There is a considerable amount of interest in high-speed Ethernet LANs on the part of libraries now that there is a standard for transmission of up to 100 Mbps. The 100 Mbps data transfer rates will be necessary as libraries begin to move full-text, images, and multimedia over their networks. Unfortunately, there is a lack of agreement for achieving 100 Mbps over Ethernet.
In August, 1995 an IEEE decision established 100BaseT as the official Past Ethernet standard. Later, however, responding to vendors supporting the competing 100VC-AnyLAN approach, it designated the competing technology as an option.
IEEE made this decision because, despite its endorsement of 100BaseT, nearly 40 vendors continue to support 100VG Ethernet technology. Companies such as Cabletron Systems Inc., Cisco Systems Inc. , Compaq Computer Corp. IBM Corp. , Motorola Corp., Pericom Semiconductor Corp. , and Thomas-Conrad prefer 100VG-AnyLAN, a technology developed by Hewlett-Packard, and are committed to continuing its use as the product is renamed 100BaseVG.
The 100BaseVG method uses a demand-priority access method instead of CSMA/CD, which allows priorities to be given. In contrast, the 100BaseT protocol relies on a collision-detection method, which will check to see if the network is free when a device wants to gain access to the LAN. If it is not, it waits a certain amount of time before retrying. If the network is free and two devices attempt access at exactly the same time, they both back off to avoid collision. While the 100BaseVG standard delivers data at 100 Mbps, it supports 10BaseT Ethernet and Token Ring networks, allowing network managers to use existing networks and cabling while upgrading to higher speeds in phases.
While currently an estimated 70 percent of high-speed LANs are based on 100BaseT, 100BaseVG probably will gain enough ground within the next year that neither standard will emerge as a clear winner.
The safest course of action is to purchase a product from a major company with the resources to continue support even if new sales decline as the result of another standard becoming dominant. Commitments for at least three years of support generally are available to purchasers spending more than $50,000.
