Network-Initiated Handover Based on IEEE 802.21 ... - IEEE Xplore

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Dept. of Computer Science and Engineering,. Pohang ... Samsung Electronics Co., LTD. Korea. Email: {euiseok.hwang, yd.chung}@samsung.com. Abstract— In ...

Network-initiated Handover Based on IEEE 802.21 Framework for QoS Service Continuity in UMTS/802.16e Networks Joo-Young Baek, Deok-Jin Kim, and Young-Joo Suh

Eui-Seok Hwang and Young-Don Chung

Dept. of Computer Science and Engineering, Pohang University of Science and Technology (POSTECH), Korea Email: {nalsunia, dj0152, yjsuh}@postech.ac.kr

Telecommunication and Network R&D Center Samsung Electronics Co., LTD. Korea Email: {euiseok.hwang, yd.chung}@samsung.com

Abstract— In the next-generation networks, guaranteeing QoS is one of the important factors, which allows QoS supportable networks such as UMTS and 802.16e to be deployed together. Under such networks, a mobile node (MN) with multiple interfaces demands for the QoS service continuity during a handover. The 802.21 framework enables MNs to freely move in multiple networks. However, supporting QoS service continuity remains as a problem to be solved. In this paper, we propose a network-initiated handover based on the 802.21 framework to provide the QoS service continuity in UMTS/802.16e networks. To support the QoS service continuity, we design a detailed handover procedure that consists of three steps; QoS Measurement, Passive Reservation, and Activation. Through our performance evaluation, we show that the proposed handover scheme provides the QoS service continuity of MNs during a handover in terms of guaranteed data rates and latency.

I. I NTRODUCTION In the next-generation mobile networks, where diverse network technologies coexist and are integrated, users can experience a great variety of end-user services. Under this circumstance, one of the main issues for the next-generation mobile networks is offering users seamless multimedia services that require various QoS constraints during a handover across heterogeneous access networks. There are several wireless technologies that are trying to support QoS by defining service classes and designing the control mechanisms. Among them, the Universal Mobile Telecommunications System (UMTS) and IEEE 802.16e can be classified into such technologies. UMTS defines four service classes and the session negotiation procedure through the PDP context, and 802.16e defines five service classes and session negotiations through DSx messages. Moreover, UMTS supports universal roaming and 802.16e can provide high data rates and mobility up to 60km/h in 1 kilometer cell coverage. Even though UMTS and 802.16e can be dominant wireless networks, UMTS supports a limited data rate up to 2 Mbps and 802.16e provides smaller coverage than UMTS. Thus, an integration of both networks can be represented as one of the models for the next-generation networks. Many researches have been studied for the coexistence of different wireless technologies as a general network model

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in the next-generation networks. The research trends can be divided into two groups: One trend [1, 2] focuses on the integration of distinct networks, while the other trend [3-5] focuses on the supportability of mobility in inter-working networks. The former research trend has been studied for a long time, and there are many research results with two integration types, tight integration and loose integration. On the contrary, the latter trend has only recently began to be studied. Especially the mobility issue with the 802.21 framework has been considered as a reasonable solution in the nextgeneration networks, since the integration of networks such as UMTS/802.16e demands a robust, reliable, and efficient framework. IEEE 802.21 Media Independent Handover (MIH) Service Working Group is developing a standard [6] for handovers without being tied into the features or specifics of particular radio networks. In the IEEE 802.21 standard, Media Independent Handover Functions (MIHFs) are defined to provide a generic link layer, and a MN that has MIHF which can move across heterogeneous access networks such as 3G (UMTS), 802.16e, and WLAN. In this paper, we focus on the mobility issue with the 802.21 framework in the UMTS/802.16e networks. The current MIH based mobility over the UMTS/802.16e has mainly focused on providing a seamless mobility environment through exchanging MIH messages. In addition, the QoS service continuity during a handover is also an important factor, since the importance of QoS has recently been increased due to the rapid growth of QoS sensitive applications such as VoIP and video streaming. However, existing researches for the QoS service continuity in the UMTS/802.16e have not been active, even though UMTS and 802.16e provide distinct QoS classes and QoS control mechanisms. In this paper, we propose a handover mechanism for QoS service continuity by utilizing the resource information on networks based on the 802.21 framework in UMTS/802.16e networks. II. I EEE 802.21 S TANDARD A. Basic Components The IEEE 802.21 standard defines a MIH middleware architecture and a cross layer communication protocol. The 802.21

