Mobility and session management: UMTS VS. cdma2000

(1)

RNC

UTRAN Node B

SGSN

M

OBILITY AND

R

ESOURCE

M

ANAGEMENT

INTRODUCTION

Universal Mobile Telecommunication System (UMTS) and cdma2000 (based on code-division multiple access, CDMA) are two major stan-dards for third-generation (3G) mobile telecom-munication or IMT2000 [1–4]. Many operators commit to deploying UMTS and/or cdma2000-based 3G networks. Evolving from existing 2G networks, construction of an effective 3G net-work is critical for provisioning future mobile services. This article describes two important functionalities of 3G networks, mobility manage-ment and session managemanage-ment, and compares their design guidelines for UMTS and cdma2000. We focus on discussions and comparisons for the UMTS and cdma2000 packet-switched (PS) ser-vice domains. The reader is referred to [5] for interoperability between the circuit-switched (CS) service domains of UMTS and cdma2000.

The mobility management functions are used to keep track of the current location of a mobile user. There are three types of mobility: radio mobility, core network (CN) mobility, and IP mobility. Radio mobility supports handoff (i.e., radio link switching) of a mobile user during conversation. CN mobility (or link layer mobili-ty) provides tunnel-related management for

packet rerouting in the CN due to user move-ment. The IP mobility mechanism allows the mobile user to change its access point of IP con-nectivity without losing ongoing sessions. Net-work nodes such as the gateway GPRS support node (GGSN) and home agent (HA; their func-tions will be elaborated later) hide the mobility of the mobile user from the external network so that the corresponding user (communicating with the mobile user) is not notified.

Session management maintains the routing path for a communication session between a mobile user and the 3G CN, which provides packet routing functions, including IP address assignment, quality of service (QoS) setting, and so on. Details of mobility and session manage-ment mechanisms for UMTS and cdma2000 will be elaborated on later. In the remainder of this section we briefly describe the UMTS and cdma2000 network architectures, and explain the roles of different nodes regarding mobility and session management.

UMTS is evolved from the Global System for Mobile Communications (GSM) and General Packet Radio Service (GPRS). The network archi-tecture of UMTS (Release 99) is shown in Fig. 1 [6]. In this figure, the dashed lines represent sig-naling links, and the solid lines represent data and signaling links. The CN consists of two service domains, a CS service domain and a PS service domain. In the CS service domain, UMTS con-nects to the public switched telephone network (PSTN) through a mobile switching center (MSC). In the PS service domain, UMTS connects to the packet data network (PDN) through the serving GPRS support node (SGSN) and GGSN. The SGSN in the PS service domain is “equivalent” to the MSC in the CS service domain. The GGSN provides interworking with external PDNs, and is connected with SGSNs via an IP-based GPRS backbone network. Both SGSN and GGSN pro-vide session management functions in a data com-munication session. Mobility management is exercised between the SGSN and the home loca-tion register (HLR). The UMTS terrestrial radio access network (UTRAN) consists of Node Bs

A

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HUN

P

ANG

, N

ATIONAL

T

AIWAN

U

NIVERSITY

J

YH

-C

HENG

C

HEN

, N

ATIONAL

T

SING

H

UA

U

NIVERSITY

Y

UAN

-K

AI

C

HEN

, C

HUNGHWA

T

ELECOM

C

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., L

TD

.

P

RATHIMA

A

GRAWAL

, T

ELCORDIA

T

ECHNOLOGIES

ABSTRACT

This article describes the mobility and session management mechanisms for UMTS and cdma2000 packet-switched (PS) service domains, and compares the design guidelines for these two third-generation technologies. We first introduce the network architectures and proto-cols for UMTS and cdma2000, and then elabo-rate on the PS service domain’s mobility management, session management, and IP-level mobility mechanisms. Based on the mobility and session management mechanisms of the UMTS and cdma2000 PS service domains, an integrated architecture and intersystem roaming procedures are proposed to show the implementation feasi-bility of UMTS-cdma2000 IP-level interworking.

M

OBILITY AND

S

ESSION

M

ANAGEMENT

:

UMTS

VS

.

CDMA

2000

UMTS and cdma2000

are two major standards

for 3G mobile

telecommunication or

IMT2000. Many

operators commit to

deploy UMTS and/or

cdma2000-based 3G

networks. Evolving from

the existing 2G

networks, construction

of effective 3G network

is critical for provisioning

future mobile services.

(2)

(the UMTS term for base stations) and radio net-work controllers (RNCs) connected by an asyn-chronous transfer mode (ATM) network. The interface between a Node B and an RNC is Iub. The interface between two RNCs is Iur; it sup-ports soft handoff. An RNC connects to an MSC and an SGSN through the Iu-CS and Iu-PS inter-faces, respectively. These Iu interfaces are based on ATM technologies. The mobile station (MS) or user equipment connects with Node Bs through the radio interface Uu based on wideband CDMA (WCDMA) radio technology [7].

In UMTS, the Mobile Application Part (MAP) provides mobility management interfaces

between the SGSN and the GSM network nodes; for example, Gr for the HLR and Gs for the MSC/visitor location register (VLR). SGSNs and GGSNs communicate by using the GPRS Tun-neling Protocol (GTP) through the Gn interface [8]. Details of Gr, Gs, and Gn can be found in [6]. We will elaborate on GTP later.

Figure 2 shows the cdma2000 architecture [9]. In this figure, the base station controller (BSC) connects to the CN through the selection and distribution unit (SDU). Like UMTS, cdma2000 supports both the CS and PS service domains. The SDU distributes the CS traffic (e.g., voice) to the MSC via interfaces A1, A2, and A5.

■Figure 1. UMTS network architecture.

PSTN PDN HLR Gs Iu-CS Iu-PS Iu-PS Iu-CS Gc Gr Gn D GGSN

HLR: Home location register MS: Mobile station

PSTN: Public switched telephone network SGSN: Serving GPRS support node Node B: Base station

UTRAN: UMTS terrestrial radio access network

GGSN: Gateway GPRS support node MSC: Mobile switching center RNC: Radio network controller VLR: Visitor location register PDN: Packet data network Uu MS Node B Node B Iub Iub Iur

UTRAN Core network

MS

RNC MSC/VLR

SGSN RNC

■Figure 2. cdma2000 architecture.

MS

MS BTS

Radio network

AAA: Authentication, authorization, and accounting BSC: Base station controller

HA: Home agent MS: Mobile station PCF: Packet control function PDN: Packet data network

SDU: Selection and distribution unit

BTS: Base station transceiver system HLR: Home location register MSC: Mobile switching center PDSN: Packet data serving node

PSTN: Public switched telephone network VLR: Visitor location register

SDU PCF BSC SDU _SDU BSC BTS _A3/A7 A8/A9 A8/A9 A10/A11 A1/A2/A5 A1/A2/A5 A10/A11 PSTN PDN HLR AAA HA MSC/VLR PDSN

GGSN provides

interworking with

external PDN, and is

connected with SGSNs

via an IP-based GPRS

backbone network. Both

SGSN and GGSN provide

session management

functions in a data

communication session.

