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BUILDING NETWORKS WITH GIGABIT ETHERNET

Gigabit DTEs can be connected via a direct link, via CSMA/CD repeaters for shared media solutions, via full-duplex repeaters for shared media solutions and with switches for dedicated bandwidth solutions.

Half-duplex repeaters are the traditional means for providing shared bandwidth to Ethernet users. The standard defines operation of a half-duplex CSMA/CD repeater, which supports collision domains of up to 200 meters in diameter. Only one repeater can be contained within a single collision domain. Half-duplex repeaters offer an extremely low-cost method for sharing access to 1000M bps service, but they also offer reduced performance, compared with Full Duplex Repeaters and switches.

Full duplex repeaters (FDRs), also called buffered distributors, offer the traditional low-cost shared media operation of repeaters, but with support for full duplex operation. They utilize the full duplex flow control mechanism to arbitrate access instead of Ethernet's traditional CSMA/CD. On-board buffers store incoming packets until they can be repeated to other ports. Asymmetric flow control is used to temporarily halt the flow of incoming packets when the input buffers fill. When the buffers empty, the halted transmitting units are allowed to resume transmission. The combination of full-duplex operation, input buffers, and flow control means that FDRs can support effected shared media operation at close to 1000M bps, providing much higher throughput than traditional half-duplex repeaters.

Switches provide dedicated bandwidth connections and a means for connecting networks with different bandwidths. Each link in a collision domain represents a separate collision domain and, since there are no collisions, links can operate at either half-duplex or full duplex.

Gigabit Ethernet switches fall into two categories: aggregating and backbone. Aggregating switches are used to connect one or two gigabit links to a number of 100M bps ports. Flow control is used to keep the gigabit links from overwhelming the switch buffers when a gigabit flow is directed to one or two 100M bps ports. Backbone switches provide multiple gigabit ports and have multi-gigabit backplanes to provide wire-speed connectivity between ports. They typically have larger buffers than aggregating switches and may offer advanced features such as layer 3 switching and virtual LANs.

MANAGEMENT OF GIGABIT ETHERNET

As with 100BASE-T, Gigabit Ethernet makes use of the current 802.3 Ethernet management suite as defined in Clause 30 of 802.3u. The basic Ethernet frame format, CSMA/CD operation, and both the RMON and SNMP MIBs remain virtually unchanged (although some minor changes were made.) This means most management tools should continue to work seamlessly with Gigabit Ethernet products.

SUPPORTING ORGANIZATIONS

Two multi-company organizations are significant contributors to Gigabit Ethernet technology: the Gigabit Ethernet Alliance and the Gigabit Ethernet Consortium. The Gigabit Ethernet Alliance is an organization composed of more than 120 companies to facilitate the development of the standard and provide technology marketing support. Headquartered in Silicon Valley, the GEA has supported technology development by providing mechanisms to facilitate progress on the standard between formal IEEE-sponsored meetings and to develop test suites to ensure product conformance and interoperability. The technology marketing arm of the GEA has focused on promoting Gigabit Ethernet technology through press releases, a Web site, technology demonstrations, and seminars. Since the major goal of the GEA is to support the development of the Gigabit Ethernet standard, it has a limited lifespan and may disband as early as mid-1998.

Until it disbands, the GEA will maintain a Web site (www.gigabit-ethernet.org), which provides information about the technology, standards status reports, and links to GEA member company sites.

In the summer of 1997, a GEA team working with staff members of the University of New Hampshire Interoperability Laboratory established the Gigabit Ethernet Consortium. Founded July 7 with 15 member companies, the GEC provides an independent forum for testing Gigabit Ethernet products for conformance and interoperability. This program will provide vendors with critical development information and provide users with the confidence that first-generation products will have a high degree of interoperability. Unlike the GEA, the Gigabit Ethernet Consortium is intended for long-term operation.


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