Ubiquitous IMS Emergency Services over Cooperative Heterogeneous Networks Chi-Yuan Chen†, Kai-Di Chang‡, Han-Chieh Chao‡, § and Sy-Yen Kuo† †
Dept. of Electrical Engineering, National Taiwan University, Taipei, Taiwan
‡
Dept. of Electronic Engineering and Institute of Computer Science & Information Engineering, National Ilan University, I-Lan, Taiwan § Dept. of Electrical Engineering, National Dong Hwa University, Hualien, Taiwan
[email protected],
[email protected],
[email protected],
[email protected] and even at movement. Thus, it can reach the goal of next generation communication network.
ABSTRACT There are various emergency services based on wireless sensor network being proposed recently. However, the ability of these services/networks is inherently limited by geographical restrictions and need to be deployed in advance. This paper proposes an application level approach to enhance the service coverage and availability of emergency services. Specifically, we augment these services with All-IP network infrastructure based on IP Multimedia Subsystem (IMS). Furthermore, we integrate the IMS Emergency Services architecture with Cooperative Network technology to provide ubiquitous emergency services. We also investigate the prime problems of cooperation between heterogeneous networks and IMS. Finally, we present and discuss the experimental results of performance in our Cooperative Emergency IMS Testbed.
The IMS is a network subsystem specified by 3GPP (3rd Generation Partnership Project). The concept of IMS is to merge telecommunication technologies, wireless networks and wired networks under the All-IP environment to provide more extensible, real-time and interactive multimedia services at 3G and even future 4G networks. IMS can be regarded as the trend of the future wireless communication network. IMS uses the modified IETF SIP (Session Initiation Protocol) to establish the service session. The main function is to combine circuit-switched and packet-switched domains. The contents are not limited by the access medium but become more extensible to offer more valueadded services to user. However, IMS Emergency Services was not discussed until 3GPP Release 6. With the demand to delivery emergency service between circuit-switched network and packetswitch network, 3GPP Release 6 and Release 7 [1] begun to specify the architecture and signaling process of emergency services. At present, the latest Release 8 TS 23.167 [2] has defined the key components of emergency service.
Categories and Subject Descriptors C.2.1 [Network communication.
Architecture
and
Design]:
Wireless
General Terms Measurement, Performance, Design, Experimentation.
In order to provide various and reliable services to user, we adopt the concept of cooperative networks. We propose the application level scheme to integrate the IMS Emergency Services with Cooperative Network technology, called CE-IMS (Cooperative Emergency IMS) services. Furthermore, we use the medical services as examples. Users could use these emergency medical services without geographical restrictions through the cooperative heterogeneous networks.
Keywords IP Multimedia Subsystems, Cooperative Networks, Emergency Service.
1. INTRODUCTION The architecture of UMTS (Universal Mobile Telecommunications System) can be divided into circuit-switched network (CS), packet-switched network (PS) and IP Multimedia Subsystem (IMS). The services on the UMTS can be roughly divided into voice service, data service and packet-based multimedia service. When UMTS integrates with these heterogeneous wireless network technologies, such as the 802.11 series wireless local area network (WLAN) and 802.16 series network (Worldwide Interoperability for Microwave Access, WiMAX), it could offer ubiquitous services anytime, anywhere
This paper is organized as follows. In Section II, we review and discuss the related works and technological background. In Section III, we propose the architecture of CE-IMS service. We present our experimental results in Section IV. In Section V, we discuss the performance measured in our testbed. Finally, we present our conclusions in the final section.
2. Related Works Recently, the integration of wireless sensor networks and IMS for medical services [3] has been proposed. Alarm-Net [4] and CodeBlue [5] are two works of integrating wireless sensor networks with Internet for medical monitoring. However, there are geographical restrictions in wireless sensor networks and people need to deploy the natural-restricted wireless sensor network in advance. Hence, we need a brand new network infrastructure to support emergency medical services. Based on the IMS emergency service standards specified by 3GPP, we
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Figure 2. IMS Emergency Service Architecture.
Figure 1. Cooperative Network in Layered Architecture. propose a cooperative scheme to achieve the goal of emergency medical services.
