• Poll your audience
• Interact with the "white-board" • Chat live
6.2.2 VNC
• No state is stored at the viewer. This means you can leave your desk, go to another machine, reconnect to your desktop and finish your job.
• Small and simple. The Win32 viewer, for example, is about 150K in size and can be run directly from a floppy. There is no installation needed.
• Platform-independent. A desktop running on a Linux machine may be displayed on a PC, PDA. Or a Solaris machine. Or any number of other architectures. There is a Java viewer, which will run in any Java-capable browser.
• Sharable. One desktop can be displayed and used by several viewers at once, allowing CSCW-style applications.
• Free! It is downloadable. Both binaries and source code are available from http://www.uk.research.att.com/vnc , along with a complete copy of documentation.
6.3 The Shared Display
6.3.1 WebEx
6.3.1.1 Vector Graphics
Text and graphics are sent in a vector format (i.e. drawing primitives lines, rectangle, text, etc.) and not as bitmaps. This produces high quality images and also drastically reduces the size of the data.
6.3.1.2 Compression
All large data transfer and file uploads are compressed. This not only
reduces network traffic it also adds a level of ‘encryption’ to the data stream.
6.3.1.3 Incremental Update
During application sharing the contents of the window are dynamic. WebEx MeetingCenter incrementally updates only those portions of the screen that have
changed. Furthermore the updates are transmitted as vector graphics commands and not as bit maps.
6.3.1.4 Video Compression
Several video compression and optimizations have been incorporated into meeting center. The data stream produced by video transmission is directly related to the rate of change of the video.
6.3.1.5 Network communication
The shared display of the WebEx is based on real-time multi-point data communication. It is following industry standard, T.120.WebEx has optimal protocol. WebEx
MeetingCenter is able to work through all firewalls using the HTTP protocol. However, it first checks to see if communication can be established using the lower level TCP
protocol. This is more efficient and reduces network traffic. Using the TCP protocol reduces network traffic by about 10% when compared to HTTP.
6.3.2 VNC
6.3.2.1 Bitmap image
Since the bitmap is easy to handle on the various platforms, all images from the VNC server are in bitmaps.The VNC simply works with a server to update the framebuffer displayed on a viewer. Because it works at the framebuffer level it is potentially applicable to all operating systems, windowing systems and applications.
6.3.2.2 Incremental Update
When the VNC client or server is sharing the contents of the window or events VNC incrementally updates only those portions of the screen that have changed.VNC has a variety of different encoding schemes for the pixel data, and it can select the appropriate scheme for each rectangle the server sends, and make the most of network bandwidth, client drawing speed and server processing speed.
6.3.2.3 Adaptive update protocol
The update protocol is demand-driven by the client. That is, an update is only sent by the server in response to an explicit request from the client. This gives the protocol an adaptive quality. The slower the client and the network are, the lower the rate of updates becomes.
6.3.2.4 Input protocol
The input side of the protocol is based on a standard workstation model of a keyboard and multi-button pointing device. Input events are sent to the server by the client whenever the user presses a key or pointer button, or whenever the pointing device is moved. These input events can also be synthesised from other non-standard I/O devices. 6.3.2.5 Network communication
The VNC operates over any reliable transport such as TCP/IP, and it is basically point-to- point network. Each client uses differnet number of port and each platform is accessed via pre-defined port. Thus, the server should open the connection for each client and send image even if they are all same images.
7 Instant Messengers
By Sangyoon Oh Collaboration Tool: Instant Messenger
Instant message service on Internet is so popular and there are lots of companies, which provide free messenger service. If we consider Internet Relay Chatting (IRC) and other Internet text-chat client, the area we are looking is broader. Messenger service is a free service that allows you to communicate with an online friend instantly. Sending text messages is one of communication method with, in addition the free phone call features also provided by Internet-phone company (Most company has a contract with
Net2Phone). List of major Instant Messenger service is MSN messenger service, Netscape/AOL messenger service, and Yahoo messenger service. Jabber.com released Jabber 1.2 server and client, which is Internet Messaging (IM) platform (including a service itself). This is XML based, flexible, distributed network, and open source. So it is possible to have independent IM server, which is interoperable with Major Instant
Messenger service.
Yahoo messenger: messenger.yahoo.com
MSN messenger 3.0: messenger.msn.com
Jabber: www.jabber.com
Trillion: www.trillion.cc
Text Chat Client List: winfiles.cnet.com/apps/nt/chat-text.html