let LGG and LGV denote the location update costs to
and the PMIPv6 domain is identical to the MAP domain. register with the GDB and the VDB, respectively. LGC
denotes MNs location query cost of CNs. LGPMIP denotes
5.2 Fluid flow mobility model the average location update cost for GPMIP. By applying
the GPMIP protocol procedure described in Fig. 3 to the
The fluid flow mobility model in [2830] is adopted to network model given in subsection 5.1, we can obtain LGL,
analyze the costs for GPMIP and HMIPv6. In this model, it LGC and LGPMIP as shown in the equations below.
is assumed that a PMIPv6 or MAP domain is composed of
N identical subnets. All the subnets are circular and of the LGG q 2c ah 2ch q 2q 2c ah
same size and together form a contiguous area. The subnet 4q 6c 4ah 5
handover in a PMIPv6 domain is a MAG handover. It is
assumed that the MNs are moving at an average speed v,
and their movement direction is uniformly distributed over LGV q 2c ah 2ch q 2q 2ch
[0, 2]. Let S denote the subnet area. Following [28], the
MNs subnet residence time tsub can be derived as the 4q 6c 2ah 6
following equation:
p LGC 2q 2c 2ah 7
pS
tsub 1
2v
Furthermore, state i (0iN) is defined as the number of LGPMIP p 0  LGG "LGC N
1  LGV 8
subnets wherein a mobile node has stayed within a given where is the average number of CNs when an MN moves
domain. State 0 represents the situation that the mobile into/out of a given domain. The term p 0  LGG "LGC in
node stays outside of a given domain. It is assumed that a (8) accounts for the inter-domain cost and N
1  LGV
mobile node moves out of a given domain within a for the intra-domain cost.
maximum of N movements. Let i be the steady-state On the other hand, let DGPMIP be the average packet
probability of state i. Then we have delivery cost for GPMIP. Then DGPMIP is given by the
81 following equation:
>
> if i 0
>2
<  i
1 DGPMIP p  tsub  N  2q 2tc bh 9
1 p1
1
p1 if 1  i  N
1
pi 2 N N 2
>
>  N
1 where p is the average packet arrival rate at an MN per
>
: 1 1
p1
2 N
if i N subnet.
Finally, the total cost CGPMIP for GPMIP can be
Let (N) denote the average number of subnets within a expressed as follows:
given domain that an MN visits. Then we have
X
N CGPMIP LGPMIP DGPMIP 10
N ip i 3
i1
5.4 Cost functions for HMIPv6
Finally, the average domain residence time of an MN,
tdomain, is obtained as Let LHM, LHH and LHC denote the location update costs to
tdomain tsub  N 4 register with the MAP, the HA and the CN in HMIPv6,
respectively. LHMIP denotes the average location update cost
in HMIPv6. According to the HMIPv6 protocol procedure
5.3 Cost functions for GPMIP described in Fig. 5, LHM, LHH, LHC and LHMIP can be
obtained as the following equations:
Although signaling messages as defined in GPMIP have
different sizes, for sake of simplicity, it is assumed that they
all have the same size. Thus, the location update costs are
proportional to the link hops between the source and LHM 2q ch bh 4q ch 2q ch
destination of a message. Let and denote the unit
transmission costs in a wireless and a wired link, 8q 8c 2bh 11
Mobile Netw Appl

LHH 2q 2c bh 12 2500
GPMIP location update
GPMIP packet delivery

LHC 2q 2b c 2ch
GPMIP total
2000 HMIPv6 location update
HMIPv6 packet delivery
2q b 2ch 2q b 2ch HMIPv6 total

1500
6q 8c 4bh 13

Costs
LHMIP p 0  LHM LHH "LHC N
1
1000
 LHM 14

The term p 0  LHM LHH "LHC in (14) is the inter- 500

domain cost and N
1  LHM is the intra-domain cost.
Let q be the probability that a single packet is routed
directly to the MN without being intercepted by the HA. 0
0 5 10 15 20 25 30 35 40
Dhdir, Dhindir and DHMIP denote the packet delivery cost Average moving speed (km/hr)
incurred by a direct packet delivery (not intercepted by the
Fig. 7 Costs as a function of the average moving speed
HA), by delivering a single packet routed indirectly through
the HA, and for HMIPv6, respectively. Then Dhdir, Dhindir
and DHMIP can be expressed by the equations below. speed v is changed. As Fig. 7 shows, the location update
costs generated by a mobile node during its average domain
Dhdir 2tq 2tc bh 15 residence time are independent of average moving speed
because the average number of subnets that an MN stays
within a domain, given by Eq. (3), is not affected by the
Dhindir 2tq t 2c bh 2c bh 16 average moving speed. This means that a slowly moving
MN may cross a lot of subnets within a domain, whereas a
fast moving MN may cross few subnets within a domain,
DHMIP p  tsub  N  fqDhdir 1
qDhindir g 17 and vice versa. In addition, Eq. (1) shows that the MNs
Finally, the total cost CHMIP for HMIPv6 can be subnet residence time decreases as average moving speed
expressed as follows: increases. Therefore, the packet delivery costs, given by
Eqs. (9) and (17), decrease as the average moving speed
CHMIP LHMIP DHMIP 18 increases. So, the total costs decrease as the average
moving speed increases. Contrarily, when the average
6 Numeric results moving speed approaches zero, packet delivery costs
approaches infinity, but for clarity of presentation, this is
This section evaluates the performance of GPMIP and not indicated in Fig. 7.
HMIPv6 based on the analytic cost functions in section 5.
The default parameter values for the analysis are given in 0.79
Table 1. Some parameter values are taken from [28].
0.78

