DMS Client Environment

For multimedia data <#2447#> storage<#2447#>, the client site should be capable of converting the analogue signals needed to be stored within the DMS into digital streams that can be understood by the DMS. For data <#2448#> retrieval<#2448#>, the client should be able to decompress the digital streams received from the DMS if they are compressed , convert them into analogue signal, if required, and display them. On the other hand the server would receive digital data streams from clients, process them if necessary and store them in its physical storage devices. It will load the digital streams from the physical devices, process them if necessary and transmit them back to clients.

Figure: Client-DMS Environment

Figure #environment#2454> shows a typical client environment (the one used at the moment) and how multimedia data can be transmitted to the DMS and back. In the diagram the client site is equipped with a Codec (GPT H.261) that digitizes video and audio signals and compresses them. The codec is connected to the client machine via an RS449 serial interface which receives the digital data, packetizes them and sends them over the local client Ethernet to the ISDN gateway. The ISDN gateway receives the data packets addressed to the server, encapsulates them in ISDN frames, initiates an ISDN connection to the server gateway and starts sending the data over ISDN. The packetized data can also be sent over PSDN if a high bandwidth link between the client and the DMS is available (e.g. SuperJanet). Alternatively the codec can be connected to the client machine via an ISDN board. In this case data would be sent directly to ISDN not through the ISDN gateway. The server ISDN gateway on the other hand receives the ISDN data addressed to the server, strips off the ISDN headers and sends the data packets to the Server machine. To retrieve data from the Server, the same process happens in the reverse order. The server can have direct access to ISDN via an ISDN board instead of using the ISDN gateway. The Codec constitutes the most expensive part of the scenario. It mainly has two functions:

  1. Analogue to digital and digital to analogue conversion of the audio/video signals;
  2. Compression/decompression of the audio/video signals so that the size of data needed to be transmitted and stored is suitable for the network resources (bandwidth) used at the moment.
The compression process is usually more expensive than the decompression process. The compression process is needed just once by the client initiating the object storage request whereas the decompression process is needed by each client wishing to retrieve the compressed object. Development in the processing power available to end users makes it possible to compress and decompress audio in software and to decompress low quality video data using software instead of hardware. This means that one of the most expensive elements in the above scenario would just be needed for clients wishing to store data within the DMS or retrieve high quality video data. With more and more processing power being available at the client end and more efficient frame grabbers the codec can be completely exchanged with a software replacement.