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
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
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
Analogue to digital and digital to analogue conversion of the audio/video
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.