Handbook of Local Area Networks, 1998 Edition:LAN Interconnectivity 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 HIGH SPEED While switches reduce the number of devices sharing the bandwidth, and may have only a single device per port, it is clear that not all the devices in an installation are equal. Not only are there users who require different amounts of bandwidth, there are servers that demand a great deal. Some LAN switches accommodate a range of throughput: shared segment, dedicated device, full duplex, high speed, as well as combinations. The most common use occurs with Ethernet, where regular users and printers operate at 10M bps, while some servers can benefit from 100M-bps connections (see Exhibit 3-6-6). Exhibit 3-6-6.  High Speed and Switched Benefit. Switches are available that can accommodate a mix of speeds. Management In a shared media LAN, things that can be counted (number of frames, frames in error, number of bytes) can be counted by adding capability to the wiring hub. This information can then be reported to a management station by SNMP (Simple Network Management Protocol), in order to manage the network. For in depth analysis a probe inserted into the LAN segment captures frames and provides a trace, a detailed list of activity, and augments the basic counts provided by the wiring hub. This probe is often implemented by a very fast network adapter, a fast portable computer, and software. Many users call all probes by one of the brand names, a Sniffer. In a LAN switch environment, this information is distributed among all the ports of the switch. Counting things is relatively easy, and many switches provide that type of information via SNMP, the same as better wiring hubs. In order to capture the trace type information, however, the challenge is where can the probe be inserted? There is no common LAN segment, where all the frames can be seen. To address this requirement, better switches have the capability via network management commands to duplicate the information flowing on any port of the switch to another port, where the probe tool can be connected. Switches designed in a modular fashion can have an RMON (Remote MONitoring) version of the probe designed as one of their add-in modules. Thus, while it is not possible to trace all of the information at the same instant, all the flows for any given device can be captured. Benefit. Switched LANs can be managed, but the capability must be built into the switch. SUMMARY As with any product, there are many factors involved in a purchase decision. You should first determine your network needs. Is the traffic such that installing a switch will benefit? Where are the bottlenecks? Are some devices accessed by many or even most users? Will a switch with faster ports allow high speed access to that device, without requiring change to the bulk of your devices? If you need a switch for the middle of your network, a high capacity, backbone switch should be chosen. How many devices does your network contain? Make sure the address table capacity of the switch you choose is large enough. Are a few users demanding more capacity now, while most are satisfied? Installing a work group switch for the demanding users may solve their concerns. Make certain that it is large enough, and that it will fit with other products if you plan installing them in the next year. How much will your users network demands, or the number of devices your network serves, grow in the next few years? Choose a switch that has easy upgrade capability to add additional ports, full duplex, higher speed, or all of the above. What level of network management do you have, or will you install in the next year? Make certain that the switch you choose has the level of management you need. (See Exhibit 3-6-7.) There are a variety of switches available from many different vendors, so you should be able to choose a vendor that exactly meets your needs. Exhibit 3-6-7.  LAN Switching Considerations The problem of increasing the speed of the LAN connection was more immediate in the Ethernet community, so Ethernet switches were first on the market. Whether from need, or the desire to maintain parity, Token Ring switches soon followed. More recently, switches for FDDI and 100M-bps Ethernet became available. As the ability to dramatically increase the number of available ports grew, and the price per port came down, it became possible to dedicate a port to a single device, such as a server. As is common with PC technology, increased component volume attracts new manufacturers, which drives down prices, which increases volume. As this happens with LAN switching, the LAN wiring hub market becomes a per-port LAN switch market. 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.