A Framework for SIP-Based Wireless Medical Applications - IEEE Xplore

A Framework for SIP-Based Wireless Medical Applications Abderrahmane Lakas

Khaled Shuaib

College of Information Technology UAE University, Al Ain, UAE [email protected]

College of Information Technology UAE University, Al Ain, UAE [email protected]

Abstract—With advances in wireless networks and portable handheld devices, it becomes natural to use such technologies to improve the effectiveness of health service providers. These technologies enable hospital staff to remain connected to their critical systems regardless of their location in the medical facility. In this paper, we describe how SIP, Zigbee and WLAN technologies are used to support mobility and event management in the medical environment. SIP, a signaling protocol, is now adopted as a standard for VOIP. It is also used for presence monitoring, event management, and instant messaging. In conjunction with SIP, WLAN networks are widely deployed in many campuses, enabling mobility. Zigbee is a new standard that can be used for short range, low rate, low power wireless device level communications providing sensing and data acquisition. WLAN and Zigbee proved suitable for deployment in medical premises causing no interferences with medical equipments. In this paper we describe an integrated framework for mobility, presence and event management using SIP, WLAN and Zigbee. Keywords: SIP; WLAN; Zigbee; Medical applications

I.

INTRODUCTION

Hospitals and medical clinics are the typical environment that requires an advanced event management and communication system in order to deliver effective health services, and optimize the management of resources. This environment includes monitoring patients, managing and processing various events in a fast pace and in a real-time fashion. The medical community was stunned in 2000 when the Institute of Medicine (IOM) published a report [1] which indicates that medical errors are one of the leading causes of death and injury. The IOM report, estimated that as many as 44,000 to 98,000 people die in U.S. hospitals each year as the result of medical errors. Similarly in Canada, experts estimate 5,000 to 10,000 deaths every year due to medical errors. The encouraging news is that research shows that over half of all adverse drug reactions are preventable through alerting systems and controls on administration and ordering. Used appropriately, new and emerging wireless technologies can improve care, reduce costs, and increase patient satisfaction. In this paper we describe how the Session Initiation Protocol (SIP) [2] and associated technology like Instant Messaging (IM) in a Wireless Local Area Network (WLAN) [3] can be used to assist in providing an optimal infrastructure for event notification, and for managing and communicating medical tasks. We propose an integrated system for medical event and communication management using SIP, WLAN and Zigbee [4]. SIP is a signaling protocol used for establishing and maintaining communication sessions involving two or more 0-7803-8887-9/05/$20.00 (c)2005 IEEE

participants. SIP was initially designed for Voice over IP and multimedia conferencing, and then extended to support other services such as instant messaging and presence management [5, 6]. Today, SIP is also adopted to be used with 3G wireless networks. SIP has various methods that support a variety of applications such as subscribing to a service, notification of an event, status update, and location and presence services. There have been only fewer and limited attempts to use SIP as an integrating technology for a medical communication system. In [7], authors propose a monitoring system using SIP and Bluetooth. In [8], the authors proposed a model for a diagnosis assistant system using mobile agents and SIP. The advances achieved recently in the field of data wireless networks facilitated the introduction of wireless LAN in the medical environment [9, 10]. High data rate of bandwidth provided by WLAN render voice and multimedia communications practical without any risk of signal interference with the medical equipments [11]. WLAN allows mobile communications within a medical premise. The medical staff is now no longer tied with a specific location to access the medical information system. SIP technology provides the support for establishing and managing the sessions among the staff, and the sessions between the staff and the various information resources (Laboratories, schedules, databases, equipments, etc.). SIP provides support for a flexible voice communication to the medical staff. In conjunction with wireless technologies like WLAN and Zigbee, portable hand-held devices allow instant access to all members of staff through applications such as instant messages, mobile multimedia conferencing, location and presence management. Thus, allowing instant knowledge of the staff presence, and updates on status of various resources. The new short range, low power, low rate wireless networking Zigbee standard (IEEE 802.15.4) complements the high data rate technologies such as WLAN and open the door for many new applications. This standard operates at two bands, the 2.4 GHz band with a maximum rate of 250 kbps and the 868-928 MHz band with data rates between 20 and 40 kbps. When it comes to a medical environment, Zigbee can be used in many applications such as: monitoring and updating a location server with a medical staff location and information exchange between medical devices. The patient’s bedside can be equipped with wireless sensing devices that allow real-time monitoring of the patient’s vital signs such as: heartbeat updates, Glucose level…etc. Currently the IEEE 1073 working group [12] is working on standards for medical device communications. These