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framework is intended to provide methods and procedures that enable transparent service continuity across heterogeneous networks. The main component of the 802.21 framework is the Media Independent Function (MIHF) that supports a unified interface to the upper layers, which is independent of the underlying access technologies. MIHF provides three services - Media Independent Event Service (MIES), Media Independent Command Service (MICS), and Media Independent Information Service (MIIS). MIES reports local and global events to deliver the dynamic changes in link characteristics such as link quality and BER, to the upper layers. MICS provides sending commands from higher layers to lower layers to manage and control link behaviors. MIIS provides a framework and mechanism for the MIHF entity to discover the available neighboring network information within a geographic area. Assume that there is a MN which has multiple interfaces in the 802.21 framework. When the channel quality of the MN is about to become poor in the current network, MIES delivers a triggered event to indicate the status of the physical and link layers. The events include Link Parameter Change, Link Down, Link Going Down, etc. If a communication protocol receives the ”Link Going Down” event from the link layer through MIES, then it can gather the information of neighbor networks through MIIS to find the most proper network to handover. Next, the upper layer commands to conduct a handover to the selected network through MICS. Through this process, the MN executes a handover based on the 802.21 framework. B. Terminal-initiated handover vs Network-initiated handover Here, we introduce the terminal-initiated handover and network-initiated handover which have been defined in the 802.21 standard [6]. The main difference between the terminalinitiated handover and the network-initiated handover depends on which entity mainly controls handovers. The MN itself decides the execution of a handover in the terminal-initiated handover, while the serving network of the MN decides the execution of handover in the network-initiated handover. For terminal-initiated handover, the 802.21 standard defines MIH messages to collect the status of the current wireless device and the preparation of a handover. The defined MIH messages are as follows: • MIH Link Parameters Report is generated by MIHF when the current link parameters such as the speed of the link, QoS, or BER, have crossed a threshold set. • MIH Get Information Request/Response are exchanged between the MN and the MIIS server. When the MN comes to need a handover, the MN sends the MIH Get Information request to retrieve its neighboring network information to the MIIS server. Then, the MIIS server sends a response which includes the neighboring network information. • MIH Link Going Down is delivered from the lower layer through MIHF to notify that the current link will be down, and the MN starts to activate the new interface to

TABLE I Q O S M APPING 802.16e

Class

QoS Constraints

UMTS

UGS / ertPS

Conversational

rtPS

Streaming

nrtPS

Interactive

BE

Background

Minimum Reserved Rate

Guaranteed bit rate

Maximum Latency

Transfer Delay

Jitter

Transfer Delay Variation

BER

Lower bit error rate

which the MN decides to connect based on the received neighboring network information. On the other hand, for network-initiated handover, the 802.21 standard defines MIH messages to gather the required QoS information from the MN and check the availability of supporting the required QoS of the MN from the neighbor networks. The defined MIH messages are as follows: • MIH Get Information Request/Response are exchanged between the serving network and the MIIS server, to retrieve the neighboring network information of the MN. • MIH Net HO Candidate Query Request/Response are exchanged between the serving network and the MN. The serving network sends a request to retrieve the requested QoS constraints from the MN by the Query Resource List field in the request message. Moreover, the MN responds to the required QoS constraints and value through the Requested Resource Set filed in the response message. • MIH N2N HO Query Resource Request/Response are exchanged between the serving network and the neighbor networks. After receiving the required QoS constraints from the MN, the serving network requests the availability to support the required QoS to each neighbor network, and the neighbor networks send a response, which includes the availability of the QoS by measuring available resources. To provide QoS continuity, it is critical to evaluate the availability to support the required QoS of an MN from each of the neighbor networks. However, it is difficult to obtain the resource information and QoS constraints of neighbor networks from the perspective of the MN. Thus, in general to support QoS service, the network-initiated handover performs better than the terminal-initiated handover. But, the standard [6] does not specify the details of some QoS related types such as Query Resource List and Requested Resource Set which are exchanged between the MN and the networks (including the serving network and its neighbor networks). Moreover, there is no method to measure QoS between UMTS and 802.16e networks which use different QoS constraints. Thus, in this paper, we supplement unclear facts on QoS related information and newly design a network-initiated handover for QoS service continuity based on the 802.21 framework. III. T HE P ROPOSED S CHEME Based on the 802.21 framework, we introduce how to operate the network-initiated handover to effectively provide guaranteed QoS service between UMTS and 802.16e networks.

