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Because the 3Com switch uses NNI connections to communicate among switches, it also suffers from a longer fail-over time. By default, the time-out for an NNI connection is set to 30 seconds, but it can vary from 3 seconds to 90 seconds. The trade-off is the amount of maintenance traffic th e switches must communicate--the shorter the time-out, the greater the amount of maintenance traffic. During our tests, the CELLplex 7000 HD took 1 minute and 43 seconds to recover from disconnecting an ATM link. The CELLplex load-balances on a per-call basis, similar to the way the Centillion 100 manages its call setup routines.

But the CELLplex is basically fast and furious. In our benchmarks, it can utilize its dual ATM uplinks to 98.1 percent of maximum capacity. It can sustain 20 unidirectional Ethernet streams without dropping a single packet, and it forwards two 100-Mbps streams with 99.2 percent efficiency. Like Bay Networks' Centillion 100, the CELLplex 7000 HD offers a full suite of LANE services and supports multiple LANE Servers (LESes) on a single emulated LAN via a proprietary protocol. Unlike the Centillion, the CELLplex's LANE services are redundant, but not load-sharing.

In addition to providing great performance at a reasonable price, the 7000 HD offers advanced traffic management fe atures. In a network with traffic management enabled, the switch can continuously monitor the interswitch links to ensure that no LAN Emulation Client (LEC) is starved for bandwidth. It is also possible for other devices to negotiate Constant Bit Rate (C BR) or ABR connections with the switch, as the device's traffic management protocol is standards-compliant.

Bay Networks Centillion 100
Bay Networks' Centillion 100 is a five-slot, midsize chassis switch. The top module is filled with a switching processor that also contains eight Ethernet ports. The remaining four slots can be populated with a variety of interfaces, including switched Token-Ring, 10BASE-T, 100BASE-TX and single-mode or multimode OC-3 ATM connections. The Centillion 100BASE-TX module was not available in time for our tests, so we tried out the 10BASE-T version.

Of all the products we tested, the Centillion 100 was b y far the easiest to configure, thanks to Bay Networks' SpeedView. This Microsoft Windows-based configuration software gives you an at-a-glance view of the different modules installed in the switch, without you ever having to touch a command-line interface. Clicking on the module brings up an interface that enables you to configure the device. With just a few clicks, you can configure the LES, LAN Emulation Configuration Server (LECS), User-to-Network Interface (UNI) signalling and static routes for switch-to-switch connections. SpeedView also can poll basic Simple Network Management Protocol (SNMP) statistical information from modules.

SpeedView is not a replacement for a management station; it utilizes a serial connection between the Centillion 100 and the PC to get the job done. Managing a network of Centillion switches is a function of Bay Network's Optivity management software. However, one particularly useful feature of SpeedView is its ability to save the configuration of the Centillion it is conn ected to, letting you migrate one configuration to multiple switches. In our case, Bay configured a switch in its labs to our specifications and then sent us the configuration file via e-mail.

Bay asked us to test in two scenarios. The first was our planned benchmarking configuration (s ee "At the Edge With ATM: How We Tested," on page 90). Bay also asked us to test its product without the CELLplex 7000 in the middle, claiming 3Com would have an unfair advantage in a homogeneous environment. Using a back-to-back configuration enabled the Centillion to take advantage of its proprietary redundant LANE services.

We found that the Centillion could sustain nine streams of wire-speed traffic with two ATM links in the original configuration; indeed, adding the second ATM uplink only increased performance by 1 percent to 4 percent--a negligible amount. In the back-to-back configuration, however, the Centillion was capable of forwarding as much traffic as we could throw at it--20 wire-speed Ethernet streams--w ithout dropping a single packet. Getting the original configuration to function at all was a three-day process involving two engineers from Bay and two from 3Com. Clearly, some standards are not being met by one or both vendors.