Switched Ethernet emerges as high-speed LAN favorite
- By Paul Korzeniowski
- Apr 05, 1998
The organization has installed two switches, completed 85 percent of its upgrade and expects to finish the installation during the summer. Currently, only a few users have 100 megabits/sec connections, but the Maryland Veterans Administration Health Care System can easily upgrade its employees' network access— a change that requires only a minor alteration to one of the LAN switches. The organization can keep its network cards and network management tools in place. ~Moving to ATM, in contrast, requires that an agency install new network cards, switch connections and network management software. ATM equipment also costs more than Ethernet wares. While 10/100 megabits/sec Ethernet cards sell for $200 or less, ATM adapter cards, which support transmission speeds of 155 megabits/sec, are priced from $500 to $1,500. ~~Quality of Service~Still, some agencies have decided to migrate to ATM rather than go with switched Ethernet or other high-speed options. In some cases, ATM, although more costly, is the better option, vendors said. "Organizations usually opt for ATM for one reason: a desire to run desktop video applications,'' said Xylan's Michaels. ~For instance, the Navy's Information Technology for the 21st Century project is designed to upgrade the network infrastructure on board Navy ships as well as ashore. The Navy's Pacific Fleet, based in Honolulu, has 500 users working on a classified network and 400 more users working on an unclassified network. In 1997 the organization started to upgrade its infrastructure. Rick Kooker, the director of information systems for the fleet, said, "Our long-term goal is to run data, video and voice transmission on our LANs.'' ~The Navy selected an ATM infrastructure because it includes Quality of Service (QOS) features that ensure continuous bandwidth availability, said Kooker— a critical feature for interactive video or voice applications. ~Barry Morris, the director of federal operations at Bay Networks Inc.'s Alexandria, Va., office, said QOS addresses a couple of limitations found with other networking techniques, such as Ethernet. With these other techniques, information travels across a network in a random fashion. In a series of 10 packets, packet No. 8 may arrive before packet No. 6. The computer system at the receiving end shuffles the packets so that the information is presented correctly to an end user. ~Packet arrival order is not important with most applications because the user does not examine data as it arrives; for instance, an e-mail message may sit for hours before a user opens it. But that is not the case with interactive applications. If packets arrive in an improper sequence, a picture may fluctuate or a voice may sound garbled. Because interactive applications require that information arrives in sequence, companies are leery of running them on Ethernet networks. ~A second problem is bandwidth contention. On an Ethernet network, bandwidth is parceled out on the fly. A user may begin sending a large file when no one else is using the network, and the transmission will start out fine. A neighbor may start to access a database, and the transmission could slow to a crawl. With a file transfer, the only impact is that the user has to sit and wait a little longer before the transfer is complete. Interactive video and voice applications cannot tolerate such fluctuations. ~~Shrinking Token Ring~While QOS is helping ATM carve out a small desktop niche, token-ring technology is seeing its market share erode, vendors and analysts said. ~Robert Travis, the director of product marketing for federal systems at Cabletron, said, "Price has been a major inhibitor with token-ring LANs. Switched token-ring connections cost two to three times more than switched Ethernet connections.'' ~Another problem is that token-ring customers have been limited to 16 megabits/sec transmissions because token ring for a long time lacked a higher-speed migration path. ~That situation is changing. Beginning in February 1997, IBM Corp., Madge Networks Inc. and Olicom have been outlining a way to boost token ring's top transmission speed from 16 megabits/sec to 100 megabits/sec and eventually to 1 gigabit/sec. Vendors expect to start delivering their high-speed wares during the second quarter of 1998. ~How much interest these products will generate is unclear. Token-ring vendors will have difficulty matching Fast Ethernet pricing, analysts said. Because token ring technology is more complicated than Fast Ethernet, it requires more complex adapter cards and switch connections. ~Because of the difference, a number of organizations have started to move away from token ring and toward Ethernet technology. The Dell'Oro Group, a Portola Valley, Calif., market research firm, found that token-ring revenue had peaked in 1996, and the firm expects it to decline during the next few years. ~"The debate about which high-speed networking option organizations will adopt is over: Most are moving to some form of Ethernet," said David Passmore, a principal at Net Reference Inc., a Sterling, Va., consulting firm. ~~-- Korzeniowski is a free-lance writer in Sudbury, Mass., who specializes in networking issues. He can be reached at firstname.lastname@example.org.Although the demand for more network bandwidth could lead some agencies to adopt Fast Ethernet or other high-speed networking technologies, network vendors also are pushing switched networking as a more practical option.
