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 The 258A standard has become the most widely accepted standardfor new installations because it can accommodate signaling for bothEthernet (10Base-T) and Token Ring LANs running over UTP withoutrequiring that the wall jack be rewired. The 258A standardspecifies a configuration only for four-pair wiring, so mostinstallations today run only four-pair cabling to each wall jackand are terminated in an RJ-45 form. Exhibit 1-3-4 shows the USOC,258A, EIA, and 10Base-T wire sequences. Exhibit 1-3-4.  USOC, 258A, EIA and 10Base-T Wiring Sequences for Twisted Pair Cabling The EIA/TIA standard for wire sequences is based on the 258Astandard but it is modified to be backward compatible with two-pairUSOC wiring. The IEEE has specified the Ethernet 10Base-T standardwith an RJ-45 form factor, connection at the wall plate using onlytwo pairs, and a sequencing that is a subset of the 258A standard.The thinking behind only specifying two pairs is that Ethernet onlyneeds two pairs to function, and leaving the other pins unconnectedreduces the risk of the wrong equipment (i.e., a telephone) beingmistakenly connected to a data jack. For fiber media, the standard is multimode 62.5/125 mm (the twonumbers refer to the diameter of the core and cladding). Nomechanical end termination is specified, however, one of the mostpopular terminations today for fiber cable is the ST connector. Theother major fiber termination is the FDDI termination, which isessentially just two ST connections molded into one housing so thatone cable containing two fibers can be attached to a device. There are additional standards for form factors and wiringsequences for different applications and media types (e.g.,thicknet and thinnet coax). The preceding paragraphs have coveredthe main techniques used in LAN installations. There are alsostandards covering all other aspects of the wiring system design.This includes Underwriters Laboratory and National Electrical Codeelectrical and fire safety standards for cabling, both aboveceilings and in and between wiring closets, and EIA specificationsfor maximum wiring run distances for horizontal and backbone cabling, minimum wiring closet size, power configurations and conditioning, and other general facility specifications. Some of these standards are required by law and compliance is mandatory. Other standards are considered “best practices” and it is in the best interest of the organization using the wiring system to comply as much as possible. Other standards must be selected (e.g., whether to use a 258A or EIA wiring sequence at the wall jack) to ensure interoperability with other network electronics equipment and end user devices. NETWORK WIRING COMPONENTS The choice of electronic components may have more to do with how many users there will be on one Ethernet segment and where to bridge or route traffic than with the wiring plant, but may have implications for the wiring plant. Component selection should be anticipated when a wiring scheme for an organizational LAN is being designed. These components can be classified as passive (i.e., they need no power supply of their own) and active (i.e., they have to be plugged into a current source). Passive devices mechanically concentrate the wiring at central points and provide the flexibility and modularity to handle changes quickly and easily. The first of the nonelectrical components is the punch down block. This is the device on which all twisted pair wires from the work area, or wiring from several telecommunications closets that lead to a main distribution frame, are connected. It accepts hundreds of terminations or punch downs and makes a wiring system modular and accessible. It is also called the cross connect panel because it allows different terminations to be cross connected to each other. The punch down block site is where much of the network’s electronics (hubs, repeaters, bridges) can tap into the wiring system. Two popular types of punchdown block are the 66 block and the newer 110 block. The same type of device is used for terminating voice connections, although some data punch down blocks have additional features (e.g., built in RJ-45 connectors for every termination to allow easier cross connecting and interfacing to the wiring system). A patch panel is similar to a punch down block (its purpose being to cross connect wires), however, it has RJ-45 interfaces to the wiring for easy access. A 110 or 66 punch down block used as the twisted-pair termination point can easily connect to an RJ-45 patch panel. Exhibit 1-3-5 shows the different cross connect components. Exhibit 1-3-5.  Punchdown Block and Patch Panel in Wiring Closet For fiber terminations the same concepts apply, however, the terminology is different. There is usually much less fiber than UTP or STP in a telecommunications closet, but fiber terminations must be made with much more care. Usually all fibers are contained in one cable, the strands being split out at a breakout box in the wiring closet and connected to a fiber patch panel with ST connectors. Transceivers and baluns are simple devices for interconnecting media types (e.g., AUI and UTP) that have different signaling characteristics and impedances. Some computers are equipped with AUI interfaces. To connect these computes to the RJ-45 wall jack and use the UTP infrastructure of the building, a transceiver is connected between the computer’s AUI connection and the RJ-45 plate. 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.