(3)

Specifically, the A1 interface supports call con-trol and mobility management between the MSC and BSC. The A2 and A5 interfaces support voice traffic and CS data traffic between the BSC and MSC, respectively. The MSC, VLR, and HLR functions are basically the same as those in UMTS, which will not be re-elaborated. The SDU distributes PS traffic to the packet control function (PCF) and then to the packet data serving node (PDSN). Interfaces A8 and A9 support PS data and signaling between the PCF and SDU, respectively. Interfaces A10 and A11 (i.e., the R-P interface) support PS data (which is delivered in sequence) and signaling between the PCF and PDSN. The generic rout-ing encapsulation (GRE) tunnel [10] with stan-dard IP QoS is used for data routing in A10, and A11 utilizes Mobile IP (MIP) [10, 11] based messages to convey the signaling information between the PCF and PDSN. The R-P interface (i.e., A10/A11 interface) also supports PCF handoff (inter- or intra-PDSN), described later.

A PDSN connects to one or more BSCs, which establishes, maintains, and terminates link layer sessions to the MS. The PDSN supports packet compression and packet filtering (see the Point-to-Point Protocol, PPP, description below) before the packets are delivered through the air inter-face. The PDSN provides IP functionality to the mobile network, which routes IP datagrams to the PDN with differentiated service support. A PDSN interacts with authentication, authorization, and accounting (AAA) [12] to provide IP authentica-tion, authorizaauthentica-tion, and accounting support for packet data services (note that user and device authentication functions are not provided in the PDSN1_{). The PDSN may act as an MIP foreign}

agent (FA) in the mobile network, which provides mobility management mechanisms with the MIP HA. The interfaces among the PDN nodes (i.e., PDSN, HA, AAA) follow Internet Engineering Task Force (IETF) standards.

From the above discussions, the network architectures of mobility and session manage-ment are basically the same for both UMTS and cdma2000. However, the protocols exercised on these network architectures are different. For example, cdma2000 uses IETF protocols (e.g., MIP and PPP) to support mobility and session management mechanisms. On the other hand, the UMTS protocols include SS7-based MAP and IP-based GTP. Moreover, one of the key 3G goals is to provide independence between the radio and core networks. As we shall see in the following sections, UMTS provides clear demar-cation between the RAN and CN. On the other hand, this goal is only partially achieved in cdma2000, where the MSC is still involved in radio resource allocation for a packet session.

The remainder of this article is organized as follows. The following section describes the pro-tocol stacks that support mobility and session management for cdma2000 and UMTS. Next, the mobility and session management mecha-nisms for cdma2000 and UMTS are presented and compared. Then IP mobility supported in cdma2000 and UMTS is elaborated on. The architecture and algorithms for UMTS-cdma2000 IP-level interworking are proposed. Finally, a summary is given.

PROTOCOL

STACKS

In this section we briefly discuss the lower layer protocols that support mobility and session man-agement and user data transport. Figures 3 and 4 illustrate the control planes and user planes for cdma2000 and UMTS networks, respectively.

The control plane carries out tasks for mobil-ity management, session management, and short message service. The mobility and session tasks in cdma2000 are based on the same lower layer protocols (i.e., IP-based protocols; Figs. 3a and 4a) for user data transportation except that the user data flow bypasses the link access control (LAC) layer. An advantage of the cdma2000 approach is that the same lower layer protocols can support both control and user planes.

In UMTS, the lower layer protocols support-ing these tasks in the control plane (Fig. 3b) are different from those in the user plane (Fig. 4b). The UMTS control plane protocols such as radio resource control (RRC) and RAN Application Part (RANAP) are utilized for signaling. Specifi-cally, the signaling path between MS and SGSN consists of an RRC connection between MS and UTRAN, and an Iu connection (“one RANAP instance”) between UTRAN and SGSN. The RRC protocol is responsible for reliable connec-tion between MS and UTRAN; that is, radio resources are managed by RRC exercised between MS and UTRAN. The Signaling Con-nection Control Part (SCCP) is responsible for reliable connection between UTRAN and SGSN. On top of SCCP, the RANAP protocol supports transparent non-access stratum (e.g., mobility management, session management) signaling transfer between MS and CN, which are not interpreted by the UTRAN.2_{By using these}

sig-naling protocols, efficient radio resource man-agement, session manman-agement, and mobility management can be achieved. In cdma2000 the task of radio resource management involves the MSC [10]. That is, the MSC instructs the BSC to assign the radio resource through the A1 inter-face. The details are for further study in cdma2000 specifications.

In UMTS, the PS domain services are sup-ported by the Packet Data Convergence Proto-col (PDCP) in the user plane. The PDCP contains compression methods needed to pro-vide better spectral efficiency for IP packet transmission over radio. In cdma2000, the head-er and payload compression mechanism is pro-vided by PPP between the MS and PDSN.

Both the UMTS radio link control (RLC) protocol (Figs. 3b and 4b) and cdma2000 LAC protocol (Figs. 3a and 4a) provide segmentation and retransmission services for user and control data. In addition, the cdma2000 LAC protocol supports the authentication functionality for wireless access, which is equivalent to GPRS transport layer authentication in UMTS. In the remainder of this section we elaborate on the protocols regarding IP support and tunneling.

PPP

In both the control and user planes for cdma2000, PPP is carried over the LAC/MAC and R-P tunnels (to be elaborated on later) and utilized to establish connection between the MS

1_{In cdma2000, user and}

device authentication functions are handled by the MSC/VLR/HLR. In UMTS, the SGSN directly interacts with the HLR to exercise user, device, and service authentication.

2_{In UMTS, the UTRAN}

utilizes the direct transfer procedure for handling mobility and session man-agement messages exchanged between the MS and SGSN. The direct transfer procedure relays these messages between the MS and SGSN by converting the message formats without interpret-ing the contents of the messages. In cdma2000 these messages are deliv-ered using a PPP session (between the MS and PDSN), where the RN is not involved in format translation of these mes-sages.

The control plane carries

out tasks for mobility

management, session

management, and short

message service. The

mobility and session

tasks in cdma2000 are

based on the same

lower layer protocols for

user data transportation

except that the user

data flow bypasses

the LAC layer.

(4)

and PDSN. The PPP provides a standard method for transporting multiprotocol datagrams (e.g., IP) over point-to-point links [13]. PPP encapsu-lates network layer datagrams over a serial com-munications link, and allows two network nodes to negotiate particular types of network layer protocols (e.g., IP) to be used during a session. In cdma2000, a PPP connection is equivalent to a packet data session, which is comparable to a UMTS PDP context below. After establishing a PPP connection, the MS registers with the MIP HA to indicate its presence and acquire a tem-porary home address (which is an IP address). The details will be given later.

In the UMTS control plane, no PPP/IP con-nection is established between the MS and

SGSN. Instead, signaling is carried over the RRC and Iu connections as previously described. The UMTS user plane provides two alternatives for IP services. For the scenario where IP is sup-ported by non-PPP lower layer protocols (specif-ically, PDCP in the MS and GTP-U in the GGSN), the IP address of an MS is either per-manently (statically) allocated or dynamically assigned by the GGSN. Alternatively, the MS’s IP address can be assigned by the network nodes outside the GGSN, where the IP protocol is sup-ported over PPP. This alternative is utilized when MIP is introduced to UMTS for global network roaming. In this case the MIP HA is responsible for the MS’s IP address assignment. That is, the MS sends the MIP registration

mes-■Figure 3. The control planes for a) cdma2000; b) UMTS.