standards aim to encompass transparent plug-and-play interoperability, ease of reconfiguration, and ease of use. In this paper we are suggesting the use of Zigbee for such needs of the medical community. The rest of the paper is organized as follow: Section 2 presents examples of medical applications that can be conducted utilizing SIP. Section three provides a detailed explanation and discussion of our proposed SIP architecture for medical applications and Section 4 concludes the paper. II.

multimedia communication made possible by an integrated UMTS/WLAN network infrastructure. A

B

Proxy Server 2. SUBSCRIBE(A) 1. REGISTER 3. NOTIFY(A, L1)

Location: L1 5. NOTIFY(A,L2)

4. UPDATE(L2)

SIP-BASED MEDICAL APPLICATIONS

Many medical applications are facilitated with the use of WLAN and Zigbee devices. For example: Physicians can electronically issue prescriptions while on rounds immediately sending the prescription to the patient’s choice of pharmacy while automatically checking for known allergies and conflicting medications. This improves accuracy and safety while minimizing paperwork. Another application is that physicians can electronically order detailed tests for their patients and securely view results as soon as they are available. In addition, the integration of wireless technologies with mobile communications devices will allow physicians to have real time access to their patients’ records at different hospitals. Moreover, with the presence services provided by SIP, the medical staff is able to publish their current location and their availability status. For example, when a doctor's attention is requested, one can consult the presence/location server to enquire about the doctor’s availability and current location. In SIP, as soon as a device subscribes with the presence/location server to another device, it gets a notification when the later moves from one location to another, or changes its availability status. Figure 1 illustrates how status and location changes of a given device is updated and notified. In this figure (1) Device A registers with the SIP proxy server. By doing so, the device also publish its contact address at which it can be contacted. (2) Device B subscribes to the proxy and provides as a parameter the device ID (here A) for which it wants to monitor the availability and location. (3) The server responds by the current status and location of A (here location L1). (4) As soon as A moves to a new location, it updates the server with the new location (here location L2). (5) The server takes note, and notifies device B with device A’s new location. Typically, this method can be generalized to monitor the staff’s current location and availability information from the minute they enter a medical premise. The doctor’s location can be determined by the WLAN access point that his/her device is attached to. The location is then mapped according to a specific department, floor or location. Another way to determine a location more precisely is by using short range communication devices using Zigbee sensors. For example, as soon as a doctor arrives at a patient’s bed, the location server gets notified. If the doctor publishes that he/she is in a visit round, the application automatically downloads the patient’s medical prognosis to the doctor’s hand-held device. On the other hand, the doctor can log his/her notes, and based on the patient’s condition may enter requests for any further treatments. In another example, a transported patient change in status and prognosis can be uploaded to the hospital medical servers and therefore is made available for immediate recommendations or for needed ahead of time preparations. This can be made available through always on

Location: L2

Figure 1: Location change notification III.