The application servers provide users a wide range of IMS service. Operators can use the standard IMS architecture to build up their application servers.
2.1 Cooperative Networks
2.3 IMS Emergency Services
The concept of “Cooperation” is that nodes or users work together to achieve the whole or personal goal. There is a real life example that bats flying together to maintain their life. In wireless networks, nodes cooperate to reduce the power consumption [6]. In this paper, we discuss the cooperation in wireless networks [7]. Three major cooperation categories as shown in Figure 1 that correspond to these three layers: physical layer, network layer and application layer [8].
The IMS Emergency Service architecture is as shown in Figure 2, which composed of UE (User Equipment), P-CSCF, E-CSCF (Emergency-CSCF) and LRF (Location Retrieval Function) [1]. P-CSCF and E-CSCF are both SIP servers in the same domain/realm. P-CSCF is used to detect the request of emergency sessions, and E-CSCF is used to handle emergency session. UE is responsible for launching an emergency session, and also used to identify an emergency session. LRF is used to obtain the location information of UE. When issues an emergency session establishment, the UE could detect this emergency session request itself (e.g. evaluating the URI or number, a variety of emergency numbers, SIP URIs, and TEL URIs specified in TS 22.101) and send this request to P-CSCF for registration. This request includes Emergency session indication, Emergency Public User ID, and location information of UE (if available). The P-CSCF handles registration requests with an Emergency Public User ID like normal IMS registration, and selects an E-CSCF in the same domain/realm to handle this request. When the location information is not included or validated in the emergency request, the E-CSCF may request the LRF to retrieve more location information. Furthermore, according to the policy, the E-CSCF could route this emergency call to PSAP (Public Safety Access Point) or ECS (Emergency Call Server) for further call process.
Physical layer is the most important layer in Cooperative Networks. The major concepts of “Communicational Cooperation＂ in this layer are Cooperative Coding, Network Coding and Cooperative Antennas. Different from the physical layer, the concept of network layer is “Operational Cooperation”. Network layer cooperation is usually used in heterogeneous networks, including the interaction and negotiation procedures of different network nodes to ensure that different network nodes can achieve end-to-end connection services without interruption. The major concept of the application layer is “Social Cooperation”. It focuses on the establishment and maintenance of cooperative nodes in dynamic networks, such as cooperative terminal in wireless networks. For example, in an Ad-Hoc network, each node must decide whether to participate in this network or not. Unlike other layers, each user's decision has a significant impact on system performance. In this paper, we intend to achieve the Communicational Cooperation approach to extend service coverage and availability by using application level scheme. Thus the cross-layer cooperation mechanism will be independent from the hardware (physical layer) and protocol suites (network layer).
3. Cooperative Emergency IMS Service 3.1 Architectures of CE-IMS In this section, we propose the CE-IMS (Cooperative Emergency IMS) service architecture for heterogeneous networks. We also adopt the healthcare services and emergency medical services to discuss and valid our architecture. The CE-IMS is not only suitable for regional monitoring service in hospital or home care, but also support the reliable and ubiquitous connection for Implantable Medical Device (IMD). Compared with the fixed wireless sensor networks, the CE-IMS does not need to be deployed in advance and without geographical restrictions. As Figure 3 shows, the CE-IMS service architecture is layered as follows:
2.2 IP Multimedia Subsystem (IMS) The architecture of IMS can be divided into three tiers: the Media/Transport plane, Control/Signaling plane and Service/Application plane. The Media/Transport plane is a referral to a wide range of different access technologies. Basing on IP transport layer, users go through Wireless LAN, GPRS (General Packet Radio Service) or UMTS to acquire connectivity. Once connected to IMS, users can access a variety of multimedia services. There is a set of IMS core components in Control/Signaling plane– CSCFs (Call Session Control Functions), which includes Proxy-CSCF (P-CSCF), Interrogating-CSCF (ICSCF) and Serving-CSCF (S-CSCF). The SIP signaling will be processed and routed to the destination through this plane. In the Service/Application plane, there are various application servers.