(a) (b) MIP UDP IP PPP LAC MAC L1 LAC MAC L1 R-P PL MS GMM/ SM/ SMS RRC RLC MAC L1 RRC RLC MAC L1 RANAP SCCP Signaling bearer ATM AAL5 MS

ATM: Asynchronous transfer mode GGSN: Gateway GPRS support node MS: Mobile station

RLC: Radio link control

SGSN: Serving GPRS support node

GMM/SM/SMS:GPRS mobility management/session management/short message service

GTP-C: GPRS tunneling protocol - control plane UTRAN: UMTS terrestrial radio access network

AAL5: ATM adaptation layer type 5 MAC: Medium access control RANAP: Radio Access Network Application Part

RRC: Radio resource control

SCCP: Signaling connection control part UTRAN RANAP SCCP Signaling bearer L1 GMM/ SM/SMS GTP-C UDP/IP L2 ATM AAL5 SGSN L1 GTP-C UDP/IP L2 GGSN IKE: Internet key exchange

IPSec: IP security LAC: Link access control MIP: Mobile IP

PDSN: Packet data serving node PL: Physical layer

R-P: RN-PDSN interface

IP: Internet Protocol HA: Home agent

MAC: Medium access control MS: Mobile station

PPP: Point-to-Point Protocol RN: Radio network

UDP: User Datagram Protocol RN Link layer PL R-P PL IKE MIP IP/ IPSec IP UDP MIP IKE UDP PL IP/IPSec Link layer PPP PDSN HA

In both control and user

planes for cdma2000,

PPP is carried over the

LAC/MAC and R-P

tunnels and utilized to

establish connection

between the MS and

the PDSN. The PPP

provides a standard

method for transporting

multi-protocol datagrams

(e.g., IP) over

point-to-point links.

(5)

sage to the MIP HA via the PPP connection before obtaining a temporary home address.

T

UNNELING

P

ROTOCOLS

In both UMTS and cdma2000, tunneling is used to support various types of mobility. Figure 5 shows the tunneling approaches used in UMTS and cdma2000. In UMTS, the PDCP/RLC/MAC links between the MS and UTRAN support radio link mobility (i.e., handoff). The GTP tun-nels between the UTRAN and SGSN, and between the SGSN and GGSN are used to pro-vide serving RNC relocation [6] and CN mobili-ty, respectively. On the other hand, cdma2000 utilizes MIP, R-P, and LAC/MAC connections to support IP mobility, CN mobility, and radio mobility, respectively.

In this subsection we focus on the compari-son of CN tunneling implementations for UMTS

and cdma2000. GTP is utilized in both the user and control planes of UMTS. In the user plane, the GTP user plane (GTP-U) provides services for carrying user data packets between SGSNs and/or GGSNs, and between an SGSN and an RNC. In the control plane, the GTP control plane (GTP-C) provides GTP-U tunnel-related management and MS mobility-related manage-ment between SGSNs and GGSNs.

On the other hand, cdma2000 utilizes a MIP-based tunneling protocol to maintain the R-P connection between PCF and PDSN. We com-pare UMTS GTP and cdma2000 MIP-based tun-neling protocols below.

Tunnel Establishment — In UMTS the SGSN

initi-ates tunnel establishment through the Create_ PDP_Context_Requestmessage to the GGSN. In UMTS, every UMTS node (RNC, GGSN, or

■Figure 4. The user planes for a) cdma2000; b) UMTS.

ATM: Asynchronous transfer mode GGSN: Gateway GPRS support node IP: Internet Protocol

MS: Mobile station PPP: Point-to-Point Protocol SGSN: Serving GPRS support node

UTRAN: UMTS terrestrial radio access network

AAL5: ATM adaptation layer type 5 GTP-U: GPRS tunneling protocol - user plane MAC: Medium access control

PDCP: Packet Data Convergence Protocol RLC: Radio link control

UDP: User Datagram Protocol IP: Internet Protocol

HA: Home agent

MAC: Medium access control PDSN: Packet data serving node PL: Physical layer

R-P: RN-PDSN interface

IPSec: IP security LAC: Link access control MS: Mobile station PPP: Point-to-Point Protocol RN: Radio network PPP LAC MAC MS L1 LAC MAC RN (a) (b) L1 R-P PL PPP R-P PDSN PL Link layer PL IP IP/ IPSec HA PL Link layer Link layer PL IP IP/ IPSec IP PDCP RLC MAC MS L1 PDCP RLC MAC UTRAN L1 GTP-U UDP/IP AAL5 ATM IP, PPP GTP-U UDP/IP L2 GGSN L1 IP, PPP GTP-U UDP/IP AAL5 SGSN ATM GTP-U UDP/IP L2 L1

In this case, the MIP HA

is responsible for the

MS’s IP address

assignment. That is,

the MS sends the MIP

registration message to

the MIP HA via the PPP

connection before

obtaining a temporary

home address.

(6)

SGSN) is assigned an IP address. A UMTS GTP tunnel is identified with a tunnel endpoint iden-tifier (TEID), an IP address (i.e., the IP address of the receiving node), and a UDP port number. The TEID is locally assigned by the receiving side of a GTP tunnel, which unambiguously identifies the tunnel endpoint. The TEID values are exchanged between the tunnel endpoints using GTP-C messages.

In cdma2000 PCFs and PDSNs are assigned unique IP addresses. The PCF uses the MIP Reg-istration Requestmessage to initiate R-P con-nection establishment. In this MIP Registration Requestmessage, the Care-of-Address and Home Agent fields are set to the IP addresses of the PCF and PDSN, respectively. For each packet data bearer, the PCF assigns a PCF session identifier (PSI), which is set in the session-specific extension of the MIP Registration Request message. The PSI, PCF-IP-Address, and PDSN-IP-Address form a unique ID for each R-P connection.

Tunnel Release — The UMTS GTP tunnel release

procedure is initiated by either the SGSN or GGSN by issuing the Delete_PDP_Context_ Requestmessage. Details of this procedure can be found in [6]. Release of an R-P connection in the cdma2000 network is controlled by the PCF. The PCF initiates the R-P connection release proce-dure by sending an MIP Registration Request message to the PDSN with the lifetime field set to zero (to be elaborated on later). If the PDSN initi-ates release of an R-P connection, an MIP Regis-tration Updatemessage is sent from the PDSN to the PCF. Then the PCF sends the accounting related information to the PDSN through the nor-mal R-P connection release procedure.

MOBILITY AND

SESSION

MANAGEMENT

MECHANISMS

As we mentioned in the introduction, the network architectures of mobility and session management are basically the same for both UMTS and cdma2000. However, the protocols exercised on these network architectures are different. Table 1 compares the mobility and session management mechanisms of UMTS and cdma2000. This section will elaborate on mobility and session manage-ment mechanisms. These mechanisms are imple-mented in layer 3 protocols of the control plane; specifically, GPRS mobility management/session management/short message service (GMM/SM/SMS) for UMTS (Fig. 3b), and MIP (over UDP) and PPP for cdma2000 (Fig. 3a). We assume that the reader is familiar with generic mobility and session management operations (e.g., registration, authentication, and session activation, maintenance, and release). For more details the reader is referred to [1, 6, 14, 15]. We will focus more on the finite state machines of mobility man-agement and session manman-agement. This issue is seldom discussed in the literature.

