NORTHEAST
PARALLEL ARCHITECTURES CENTER AT SYRACUSE UNIVERSITY
NORTHEAST
PARALLEL ARCHITECTURES CENTER AT SYRACUSE UNIVERSITY
NPAC Conferencing System
Created in October 1996 by Tomasz
Stachowiak, NPAC
NPAC Conferencing System (NCS) consists of two main modules. First module is the Conference Engine(CE) which contacts the remote hosts, processes control messages from them and passes the indications of events to the Conference Manager(CM). CE also processes the local messages from CM. To create CM the set of API functions is provided. There is also the API for the conference application management.
NCS uses UDP (User Datagram Protocol) to speed up data exchange.
For real-time applications it fulfills the performance requirements
without affecting quality of service. It's up to application to
create higher level, more reliable protocol if necessary. However
implementing such a protocol for priority messages is also predicted
as internal part of CE.
The conference in NCS is based on the notion of session. Session is a group of users on different machines connected in virtual many-to-many channel. So far there can only be one session on one machine an just one user on the machine can participate in conference. Many applications can be attached to the session.
User can start new session and invite others. Invitation will be visible for remote user providing he has his CM running. In this case he can accept or reject the invitation. If he accepts he will become conference participant. From this moment all his NCS application will collaborate within the current session. Each conference participant is free to invite users to participate in conference. There is no other way to join the conference.
Each participant can start Conference Application(CA). If it is
invoked from CM panel it will be started automatically on all
participant machines. Also exiting the application from CM panel
causes closing all participant applications.
Right now following NCS applications exists:
Using H.261 and H.263 compression it offers very low bandwidth
having very good picture quality at the same time. H.263 option
takes less bandwidth but is more CPU intensive so for slower machines
H.261 algorithm is recommended. Speed can be increased even more
by choosing Intra frames only option. However it causes
significant increase of used bandwidth.
It has two compression options:
GSM - used in digital cellular telephony, very bandwidth efficient but designed just for the speech transmission.
ADPCM - takes more bandwidth but offers much better quality, good enough even for the music.
So far both option exchange 8000 frames per second sound.
Allows conference participants sharing the same drawing area.
Simple geometric figures drawing, text writing, color and line
width changing, saving and restoring pictures from a file features
are supported.
Existing version if NCS is a draft version. It can be changed or replaced at any time. By now we have working version only on SGI Indy, IRIX 5.x. Other platform versions can be expected soon. You can download all the files by clicking here.