Handbook of Local Area Networks, 1998 Edition:LAN Basics Click Here! Search the site:   ITLibrary ITKnowledge EXPERT SEARCH Programming Languages Databases Security Web Services Network Services Middleware Components Operating Systems User Interfaces Groupware & Collaboration Content Management Productivity Applications Hardware Fun & Games EarthWeb sites Crossnodes Datamation Developer.com DICE EarthWeb.com EarthWeb Direct ERP Hub Gamelan GoCertify.com HTMLGoodies Intranet Journal IT Knowledge IT Library JavaGoodies JARS JavaScripts.com open source IT RoadCoders Y2K Info Previous Table of Contents Next Repeaters and Repeater Connections Repeaters provide for shared media operation in 10BASE-T and 100BASE-T via the CSMA/CD protocol. 10BASE-T networks have a collision domain diameter of 1,000 meters. This permits building large, single collision domain networks using hierarchical, cascaded repeating hubs to increase port density. 100BASE-T does not permit hierarchical cascading of hubs, because the maximum collision domain for UTP is slightly more than 200 meters (see Exhibit 1-2-10). Exhibit 1-2-10.  Repeater Connection Styles Two techniques can be used to build large, single collision domain networks (i.e., increase port density). One technique is to use modular hubs, where ports can be added by inserting additional multi-port cards into the hub chassis. A second is to use stackable hubs—standalone repeaters that can be connected via high bandwidth stacking ports that do not impact the collision domain. Topology Rules Topology rules for half-duplex 100BASE-T networks are shown in Exhibit 1-2-11. Copper links are limited to 100 meters by the US cabling standard EIA/TIA-568-A. A collision domain containing two copper links can contain one class I repeater and two 100-meter copper links or two class II repeaters, two 100-meter copper links and a 5-meter copper inter-repeater link. A collision domain containing a class I repeater with two fiber links can support two fiber links of 136 meters, for a collision domain diameter of 272 meters. A collision domain containing a class I repeater also can support one copper link of 100 meters and a single fiber link of 160 meters. Exhibit 1-2-11.  100Base-T Topologies A fiber DTE-DTE half-duplex collision domain (e.g., a switch-to-switch or switch to server) can support a 412-meter fiber link. Links of up to 2 kilometers can be supported over fiber by operating in full-duplex mode, which turns off the CSMA/CD portion of the protocol and requires a dedicated link (see Exhibit 1-2-12). Exhibit 1-2-12.  Full Duplex Gigabit Ethernet Work to extend the Ethernet family to 1000M-bps (gigabit) operation is well underway. The first products using the new technology were demonstrated at Networld + Interop Las Vegas in May 1997 and the first products started shipping during the summer of 1997. Initial products will support operation over 62.5 micron multi-mode fiber (1000BASE-SX), 50 micron single-mode fiber (1000BASE-LX) or short lengths (to 25 meters) of coaxial cable (1000BASE-CX). The operation of these products is being defined in a supplement to the IEEE 802.3 standard entitled 802.3z. It is scheduled for completion in early 1998. A second supplement, entitled 802.3ab, will define gigabit Ethernet over 100-meter, four-pair Category 5 copper links (1000BASE-T). It is scheduled for completion in late 1998. IMPACTS ON NETWORK DESIGN Fast Ethernet is a family of 100M-bps signaling systems for use with the standard Ethernet MAC layer. The family consists of four signaling systems (100BASE-TX, 100BASE-T4, 100BASE-T2, and 100BASE-FX) and technologies that support automatic start-up (Auto-Negotiation), shared media operation (Repeaters), full-duplex operation, and flow-control to manage traffic flow. Fast Ethernet devices work seamlessly with legacy Ethernet systems: they have the same MAC layer, the same frame format, and the same CSMA/CD protocol for shared media operation. Auto-Negotiation ensures that all 100BASE-T devices operating over copper links automatically configure themselves to operate with link partners. This makes 100BASE-T a very economical technology for adding high-bandwidth links to legacy systems. Higher-speed operation reduces the diameter of 100BASE-T shared media collision domains to approximately 200 meters for copper. Collision domains can be extended through the use of fiber and connected via switches to build large, complex networks. Full-duplex operation improves bandwidth for bi-directional links and increases the maximum length of fiber links to kilometers. Port density within a single collision domain is expanded through the use of modular and stackable hubs. 100M bps is not the end point for Ethernet. 1000M-bps (gigabit) devices were demonstrated in the spring of 1997 and began shipping in the summer of 1997. Targets for gigabit Ethernet operation are 700 meters for full-duplex single mode fiber links, 25 meters for short-haul copper coax links, and 100 meters for Category 5 copper links. Previous Table of Contents Next Use of this site is subject certain Terms & Conditions. Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. Reproduction in whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Please read our privacy policy for details.