Indian Space Research Organisation
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Voice - Audio tools include the interactive technologies of telephone, audio conferencing, and short-wave radio. Passive (i.e., one-way) audio tools include tapes and radio. Video - Video tools include still images such as slides, pre-produced moving images (e.g., film, videotape), and real-time moving images combined with audio conferencing (one-way or two-way video with two-way audio). Data - Computers send and receive information electronically. For this reason, the term "data" is used to describe this broad category of Telemedicine tools. The clinical data and images of the patient, before transmission must fIrst be converted to digital format, usually via a "codec" (short for coder/decoder) and for the video presentation, another similar device is needed at the receiving end. This step is not necessary for data that are already in digital format. If the volume of a ille is less, then less storage space and less time is required when it is transferred through a network. Compression is the technique used to achieve this. Such compression softwares are very useful in transmitting medical images where even complex images can be transmitted in short periods of time. For Telemedicine in particular, Digital Imaging and Communications in medicine (DICOM) compression is the recommended standard. Then comes the telecommunication link, which may fall under any of the following two types of communication means:
Regular Telephone Service Data Networks Digital networks are capable of supporting high bandwidth and also provide the voiceand data integrity required for diagnostic purposes. In packet-switching type of data transmission, data is sent in the form of packets that contain information on origin, destination and transmission error detection. The packets where error is detected have to be re-sent, and different routes can be used depending on density of trafftc. In India, almost all lines now have the capability to take digital data. Modems Low cost modems offer data rates of up to 19.2 kbps, which are faster than many telephone networks in delivering the data. Modems are useful for applications like patient data transfer. e-mail Electronic mail allows different computer users to communicate through a network. It can be used for complex ftle transfers and case studies. Internet Internet provides an enormous medical and health care resource. Medical professionals can access worldwide information and can participate in group discussions to exchange ideas. The Internet can be successfully used for medical training, patient care, remote consultations and education. Medical image fIles can also be transferred using Internet protocols. DSL Technology What makes DSL technology appealing, first of all, is its speed. In its very fastest incarnations, DSL offer more than 100 times the network performance of a traditional analog modem. DSL uses the same telephone line wiring as traditional modems, and works on the unused (high) frequencies of the line. DSL modems contain an internal signalsplitter that carries voice signals on the usual low frequencies (from 0 up to 4kHz) and data signals above that. This splitter, consequendy, allows simultaneous access to the line by the telephone and the computer. ISDN and Broadband ISDN is a widely accepted standard for digital communications allowing a user to confIgure installations to suit his bandwidth needs in the multiples of 64 or 16 kbits per second. ISDN networks can be used to deliver multimedia Telemedicine conference systems where there is simultaneous use of text, sound, images, color and motion. The higher the bandwidth the sharper the images transmitted. Videophones Videophones help specialists to see and talk to each other and exchange information regarding diffIcult cases thus eliminating the need for patients travelling great distances for special consultations. ATM ATM - Asynchronous Transfer Mode is a fast packet switching technology where messages are assembled into one or more packet, and sent through a network, collectedand the re-assembled into the original information at the destination. ATM is designed to route all types of digital information like data, graphics, voice, video and multimedia over a common network. Radio Radio pagers can receive messages by callers using a telephone. Today's pagers incorporate voice and email facility where the caller cantransmit voice or text and information using a telephone. This facilitates in sending large amount of medical data direcdy. Currendy, the Pagers in India are not much used. Cellular Radio Cellular radio can be used in cases of data transmission between the ranges 2.5 to 16 Kbps. Cellular radio can also be used to transmit ECGs from ambulances to hospitals. Cellular telephones allow two-way communication using radio links established between the phones and radio sites within a particular area,very useful in cases of medical emergencies. A cellular telephone can also transmit and receive text and data if it is interfaced with PC, MODEM and Communicating software. When interfaced with a small scanner the computer can act a fax machine capable of receiving and transmitting medical reports, pictures and bio-signals. Wi-Fi Otherwise known as Wireless Fidelity, WiFi is a system of wirelessly connecting devices that use radio waves, allowing for the connection between devices without needing them to be facing one another. It requires a radio transmitter called router, and receivers called access points and a high-speed pipe in order for multiple devices to do tasks without significant loss of speed. Wi-Fi generally uses S-band (2.4 GHz) and frequency-hopping techniques to connect multiple devices together. Wi-Fi has a range of about 1000 feet outdoors and is mainly intended to be used for LAN in residential homes, for public access hotspots, and in business. Real Wi-Fi follows 802.11 b standard for data speed of up to 6 Mbps under ideal world conditions. This technology is found in computers and PDA allowing Internet through access points called hotpots. Wi-Max Wi-Max, short for 'Worldwide Interoperability for Microwave Access,' refers to any broadband wireless access network for point to multipoint non line of sight access, with a range of 30miles for 70 Mbps is based on the new IEEE 802.16 standard. This specification covers both the Media Access Control (MAC) and the physical (PHY) layers for fixed systems employing a point-to-multipoint (PMP) architecture operating between 2 GHz and 66 GHz. Wi-Max also refers to the technical working group organized to establish conformance and testing standards for the 802.16 technology, to promote vendor interoperability. Wi-Max is capable of transmitting network signals covering in excess of 30 miles of linear service area,which is much greater than Wi-Fi's coverage of several thousand square feet. It provides shared data rates of up to 70M bit/sec., which is also greater than Wi-Pi's theoretical high of 54M bit/sec (for 802.11g). Like Wi-Fi, it is divided into two groups by frequency: 2-11 GHz and 10-66 GHz. This is because PHY considerations require line of sight transmission for higherfrequencies, but not for lower frequencies. Its MAC was flexibly designed to carry any transport protocol like Ethernet, Internet Protocol, and ATM. Satellite Communication Satellites now a day are used to provide instant connectivity with least efforts to reach the uncovered or inaccessible regions. It also provides thin to very thick bandwidth pipe for variety of purposes. The advantages are quick deployment, not requiring permanent infrastructure and instantaneous global coverage. Very SmallAperture Terminals called VSATs are normally used for thin route or dedicated single user. It provides cost effective connectivity and bandwidth on demand based on usage through small terminals. All the network management complexities are located in a bigger antenna installation called HUB. The VSAT is only provided essential functionality to access user on other side.The advantage is that same VSAT can support different data rate for varied users. Of the three different transmission schemes are used for interactive hubbed VSAT networks i.e. TDM/TDMA, Demand Assigned SCPC and CDMA, the DAMA access in mesh topology is currently used in Telemedicine. Though it is costly in terms of recurring cost as the bandwidth is dedicated during the time of connectivity but has the advantage that one can get dedicated connectivity with required bandwidth. Satellite services can be used for teleeducation, administration of community initiatives, by relief organisations during emergencies, accessing medical databases and international libraries. Which is the best option? The key to effective Telemedicine is focusing on the needs of the doctors, the requirements of the content, and the constraints faced by the doctor, before selecting a delivery system. As such, amongst a variety of telecommunications technologies previously discussed, any appropriate communication medium may be utilised. Typically, a systematic approach will result in a mix of media, each serving a specific purpose. For example:
The table 'A' below illustrates the real world performance of a number of connection methods. The base factor for this table is a standard "33.6 modem". A device that can transmit data at a rate of 33,600 bits per second, which is equivalent to 4200 characters per second. 
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