ATM* Asynchronous Transfer Mode. Packages, transmits and switches data to optimise the connection. Advantages: very high quality of image; dedicated lines. Disadvantage: very expensive.
ADSL/DSL* (Asymmetric) Digital Subscriber Line. Uses the frequencies in telephone lines not used in regular telephone calls. Advantages: High quality image; dedicated lines; not very high cost. Disadvantages:BT is allowing very high contention ( number of subscribers sharing a bandwidth) which means if a lot of your neighbours install it, the bandwidth drops.
ISDN Integrated Services Digital Network. Advantages: High quality; dedicated lines. Disadvantages: High cost to install and use; BT responsible for maintenance so unless regularly used tend to be poorly maintained and therefore unreliable; location of ISDN connection tend to be into meeting rooms, not classrooms.
IP gateway systems Using a gateway system enables the user to connect any IP port to the ISDN line, in effect extending the ISDN link into any room with an IP port. Advantages: High quality; flexible use. Disadvantages: expensive equipment; experienced technical knowledge required to set up.
IP room-based systems Videoconferencing equipment that can plug into IP ports. Advantages: high quality, flexible, easy to operate. Disadvantages: expensive; does not have a dedicated line, so will have to share bandwidth with other users of the network.
IP desktop systems A computer with a camera attached. These can be used either for 1 - 3 students (sitting around the computer) or larger groups (by projecting the monitor image via a data projector). Advantages: easy to use; flexible; no cost; can use other applications with the image; does not require high bandwidth. Disadvantages: low quality. See appendix 2 for more details.
A VLAN (Virtual Local Area Network) is a netwrok run in parallel with the regular network of computers within an institution. The advantages is that it can have bandwidth dedicated to just those maching on the VLAN, reducing the competing demands that often reduce the quality of the videoconference. Network ports can be assigned to the VLAN through the software that runs the network
Before 2004, this was the standard videoconferencing software. Since it is a Microsoft product it comes as standard on all PCs. For XP operating systems, jsut go to the Run program and type in conf.exe. Early operating systems had an icon for the program. NetMeeting works well at connecting two PCs but will not effectively link more than two. NetMeeting has the advantage on enabling the two monitors to be linked, so one person can share their documents and programs with the other. Whiteboard, chat and file transfer are also available. To use NetMeeting you will need to inform people of your IP address, since this is the information used to connect the two PCs.
MSN has supplanted NetMeeting as a general communication tool and has two advantages over NetMeeting; 1) it seamlessly integrates text, audio only and video into one interface; 2) users connect via each others’ email addresses. The disadvantage is that users need to either register for a Microsoft Passport or have a hotmail email address to use it. Application sharing is supported through the Activities menu. MSN will link any number of PCs, but lower spec PCs will not be able to process large numbers of participants.
This freeware can be downloaded from the iVisit website. Users all log in to the iVisit website and enter a pre-arranged room. Several users can share a room at the same time. A chat function is also available, which works better as a means of communication than audio.
As with iVisit this links together several users within a shared room. This software has not yet been tested as part of the ANNIE project.
A Swedish proprietary software, not widely available as yet. This effectively supports many speakers at once, and enables application sharing, however it only supports cameras on USB ports, so if your operating system is NT, it’s not an option.
Again this supports multi-way audio very effectively, and one-to-one video. Multi-way video hasn’t been tested within the project. Applications can’t be shared using the system, though. Yahoo supports cameras on both USB and parallel ports. The audio has the odd effect of cutting out, but this can be fixed by clicking on the voice on/voice off button. The software also can turn off the master record setting for your PC’s microphone when it starts running. Instructions for correcting this are below.
The volume icon (in your taskbar) usually gives you the setting for Master Out i.e. your speakers. However there are two more states Master Record and Other.
If Yahoo has turned off your microphone
- You must check that the microphone is enabled in Master Record.Double Click on the volume icon to bring up the setting
- Click on Options and then choose properties
- Click on Recording and in the list of volume control make sure microphone is selected
- Click OK and the settings shown should now be for Master Record
- Make sure the microphone is not muted (the problem is that it is set as muted in the record but not in the master out)
Bits and bytes A bit (abbreviation for binary digit) is a 0 or 1, the most basic unit of information. Symbol = b.A byte is a string of bits (nearly always 8) and is the standard unit of computer memory. A byte carries the information needed to store a single alphanumeric character. Symbol =B.
Prefixes The prefixes used as multipliers of these are adopted from the SI system (Tennent, R.M. (ed). (1971) Science Data Book, Oliver & Boyd) . They are:
|1 000 000 000 000||tera||T||
Note that T, G and M are upper case, k is lower case. The only one it is important to get right is "M", since "m" is the symbol for milli (a thousandth), although it should be obvious from the context which is which.
|1 000 000 000||giga||G|
|1 000 000||mega||M|
The normal prefixes and those used in computing are not exactly equivalent. Because computer memory increases in multiples of 2 not 10, in computing a kilobyte is actually 1024 bytes, a megabyte is 1024 kilobytes, etc. (1024 = 210). However, the distinction is rarely made.
Rates Rates are always expressed per second, usually abbreviated to "ps", although "/s" and "s-1n" also occur.
Baud rate This is another term used to describe bandwidth - and is slightly different from bits per second in that it is the number of changes of signal per second