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 3-5The Evolution of the Desktop ROBIN L. ZAK Computing has made some profound changes over the past 20 years. In the early 1980s, computers took the space of an entire room and the I/O devices were the size of a small table and acted as the terminal and printer all in one. Response time was on the order of seconds to minutes for minor operations and everything was done in batch mode. Then along came the personal computer, such as IBMs with one or two 5 G diskette drives, 256K bytes of RAM, 4M bytes hard drive, and a 1,200 bps modem. A few years later, while the engineers were still playing around with mainframes, a new movement began to arise. Colleges across the US started to provide a room at the library called a “PC Lab.” IBM PC ATs and Macintosh Classics were lined up in rows, with a printer at the end of each row. Each PC would plug into some external device that would allow use of a printer. Only one PC could print at a time, so you had to keep an eye on this device to see when it was free before you sent your print job. Around this time, file sharing evolved from the “sneaker net” to actual sharing of files over local area networks (LANs). Black cables lying across the floor connected everyone’s PC and connected to a larger PC that was used as a file server. The black cables were a bit temperamental—one minor adjustment could wipe out everyone’s connection to the server. This was an early Ethernet network. Most files would be stored locally on each PC, but shared files would be stored on the file server where anyone connected to this Ethernet could have access. It did not take long before sharing files within a department was just not good enough. Users needed to share files between departments, and this is where the problems started. Not every department used the same type of LAN to connect their users to the file server. Not every department used the same word processing or spreadsheet programs either. Not only did files need to be shared, but now applications needed to be shared as well. One version of application sharing involves the members of a workgroup actually running the applications from the server instead of locally from their PC. It makes more sense to load the application once and to allow 20 users access, than to load the same application 20 times on 20 different machines. While this frees quite a bit of disk space on the individual PC, the load on the network becomes tremendous. Each PC must “pull down” a subset of the application each time it is in use. This can be Mbytes worth of information for each user, which can cause network congestion and delays. THE CHANGES IN DESKTOP APPLICATIONS Let’s focus on these applications for a moment. Why is it that the average life cycle of a PC is a year or less? Why is the PC purchased five years ago (a 386, 33Mhz, 80Mbyte hard disk and 8Mbyte memory) worthless today? One answer is that applications keep adding new features, thereby requiring more processing power, hard disk space, and memory. Five years ago, that PC could run the applications designed five years ago, but attempting to update the applications to the latest and greatest will most likely require an upgrade to the PC or worse, a new PC with a lot more horsepower. The changes in applications such as word processing and spread sheet programs are obvious, but what about the new emerging applications that require hefty processors and lots of memory? Multimedia and video applications are beginning to emerge that also require quite a bit of processing, memory, and network resources. The latest craze is Web-based applications. These are not only being used for the Internet, but the Intranet and network management services as well. All of these applications require some sort of network to share important information. It appears that the application designers automatically assume infinite bandwidth when it comes to networking, but networking professionals know better. Bandwidth is definitely finite and costly— especially on the wide area. The bulk of this chapter discusses the networking issues that arise when attempting to share these applications and files, not just within a department, but across departments and across buildings. THE EFFECTS OF THE CHANGING DESKTOP ON THE NETWORK Shared LANs Remember that black cable? That was the local area network. It was, often, a 10M-bps Ethernet LAN that connected a limited number of users together to the file server. The 10M bps was shared so that each user had about 400K bps (10M bps/24 = 416K bps) on the average. 400Kbps is more than adequate when the files being transferred are on the order of 10-20Kbytes in size. Exhibit 3-5-1 shows a shared Ethernet LAN. Exhibit 3-5-1.  A Shared Ethernet LAN Most departments did not have a cable running across the floor, they had wall jacks where a cable from the PC would connect. The wiring from the wall jack would run back to a central closet to a wiring hub. This hub would act as a single Ethernet and would make troubleshooting of the Ethernet much easier. Exhibit 3-5-2 shows a shared Ethernet LAN using a central wiring hub. Exhibit 3-5-2.  Shared Ethernet using Central Hub Ethernet was not the only LAN technology to be used. Token ring was a common LAN technology among IBM customers. Also a shared LAN, Token Ring offers 4M-bps and 16M-bps versions. If network response time on a 4M-bps Token Ring is slow, there is an option to upgrade the ring speed to 16M-bps by changing all the Network Interface Cards (NIC) on devices attached to the ring and upgrading the Multiport Access Unit (MAU). Exhibit 3-5-3 shows a shared Token Ring with a centralized MAU. Exhibit 3-5-3.  A Shared Token Ring LAN Previous Table of Contents Next Use of this site is subject certain Terms & Conditions. Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. 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