A SIP-BASED ARCHITECTURE FOR MEDICAL APPLICATIONS (SIPAMA)

The SIPAMA architecture basic components include the use of WPAN (Wireless Personal Area Network) Zigbee networks interconnected through the medical facility WLAN infrastructure. SIP and companion protocols are used as a signaling means for establishing communication sessions, and event notification. The SIPAMA components are shown in Figure 2. The SIP proxy server acts as the point of contact for all SIP requests. The proxy forwards the SIP requests to dedicated servers according to the service requested. For instance, the proxy processes all registrations and updates the presence and location server with the status and location information of the connected devices. The proxy also relays event notifications to the subscribed devices, each for the subscribed service. The SIPAMA also includes other servers which implement the application logics. For instance, the medical content server contains all medical records including medical files, x-rays, exams and lab results …etc. To extend communications beyond the local medical facility; i.e., medical staff on the road or in other hospitals, the SIPAMA architecture includes a SIP/PSTN and a WLAN/UMTS gateways. These gateways make it possible for medical information to be exchanged and updated remotely and on the fly in critical situations. Proxy Server

Medical Content Servers SIP Diameter AAA Server

SIP SIP

Operation Room

Location Server

WLAN Medical equipments GPRS UMTS

Other Hospital

ZigBee Sensors SIP/PSTN Gateway

Figure 2: SIPAMA Architecture

A. Presence and Instant Messaging SIP is extended to support instant messaging and presence information [5] Presence information includes status and location information such as that contained in “buddy” list. This extension includes functionalities such as: • • •

Publishing and uploading of presence information Presence and event notification Delivering of instant messages

Figure 3 below illustrates an example of SIP messages sequence for exchanging presence information between two devices. The SUBSCRIBE message is used to subscribe to the presence status information of another device. A device can subscribe to one or more devices. For instance, a nurse at the hospital’s dispatching desk can subscribe to all the medical staff of the hospital. The NOTIFY message is sent by a device to the server when a change occurs in the presence information of the device. For instance, presence status values can be any of the following: “offline”, “in visit rounds”, “in operation room”, “not available”, “at lunch” …etc. The presence status can be changed manually by the person carrying the device, or automatically as programmed. In the later, a status change can be automatically triggered through sensors. A change of status which occurs either manually or automatically invokes a callback function that is destined to carry out a corresponding task. For example, when a doctor enters in a patient’s room for a routine visit, a change in the status is caused by a sensor in the patient’s room. This change will, consequently, trigger a callback function that will fetch the patient’s medical record form a medical media content server, and download it to the doctor’s device.

Proxy

Dr Smith

Dr Phillips NOTIFY (off-line) 200 OK

SUBSCRIBE (phillips) 200 OK NOTIFY (off-line) 200 OK NOTIFY (available) 200 OK NOTIFY (available) 200 OK Message (Hello)

NOTIFY sip:[email protected] SIP/2.0 Via SIP/2.0/TCP proxy.hosp.ae:5060 To: sip: phillips @hosp.ae> From: sip:[email protected]> Call-ID: 1234567890 CSeq: 1010 NOTIFY Allow-Events: presence Contact: sip: [email protected]> Subscription-State: active;expires=1800 Event: presence Content-Type: application/cpim-pidf+xml Content-Length: 325 available sip:[email protected];transport=tcp

Figure 4: SIP NOTIFY Message B. Location Information Typically location information is determined using location beacons (LB). Location beacons consist of short range sensors which announce their location to the mobile devices in the vicinity. When the mobile device gets its location, it uses it to update the location server. These sensors can be located anywhere in the hospital. A number of selected sensors can be used as LBs and will carry ID numbers. Each selected sensor with an ID can be mapped to a specific location by the location server. Once a medical staff who is equipped with a mobile device that can be recognized and seen by at least one LB in the vicinity, the medical staff mobile device will send a notification message via SIP to the location server with the LB ID. A careful design allocating LBs around the medical facility is crucial and should be optimized so that signaling of location monitoring is kept under a desired limit while optimizing location identification of medical staff. For example, the medical equipments around the patient’s bed can be all equipped with sensors for patient status monitoring, but only one can be classified as a LB capable sensor that can be mapped to the patient room and bed number. Location Beacon

Mobile Device

Location Server

Figure 3: Status change notification. The NOTIFY message as shown in Figure 4 describes an example of a notification message send by a device when a change in the status occurs. The NOTIFY message contains the mandatory information of the source and the destination URI, and an imbedded XML-based description of the presence information. The presence information includes among other thins, the status (here available), and the contact URI at which the notifying device can be reached at. The XML specification of the presence information is based on the IETF document [13].