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TABLE II MIH PASSIVE R ESERVATION M ESSAGES Network Detection

Variable

Class of flow(s) Requested Resource List

MIHF

Variable

MAC-S (UMTS)

Serving Network MAC-C (WiBro)

RNC

SGSN

Candidate Network

MIHF

RAS

ACR

MIIS Server

MIHF

Link_Parameters_Report.indication MIH_Link_Parameters_Report INDICATION (LinkType = UMTS) MIH_Link_Parameters_Report.indication

MN’s MAC Address Information Result of reservation

Periodic Report

MIH_Get_Information Request MIH_Get_Information Response

MIH_Net_HO_Candidate _Query Request MIH_Net_HO_Candidate _Query Response

Reservation Holding Time

Before a handover, MIHF of a MN periodically receives the link status information with Link Parameter Report indication from the current link layer and then delivers the information to its serving network. This periodic report process continues until a handover occurs. When the serving network decides that a MN’s handover is needed, the proposed scheme is activated. Fig. 1 shows the proposed handover scheme, which consists of the following three steps: • QoS Measurement: The serving network of the MN checks the QoS service capability of neighboring networks with the requested QoS constraints of the MN. • Passive Reservation: The serving network reserves the network resources for the MN to maintain the QoS capability of the network until the MN moves. • Activation: During the L2 connection establishment, the MN activates the reserved resources by operating the session initiation process depending on the target network mechanism. A. QoS Measurement Step During this step, the serving network checks whether or not the neighbor networks can support the QoS constraints that the MN wants to guarantee, based on the 802.21 framework. But, there are some limitations for efficient QoS measurement in the existing 802.21 framework. Thus, we considered two components in this step. First, we consider the specific QoS information which is exchanged between the MN and the serving network, as well as the serving network and the neighbor networks. Even though the required or supportable QoS information is an important factor for the QoS service continuity, the 802.21 standard merely defines the name of types, not any specific type of fields. Thus, we have specified the detail QoS information which is included in three types; Query Resource List, Requested Resource List, and Available Resource Set. The QoS information corresponds to {class, bandwidth, delay, jitter, BLER}, which can be the information of each flow, the aggregate information of multiple flows, or the remaining resource information of neighbor networks. Second, it is necessary to consider the QoS mapping between UMTS and 802.16e after gathering the required or supportable QoS information. The reason is that UMTS and 802.16e have defined their own traffic classes to differentiate service quality or priority, and each traffic class has its own mandatory QoS constraints. However, there is no criteria on

HO Init. and Prep.

MIH_N2N_Passive_ Session_ Reserve Response

Parameters MN’s MAC Address Information

MIH_N2N_HO_Query_Resources Request

Step 1 QoS Measurement

Qos Mapping MIH_N2N_HO_Query_Resources Response Target Decision MIH_N2N_Passive_Session _Reserve Request Passive DSA-REQ

Step 2 Passive Reservation

Passive DSA-RSP MIH_N2N_Passive_Session _Reserve Response MIH_Net_HO_Candidate _Commit Request Establish L2 Connection

HO Exec.

MIH_N2N_Passive_ Session_ Reserve Request

Length

MIH User

Active DSA-REQ

Step 3 Activation

Active DSA-RSP Establish L3 Connection MIH_Net_HO_Candidate _Commit Response Packet Flows on WiBro Network

HO Completion

Type

Mobile Node UP Entity

MIH_N2N_HO_Complete.Request MIH_N2N_HO_Complete.Response

Fig. 1.

The proposed handover scheme

how to handle the required QoS of the on-going flows between 802.16e and UMTS. To resolve the management of QoS classes and constraints between UMTS and 802.16e, we design a QoS mapping table. Table I shows the QoS mapping table between IEEE 802.16e and UMTS, where traffic classes and QoS constraints of 802.16e are mapped with the correspondent traffic classes and QoS constraints of UMTS, respectively. Based on the two components, the QoS measurement step works as follows. In Fig. 1, when the serving network needs the handover of the MN, it collects the required QoS information from the MN by Query Resource List/Requested Resource List in the MIH Net HO Candidate Query Request/Response messages. Then, the serving network delivers the collected QoS information to each neighbor network through MIH N2N HO Query Resource Request message. After that, the MIHF of each neighbor network translates the information of the received Query Resource List from the serving network into its own QoS class and constraints through the QoS mapping table. Next, MIHF delivers the translated information to the resource management function of each network. The resource management function is generally located in SGSN and GGSN in UMTS, while it is located in RAS and ACR in IEEE 802.16e. Finally, the resource management function evaluates the availability with the received QoS constraints of the MN, and each neighbor network sends the result of the requested QoS supportability by Available Resource Set in the MIH N2N HO Query Resources Response message.

