a iiiodulc for overlaying a motion vidco. Displayiiig a fiill-iriotioii vitlrw OII a coniputcr display requires special liarclware aiid proprirt ary software. When a motion video overlay adapter is changecl, the motion video display module also has to be changed. The extciisibility aiitl custoinid>ility iiiciitioiicd abovc h i icfit dcvclopc~s the iiiost, but thcp arc also useful for users. If a i i s~r doc^ iiot ricctl all of tlic tools provided lq-a conferencing teni. he or she should be ahle to in5tall only those that are required. A user niay also want to change the size aiid position of a chalkhoard window. or to spccify tlic pcriod for wiidiiig t&point-iiig data. Dr$spitc tlic iiriportaiicc of c~xtciisil~ility aiitl customixaliility in desktop confrrencing $ptems, the) have iiot been ~iiiich discused [l]-[GI.In t his paper, w e present an extensilile and ciistonii7ahle conferenciii eiii naiiied ConverStatioii/2. CoiivcrStatio a realtiiiic iiiultiiiicdia dcsktop corifcrciiciiig tliat supports tlpnaiiiic modiile attachnient at initiali7ation tinip. A iiwr can select tool iiiodiiles that he or she wants to iiw. 11y describing them in a tool file. ConverStation/2 provide5 a coiiiirioii c oiiiriiuiiicatiori iiitcrfacc 50 tliat coinniuiiic atioii rriotlulcxs caii bc cliaiigcd msily . A c lialkboard iiwd iii tlic systri~i c ari also bc, cxtciidcd by addiiig a function as a dynamic link library (DLL) or writiiig a niacro coniniand. In addition, the ports ciistoniization at a iiser level. A iiser can decide tlic sim aiitl positioii of cc~cli wiiitlow, and othcr tool parallid crs.
ConfigurationCoiivcrStation/2 consists of two pcrsoiial coiiiputers conncctcd by aii ISDN or a LAN a s 5hO\Vii iri Fig. 1. Tlic coiiiputcr coiitairis a iiiotiori vidco CODEC adapter and a motion video overlay adapter for 1110-tion yideo coiiiiiiiiiiicatioii. The motion video CODEC adapter has analogue inpiit/outpiit of a motion video and aii ISDN iiitcrfacc. A vitlco caiiicm is coiiiiectctl t o tlir adapter, wliicli proccsscs aiialoguc-to-digital coilvcrsioii. coiiiprcssiori, arid traiisriiissioii of vitlco slid aiidio data. The adapter also does receiving. deco~ii-pression, and digital-to-aiialogiIr conversion of video 9 -1 -1