1) In the Transport layer, user equipment (nodes) can adopt “Communicational Cooperation” or “Operational Cooperation” according to different demands. In this paper, we present the Communicational Cooperation scheme with experimental results.
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Figure 4. System Model. our consideration. and denote the cost from the source and relay nodes charged by service provider, and denote the transmit power from the source and relay nodes. These system constraints are formulated as follows:
Figure 3. Layered CE-IMS Architecture. 2) In the Network Attachment layer, different QoS and Security levels are provided depending on different access technologies(e.g. Packet-switched Network, WiMax, or WLAN).
, .
3) In the Application and Service Control layer, the goal of All-IP infrastructure is achieved through the integration with IMS.
3.3 Application Level Cooperation Scheme Most network cooperation and other researches focus on radio technologies rather than the cooperation of the application layer. In CE-IMS, the terminals cooperate not only through radio links, but also decide cooperation scheme in application layer. We use the architecture of IMS to promote the level of cooperation from physical and transport to application level. The IMS application on terminals can decide how to cooperate with other nodes according to the status of wireless connections or the connection capability, and use the IMS-SIP to exchange the cooperation message to each node. In order to incorporate heterogeneous terminals in IMS, we added the application level scheme and functionality to the IMS client program. The modified application level scheme enables the Communicational Cooperation capability for IMS Emergency Services which is illustrated in Figure 5.
We are able to cover both the short range communication and long range communication technologies to reach the goal of getting maximum coverage under this architecture. We give an example of health monitoring that provides alert while emergencies. Under normal condition, the patient’s heart rhythm is monitored by a small sensor. The monitored data are transported to the PSAP or ECS via wireless communication link. When an abnormal stroke is detected, it triggers the monitoring application to send an emergency message or establishes an emergency call. Current wireless sensor applications have the problem that the coverage of sensors is limited. In contrast to previous works, the CE-IMS provides pervasive healthcare services. As Figure 4 shown, when User A moves beyond the coverage of Access Point, he can establish or continue his connection by the Communicational Cooperation with User B or User C. Furthermore, the healthcare service may be unavailable due to the weak signal or limited bandwidth. For example, the User D (illustrated in Figure 4) wants to establish an emergency call with ECS. He could obtain higher bandwidth by the Operational Cooperation with User C and User E.
4. CE-IMS Testbed We built the testbed for CE-IMS service based on the 3GPP specifications as shown in Figure 6. The CE-IMS testbed includes: IMS Core Network, Real-life Internet, Real-life Access Network Service Provider (3.5G HSDPA), Relay Nodes and Cooperative User Nodes. In the IMS Core Network, we deploy a set of CSCFs to deal with call session control functions based on Open IMS Core [10]. The main components in IMS Domain are P-CSCF, SCSCF, I-CSCF, E-CSCF and HSS (Home Subscriber Server). User needs to trigger emergency service requests when accident occurs. There are three different scenarios of emergency service in our experiment. We describe the scenarios as follows:
3.2 Cooperation in Heterogeneous Networks In this section, we discuss the system model about cooperation in heterogeneous networks that shown in Figure 4. In this system, nodes are colored with different colors to represent those different network interfaces that the nodes equipped. The Potential Relay Nodes (r) can act as cooperative nodes to relay traffic between the Source User (s) and Destination User (d). The primary problem is how to select the network interface and which node would be the cooperative target. In order to optimize the problem of relay node selection and maximize the system rate (see [9] for details), we redefine the system rate as max
,
, ,
0.5 · log 1
,
(2)
1) When the user is under the coverage of WAN (Wide Area Network), he can acquire the connection through the 3.5G HSDPA modem directly. 2) When the user is out of the WAN, he may through the cooperation of relay node equipped with Bluetooth (Personal Area Network, PAN) and 3.5G HSDPA to get connected.
(1)
where the 0.5 is due to the spectral efficiency loss of two hop transmission and the is Signal to Interference plus Noise Ratio. The network cost and power consumption are also under
3) When the user is out of the WAN, he may cooperate with the relay node, which has the capability to access 802.11 WLAN and 3.5G HSDPA, to get connectivity to the Internet.
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