Subscriber Device

SUBSCRIBE Signal (loc) NOTIFY (loc) 200 OK

UPDATE (loc)

Message

Figure 5: Location Information

Figure 5, illustrates an example of how a medical device can be located utilizing location beacons and the location server. The next subsection shows how the IEEE 802.15.4 is considered to serve as the sensor network for location updates. C. Zigbee Sensors The IEEE 802.15.4 or Zigbee standards is an integrated part of SIPAMA and serve the purpose of deploying a sensor network in a medical facility as well as equipping medical devices with short range wireless communication interfaces. This will satisfy the need for continuous patient monitoring, medical staff location and transfer of medical data. Zigbee is designed as a low complexity, low cost, low power consumption and low data rate wireless connectivity standard. Zigbee supports scalable data rates, for example it can be used for medical file transfer at the rate of 250 kbps while supporting sensor based applications at the rate of 20 kbps. Table 1 summarizes the frequency bands and data rates supported by Zigbee. Table 1: Frequency bands and data rates of Zigbee PHY MHZ 868/915 2450

Frequency band (MHZ) 868-868.6 902-928 24002483.5

Modulation BPSK BPSK O-QPSK

Data Parameters Bit Rate Symbols (kbps) 20 Binary 40 Binary 250 16-ary Orthogonal

The Zigbee standards define two types of devices, a fullfunction device (FFD) and a reduced function device (RFD). The FFD can operate in three different modes, a personal area network (PAN) coordinator, a coordinator or a device. The RFD is intended for very simple applications that does not require the transfer of large amount of data and needs minimal resources. A WPAN is formed when at least two devices are communicating with one being an FFD assuming the role of a coordinator. Depending on the application requirements, Zigbee devices might operate either in a star topology or a peer-to-peer topology. Figure 5 shows both topologies. As seen in Figure 6, in a star topology the flow of communication is established between devices and an FFD acting as the PAN coordinator. The PAN coordinator is a device that is responsible for initiating, terminating and routing information around the network. The star topology is mostly used in small areas such as home automation, personal health care management and hospital rooms.

In the SIPAMA architecture, a number of RFDs and FFDs can be deployed as a star with a single FFD acting as a PAN coordinator who is also acting as a location beacon. Information gathered by any of the devices can be forwarded to hospital servers through the FFD utilizing a dual Zigbee/WLAN capable device such as an Access Point and using SIP as the signaling protocol. D. GPRS/UMTS WLAN Gateway While GPRS/UMTS networks provide always-on widearea connectivity with low to moderate data rates to users with high mobility, WLANs offer much higher data rates to users with low mobility over smaller areas. The proposed SIPAMA architecture utilizes a GPRS/UMTS WLAN gateway to facilitate seamless roaming and the delivery of mobile health care or e-health care and allow mobile devices equipped with both UMTS and WLAN interfaces to move freely between the two networks while being always connected. There have been several proposed solutions in the literature to facilitate and manage the movement of a mobile user within an integrated heterogeneous wireless network such as a UMTS/WLAN network [14, 15, 16]. Generally, there are two different ways to form an integrated UMTS/WLAN network architecture, tight coupling and loose coupling [16]. In a tight coupling architecture, a WLAN gateway is connected to an UMTS core network just like any other UMTS radio access networks. In the loose coupling approach, there is no direct connection between the WLAN gateway and the UMTS network. Connectivity between the two is made through the Internet or an IP backbone network. In the SIPAMA architecture, loose coupling is implemented since mobile devices carried by the medical staff are assumed to have a dual WLAN/UMTS interfaces. Figure 7 shows the SIPAMA WLAN/UMTS integration in a loose coupling environment. Internet Medical Facility Backbone Network