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CN 1.6

MIIS Server

B

A

C

1.4

SGSN ACR1

Node B RAS1 Node A

B

UMTS

1.2

ACR2

Data Rates (Mbps)

RNC

RAS2

UMTS

802.16e (RAS2)

1.0 0.8

802.16e (RAS1)

0.6 0.4

C

Proposed Scheme Normal Sceheme

0.2

Fig. 2.

Simulation Topology

0.0 50

100

150

200

Time (sec)

B. Passive Reservation Step

C. Activation Step Once the passive reservation has been completed by receiving MIH N2N Passive Session Reserve response message from the selected network, the serving network sends a

(a) VoIP flow

500 Proposed Scheme Normal Scheme

400

Latency (msec)

Once the target decision is made by the serving network after receiving responses from all neighbor networks, the MN performs a handover to the selected neighbor network. However, a time difference exists between the time when the QoS checking is executed in the neighbor networks and the time when the real handover of the MN is executed. The time difference can be small or large, since there are many uncertain factors in wireless networks. For example, burst flows of existing nodes can be generated or many nodes may move into the selected network during the time difference. In this case, the MN cannot receive the QoS service continuity in the selected network even though the selected network has been chosen through QoS measurement. It means that the exchange of the QoS information and the QoS measurements may be useless. Therefore, we design a passive reservation scheme to guarantee the QoS capability of the selected network. As shown in Fig. 1, the serving network performs a passive reservation scheme after the target decision. To perform the passive reservation scheme, we have defined new MIH message, called MIH N2N Passive Session Reserve, and this message includes the received QoS information from the MN, which is summarized in Table II. The serving network sends a MIH N2N Passive Session Reserve request message to the MIHF of the selected network to reserve the QoS capacity for the MN. MIHF performs a resource reservation by sending Passive DSA-REQ/PDP Context messages, which are made from the original DSA-REQ/PDP Context messages by utilizing the reserved field to notify the passive reservation to RAS/RNC. After receiving the passive reservation messages, the UMTS/802.16e networks have reserved resources at a soft state. It means that the passive reservation is maintained for a certain time, so that the resource reservation can be released to be used for other MNs, if the MN does not move to the selected network before the timer expires. Thus, the MN can receive the QoS service continuity, if the handover is completed within the timer value.

300 802.16e (RAS1)

200 UMTS

100

802.16e (RAS2) UMTS

0

C

B

A

0

10000

20000

30000

40000

50000

Sequence Number

(b) Real-time flow Fig. 3.

The First Scenario Performance

MIH Net HO Candidate Commit request message to inform the selected network information to the MN. Next, the MN begins to establish an L2 connection with the selected network, during which, the MN sends an Active DSA-REQ/PDP Context Request message to use the reserved resources for ongoing flows. When the L2 connection has been completed, the L3 connection begins and then the MN receives the service from the selected network and the HO complete stage finishes by exchanging a MIH N2N HO Complete message between the previous serving network and the current serving network (the selected network). IV. P ERFORMANCE E VALUATION In this section, we study the performance of the proposed scheme with NS-2. The simulation topology is shown in Fig. 2, where a MN moves in the heterogeneous networks composed of multiple 802.16e networks and the UMTS network. According to the topology, the MN experiences different available networks, and the simulation period can be divided into three sections; A, B, and C. In section A, the accessible network

2160

1.6 B

C

1.4

Data Rates (Mbps)

802.16e (RAS 2)

UMTS

1.2 1.0 0.8 0.6

802.16e (RAS 2) 0.4 Full Scheme Partial Scheme

0.2 0.0 100

120

140

160

180

200

Time (sec)

Fig. 4.