M

OBILITY

M

ANAGEMENT

In UMTS, the base stations covered by an SGSN are partitioned into several routing areas (RAs). When the MS roams into a new RA, location update is performed. Mobility management in UMTS is carried out by the mobility management (MM) finite state machine. The MM finite state machines executed in the MS and SGSN are not the same. The details are given in [14]. In this article we only provide common parts of the MS

■Figure 5. Tunneling approaches for a) UMTS; b) cdma2000.

UTRAN SGSN GGSN PDCP/RLC/MAC MS GTP (a) (b) GTP Core network Radio network PDSN HA LAC/MAC MS R-P MIP PDN

■Table 1. A comparison of MM and SM between UMTS and cdma2000.

UMTS cdma2000

Protocol (MM) Mobile Application Part Mobile IP

Involved network nodes (MM) Serving GPRS support node and home Packet data serving node and

location register home agent

Protocol (SM) GPRS tunneling protocol Point-to-Point Protocol Involved network nodes (SM) Serving GPRS support node and gateway Packet data serving node

GPRS support node

In UMTS, the base

stations covered by an

SGSN are partitioned

into several routing

areas. When the MS

roams into a new RA,

location update is

performed. Mobility

management in UMTS is

carried out by the

Mobility Management

finite state machine.

(7)

and SGSN MM state machines (Fig. 6), which give necessary details to compare UMTS and cdma2000. In Fig. 6 three MM states are defined:

•In the PMM-DETACHED state, the MS does not yet perform a PS attach and is not known to the CN nodes (e.g., SGSN and HLR). When the MS attaches to the PS service domain (e.g., the MS powers on and performs a PS attach), the MM state moves into

PMM-CON-NECTED.

•In the PMM-IDLE state, the PS signaling connection does not exist; that is, the Iu connec-tion and RRC connecconnec-tion are released. The MS is attached to the PS service domain, and its location is known by the SGSN with accuracy at the RA level; that is, the RA of an MS is tracked by the SGSN. In this state the MS can be reached by paging, and no packet arrives at the MS. The MM state moves into PMM-CONNECTED if packets are exchanged between the SGSN and MS. The MM state moves into PMM-DETACHED if the PS detach procedure is executed.

•In the PMM-CONNECTED state, the PS signaling connection is established. Packets can only be delivered in this state. The SGSN tracks the MS with accuracy at the RA level, and the RNC is responsible for cell-level tracking. The MM state moves into PMM-IDLE if, for exam-ple, no packet is delivered for a period of time. The MM state moves into PMM-DETACHED if the PS detach procedure is executed.

In both the PMM-IDLE and

PMM-CON-NECTED states, two types of RA update are

performed. Normal RA update is performed when the RA of an MS has been changed. Peri-odic RA update is periPeri-odically initiated by an MS to report its “presence” to the network even if the MS does not move. A periodic RA update timer (PRUT) is maintained in the MS. The length of the PRUT is sent from the SGSN to the MS in the Routing Area Update Accept or Attach Accept message. The timer is unique to an RA. Upon expiration of a PRUT, the MS starts a periodic routing area update procedure. Corresponding to the PRUT, a mobile reachable timer (MRT) is maintained in the SGSN. An MRT is slightly longer than a PRUT, and both are stopped in the

PMM-CON-NECTED state and started in the PMM-IDLE

state. Details of mobility management proce-dures for UMTS Release 99 can be found in [6, 14]. The IP-level mobility for UMTS will be elaborated on below.

In cdma2000 the MIP protocol is utilized for mobility management.3_{Each PCF corresponds}

to a packet zone. An FA (PDSN) usually covers one or more packet zones. Location update is performed when the MS roams into a new PCF area. When detecting a change of packet zone in the same FA coverage (i.e., intra-PDSN move-ment), the MS registers by issuing an Origina-tion Messageto the BSC. Then the BSC establishes an A8/A9 connection to the new PCF. When an MS moves into the coverage area of a new FA (i.e., inter-PDSN movement), the MIP registration is activated. Thus, in addition to sending the Origination Message to the BSC, the MS performs MIP registration to the HA by issuing a Registration Request mes-sage to its FA. A lifetime value is included in this message. If the registration request is accept-ed, the HA may grant or change the lifetime value. The negotiated lifetime is included in the Registration Replymessage sent to the MS. The MS must perform the re-registration opera-tion before the lifetime expires. Details of cdma2000 mobility management procedures are elaborated on below.

To detach an MS from the cdma2000 network, the MS simply issues a Registration Request with zero lifetime period, which is equivalent to the Detach message in UMTS. As previously mentioned, the MS initiates re-registration before the lifetime expires, which performs the same function as periodic RA update in UMTS.

S

ESSION

M

ANAGEMENT

Both UMTS and cdma2000 adopt similar pipe concepts for session management. However, dif-ferent approaches are used to implement the packet data session between the MS and the gate-way node (i.e., GGSN in UMTS and PDSN in cdma2000). That is, a PPP connection represents a session pipe between the MS and the PDSN in cdma2000. A Packet Data Protocol (PDP) context represents a session pipe between the MS and the GGSN in UMTS, which consists of a PDCP nel between the MS and the RNC, a GTP-U tun-nel between the RNC and the GGSN, and a GTP-U tunnel between the SGSN and the GGSN. In UMTS, the PDP context [6, 14] provides information (specifically, PDP state for session management) to support packet delivery between an MS and the CN.

That is, to support packet routing in a data communication session, the PDP contexts must be created in the MS, GGSN, and SGSN. This action is called PDP context activation. Some properties of the PDP context (e.g., QoS profile) are not found in the PPP connection of cdma2000. Figure 7 illustrates the PDP state dia-gram for UMTS session management. Two states are defined in the diagram:

•In the INACTIVE state the data service is characterized for a certain PDP address (e.g., IP address) of an inactive subscriber. In this state, the PDP context contains no routing or mapping information related to that PDP address. There-fore, no data can be transferred. The state moves to ACTIVE when the PDP context is activated.

•In the ACTIVE state, the PDP context for the PDP address is activated in MS, SGSN, and GGSN. Specifically, the PDP context contains

■Figure 6.The UMTS mobility management state diagram (common parts in both the MS and SGSN). PS attach PS detach Detach PS attach reject, RAU reject PS signaling connection release PS signaling connection establish PMM-DETACHED PMM-IDLE _CONNECTED

PMM-3_{We note that MIP is}

appropriate for roaming management, but may not support efficient handoff (micro-mobility) manage-ment. The micro-mobility issue in cdma2000 is for further study.

Both UMTS and

cdma2000 adopt similar

pipe concepts for session

management. However,

different approaches are

used to implement the

packet data session

between the MS and

the gateway node.

(8)

mapping and routing information for delivering PDP protocol data units (PDUs) between the MS and GGSN for that particular PDP address. The state moves to INACTIVE when the PDP context is deactivated or the MM state moves to

PMM-DETACHED.

