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  The Road To Fast Ethernet Networks Tracking the conn ection losses was a more difficult challenge. After several weeks we discovered that the problem lay in our old Cisco (Crescendo) FDDI concentrators. For some reason they were spontaneously resetting, causing the FDDI ring to reset up to 50 times per minute. The clients, now directly on the ring via switches, as opposed to hiding behind routers, were directly experiencing the symptoms of this random reset phenomenon. We weren't sure how long this had been going on, but after several more days of troubleshooting and calls to Cisco technical support, we were able to get the concentrators replaced. This seems to correct the problem. Whether the faster workstations were having any affect on the FDDI ring is undetermined, but this event proves that changing your network topology may have undesired side effects. We put our new network through some simple application tests to find out what kind of benefits our users were getting. Unlike ou r infrastructure tests, where we configure our clients for maximum performance and offer no mercy on servers, our real-world clients were installed with a standard copy of the Virtual Loadable Module (VLM) shell, and the only parameters we changed were to turn on large Internet packets. Our workstations were Pentium Pro 200s with 64 MB of memory running Microsoft Windows 3.1 and SmartDrive with write caching enabled. We tested application response time using Microsoft Word and several 1-MB documents containing a mix of text and graphics. We found that application load time decreased by 18 percent after switching to Fast Ethernet. Writing to the network was consistently 50 percent faster on the new network. Loading multiple smaller files totaling 3 MB yielded a 20 percent speed increase. We also tested TCP/IP applications using the Novell RapidFiler FTP application. We were able to FTP an 8-MB ZIP file in 8 seconds (about 1 MBps), while our old network poked along at about .5 MBps. Shortly after we inst alled our Fast Ethernet network we made the decision to migrate our workstatio ns to Windows NT 4.0. The move to Windows NT showed off the power of our new network. Our application load time dropped from 9 seconds on a 10-Mbps Windows 3.1 client to 1 second on a 100-Mbps Windows NT client. FTP speeds went up dramatically. We were able to FTP our test file at a blazing 3.6 MBps--2.2 seconds to move the entire file from our FDDI-attached NetWare server to our Fast Ethernet Windows NT workstation. AutoCad and Visio showed similar improvements. During our tests, we found that FTP transfers bumped our FDDI ring from 40 percent up into the high 50th percentile for a single workstation. Bursty traffic may push your backbone to similar or higher extremes. Another factor to keep in mind is your server's buffering capacity for high-speed traffic. Our NetWare servers have between 96 MB and 128 MB of RAM, and our environment didn't suffer from the higher-speed traffic. But your environment and users' needs will de termine if this is a factor in your network. Overall, it is clear that Fast Ethernet gives you a serious speed boost. Thirty-two-bit operating systems will dramatically increase the throughput your users realize. Planning your network requires considering more than just the box that goes in the closet: Wiring needs to be up to specifications; a logical layout may be affected by adding new switches; and servers may experience performance problems in some environments. Existing diagnostic software and hardware will need to be replaced to help troubleshoot networking problems. Fast Ethernet is extremely stable and shops should have no fear of deploying large-scale networks. Just be sure to plan for contingencies and follow the specifications for a successful deployment. Joel Conover can be reached at jconover@nwc.com. |
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by Thach Vo Updated Februayr 7, 1997 |
