introduction

30 April 2014 at 12:07pm
Hi All, A lot of you in the NI HE and FE sectors will already know me by my work with the Jisc RSCni.  However, for those of you who do not know me, I would like to take this opportunity to formally introduce myself, Noel McDaid, as the new Janet Customer Engagement and Service Manager for Northern Ireland. My background is in the education sector within Northern Ireland, where I have a total of 17 years experience.  4 years experience as a Systems and Network Engineer at North West Regional College and, for the last 13 years, as Technical Adviser for Jisc RSCni.
Anonymous
When videoconferencing over ISDN, IP and other networks, although echoes can be reduced to a manageable level delays on the sound or “Latency” remains. This introduces an unnatural element into a videoconference that participants need to be aware of. All participants have to learn to conference within the limitations of the time delay, and so interaction is less spontaneous than with a face to face meeting. As most conferences are voice switched, sharp interjections will cause the conference to switch automatically to that site; this may clip another site’s presentation.
Anonymous
To reduce echoes caused by transmission delays, special devices known as “Echo Cancellers” are used. These devices when operating efficiently can almost eliminate all traces of echo during a conference. Room acoustics and microphone positions also affect the level of echo. If a microphone is moved or its sensitivity is altered during the conference, echo could be introduced until the echo canceller has realigned itself to the new environment.
Anonymous
To keep transmission costs to a minimum, the data rate for videoconferencing is generally very low. This means that the vision signals need significant compression to squeeze into the small space available. Compression requires a considerable amount of electronic processing. One penalty to pay for this is the time taken for the vision signals to travel through all the circuitry. The delays are appreciable and can be of the order of 0.25 second. The delays introduced in compressing the sound signals are very much less, as not so much signal processing is needed.
Anonymous
Videoconferencing is a form of television so the guidelines for appearing on television are relevant. Because videoconferencing uses a reduced quality network link to keep costs down some other limitations are also introduced. Television cameras can only handle a very limited range of contrast so wear clothes in pastel shades and plain weaves. Strong saturated colours and white shirts are not recommended. Within a videoconference, faces are the focal point, so clothing must not pre-dominate the image. Avoid clothes that are brightly coloured or with a distinctive pattern.
Anonymous
A third option is “Continual Presence” where the picture is segmented to show images of each site continuously, with the sound being voice switched. With continual presence it is important to appreciate that the greater the number of sites and the smaller their individual images the less easy it is to recognise anything meaningful on the viewing screen. It does depend on viewing distance etc. but generally, continual presence is unworkable for more than four sites.
Anonymous
Another option with Multipoint working is “Chairman Control” where all sites receive pictures from the Chair site alone. The Chair site will see images from the remote site currently speaking. All sites receive all sound. 
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
Conferencing between two sites is termed “Point to Point” and is the most frequently used method. It only requires equipment at each site and the network of choice. If more than two sites require a simultaneous conference, this is termed “Multipoint” conferencing, and an additional specialised piece of equipment is required, called a “Multipoint Control Unit” or MCU. Some videoconferencing CODECs can support limited multipoint working (e.g. up to 4 sites). Generally, MCU’s are very expensive and are rented from service providers just for the duration of a conference.
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.
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