2002 - cesnet

programs which control the integration process. More participants in a videoconferenceroom, and an emphasis on presentation and on sharing visualizedtools, require more projection technologies, cameras and a higher quality ofsound processing, i.e., more computer technologies for coding/encoding of imageand sound.It is obvious from the required characteristics of AG that the volumes of dataexchanged along the network will be significant and that the minimum acceptableconnection of the entire AG is 100 Mbps, with individual AG componentsconnected with a fully switched link of 100 Mbps. AG makes use of the serviceoffered by the MBone network, wherever it is available. Otherwise, bridgingwas provided to the nearest available MBone node. Wherever it is impossibleto make use of bridging, a mirror is used (UDP Packet Reflector), similar to thatdescribed above.Video is therefore developed on tools with the H.261 protocol and as regardsthe quantity, it is necessary to be able to accept, process and present at least18 × QCIF (177 × 144 pixels) and 6 × CIF (352 × 288 pixels) and read, encode andtransmit 4 × CIF. Transmission is carried out using the RTP protocol.It is necessary to make sure that the audio section can accept, decode andpresent at least six 16-bit 16 kHz audio-streams and accept, encode and sendone audio stream of the same quality. It is necessary to realize that echo andother sound effects may become a problem inside a room. The quality of theoutgoing sound must be ensured with suitable equipment – from microphonesto echo-cancellation devices.Presentations can be shared with the use of MS PowerPoint, enabling usersto control PowerPoint applications within more remote computers in theserver–client mode. Progress of computation or dynamic visualization can beshared using the VNC (Virtual Network Computing) tool. This system allows todisplay of the desktop of a remote computer or share this desktop with moreusers, independent of the operating system and architecture. VNC contains twocomponents: the image-generating server and a viewer, presenting the image onthe screen of a connected client. The server may be run on architecture differentfrom that of the viewer. The protocol connecting the server and the vieweris simple and platform independent. No status is saved in the viewer, whichmeans that in case of an interrupted connection, no data get lost and connectioncan be restored again.AccessGrid nodes form a worldwide network concentrated particularly at locationswith grid infrastructure and at places of “big” users, i.e., particularly thehigh energy physicists and astrophysicists. At present, there are 132 nodes inoperation, of which more than 40 serve for international communication. Noneof them has been installed in the Czech Republic, as of yet. The nearest nodesare at TU Berlin and CERN. In addition, a new node is being constructed inHigh-speed National Research Network and its New Applications 200289