In cdma2000 a session pipe is established between the MS and the PDSN through a PPP connection. The session management for cdma2000 is similar to that for UMTS. That is, the session states are either open or closed. In the open state, a PPP connection is established between the MS and the PDSN. On the other hand, the logical pipe between the MS and the PDSN does not exist in the closed state. Fur-thermore, Fig. 8 shows the cdma2000 packet data service state diagram. Three states are defined in this diagram. The relationship between the transmission links (i.e., A8/A10 con-nections and PPP link) and the packet data ser-vice states is elaborated as follows:

•In the NULL/INACTIVE state, the MS pow-ers off, and the packet services are released. That is, the physical traffic channel, A8/A10 con-nections, and PPP link are released or not estab-lished. The state moves to the ACTIVE/

CONNECTED state when the MS powers on

and the packet data services are requested. •In the ACTIVE/CONNECTED state, a phys-ical traffic channel exists between the MS and the BSC. The PPP link between the MS and the PDSN, A8 connection between the BSC and the PCF, and A10 connection between the PCF and the PDSN are maintained.

The BSC for the MS maintains a packet data inactivity timer. This timer is reset when a non-idle data frame is sent or received. If the timer expires, the traffic channel is disconnected and the state moves to the DORMANT state. When the MS powers off, the state moves to the

NULL/INACTIVE state.

•In the DORMANT state, the PPP link between the MS and the PDSN, and A10 connection between the PCF and the PDSN are maintained. No physical traffic channel exists between the MS and the BSC, and A8 connection between the BSC and the PCF is released. When a packet is des-tined to the MS in the DORMANT state, the PDSN transmits this packet to the PCF through A10 connection. Then the PCF establishes A8 con-nection to the BSC. The BSC communicates with the MSC for packet session setup admission. After the MSC has approved the session request, the BSC pages the MS and establishes the traffic radio channel with the MS. At this point, the state moves to the ACTIVE/CONNECTED state. The

DOR-MANT to ACTIVE/CONNECTED state transition

may also occur when the MS initiates a packet call reactivation procedure (e.g., a packet data call reconnection is requested by the MS). When the MS powers off, the state moves to the NULL/

INACTIVE state.

From the above descriptions, it is clear that A10/A11 connection and the PPP link are main-tained during ACTIVE/CONNECTED and

DOR-MANT states. On the other hand, A8/A9

connection and traffic radio channel are only maintained in the ACTIVE/CONNECTED state. In the DORMANT state we do not expect imme-diate packet transmission, and the connection

between the MS and PCF is not established, so the radio resources are not wasted.

R

EMARKS ON

M

OBILITY AND

S

ESSION

M

ANAGEMENT

Mobility management and session management are closely related. For example, if the MS moves across a PCF zone in a cdma2000 network, the old A10/A11 connection is released and the new A10/A11 connection is established. The PPP connection remains the same. If the MS moves across a PDSN area, both PPP and A10/A11 connections are re-established between the MS and the PDSN through the new PCF. If the MS moves to a new PCF zone during a communica-tion session, the A8/A9 conneccommunica-tion also needs to be switched from the old PCF to the new PCF.

In UMTS, attachment may or may not be fol-lowed by PDP context activation. That is, the session management procedure is independent of the mobility management procedure. This approach provides flexibility for PS domain ser-vices. For example, an MS can retrieve the PS domain SMS without activating the PDP context. In cdma2000 MIP registration is always followed by access registration. The advantage of this approach is that the session establishment time can be reduced if a communication session is required immediately after the attach.

As a final remark, we note that UMTS sup-ports multiple PDP contexts (i.e., sessions) simultaneously for a communicating MS. On the other hand, in cdma2000 only one PPP connec-tion can be supported at a time between the MS and the PDSN.

■Figure 7. The UMTS PDP state diagram.

Activate PDP context Deactivate PDP context or MM state changes to PMM-DETACHED Inactive Active

■Figure 8. cdma2000 packet data service state transitions.

MS powers on Packet data inactivity timer expires

MS powers off (packet services are released) MS powers off

(packet services are released)

MS or network initiates packet call reactivation

NULL/ INACTIVE

(9)

IP MOBILITY

As we mentioned in the introduction, IP mobili-ty is different from link layer mobilimobili-ty solutions (e.g., GPRS tunneling protocol vs. MIP-based tunneling protocol). The link layer mobility man-agement function is used to manage tunnels between the CN nodes (e.g., between the SGSN and the GGSN, or between the PCF and the PDSN). On the other hand, the IP mobility mechanism allows the mobile user to change its point of IP connectivity without losing ongoing sessions.

In cdma2000, two types of IP mobility are supported: Simple IP and Mobile IP. In Simple IP, IP address mobility is supported within a PDSN, but is not supported when the MS moves to a new PDSN. The IP address is dynamically assigned by the local PDSN. Challenge Hand-shake Authentication Protocol (CHAP) [16] or Password Authentication Protocol (PAP) [17] is used for authentication between PDSN and a Remote Authentication Dial In User Servic (RADIUS) server. In Mobile IP, both intra-PDSN and inter-intra-PDSN IP address mobility are supported. In this case, the HA serves as the home router of an MS, which is responsible for location information maintenance and IP data-gram tunneling of the MS. The HA interacts with AAA to provide a security association to the FA (PDSN). Three kinds of AAAs are defined in cdma2000. The visited AAA forwards the AAA request from the PDSN to the home or broker AAA based on the MS network access identifier (NAI). The broker AAA provides secure AAA message delivery between the visited and home AAAs. The home AAA authenticates the PDSN request based on NAI. The home AAA also sup-ports QoS services based on an AAA profile (that contains a differentiated service policy and HLR record). FA challenge for authentication is performed through the MN-AAA challenge extension procedure [19]. Note that in Mobile IP neither CHAP nor PAP is used because these protocols result in longer initial setup time due to additional RADIUS traversal.

In Mobile IP the IP address of an MS is stati-cally or dynamistati-cally assigned by the HA. This persistent IP address is maintained when the MS moves around PDSNs. The location update pro-cedure is illustrated in the following steps (Fig. 9).

Step 1 — When an MS moves into a new

PDSN (MIP FA), the PPP connection is estab-lished between the MS and the PDSN. Then the agent discovery procedure is exercised. Specifical-ly, the MS sends Agent Solicitations and the PDSN transmits Agent Advertisements. Note that unlike the standard MIP environment, the MS is known by the PDSN/FA in cdma2000 during PPP connection setup. Thus, the Agent Solicitationsmessage can be eliminated for efficiency.

Step 2 — Upon receiving Agent

Adver-tisements, the MS initiates the registration procedure by sending an MIP Registration Requestto the PDSN.

Step 3 — The PDSN then stops sending Agent

Advertisementsand issues a RADIUS Access Requestto the home RADIUS server (via bro-ker servers if required) to perform FA challenge authentication. If authentication succeeds, the home RADIUS server sends the HA Request message to the HA, which includes the MIP reg-istration request of the MS. The HA validates the registration request and sends a response back to the home RADIUS server. Then the home RADIUS server acknowledges the PDSN by issuing the RADIUS Access Accept mes-sage.

Step 4 — The PDSN sends MIP

Registra-tion Replyto the MS, and the location update procedure is completed.