6.1 Costs vs. Average moving speed 0.77

0.76
Figure 7 shows the location update, packet delivery, and
0.75
Costs ratios

total costs of GPMIP and HMIPv6 as the average moving location update
0.74 packet delivery
total
Table 1 Parameters for performance evaluation 0.73

N S v a 0.72

0.71
25 10Km2 20Km/hr 6
0.7
b c p
4 2 2 100Kpkts/hr 0.69
0 5 10 15 20 25 30 35 40
q Average moving speed (km/hr)
2 1 1.2 0.7
Fig. 8 Cost ratios vs. average moving speed
 Mobile Netw Appl

0.85
Figure 8 shows the ratio of the costs of GPMIP to those
of HMIPv6. The ratio of the location update costs is a fixed
0.8
value of 69.2%. The ratio of the packet delivery costs is
also a fixed value of 78.8%, and the value represents the 0.75
ratio of a single packet delivery costs. GPMIP requires only

Costs ratios
78.875.8% of the total cost of HMIPv6. This is due to the 0.7
fact that there is no tunnel establishment between MAG and
MN and that MN does not generate mobility messages. 0.65
location update
Furthermore, Fig. 8 shows that when the average moving packet delivery
speed approaches zero, the ratio of total costs approaches 0.6 total

that of the packet delivery costs as they become the

dominant factor. The ratio of total costs decreases as 0.55

average moving speed increases because of short subnet

0.5
residence time and location update costs becoming the 0 5 10 15 20 25 30
dominant factor. Domain size

Fig. 10 Cost ratios vs. domain size

6.2 Costs vs. Domain size
only 70.676.8% of the total cost of HMIPv6 and the ratio
Figure 9 shows the location update, packet delivery, and of total costs increases as average domain size increases.
total costs of GPMIP and HMIPv6 increase as the domain Note that if the domain size becomes very large, the ratio of
size N increases. This is because the average number (N) the location update costs approaches 0.8, the ratio of LGV
of subnets that an MN stays within a given domain and LHM, because the intra-domain location update costs
increases as domain size increases. Moreover, the average become the dominant factor. The ratio of total costs
domain residence time of the MN increases. Consequently, approaches that of packet delivery costs because they
the MN performs more movements and requires more increase faster than location update costs.
frequent location updates and higher delivery costs.
However, as given by Eq. (3), (N) is not sensitive to the 6.3 Costs vs. Link hops between the first tier
change of N. Thus, the costs increase slowly. and the second tier nodes
Figure 10 shows the ratios of the costs of GPMIP to
those of HMIPv6. The ratio of the packet delivery costs is The location update, packet delivery, and total costs of
also a fixed value, i.e., 78.8%.The inter-domain cost is HMIPv6 are not affected by the link hops between the first
fixed for GPMIP and HMIPv6, therefore the intra-domain and second tier nodes. This is due to the fact that there are
costs become the dominant factor and the location update no global location database server and AAA server in
costs for GPMIP grows rapidly. This is reflected in the HMIPv6. On the other hand, the location update cost
curve of location update cost ratio. Finally, GPMIP requires
1.1
700 location update
GPMIP location update pa cket delivery
1
GPMIP packet delivery total
600
GPMIP total
0.9
HMIPv6 location update
500 HMIPv6 packet delivery
HMIPv6 total 0.8
Costs ratios

400 0.7
Costs

300 0.6

200 0.5

0.4
100

0 2 4 6 8 10 12
0
0 5 10 15 20 25 30 Link hops between the first tier and the second tier nodes
Domain size
Fig. 11 Cost ratios vs. the link hops between the first tier and the
Fig. 9 Costs as a function of domain size second tier nodes.
Mobile Netw Appl

0.79
increases linearly with a for GPMIP. However, packet
delivery cost is independent of a because MN and CN 0.78

always communicate directly in GPMIP. 0.77

location update
Figure 11 shows the ratios of the costs of GPMIP to 0.76 packet delivery
those of HMIPv6. The ratio of the packet delivery costs is a total
0.75

Costs ratios
fixed value of 78.8%. GPMIP requires only 71.083.0% of
the total cost of HMIPv6 and the ratio increases with a 0.74
because of the linear increase of location update cost for 0.73
GPMIP. Calculation reveals that when a equals 31, the ratio
0.72
of total costs is 1. However, the hop count between any two
nodes in the underlying Routing Infrastructure is typically 0.71

smaller than 16. 0.7

0.69
6.4 Costs vs. Link hops between second tier nodes 0 50 100 150 200 250 300
Average packet arrival rate per subnet (Kpkts/hr)

