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Be assured:100VG-AnyLAN is not your father's Ethernet. At 100 megabits per second (Mbps), demand-priority delivery of stream data, and high usable bandwidth, 100VG is a new breed of speed demon. And just in time, since these days we're asking our networks to carry the heavy data burdens of multimedia, imaging, and client-server applications-and users need every bit of throughput speed and performance possible.
Granted, 100VG isn't the only technology breaking the old LAN speed limits. Other fast-lane LAN technologies include Asynchronous Transfer Mode (ATM), Fiber Distributed Data Interface (FDDl), and 100Base-T (also referred to as Fast Ethernet, but this term really applies to both 100VG and 100Base-T). Each has points in its favor; but for most companies' purposes, 100VG will take the checkered flag.
Similarly, FDDl is a wonderful backbone technology too high-priced for its own good. FDDl, with its 100 Mbps speed, has proven a winner as a high-speed backbone in places that can afford its high media costs. Its future utility in LANs is more questionable as other technologies can equal its performance without the high costs.
The only close alternative to 100VG is 100Base-T. Designed as a simple extension of 10Base-T, 100Base-T provides fast connections between servers, between servers and switches, and between groups of switches. When it comes to workgroup connectivity, though, 100Base-T has many of 10Base-T's limitations, such as high-collision overhead on a heavily-loaded LAN. Even more bothersome, 100Base-T gives you only a tenth of the range of 10Base-T and can't cascade repeaters-a trick 100VG manages with ease.
Most experts agree that for smaller networks that carry traditional network loads, like burst-oriented network printing or file transfers (where small packet-delivery delays can be tolerated), either 100VG or 100Base-T will do the job. Where 100VG makes the difference is on larger networks, or where it's desirable to plan for growth. 100VG also excels in keeping multimedia or other high-bandwidth networks humming because it's ideal for stream traffic (when smooth delivery of packets is a must).
Both 100Base-T and 100VG evolved from the sturdy 10Base-T. 100Base-T, like 10Base-T, uses Carrier Sense Multiple Access/Collision Detection (CSMA/CD) to enable devices to access the network; 100VG uses a newer paradigm, called Demand Priority, described later.
In CSMA/CD, when two systems try to send at once (i.e., a collision), the systems back off for a random amount of time befor retrying. Problem is, while 100Base-T gives you faster performance than 10Base-T, you are still faced with herky-jerky network utilization after each collision. That may be tolerable with a database, but nobody wants stop-and-go video conferencing!
In short, CSMA/CD isn't terribly efficient. Adding network switches avoids much of this problem by controlling the flow of data through the network. The trouble is that by adding switches, you're also moving away from standard OSMA/OD advantages-thus negating one of 100Base-T's main selling points. Also, in this environment, switches may add expense and complexity to your net infrastructure bill.
100VG manages to roar along on cable rated for 20 Mbps, and less, thanks to quartet signaling. With this technology, the signals are split up among four wire pairs to bring the cable's electronic noise down to FCC standards.
Besides being able to bring extraordinary data throughput speeds to ordinary cable, 100VG also provides greater range. For example, in 100VG the maximum end-to-end distance for a Category 5 LAN is 1,200 meters, and for a Category 3 LAN, it's 600 meters, three times 100Base-T's maximum of 220 meters. Clearly, if you're going to want a large network, 100VG should be your first pick.
What it boils down to is that in terms of marketplace clout, both 100VG and 100Base-T are evenly matched. It's up to the customers to choose, and 100VG's technical superiority should see it to the checkered flag.
While the access method is new, 100VG is also message-frame compatible with IEEE 802.3 Ethernet and 802.5 Token-Ring networks. For the LAN administrator, this means that shifting from a traditional 10Base-T network to 100VG can be as simple as replacing the network interface cards (NICs), hooking up the 100VG hub, and upgrading the drivers. Not too much work for a ten-fold increase in speed, is it?
There's no need to reinvent the wheel: 100VG fits nicely into the ISO network architectural model and will work easily with your legacy networking system. You won't have to yank out your cables by the roots, or even worse, redesign your entire network's topology, as may be the case with 100Base-T Also, since 100VG uses the same Ethernet frame rules as 10Base-T, you can do things like use a simple bridge or switch to connect 100VG and 10Base-T segments. In short, this is one upgrade in speed that won't come at the cost of an upgrade in network software or redesign.
Everyone seems to be talking about the sheer speed of a 100 Mbps network. However, 100VG means more than performance-Demand Priority intelligently manages the network's bandwidth to get the bits where you want them, when you want them, for an estimated 96 Mbps bandwidth (versus about 50 or 60 Mbps for 100Base-T).
Demand Priority works on an intelligent hub that sits between the client connections and your server. The hub has its own CPU so it won't put any undue demands on your servers or clients. 100VG hubs are stackable with each other and with other compatible, high-speed network technologies like ATM.
Demand Priority perpetually checks each port in a round-robin fashion. First, port 1 is checked for a request or data packet. If found, it's directed to the matching destination addresses; then Demand Priority services port 2. This efficient method eliminates the risk of network capturing. In a high-priority situation, you want requests for time-critical services like video-conferencing or animation applications to get access to the network before normal priority requests. Demand Priority understands this: When the hub gets a high-priority request, it postpones its normal-priority work to service the urgent request.
Demand Priority avoids falling into the trap of unduly delaying normal-priority packets by constantly monitoring node request-to-send response times. If the delay exceeds an established maximum time, the hub automatically raises delayed normal-priority requests to high-priority levels. Thus, no request is delayed for long.
While 100VG delivers outstanding performance to 100VG nodes, you can't mix and match 10Base-T and 100VG NICs on the same segment. As a result, to get your systems with older NICs talking with nodes on a 100VG network, you'll need a bridge between the segments. With a bridge in place, there's no trouble moving traffic from the 10 Mbps speed zone to the 100 Mbps fast lane.
The heart of any 100VG system is the hub. HP's first offering is the HP AdvanceStack 100VG Hub-15. The Hub-15 comes with 15 ports, plus another port for stacking-each operating at 100 Mbps. In addition, the Hub-15 comes with a RS-232 serial port for network management. You'll need HP's SNMP/Bridge module to connect 10Base-T and 100VG LANs together.
To connect a LAN together you'll also need NICs, and HP has a full line of 100VG NICs. HP offers ISA, EISA, and PCl-bus NICs, to support older and newer machines. But don't think that 100VG is just for Intel based microcomputers; HP already offers 100VG adapters for HP-UX-based workstations, and adapters for HP-UX servers will be ready by FaIl 1995.