UMTS/GPRS provides IP mobility within a UMTS/GPRS network. However, IP mobility for inter-UMTS/GPRS networks (i.e., inter-GGSN areas) cannot be supported. Without the MIP-like solution, an MS must stay within a fixed GGSN area as long as the PDP context is acti-vated. Based on Third Generation Partnership Project (3GPP) Specification 23.923 [19], we use MIP to provide IP mobility for inter-UMTS/ GPRS networks through a three-stage evolution. Stage I allows mobile users to roam between wireless LAN and UMTS using MIP. Stage II supports IP mobility between two UMTS net-works where the GGSN is changed during a ses-sion. Stage III provides the same mechanism as stage II except that the SGSN and GGSN are combined into one node, which is similar to the cdma2000 solution in Fig. 9. Details of the three stages are described below.

In stage I, the current GPRS bearer transport is maintained to handle mobility within UMTS networks. MIP allows a user to roam between a wireless LAN and UMTS without losing an ongoing session (e.g., TCP), where the GGSN acts as an MIP FA. The access point name (APN) is used to find the desired GGSN, and the MS stays with this GGSN as long as the PDP context is activated. Since MIP is implemented at the application level, all MIP signaling mes-sages are transported over the UMTS/GPRS user plane. Figure 10 shows the MIP registration procedure in stage I, and the steps are described as follows:

■Figure 9. cdma2000 MIP location update procedure.

MS PDSN/FA

Home AAA/

home RADIUS server HA 1. PPP connection establishment

1. Agent Solicitation 1. Agent Advertisement

3. RADIUS Access Request

3. RADIUS Access Accept

3. HA Request 3. HA Answer 2. MIP Registration Request

(10)

Step I.1 — The standard GPRS attach

proce-dure is performed between the MS and the SGSN. Then the MS sends the Activate PDP Context Requestmessage to the SGSN. The APN, MIPv4FA, for MIP registration is included in this message.

Step I.2 — After receiving the Activate PDP

Context Requestmessage, the SGSN selects a suitable GGSN based on the APN. The selected GGSN must be equipped with MIP FA capabili-ty. Then the SGSN and GGSN exchange the Create PDP Context Request and Create PDP Context Responsemessage pair to set up the MS’s PDP context. Note that the GGSN is not responsible for IP address assignment, and the IP address field of the PDP context is not filled at this point.

Step I.3 — The Activate PDP Context

Responsemessage is sent from the SGSN to the MS to indicate that creation of PDP context is successful. At this point, the bearer level connec-tion is established.

Step I.4 — The GGSN (MIP FA) periodically

broadcasts the Agent Advertisement message to announce its presence. When the MS receives this message, step I.5 is executed.

Step I.5 — The MIP Registration Request

message is sent from the MS to the GGSN (MIP FA) across the UMTS/GPRS backbone through the user plane (i.e., the bearer level connection constructed in steps I.1–I.3). The GGSN (MIP FA) forwards the request to the HA. The HA assigns a home (IP) address to the MS and includes this address in the MIP Registration Replymessage. Then the message is sent from the HA to the GGSN (MIP FA).

Step I.6 — The GGSN (MIP FA) receives the

MIP Registration Replymessage from the HA and extracts the needed information (e.g., the home IP address of the MS) in this message. Then the MIP Registration Reply message is forwarded to the MS to indicate that the MIP registration procedure is complete.

Steps I.1–I.3 establish GPRS bearer level connection. Then on top of this connection, steps I.4-I.6 perform application level registra-tion (i.e., MIP registraregistra-tion). Also note that the IP address of the MS is assigned by the HA instead of by the GGSN.

In stage II, efficient packet rerouting is sup-ported. The CN is the same as that in stage I. During a session, the GGSN in the communica-tion path may be changed in two situacommunica-tions: • After inter-SGSN handoff, the GGSN is

changed to optimize the route.

• The GGSN may also be changed for load bal-ancing purposes.

Figure 11 illustrates the scenario for changing a GGSN after changing an SGSN. When chang-ing a GGSN, two tunnels are maintained between the new SGSN and the old GGSN, and between the new SGSN and the new GGSN (Fig. 11c). This will reduce the possibility of packet loss. Figure 12 shows the procedure for changing SGSNs and GGSNs in stage II.

Step II.1 — After an inter-SGSN handoff, the

new SGSN decides to change to an optimal GGSN. The Create PDP Context Request and Create PDP Context Response message pair is exchanged between the new SGSN and the new GGSN to create a new PDP context.

Step II.2 — The HA, GGSN (MIP FA), and

MS perform the standard MIP registration pro-cedure as described in steps I.4–I.6 of Fig. 10.

Step II.3 — After successful creation of the

new PDP context, a timer is set in the new SGSN. When the timer expires, the new SGSN instructs the old GGSN to delete the old PDP context by sending the Delete PDP Context Requestmessage. The old GGSN deletes the PDP context and responds to the new SGSN with a Delete PDP Context Response mes-sage. At this time, the GGSN handoff procedure is complete.

In stage III, the SGSN and GGSN will be combined into one node, called an Internet

■Figure 10. UMTS MIP registration: stage I.

MS SGSN GGSN/FA HA

I.1 Perform standard GPRS attach procedure I.1 Activate PDP Context Request

I.2 Create PDP Context Request

I.5 MIP Registration Request I.5 MIP Registration Reply I.2 Create PDP Context Response

I.3 Activate PDP context response I.4 Agent Advertisement I.5 MIP Registration Request

I.6 MIP Registration Reply

In Stage I, the current

GPRS bearer transport is

maintained to handle

mobility within UMTS

networks. MIP allows a

user to roam between a

wireless LAN and UMTS

without losing an

ongoing session,

where the GGSN

acts as a MIP FA.

(11)

GPRS support node (IGSN), and MIP is utilized to handle inter-IGSN handoff. The IGSN main functionality includes support of UMTS mobility management across UTRANs, interaction with the HLR, and provision of FA functionality. The details of the IGSN procedures are similar to those in Fig. 10 except that the SGSN and GGSN are merged into an IGSN, and will not be elaborated on in this article. In cdma2000, the Internet AAA functionality is utilized to pro-vide authentication, authorization, and account-ing. In UMTS, if the mobile operator and Internet service provider (ISP) are different, AAA is also required when MIP is introduced to provide intersystem IP mobility.4_{Figure 13}

illus-trates the network architecture for AAA support of MIP in UMTS. In this figure the MS roams to a visited UMTS network. After the MS has suc-cessfully performed UMTS-based authentication with the HLR in the home UMTS network, the AAA mechanism (between the visited and home AAAs) is initiated to authenticate the MS. Then the MS performs MIP registration to the HA in the home ISP to update the location of the MS. For more details of AAA operations in UMTS, the reader is referred to [19, 20].

UMTS AND CDMA2000 INTERWORKING

This section proposes an IP level mechanism for UMTS-cdma2000 interworking. Several Asian (e.g., Taiwan, China and Japan) and American countries have issued both UMTS and cdma2000 licenses to provide 3G services. In this case,

UMTS-cdma2000 interworking is essential to support global roaming between these two sys-tems. To achieve complete interoperability between UMTS and cdma2000, the interworking issues at the radio, CN, and IP levels must be addressed. For radio level interworking, a dual mode terminal that contains both UMTS and cdma2000 radio interfaces and the capability to perform real-time handoff among these two sys-tems is required. For CN interworking, the MM and PDP contexts have to be migrated between UMTS and cdma2000 networks. These issues are very complex and have not been effectively solved from the business and technical perspec-tives. We will only focus on the IP level inter-working that supports roaming between UMTS and cdma2000 networks. The radio and CN interworking issues are for further study, and will not be elaborated on in this article.

