There are three major modes for conducting telemedicine operations: (1) store and forward or asynchronous, (2) real time or synchronous, and (3) a combination of both
Store-and-forward telemedicine refers to asynchronous transmission of medical information that can be accessed at a later date or time. This includes images, videos, documents, lectures, podcasts, or any form of digital information that can be transmitted from one computer to another. Sending an e-mail with an attachment or transmitting a computed tomography (CT) scan to a distant radiology provider’s picture archiving and communication system (PACS) are examples of store-and-forward telemedicine. A major benefit of store-and-forward telemedicine is that information can be sent and accessed at ones earliest convenience from any location with access to the network. This means that medical images can be sent to experts around the world for analysis, Continuing Medical Education (CME), grand rounds, presentations can be accessed on demand, and electronic medical libraries can be available 24 h a day, 7 days a week. Some store-and-forward telemedicine transmissions, such as digital mammography studies, may have very large volumes of data that need to be transmitted over a very short period of time in order to allow medical service providers to meet service level agreements for the actual medical services being rendered. In this case, high bandwidth circuits will be needed. Store-and-forward applications are only as effective as the network being used to transmit the information, especially for high resolution images and video. If the network resources are not adequate or do not perform up to agreed-upon standards, then telemedicine service delivery will be negatively impacted. Network design should balance the data communications needs of the telemedicine applications, available budget, and the medical service provider service level agreements, if applicable. Store-and-forward may be the best and only means of reliable communication if the supporting network or networks are unreliable. Store-and-forward transmissions, due to their asynchronous nature, can be retried until successful, with little or no intervention or management by a person.
Real-time telemedicine is the synchronous transfer of medical information between two or more parties. Real-time telemedicine applications predominantly consist of live video conferencing which allows medical personnel to be telepresent at distant locations; however, an increasing number of medical instruments have been digitized to allow interactive examination and live monitoring of patients. A primary benefit of real-time telemedicine is the instantaneous availability of medical information and the ability to provide expertise to a distant medical staff in real-time. This is especially important in trauma and emergencies where the condition of the patient can rapidly change.
Real-time telemedicine is relatively bandwidth intensive, especially during high resolution video conferencing. Real-time video conferencing requires solid network performance. Networks that have substantial delay in data transmission of greater than 150 ms, sustained packet loss, or substantial jitter (variance in network transit time for each packet of information) result in a poor video conferencing experience. The networking infrastructure must be reliable, free of errors and congestion, and preferably managed by QoS parameters that allocate sufficient network resources to video conferencing to support effective teleconsultations possible. It is also important to consider that the quality of real-time applications is as only as good as the weakest connection. For example, in a real-time teleconsultation between video systems connected to the Internet with one system connecting through cable provider broadband and the other system connecting via a cellular third generation (3G) network connection, the quality of the conference will be limited by the 3G network connection as it can only support a limited bandwidth transmission in comparison to the cable connection. Private networks outfitted with QoS bandwidth management capability can offer the highest levels of performance for video conferencing. The Internet can also provide excellent performance, provided that all parties involved have adequate bandwidth available on their Internet connections and the Internet is not congested during the time frame that the video conference is in session.