Library items tagged: Videoconferencing

Anonymous
Multipoint conferences introduce additional constraints. With Point to Point conferences both sites can see and hear each other throughout the conference. With Multipoint conferences it would be unworkable for all sites to be seeing all other sites simultaneously. Normally, therefore, the conference is “voice switched”. In other words, the image of the site speaking takes precedence and is seen by all the other sites. 
Anonymous
Computers connected to the Internet via a modem and telephone line are limited to a data rate of around 56Kbit/s. Broadband connections using ADSL (Asymmetric Digital Subscriber Line) technology achieve rates from 512Kbit/s up to around 16 Mbit/s. The speed of both these connections will however depend on the amount of data traffic currently on the network and as the name “Asymmetric” implies, the download and upload speeds differ. Generally data can be downloaded approximately twice as fast as it can be uploaded, which for domestic users is convenient.
Anonymous
As has been previously mentioned, a CODEC is necessary to enable the sound and vision signals to be converted and then transmitted from the local site. Another CODEC is also required at the remote site to convert the digital signals back into sound and vision signals for the audience. The method of transmission for IP and ISDN are different and so require different CODECs.
Anonymous
Before the Internet achieved its present ubiquitous state and reached every school the telephone network offered its own digital communication via telephone lines. Termed ISDN (Integrated Services Digital Network), this uses the existing telephone infrastructure to carry digital signals. Offered by telecommunications providers it is available in many parts of the world. The service is accessed through dial up in the same way as a telephone, so the network does not have to be dedicated between the videoconference centres.
Anonymous
All schools now have access to the World Wide Web via the Internet. This technology uses a common method of transmitting and receiving data called IP or Internet Protocol standard to ensure information passes flawlessly between networks. The success of the WWW could not have been achieved without this single ubiquitous standard. A disadvantage of IP transmission is that because all data traffic e.g. e-mails, WWW downloads or videoconferencing has to share the same pipes, they all have to compete for the available space or bandwidth.
Anonymous
The CODEC has two components: the COder and the DECoder. The COder takes the local sound and vision signals and converts them into a form that can be transmitted over a digital network. The DECoder performs the reverse function i.e. it takes the remote site’s digital signals from the network and converts or decodes them into a form that enables the picture monitor to display images and the loudspeaker to radiate sound from the remote site. A CODEC is thus required at each end of the link for a videoconference.
Anonymous
A microphone converts sound energy into an electrical signal to enable it to be recorded or transmitted to a remote location. It has already been mentioned that microphones also pick up unwanted sounds together with the participants’ voices. If these unwanted sounds are significant they will interfere or even completely obscure the desired parts of the sound. The correct choice of microphone and its position in the room are vital to achieve high quality sound.
Anonymous
See Appendix A. The camera converts light images into an electrical signal so that it may be displayed, recorded or transmitted. The camera lens focuses the images onto a light sensitive layer sometimes referred to as a Charge Coupled Device or CCD.
Anonymous
Television camera sensitivity depends on two factors: the efficiency of the light sensitive area (Charge Coupled Device or CCD) that converts light energy into an electrical signal; and the amount of light that the lens transmits from the scene. As the CCD sensitivity is fixed, the only method of altering the camera’s response to varying scene illumination is to adjust the amount of light entering the lens. This is achieved by means of an iris-diaphragm in the light path.
Anonymous
In its most basic form, a videoconference involves transmission of the images and the voices of the participants to a remote site. Optional sources include still images and/or moving sequences from a video recorder, DVD or a PC. The basic conference requires: A television camera to capture images of the participants A microphone to pick up their speech A means of transferring this sound and vision information to the remote location