Based on the UMTS and cdma2000 mobility management mechanisms, we propose an archi-tecture and algorithms for UMTS-cdma2000 interworking to provide real-time IP multimedia services. Figure 14 shows the architecture that interconnects UMTS and cdma2000. In this fig-ure, the UMTS network connects to the IP net-work through the GGSN that acts as an MIP FA. Following the GPRS attach and PDP con-text activation procedures described above, the MS performs the MIP registration to its HA via the GGSN (MIP FA). The HA maintains the MS’s location information (e.g., the GGSN [MIP FA] address) and tunnels the IP datagrams to the MS. In the cdma2000 network, the PDSN is

■Figure 11. The UMTS scenario for changing SGSNs and GGSNs, stage II: a) before changing the SGSN; b) after changing the SGSN;

c) after construction of the second tunnel; d) after changing the GGSN. (a) Old GGSN New GGSN Old SGSN New SGSN (b) Old GGSN New GGSN Old SGSN New SGSN (c) Old GGSN New GGSN Old SGSN New SGSN (d) Old GGSN New GGSN Old SGSN New SGSN

■Figure 12. UMTS handoff in stage II.

MS

II.2 Agent Advertisement

II.3 Delete PDP Context Response II.3 Delete PDP Context Request II.1 Create PDP Context Response II.1 Create PDP Context Request

Old GGSN New GGSN _HA New SGSN

II.2 Perform standard MIP registration procedure

4_{In the IETF, the AAA}

working group has incor-porated requirements pro-vided by the Mobile IP working group.

(12)

a MIP FA, which communicates with the HA through the IP network as described previously. Both the UMTS and cdma2000 networks con-nect to the IP multimedia network through the MIP HA. That is, when a terminal in the IP multimedia network originates a multimedia call to the UMTS or cdma2000 MS by using proto-cols such as H.323 [21] and Session Initiation Protocol (SIP) [22], the voice packets are first delivered to the MIP HA. Then the MIP HA forwards these packets to the MS through the MIP FA (GGSN or PDSN).

When an MS in communication roams between cdma2000 and UMTS systems, intersys-tem roaming occurs. We first elaborate on the intersystem roaming message flow from cdma2000 to UMTS (Fig. 15).

Step A.1 — The MS performs the standard

attach and PDP context activation procedures to register with the UMTS network and set up the bearer communication. This step is the same as steps I.1–I.3 in Fig. 10. Then the AAA proce-dure is performed at the end of this step.

Step A.2 — After creating the PDP context,

the GGSN (MIP FA) issues the MIP Agent Advertisementmessage to the MS. Upon

receipt of the FA advertisement message, the MS performs the MIP registration to the HA via the GGSN (MIP FA). This step is the same as steps I.4 and I.5 in Fig. 10.

Step A.3 — The new FA (GGSN) and the old

FA (PDSN) exchange the MIP Binding Updateand MIP Binding Acknowledge mes-sage pair to perform data forwarding, which pro-vides smooth handoffs between the old and new FAs [11]. Then the PDSN (MIP FA) starts to forward the arriving datagrams to the GGSN (MIP FA). The forwarding operation is used to minimize packet loss during the intersystem roaming procedure.

Step A.4 — The GGSN (MIP FA) responds to

the MS’s MIP registration request by sending the MIP Registration Reply message. This step is the same as step I.6 in Fig. 10.

Step A.5 — Finally, the PDSN performs

stan-dard cdma2000 packet data session clearing operation and de-registration procedure with the BSC/PCF and AAA.

The intersystem roaming message flow from UMTS to cdma2000 is illustrated in Fig. 16.

Step B.1 — The standard cdma2000 access

registration procedure is performed. Then the

■Figure 13. The network architecture for AAA support in UMTS.

Visited AAA

SGSN/GGSN/FA Visited UMTS network

HA Home ISP

Home UMTS network UTRAN

MS HomeAAA

HLR Internet

■Figure 14. UMTS and cdma2000 interworking.

RNC UTRAN Node B BCF+ PCF cdma2000 access network BTS SGSN HA IP network cdma2000 UMTS HSS/ HLR GGSN /FA AAA IP multimedia network PDSN /FA

Based on the UMTS and

cdma2000 mobility

management

mechanisms,

we propose an

architecture and

algorithms for

UMTS-cdma2000 interworking

to provide the real-time

IP multimedia services.

(13)

PDSN (MIP FA) and MS exchange the Agent Solicitationand Agent Advertisement to perform the standard MIP agent discovery oper-ation. This is the same as step 1 in Fig. 9.

Step B.2 — Upon receipt of an Agent

Adver-tisement, the MS performs the MIP registra-tion to the PDSN (MIP FA) as described in step 2 of Fig. 9.

Step B.3 — The PDSN (MIP FA), AAA, and

HA perform standard authentication and MIP registration procedures. This step is the same as step 3 of Fig. 9.

Step B.4 — The new FA (PDSN) and old FA

(GGSN) exchange the MIP Binding Update and MIP Binding Acknowledge message pair as described in step A.3 of Fig. 15.

Step B.5 — Through MIP Registration

Reply, the PDSN (MIP FA) informs the MS that the MIP registration is successful. This step is the same as step 4 in Fig. 9.

Step B.6 — When the MRT (discussed earlier)

expires, the implicit detach procedure is per-formed by the SGSN. At this point, the PDP contexts of this MS are also deactivated at the GGSN and SGSN.

SUMMARY

This article describes mobility and session man-agement mechanisms for UMTS and cdma2000, and compared the design guidelines for these two 3G technologies. We first introduce the net-work architectures and protocol stacks for UMTS and cdma2000. Then we elaborate on UMTS and cdma2000 mobility management and session management, and discuss the differences of the design guidelines between these two sys-tems. Furthermore, the IP mobility mechanisms implemented in UMTS and cdma2000 are demonstrated and compared. Based on the UMTS and cdma2000 mobility management

mechanisms, we propose an architecture and intersystem roaming procedures for UMTS-cdma2000 IP-level interworking. In this approach, the mobile user can roam between UMTS and cdma2000 systems without losing an ongoing communication session.

A

CKNOWLEDGMENTS

Ai-Chun Pang’s work was sponsored in part by the National Science Council under contracts NSC92-2213-E-002-049, NSC92-2213-E-002-092 and NSC91-2213-E-002-130, Intel, and Microsoft. Jyh-Cheng Chen’s work was spon-sored in part by MOE Program for Promoting Academic Excellent of Universities under grant number 89-E-FA04-1-4, National Science Coun-cil under grant number 92-2213-E-007-019, and Industrial Technology Research Institute under contract 2F-9303-02.

R

EFERENCES

[1] Y.-B. Lin and I. Chlamtac, Wireless and Mobile Network

Architectures, Wiley, 2001.

[2] M. Zeng, A. Annamalai, and V.-K. Bhargava, “Harmo-nization of Global Third-Generation Mobile Systems,“

IEEE Commun. Mag., Dec. 2000, pp. 94–104.