The Second Scenario Performance

is only UMTS, and 802.16e(RAS1) and 802.16e(RAS2) can be included into the accessible networks in section B and C, respectively. We assume that the 802.16e network generally has higher preference than UMTS due to the cheaper cost and higher data rates. Further, the available resources for supporting QoS service in each of the multiple 802.16e networks are different, so we assume that RAS1 has low remaining capabilities that do not provide the guaranteed QoS service to the MN. On the other hand, RAS2 has enough remaining capabilities to support guaranteed QoS service to the MN. We have performed our simulation study with two scenarios; to show the performance of the QoS measurement step (through the first scenario) and the passive reservation and activation steps (through the second scenario). Basically, all the entities of the simulation have MIHF of the 802.21 framework. In these studies, we use the terminal-initiated handover scheme based on the 802.21 framework, called normal scheme, for comparison. In the first scenario, we performed our simulation study when a MN receives a VoIP flow and real-time flow. For a VoIP flow, we consider the guaranteed data rate as the most important QoS evaluation factor, since a VoIP requires the minimum reserved rate (802.16e) / guaranteed bit rate (UMTS). On the other hand, for a real-time flow, the service latency is considered as the most important QoS evaluation factor, since a real time flow requires maximum latency (802.16e) / transfer delay (UMTS). Fig. 3(a) shows the received data rates of the VoIP flow and Fig. 3(b) shows the latency of the real-time flow during a handover. In Fig. 3, the accessible networks to the MN increase from only UMTS to 802.16e(RAS1) in the service period marked with ’B’ (section B). With the normal scheme, the MN moves to RAS1 due to the high SNR of RAS1 and the preference, and thus it does not receive the guaranteed bandwidth due to high overload status of RAS1. On the contrary, with the proposed scheme, by performing the QoS measurement step, the MN continues to receive guaranteed QoS service from UMTS from which it can receive the reliable service for VoIP. It is the same for the real-time flow, and the proposed scheme provides the guaranteed latency of below 150 msec as shown in the Fig. 3(b). Thus, we can

see that the proposed scheme with the QoS measurement step provides better performance of QoS service continuity. For the second scenario, we examined the performance of the proposed scheme when the passive reservation and activation steps are used (called full scheme) and when they are not used (called partial scheme). As shown in Fig. 4, both the full scheme and partial scheme select RAS2 based on the networkinitiated handover procedure in service period marked with ’C’ (section C), but the performance of the schemes are different. The reason is that the time difference checks the status of neighbor networks and executes the handover may vary and the network resource cannot be guaranteed during the time difference due to unpredictable network conditions. Therefore, the partial scheme shows poor performance, compared with the full scheme. This performance evaluation indicates that the proposed scheme has the capability to provide the QoS service continuity to MNs through the proposed three steps. V. C ONCLUSIONS The goal of this paper was to propose a network-initiated handover scheme based on the 802.21 framework which guarantees the QoS service continuity in UMTS/802.16e networks. First, we specified unclear types and defined a new MIH message for QoS handovers. Then, we designed the QoS measurement of networks with distinct QoS characteristics between UMTS and 802.16e. Based on these components, we designed a network-initiated handover procedure considering the QoS service continuity. Finally, we showed that the performance of the proposed handover procedure outperforms the existing handover procedure based on the 802.21 framework. VI. ACKNOWLEDGMENT This research was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (No. R01-2007-000-20154-0) and by the MIC (Ministry of Information and Communication), Korea, under the ITRC (Information Technology Research Center) support program supervised by the IITA (Institute of Information Technology Advancement) (IITA-2008-C1090-08010045). R EFERENCES [1] V.K. Varma, S. Ramesh, K.D.Wong, and J.A. Friedhoffer, “Mobility Management in Integrated UMTS/WLAN Networks,” IEEE ICC, Volume: 2, Pages:1048 - 1053, May 2003. [2] K. Ahmavaara, H. Haverinen, and R. Pichna, “Interworking Architecture between 3GPP and WLAN Systems,” IEEE Communications Magazine, Volume: 41, Issue: 11, pp. 74 - 81, Nov 2003. [3] Giuseppe Ruggeri, Antonio Iera, Sergio Polito, “802.11-Based WirelessLAN and UMTS interworking: requirements, proposed solutions and open issues,” Computer Networks, 2004. [4] Qazi Bouland Mussabbir, “Optimized FMIPv6 Handover using IEEE 802.21 MIH Services,” MobiArch, ACM, 2006. [5] Yoon Young An, Byung Ho Yae, Kang Won Lee, You Ze Cho, and Woo Young Jung, “Reduction of Handover Latency Using MIH services in MIPv6,” IEEE AINA, 2006. [6] IEEE 802.21/D005.00, “Draft Standard for Local and Metropolitan Area Networks: Media Independent Handover Services,” April 2007.

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