## 3 Telemetry System Architecture for Physiological Data Collection
The base station should include capabilities to report on data being received, log the data to a database, and interact directly with a user (for example, a doctor) in the case of an adverse event, a medical emergency, or where a threshold condition is reached (such as heart rate exceeding a certain tolerance level). It is important to note that, while the patient base station may send data regularly to the medical centre, the communication process is bi-directional. The medical centre may send a request to the patient's local device, and the patient base station will respond to that request (a poll/response message pair). The protocol must therefore possess the capability of servicing a number of types of communication, including polls and responses, and scheduled communications. However, in addition to data messages, we should maintain the ability to control, configure and diagnose the remote system. The very concept of telemetry defines that we have remote devices measuring values. It may be necessary to turn on or off specific sensors, or change the frequency of data transmissions from the patient to the medical centre. We do not want to personally visit the patient each time such a change is required. With this in mind, Table 2 identifies the different message types. The arrangement of patients to base stations is potentially a many to one relationship--that is, many patients should be able to be monitored from the same base station. Conversely, a single base station should have the ability to identify and receive transmissions from multiple patients simultaneously. As transmissions can be bi-directional (from medical centre to patient and vice versa), and there are many patients talking to a single base station, it is imperative that data are uniquely identifiable as to their point of origin and their purpose. That is, any datum must be associable with one, and only one, patient. The proposed framework will be able to facilitate communication among patients, medical professionals at local hospitals and specialists available for consultation from distant places. The most valued features of this system is to prevent the patient from re-hospitalisation and to avoid possible critical events, thus reducing the healthcare costs. Another main advantage of the proposed framework is the unobtrusive patient vital sign monitoring. A pragmatic approach to achieving high end-to-end reliability is to isolate the impact of mobility from multi-hop routing. In our network architecture we divide the problem of data delivery from the sensor nodes to the base station into two parts: single-hop communication from the patient node to the first relay and (potentially multi-hop) communication from that relay to the base station. Based on the architectural framework discussed in this section, we will propose a generic communications protocol to work inside an SMS message and provide the necessary redundancy and robustness for the transmission of medical telemetry. Such telemetry could then be transmitted from a mobile telephone or other cellular mobile engine, and this capability could be used to increase the freedom of non-critical patients requiring monitoring.