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Multimedia over LANs, as noted previously, is problematic. Bandwidth certainly is an issue, as is flow control. Multimedia is not tolerant of delay due to its isochronous voice and video elements. Current options for LAN video and multimedia collaboration include Fast Ethernet, IsoEthernet, FDDI and ATM. In any case, one must be cautious in supporting multimedia over a LAN.
Figure 14.3 IsoEthernet bandwidth allocation.
Figure 14.4 IsoEthernet network in support of videoconferencing.
Figure 14.5 Videoconferencing over FDDI.
SMDS is the one true MAN technology capable of supporting multimedia at reasonable cost. SMDS will support isochronous traffic on a priority basis. SMDS is not widely available, however.
ATM offers the greatest potential for multimedia over the WAN. Now being deployed at Gbps backbone rates and with DS1-DS3 access rates, ATM supports multimedia nicely. ATM, however, is expensive. The ultimate solution, of course, is B-ISDN, which is based on ATM network technology and which employs SDH/SONET as the physical infrastructure. B-ISDN will support a wide range of services, providing bandwidth-on-demand.
The Internet also supports videoconferencing and multimedia, with the latter being the purpose behind the World Wide Web (WWW). Although it is slow and rough, the presentation of true multimedia is routine and inexpensive. Clearly, there is a significant issue in terms of bandwidth as well. The Internet really wasnt designed to support voice or video, much less multimedia. Heavy use of the Internet for such applications places great strain on the backbone networks, causing brownouts (access delays and slow response times) and even threatening meltdown. Internet Service Providers (ISPs) sometimes discourage or even forbid videoconferencing, as it requires enough bandwidth to freeze out other users. Additionally, the bandwidth limitations of the typical local loop further affect the viability of such applications, particularly in the case of analog local loops, regardless of the speed of the contemporary modem. As always, the strength of the chain is limited by the weakest link.
The Internet supports multipoint videoconferencing through the MBone (Multicast backBONE), which allows a variety of shared, realtime collaborative applications to interact with reasonable efficiency. Videoconferencing, in specific, is supported by the CU-SeeMe software, that was developed at Cornell University and has become a de facto standard. Future, serious use of the Internet for such applications will depend heavily on improved compression technologies and increased bandwidth in the backbone [14-24].
At the international level, the ITU-Ts series of H.32x video and T.12x conferencing standards set the stage for at least a minimal level of interoperability. Related compression standards include H.323 for Ethernet and H.310 for ATM. The International Multimedia Teleconferencing Consortium (IMTC) is sponsoring a number of test events in support of ITU-T standards.
The Multimedia PC Marketing Council (MPC) was formed in 1991 as a subsidiary of the Software Publishing Association. Members include Creative Labs, Fujitsu, Microsoft, NEC, Tandy, and Zenith. MPC developed an industry standard for multimedia workstations, based on the 80386SX microprocessor, an 808386 chip with a 16-bit data path. Multimedia also is viable on late-model Macintosh computers and most RISC workstations.
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