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<HTML><HEAD><TITLE>Chapter 25 -- How Intranet Videoconferencing Software Works</TITLE><META></HEAD><BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000EE" VLINK="#551A8B" ALINK="#CE2910"><H1><FONT SIZE=6 COLOR=#FF0000>Chapter 25</FONT></H1><H1><FONT SIZE=6 COLOR=#FF0000>How Intranet VideoconferencingSoftware Works</FONT></H1><HR><P><CENTER><B><FONT SIZE=5><A NAME="CONTENTS">CONTENTS</A></FONT></B></CENTER><UL><LI><A HREF="#HowCUSeeMeIntranetVideoconferencingWorks">How CU-See-Me Intranet Videoconferencing Works</A></UL><HR><P>Intranets are all about communication. And there is often no betterway to communicate than in face-to-face encounters. However, intranetsare also about communication outside of physical boundaries likebuildings, companies, states, and countries. Often, of course,face-to-face meetings are not practical, due to time limits orbudget constraints. In a corporation with branch offices, forexample, it can be very expensive and a waste of resources tofly people from all over the country to a single location fora one-hour meeting. With intranet videoconferencing software,however, people can hold face-to-face meetings even though theyare located on the other side of the continent from each other.It allows people to see each other and talk to each other whileseated at their computers.<P>Videoconferencing requires a few simple hardware components: avideo camera, a microphone, and a sound card for each participatingcomputer. The cost of this hardware has dropped dramatically sothat it's quite affordable-and most new computers now come equippedfor sound.<P>There are many different software programs available for videoconferencingon intranets. Microsoft and Netscape, among others, are pushingvideoconferencing systems. The longest-standing videoconferencingsystem on the Internet-CU-See-Me-also has intranet-based videoconferencing.It has been around longer than any other IP-based videoconferencingproduct, and that's what we'll look at in this chapter.<P>CU-See-Me videoconferencing works on a client/server model, likemany other intranet applications. The CU-See-Me client runs ona local computer, and it can run on many different kinds, includingPCs and Macs. When someone wants to join a videoconference, theylog onto what's called a <I>reflector</I>-which is really justanother name for videoconferencing server software sitting onan intranet server. <P>Reflectors can handle multiple videoconferences. Videoconferencescan be on an ad hoc basis, with people logging in when they want,or they can be scheduled ahead of time. When someone joins a conference,they will see and hear everyone else in the conference-and everyperson in the conference will be able to see and hear them.<P>The reflector software is of special benefit to intranet administrators.It allows for security, so that administrators can block unauthorizedusers from participating in videoconferences. Administrators canrestrict access to particular users for specific conferences byusing passwords. <P>The software also allows for load balancing. When intranet useis high overall, for example, it can devote less bandwidth tovideoconferencing, to free intranet resources. When use is low,it can devote more bandwidth to videoconferencing.<P>The videoconferencing software can be used to broadcast informationas well. The head of your company, for example, could make announcementslive by video to every desktop computer so everyone in the corporationcan watch and listen to the announcement simultaneously.<H2><A NAME="HowCUSeeMeIntranetVideoconferencingWorks"><FONT SIZE=5 COLOR=#FF0000>How CU-See-Me Intranet Videoconferencing Works</FONT></A></H2><P>There are a variety of software programs available that enablepeople to engage in videoconferences on intranets. One of theearliest and most popular Internet videoconferencing software,CU-See-Me, has also been built to handle intranet videoconferencing.CU-See-Me allows people with desktop computers to have live videoconferenceswith individuals and groups anywhere across the intranet. Anyonecan do videoconferencing with software and hardware that is quiteinexpensive.<OL><LI>CU-See-Me videoconferencing works on a client/server model.People run the CU-See-Me client on their computer to log intoa special server called a <I>reflector</I>. A reflector can hostmany simultaneous live videoconferences. When you log into a reflector,you can join any conference that exists. When logged into a reflector,a signal goes out regularly from your computer to the reflector,telling others logged in that you are available for a videoconference.<LI>The video data is sent using UDP (User Datagram Protocol).Unlike TCP, the UDP does not check for data integrity, nor therefore,does it ask for bad packets to be resent; it just acknowledgesthe receipt of the data. The result is that UDP provides for amore uninterrupted data transfer and so it provides smoother transferand is more efficient than TCP when sending video data.<LI>You need a video camera, a microphone, and a sound card onyour computer. The camera converts your video image into digitaldata. The CU-See-Me software then compresses and encodes thatdata, enabling it to be sent across the Internet or intranet.If the data wasn't compressed and encoded, it would be too largeto be sent. CU-See-Me also saves bandwidth by sending only thepart of the image that has changed. So, for example, if someone'shead moves, it will transmit only the moving head, and not thebackground, which hasn't changed. The person who wants to seeyour image also has to have the CU-See-Me software. The softwaredecodes the video image, and displays it as video on the person'sscreen.<LI>The reflector software contains many tools that intranet administratorscan use to better control videoconferencing. It allows administratorsto control the intranet bandwidth devoted to videoconferencing,both to ensure the highest-possible video quality, and also tomake sure that the rest of the intranet is given the proper resources.It allows administrators to configure specific conferences atspecific times, and also enables security measures such as password-protectingthe server, so that only authorized users can log in, or so thatonly specific intranet users can log into specific conferences.Reflectors can also automatically adjust the rate of video transmissionto the amount of traffic on the intranet, sending lower-qualityvideo when traffic is congested, and higher-quality video whentraffic is lighter.<LI>People on an intranet can participate in videoconferenceswith people on the Internet (provided the firewall doesn't blockthe packets). To join an Internet conference, people log intoan Internet reflector and participate as they would normally.If they can have a direct connection, they can participate ina videoconference by using the Internet person's IP address.<LI>One-on-one conferences do not require going through a reflector.If you know the IP address of someone on the intranet who wantsto have a videoconference, you can connect directly to that person'sworkstation.</OL><HR><CENTER><P><A HREF="ch24.htm"><IMG SRC="PC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="#CONTENTS"><IMG SRC="CC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="contents.htm"><IMG SRC="HB.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="ch26.htm"><IMG SRC="NC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><HR WIDTH="100%"></P></CENTER></BODY></HTML>?? 快捷鍵說明
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