Telemetry use case: Home patient monitoring
In the collaboration between IBM® and a healthcare provider on a cardiac patient care system, an implanted cardioverter defibrillator communicates with a hospital. Data about the patient and the implanted device are transferred using RF telemetry to the MQTT device in the home of a patient.
Typically the transfer takes place nightly to a transmitter located at the bedside. The transmitter transfers the data securely over the phone system to the hospital, where the data is analyzed.
The system reduces the number of visits a patient must make to a physician. It detects when the patient or device needs attention, and in the event of an emergency, it alerts the on-call physician.
The device requires no user intervention other than supplying power, a telephone line, and being in proximity to the device for part of the day. Its operation is reliable and simple to use.
To remove the need for the patient to set up the device, the device supplier preconfigures the device. The patient only must plug it in. Elimination of configuration by the patient simplifies the operation of the device and reduces the chance the device is configured wrongly.
The MQTT client is embedded as part of the device. The device developer embeds the MQTT client implementation in the device and the developer, or supplier, configures the MQTT client as part of the preconfiguration.
The MQTT client is shipped as Java™ SE jar file, which the developer includes in their Java application. For non-Java environments, such as this one, the device developer can implement a client in a different language using the published MQTT formats and protocol. Alternatively, the developer can use one of the C clients shipped as shared libraries for Windows, Linux® and ARM platforms.
- Uneven connectivity
Communication between the defibrillator and the hospital has uneven network characteristics. Two different networks are used to solve the different problems of collecting data from the patient, and sending the data to the hospital. Between the patent and the MQTT device, a short-range low-power RF network is used. The transmitter connects to the hospital using a VPN TCP/IP connection over a low-bandwidth phone-line.
It is often impractical to find a way to connect every device directly to an Internet Protocol network. Using two networks, connected by a hub, is a common solution. The MQTT device is a simple hub, storing information from the patient, and forwarding it to the hospital.
The physician must be able to trust the authenticity of the patient data, and the patient wants the privacy of their data to be respected.
In some situations it is sufficient to encrypt the connection, using VPN or SSL. In other situations, it is desirable to keep the data secure even after it has been stored.
Sometimes the telemetry device is not secure. It might be in a shared dwelling, for example. The user of the device must be authenticated to make sure that the data is from the correct patient. The device itself can be authenticated to the server using SSL, and the server authenticated to the device.
The telemetry channel between the device and the queue manager supports JAAS for user authentication and SSL for communication encryption, and device authentication. Access to a publication is controlled by the object authority manager in IBM MQ.
The identifier used to authenticate the user can be mapped to a different identifier, such as a common patient identity. A common identifier simplifies configuring authorization to publication topics in IBM MQ.
The connection between the MQTT device and the hospital uses dial-up, and works with a bandwidth as low as 300 baud.
To operate effectively at 300 baud, the MQTT protocol adds only a few extra bytes to a message in addition to TCP/IP headers.
The MQTT protocol provides single transmission fire and forget messaging, which keeps latencies low. It can also use multiple transmissions to guarantee at least once and exactly once delivery if guaranteed delivery is more important than response time. To guarantee delivery, messages are stored at the device until they have been delivered successfully. If a device is connected wirelessly, guaranteed delivery is especially useful.
Telemetry devices are typically deployed in large numbers, from tens of thousands to millions.
Connecting many devices to a system places large demands on a solution. There are business demands such as the cost of the devices and their software, and the administration demands of managing licenses, devices, and users. Technical demands include the load on the network, and on servers.
Opening connections uses more server resource than maintaining the open connections. But in a use case such as this that uses phone lines, the expense of connections means that connections are left open no longer than required. The data transfers are largely of a batched nature. The connections can be scheduled throughout the night to avoid a sudden peak of connections at bedtime.
On the client, the scalability of clients is helped by the minimal client configuration required. The MQTT client is embedded in the device. There is no requirement for a configuration or MQTT client license acceptance step to be built into the deployment of devices to patients.
On the server, IBM MQ Telemetry has an initial target of 50,000 open connections per queue manager.
The connections are managed using MQ Explorer. The MQ Explorer filters the connections to be displayed to a manageable number. With an appropriately chosen scheme of allocating identifiers to clients, you might filter connections based on geography, or alphabetically by patient name.