Previous Table of Contents Next


LAN Networking

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.

Fast Ethernet
will support multimedia, but not necessarily very effectively. Switched Ethernet at 100 Mbps, provides plenty of raw bandwidth, but contention at the switch remains an issue. Starworks (Starlight Networks) performs both multicast and peer-to-peer networking over a FDDI backbone connected to Ethernet switches. Starlight-networks claims that up to 40 users can be supported in this fashion. The company’s StarWare, running on top of Novell’s Netware, converts an existing server into a multimedia server, prioritizing video data.
Isochronous Ethernet (IsoEthernet)
recently was formalized by the IEEE 802.9a committee. As illustrated in Figures 14.3 and 14.4, IsoEthernet runs over Cat 5 UTP at 16 Mbps, with 10 Mbps reserved for standard Ethernet packet streams and 6 Mbps available for isochronous video/multimedia. Through this process of frequency division multiplexing, isochronous data (voice and video) is supported effectively and without interfering with the basic reason that LANs are deployed—data communication. The advantage is that Ethernet is everywhere. The drawback is that it is a solution limited to a LAN (read single-site environment)[14-22].


Figure 14.3  IsoEthernet bandwidth allocation.


Figure 14.4  IsoEthernet network in support of videoconferencing.

FDDI
clearly, is the most capable LAN standard for multimedia, although it also is expensive to deploy and support. FDDI’s sheer bandwidth of 100 Mbps and its token-ring access method (Figure 14.5) will support multimedia applications reasonably effectively, although it is possible that an intensive multimedia conference can speak to all of the available bandwidth. FDDI-II, still in draft form, specifically is intended to support isochronous traffic, as well as standard asynchronous LAN traffic. FDDI II will also be expensive.


Figure 14.5  Videoconferencing over FDDI.

ATM-based LANs
in the workplace will support multimedia quite nicely, even at 25 Mbps and 50 Mbps. ATM offers low latency, prioritized cell transport, and WAN connectivity. Workplace ATM is expensive, however, at around $1,000 per seat at 25 Mbps; higher speed ATM versions are considerably more expensive.
Dedicated LAN Networks
also have been developed for videoconferencing and collaborative computing. By way of example, VideoLAN Technologies in March 1996 unveiled a system that involves proprietary equipment and transmission technology. The system will support NTSC-quality video and full-spectrum audio between terminals as much as 2,000 feet apart. The system also is designed to support video-on-demand through the use of video servers, and is expected to be used in support of distance-delivered learning over the WAN. Not inexpensive, the system sells for $4,795 per seat and requires a dedicated network, rather than running alongside data in a legacy LAN environment [14-23].

MAN Networking

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.

WAN Networking

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

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 wasn’t 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].

Multimedia Standards

At the international level, the ITU-T’s 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.


Previous Table of Contents Next