Gateway GPRS service node

WLAN Gateway

Medical Facility WLAN Mobile user UMTS Network

PAN coordinator

Figure 7: Loose coupling of UMTS and WLAN PAN coordinator

Star topology example

Peer-to-peer topology example FFD RFD Communication flow

Figure 6: Zigbee star and peer-to-peer example topology

E. Secruity Security is one of SIPAMA’s critical components. The main objective of this architecture is to meet HIPAA guidelines [17] for privacy, data integrity and confidentiality. Just as for any security strategy, there are many levels where security can be enforced. At the protocol level, SIP messages can be carried over the Transport Layer Security (TLS) protocol [18]. For controlling the mobiles devices and their access to the system, we use the authentication,

authorization, and accounting (AAA) standards [19] to implement needed authorization and authentication procedures. The current standard by which devices or applications communicate with an AAA server is the Remote Authentication Dial-In User Service (RADIUS) [20]. SIPAMA consists of an AAA server for authenticating the various parties before any transaction is committed. In order to preserve the confidentiality and the integrity of the patient’s medical records, all connected parties must be authenticated. In addition, all requests to access the medical content server are based on access control policy. All interactions over the SIPAMA network must be protected against non authorized intrusions through encryption techniques. At the network access level, the 802.11 wireless LAN standards use spread spectrum, which poses a high risk security. On 802.11 networks, we enable WEP (wired equivalent privacy), which encrypts the body of each frame. This will keep hackers from viewing sensitive content.

show how SIP can be used as an integrating framework for these different technologies. The proposed SIPAMA architecture enables many applications which help mitigate the work done by the hospital medical staff and reduce manmade medical errors. The SIPAMA architecture allows medical personal to be always connected to the information that helps them make timely decisions. It allows the continuous monitoring of the patients’ vital status and furthermore allows an efficient administration and management of the medical resources and the medical tasking and scheduling through real-time location information and status updates. REFERENCES [1] http://www.iom.edu/subpage.asp?id=14980. [2] J. Rosenberg et al. “SIP: Session Initiation Protocol”. Internet Engineering Task Force, RFC3261, June 2002.

[3] IEEE std. 802.11 Wireless Medium Access Control and Physical Layer Specifications 1999.

[4] IEEE P802.15.4/ D18, “Low Rate Wireless Personal Area Networks” draft std., February 2003

Applications

[5] M. Day, J. Rosenberg, H. Sugano, "A Model for Presence and Instant Medical Tasks

Session Control

Instant Messaging

Location Management

Security

SIP

MCD

Messaging", RFC 2778, February 2000.

Zigbee Notification and Signaling

[6] S. Tachakra, X. H. Wang, R. Istephanian, and Y. H. Song, "Mobile eSRD

Medical Facility Distribution and Backbone Network

Internet ISDN/ PSTN

Medical Facility WLAN GPRS/UMTS

IEEE 802.11

Network

WPAN IEEE 802.15.4

Figure 8: A layer architecture of SIPAMA F. SIPAMA Layered Architecture A layered architecture of SIPAMA is shown in Figure 8. In this figure, there are four main building blocks: First, the underlying technologies layer which includes the different available communication networks and standards being utilized (IEEE 802.11, IEEE 802.15.4, GPRS/UMTS, Internet, ISDN/PSTN). Second is the medical facility distribution and backbone network which is composed of access and core routers and switches running routing protocols to enable reachability among all communication networks. Third is the medical facility storage area network (SAN) that directly connects to core routers and spans vertically across several layers of the architecture. The SAN basically consists of Database Servers such as the Staff Resources Database (SRD) and the Medical Content Database (MCD). The fourth building block hosts SIP as an underlying protocol, facilitating seamless communication between the different applications and the utilized technologies and networks. In addition, the fourth block also manages all running application drivers such as security, location management, instant messaging, medical tasks, Zigbee notification and signaling, session control. IV.

CONCLUSIONS

In this paper we have presented an overall architecture for a mobile medical network that utilizes a heterogeneous network of sensors, WLAN, UMTS and wired networks. We

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