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 A repeater is another simple device. It is used when a signal path is too long or there is some other signal attenuation over the cabling, causing the connected devices to have trouble accurately receiving the signal. A repeater boosts the signal so it can travel a longer distance than the media would otherwise allow. The EIA specifications restrict wiring distances, but in certain situations (e.g., when devices are in locations with no easy access to a closet) out-of-specification cable lengths must be used, and a repeater device may be necessary. A wiring hub is the electrical device that actually forms the logical LAN, concentrating the signals from all devices at one point. It receives the connections from the patch panel and contains the software and hardware that enable one device on a LAN to communicate with another. The hub defines which devices are on the LAN. A device on Ethernet a can talk to another device on Ethernet A or one device on Token Ring B can talk to another device on Token Ring B through the hub, without going through any other device (e.g., a router). Intelligent hubs allow sophisticated management of the internals of the hub. A remote management console could be used to make moves or changes on a LAN, or monitor hub conditions (e.g., traffic levels and part failures), through an intelligent hub. Non-intelligent hubs do not allow such manageability and simply provide a concentration point for the wiring connections. NETWORK DESIGN The cable system is perhaps the longest lasting component of an enterprise network and should be designed to meet user requirements for many years. Understanding the various components of a cable system is a fairly straightforward matter. Making design decisions for an integrated, reliable, and flexible system is much more complex. If the cable system owner does not wish to undergo the expense of rewiring in only a few years, the cable system should be a high-performance specification. If the installation site is a relatively temporary location, the design only has to satisfy short term user needs. Set Goals A cable system should: •  Provide clear and understandable design guidelines. •  Provide a cable design that is responsive to user needs. •  Provide all users with the same high level of cable system access. •  Provide a cable system that does not affect a building’s aesthetics. •  Provide a cable system that meets high standards for quality. •  Make use of available energy sources or ensure an adequate power supply for air conditioning or large computers. •  Allow ease of installation and maintenance. Plan Before Installation In new buildings, architects must incorporate in the overall design of the building such wiring facilities as building cable entrance points, riser locations, and distribution frame rooms. Rebuilding or remodeling after the building is complete can be very costly. In addition to gathering information about current user requirements, network planners must anticipate future technology requirements. At the very least, the cable system must include extra capacity, and its design must be independent of the systems connected to it. A cable system should be able to support many technologies rather than a single vendor’s solution. Design a Structured System Every organization should have its own standards for wiring, based on its requirements. A consistent physical infrastructure will greatly facilitate connectivity between users. Designing the cable system is easiest if it is divided into its physical subcomponents. The major building wiring subcomponents (illustrated in Exhibit 1-3-6) are: •  Station jack. •  Horizontal distribution system. •  Distribution closets and intermediate distribution frame (IDF). •  Riser system. •  Building distribution frame (BDF) room. Exhibit 1-3-6.  Structure of Intermediate, Building, and Main Distribution Frames The station jack is the wall plate where the end user’s voice and data equipment connects to the building wiring system. The station jack physically terminates the twisted pair, coaxial, or fiber-optic cable behind the wall plate. An RJ-45 termination is generally used to connect twisted pair cable, BNC connectors usually terminate coaxial cable, and ST connectors connect fiber-optic cable. The horizontal distribution system is the cable connecting the station jack to the distribution frame closet and all the cable support hardware (e.g., conduit, molding, or cable trays). Each horizontal run connects a station jack to the nearest closet on the same floor. Twisted pair wiring is the most common horizontal distribution medium but coaxial cable and fiber-optic cable are also sometimes used. The distribution closets, often referred to as intermediate distribution frame (IDF) rooms, provide the connectivity between the horizontal distribution runs and the building backbone cable, or riser system. The closets house cable cross connect and punch down equipment and such communications devices as intelligent wiring hubs, repeaters, routers, and bridges. The riser system, or backbone, connects the individual IDFs with the central equipment room, known as the building distribution frame (BDF) room. The riser cable typically runs vertically. IDFs on different floors are usually stacked vertically to ease the job of pulling cable and for the sake of efficiency. Like horizontal cable, the riser cable may be coaxial, fiber-optic, or twisted pair. The installed base of riser cable is predominantly twisted pair, but new installations should almost always run fiber-optic cable, to concentrate traffic and for future high-bandwidth applications. The BDF room is the main telecommunications room. All building wire originates in the BDF, which usually supports both voice and data communications equipment. Examples of communications equipment housed in the BDF are LAN servers, routers, and PBXs. The usual physical relationships between the cable system components is a hierarchical star. The benefit of a physical star layout is that the network can be configured into any logical topology and can be managed easily. The IDF and BDF structure lends itself very well to a physical star, the concentration point for a single floor being the IDF, and the BDF serving as the concentration point for an entire building or as the site for departmental servers or routers. 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.