[3] J.-F. Huber, D. Weiler, and H. Brand, “UMTS, the Mobile Multimedia Vision for IMT-2000: A Focus on Standardiza-tion,” IEEE Commun. Mag., Sept. 2000, pp. 129–36. [4] D.-N. Knisely et al., “Evolution of Wireless Data Services:

IS-95 to cdma2000,” IEEE Commun. Mag., Oct. 1998, pp. 140–49.

[5] S. Kim et al., “Interoperability between UMTS and cdma2000 Networks,” IEEE Wireless Commun., Feb. 2003. [6] 3GPP, Tech. Spec. Group, Svcs. and Sys. Aspects,

“Gen-eral Packet Radio Service (GPRS); Service Description,” Tech. Spec. 3G TS 23.060 v. 5.4.0 (2002-12)}, 2002. [7] H. Holma and A. Toskala, Eds., WCDMA for UMTS,

Wiley, 2000.

[8] 3GPP, Tech. Spec. Group, Core Network, “GPRS Tunnel-ing Protocol (GTP) across the Gn and Gp Interface,” Tech. Spec. 3G TS 29.060 v. 5.4.0 (2002-12), 2002. [9] 3GPP2, “Wireless IP Network Standard,” 3GPP2

P.S0001-A-1 v. 1.0 (2001-07), 2001.

[10] 3GPP2, “3GPP2 Access Network Interfaces Interoperability Specification,” 3GPP2 A.S0001-A (2000-11), 2000.

■Figure 15. Roaming from cdma2000 to UMTS.

MS SGSN GGSN/FA HSS/HLR HA PDSN/FA AAA BSC/PCF

A.2. Agent Advertisement

A.1. Perform standard GPRS attach and PDP context activation procedures, and AAA procedure

A.4. MIP Registration Reply A.2. MIP Registration Request

A.2. MIP Registration Request

A.3. MIP Binding Update A.3. MIP Binding Acknowledge A.3. Forward PDUs

A.2. MIP Registration Reply

A.5. Perform standard cdma2000 packet data session clearing operation

and deregistration procedure

After creating the PDP

context, the GGSN

(MIP FA) issues the MIP

Agent Advertisement

message to the MS.

Upon receipt of the FA

advertisement message,

the MS performs the

MIP registration to the

HA via the GGSN

(MIP FA).

(14)

[11] C. E. Perkins, Mobile IP: Design Principles and

Prac-tices, Addison-Wesley, 1998.

[12] 3GPP2, “IP Network Architecture Model for cdma2000 Spread Spectrum Systems,” 3GPP2 SC.P000X v. 1.0.0 (2000-10), 2000.

[13] W. Simpson, The Point-to-Point Protocol (PPP), IETF RFC 1661, July 1994.

[14] Y.-B. Lin et al., “Mobility Management: From GPRS to UMTS,” Wireless Commun. and Mobile Comp., vol. 1, no. 4, 2001, pp. 339–60.

[15] Y.-B. Lin et al., “All-IP Approach for Third Generation Mobile Networks,” IEEE Network, vol. 16, no.5, 2002, pp. 8–19.

[16] W. Simpson, “PPP Challenge Handshake Authentica-tion Protocol (CHAP),” IETF RFC 1994, Aug. 1996. [17] B. Lloyd and W. Simpson, “PPP Authentication

Proto-cols,” IETF RFC 1334, Oct. 1992.

[18] C. Perkins and P. Calhoun, “Mobile IPv4 Challenge/ Response Extensions,” IETF RFC 3012, Nov. 2000. [19] 3GPP, Tech. Spec. Group, Svcs. and Sys. Aspects,

“Combined GSM and Mobile IP Mobility Handling in UMTS IP CN,” Tech. rep. 3G TR 23.923 v. 3.0.0 (2000-05), 2000.

[20] J.-H. Park, “Wireless Internet Access for Mobile Sub-scribers Based on the GPRS/UMTS Network,” IEEE

Com-mun. Mag., Apr. 2002, pp. 38–49.

[21] ITU, “Packet-Based Multimedia Communications Sys-tems,” Tech. rep. ITU-T H.323, v. 3, 1999.

[22] M. Handley et al., “SIP: Session Initiation Protocol,” IETF RFC 2543, Aug. 2000.

B

IOGRAPHIES

AI-CHUNPANG(acpang@csie.ntu.edu.tw) received B.S., M.S., and Ph.D. degrees in computer science and information engineering from National Chiao Tung University (NCTU) in 1996, 1998 and 2002, respectively. She joined the Depart-ment of Computer Science and Information Engineering, National Taiwan University, Taipei, Taiwan, as an assistant professor in 2002. Her research interests include design and analysis of personal communications services net-works, mobile computing, voice over IP, and performance modeling.

JYH-CHENGCHEN(jcchen@cs.nthu.edu.tw) is an associate professor in the Department of Computer Science and the Institute of Communications Engineering, National Tsing

Hua University, Hsinchu, Taiwan. Prior to joining National Tsing Hua University as an assistant professor, he was a research scientist at Telcordia Technologies (formerly Bell-core), Morristown, New Jersey, from August 1998 to August 2001. He received his Ph.D. degree from the State University of New York at Buffalo in 1998. He is coauthor of the book IP-Based Next-Generation Wireless Networks (Wiley, 2004).

YUAN-KAICHEN(ykchen@cht.com.tw) received his M.S., and Ph.D. degrees in computer science and information engi-neering from NCTU, Hsinchu, Taiwan, R.O.C., in 1989, 1991, and 2003. In 1991 he joined the Telecommunication Labora-tories, Chunghwa Telecom Co., Ltd. where he was involved in the implementation of SONET/SDH multiplexers and the development of an ADSL transceiver. In 1998 he worked in the 3G trial team. Since then he has been involved in the design of the radio access network, mobile packet-switched data and multimedia services, and the study of mobile net-work evolution. His research interests include design and analysis of PCS networks, 3G networks, wireless Internet, mobile computing, and performance modeling.

PRATHIMAAGRAWAL[F] (pagrawal@research.telcordia.com) is assistant vice president of the Network Systems Research Laboratory and executive director of the Mobile Network-ing Research Department at Telcordia Technologies, Morris-town, New Jersey, where she has worked since 1998. She was head of the Networked Computing Research Depart-ment in AT&T/Lucent Bell Laboratories in Murray Hill, New Jersey, where she worked from 1978 to 1998 in various capacities. Concurrently, for several years she was an adjunct faculty member of the Electrical and Computer Engineering Department at Rutgers University. Her research interests are computer networks, and mobile and wireless computing and communication systems. She has published over 150 papers and holds 30 patents. She was the recipi-ent of the Distinguished Member of Technical Staff Award of AT&T Bell Laboratories in 1985, the Telcordia CEO Award in 2000, and the 2001 SAIC Executive Science and Technology Council Publication Award. She is a member of the ACM. She was the recipient of the IEEE Computer Soci-ety’s Distinguished Service Award in 1990 and an IEEE Third Millennium Medal in 2000. She chaired the IEEE Fel-low Selection Committee from 1998 to 2000. She received her Ph.D. degree in electrical engineering from the Univer-sity of Southern California in 1977.

■Figure 16. Roaming from UMTS to cdma2000.

MS BSC/PDF PDSN/FA AAA HA GGSN/FA SGSN HSS/HLR

B.1. Perform standard cdma2000 access registration procedure B.1. Agent Solicitation