Asynchronous Transfer Mode (ATM), Fast Ethernet and high-speed token ring all have the potential to boost current local-area network bandwidth tenfold, making it easier for agencies to accommodate the graphics-intensive applications now running on many users' desktops.
But for now, few users appear to need tenfold bandwidth increases. So rather than dramatic network upgrades, most organizations have started with a simple way to deliver more bandwidth to users. Government agencies have been moving from shared networks— where groups of employees work with one LAN— to switched networks, where every user effectively has his own LAN.
"In most agencies, there is now a huge base of shared connections. I would estimate 60 to 70 of all connections now are shared,'' said Brett Michaels, the director of federal sales at Xylan Inc.'s Rockville, Md., office.
Making the Switch
Switches work by dividing a single large network into smaller, less congested LANs and passing data packets from one segment to another.
Each user can have a port on the LAN, which means that each user has a dedicated 10 megabits/sec pipe to his desktop, with the switch in the middle negotiating network traffic from one user to another. In contrast, in a traditional shared Ethernet network, every user connects to the same network and competes with every other user for the 10 megabits/sec bandwidth.
For many users, switch technology represents a large enough increase in bandwidth that they can forgo a move to 100 megabits/sec Fast Ethernet. This saves money because a move to Fast Ethernet or to ATM would require users to replace much more equipment.
The Army Medical Research Institute for Infectious Diseases, Frederick, Md., is one organization that has made the move. The agency, which has 530 users who work with Apple Computer Inc. Macintoshes and IBM Corp.-compatible PCs, looked at upgrading its desktop connections in the fall of 1996. George Privitera, a network administrator at the organization, said network slowdowns were becoming all too common.
The agency had been using shared Ethernet wiring hubs from Olicom Inc., Plano, Texas, and opted for the vendor's switching gear. The agency has upgraded one-third of its connections and expects to complete the process by the end of the year.
Sometimes, cost is not the only factor. The General Services Administration's operation in Kansas City, Mo., found that staying with one network technology reduced training requirements. The agency has relied on Ethernet equipment from 3Com Corp., Santa Clara, Calif., to connect 200 users working with a variety of PCs. Walter Johnson, a network project coordinator at the agency, said a few users work with sophisticated applications that require dedicated LAN connections.
GSA determined that using 3Com Ethernet switches to provide the users with extra bandwidth would be better than running ATM to the desktop. GSA technicians already understand how to manage Ethernet networks, so little or no training is needed with higher-speed Ethernet connections.
Deploying ATM would require network technicians to learn the nuances of a new technology and oversee a couple of networking technologies rather than just one, Johnson said.
Users' desire to minimize training requirements pushed vendors to develop standards not only for 100 megabits/sec Ethernet transmissions but also for 1 gigabit/sec Ethernet. The standards enable an organization to gradually introduce the high-speed connections to users.
For instance, the Maryland Veterans Administration Health Care System, Baltimore, has 2,000 users who mainly work with PCs. The agency's employees often moved medical images, making network delays more common. In early 1997 the organization moved into a new building and decided to migrate from shared Ethernet wiring hubs from Cabletron Systems Inc., Rochester, N.H., to a switched network architecture.
The agency quickly eliminated ATM as a desktop option. "ATM is still an emerging technology and [is] not as easy to deploy as Ethernet,'' said Marcelo Silva, a network manager at the agency.
Consequently, the agency decided to purchase Cisco 5500 Fast Ethernet switches from Cisco Systems Inc., San Jose, Calif., for its new network.