The location update, packet delivery, and total costs of Fig. 13 Costs ratios vs. average packet arrival rate per subnet
HMIPv6 increases linearly with b. A large b means that the
MN is located far away from HA or CN. Similarly, the HMIPv6 increase linearly with p, because a larger p implies
packet delivery cost of GPMIP also increases linearly with a higher delivery cost via the tunnel.
b. However, the location update cost of GPMIP is not Figure 13 shows the ratio of the costs of GPMIP to those
affected by the link hops between second tier nodes. of HMIPv6. The ratio of the location update costs is a fixed
Figure 12 shows the ratio of the costs of GPMIP to those value of 69.2%, that of the packet delivery costs is also
of HMIPv6. In terms of location update cost, the ratio fixed at 78.8%. Overall, GPMIP requires only 69.278.1%
decreases with b as explained above. In terms of packet total cost of HMIPv6.
delivery cost, the ratio also decreases because the growth
with b is slower for GPMIP than for HMIPv6. Finally, 6.6 Costs vs. Probability of a single packet being routed
GPMIP requires only 84.071.3% of the total costs of directly to MN
HMIPv6. It can be calculated that the lower bound of the
ratio for location update, packet delivery, and total costs are The location update, packet delivery, and total costs of
0, 73.5% and 60.5%, respectively. GPMIP are not affected by the probability q. Similarly, the
location update cost of HMIPv6 is not a function of q.
6.5 Costs vs. Average packet arrival rate per subnet However, packet delivery cost of HMIPv6 decreases with q
because as q increases, the number of the packets routed
The location update costs of GPMIP and HMIPv6 are not indirectly via HA to MN dwindles.
affected by p. The packet delivery costs of GPMIP and

0.95
0.95 location update
location update 0.9 packet delivery
0.9 packet delivery total
total
0.85 0.85

0.8 0.8
Costs ratios

0.75
Costs ratios

0.75
0.7
0.7
0.65

0.6 0.65

0.55 0.6
0.5
0.55
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0.45
0 2 4 6 8 10 12 Probability of a single packet being routed directly to the MN (not via HA)
Link hops between the second tier nodes
Fig. 14 Costs ratios vs. Probability that a single packet is routed
Fig. 12 Costs ratios vs. link hops between second tier nodes directly to MN
 Mobile Netw Appl

Table 2 Protocol comparison

Protocol HMIPv6 + MIPv6 GPMIP GPRS

Location management scheme host-based network-based network-based

MN software modification Yes No minimal
Location management entities HA, MAP GDB, VDB HLR, VLR
MN Lookup key HoA NAI TMSI
MN address HoA, CoA HoA HoA
Tunnel MN-MAP, per MN MAG-LMA, shared SGSN-GGSN, shared

Figure 14 shows the ratio of the costs of GPMIP to those 8 Conclusion

of HMIPv6. The ratio of the location update costs is a fixed
value of 69.2%. The ratio of the packet delivery costs This paper proposed a new global mobility management
increases as the packet delivery cost of GPMIP remains architecture and protocol procedure. The advantages of the
constant whereas that of HMIPv6 decreases with q. GPMIP Proxy Mobile IP technology are inherited by the proposed
requires only 58.988.3% of the total costs in HMIPv6. scheme. To compare with the well known HMIPv6
When the probability q approaches 1, the ratio of packet mobility management protocol, the location update, packet
delivery costs approaches 93.5% and the ratio of total costs delivery, and total cost functions generated by a mobile
approaches 88.8%. node during its average domain residence time are
formulated based on fluid flow mobility model. Then, the
impacts of various system parameters, such as the average
7 Qualitative comparison moving speed of an MN, the domain size, the link hops
between the first tier and the second tier nodes, the link
This section gives a qualitative comparison of the proposed hops between the second tier nodes, the average packet
GPMIP with HMIPv6 and GPRS from location update and arrival rate per subnet, and the probability of a single packet
packet delivery perspective. The protocol comparison is being routed directly to the MN (not via HA), on the cost
given in Table 2. Again, HMIPv6 in the table means functions are analyzed, respectively. Results of the analysis
HMIPv6 + MIPv6. indicate that the total costs generated by a mobile node
The analytical results given in Section 6 indicate that the during its average domain residence time for the proposed
total costs including location update and packet delivery of GPMIP are lower than that for HMIPv6. Moreover, a
the proposed GPMIP are lower than HMIPv6. Furthermore, qualitative comparison of GPMIP, HMIPv6, and GPRS is
the deployment of HMIPv6 requires modification to the given, which also shows the advantages of GPMIP. In the
MNs software, because HMIPv6 is a host-based solution. future, the location management and handover performance
GPMIP and GPRS are both network-based solutions. problems will be studied.
GPMIP does not need software modification on the part
of MN, and GPRS needs only minor modification. Acknowledgements This work is supported by the National Natural
Science Foundation of China (No. 60870015, 60833002) and 973
HMIPv6 mobility management has a distributed architec-
Program of China (No. 2007CB307101).
ture, and its location management is performed by Home
Agent and Local Mobility Anchor. GPMIP introduces global
and visitor location database servers and is a centralized
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