Scale Ahead Of N
et Traffic With ATM Edge Switches
In our tests, the Centillion took 1 minute and 6 seconds to fully restore connectivity in our default-test configuration. When connected back to back, this time dropped to about 30 seconds, thanks in part to the dual LESes. In both cases, the circuits broken by removing one cable were automatically moved to the second connection during the fail-over period.
The Centillion implements load-balancing on a per-ATM-call basis. When there are two or more connections from the Centillion to a destination, it will balance the calls by creating virtual circuits (VCs) in a round-robin fashion. The Centillion supports two modes of operation for creating VCs, which affect the granularity of the load-balancing process. In t
he first scenario, called Turbo LANE, blades can create their own VC. The result is a higher number of VCs per Centillion switch and a higher degree of granularity in load distribution. In the second mode of operation, called Circuit Saver, each blade requests that the switch controller establish VCs. Thus, there will never be more than one VC between two LECs in a Centillion network. This mode results in less granularity but fewer VCs on the entire network.
In its default configuration, the Centillion 100 is an ATM switch; that is, it forms NNI connections among switches. This lets it use standards-based methods for multiple ATM uplinks to a central switch. Bay uses Private NNI Phase-0 IISP signalling to connect switches, therefore, you must enter static routes for every switch-to-switch connection in the network. With PNNI Phase-1, this aspect of ATM connections will become much simpler, but the vendors in this review are still several months away from implementing this standard.
FORE Systems ES-3810 Ethernet Switch
FORE's ES-3810 differed considerably from the other devices we tested. A low-profile, six-slot chassis, the ES-3810 can host a variety of modules, including 10BASE-T, 10BASE-FL, 100BASE-TX and 100BAS
E-FX, as well as dual OC-3 155-Mbps ATM uplinks. FORE is in the process of releasing an eight-port 100BASE-TX module for the ES-3810, which will beef it up for high-speed desktop connections and server applications.
Unlike the competition, the ES-3810 is a UNI device; it doesn't inherently support multiple paths to the same box. FORE has compensated for this by providing multiple ATM uplinks that physically bind different ports to different physical interfaces. For example, in our configuration, the even-numbered ports were bound to the first ATM interface, while the odd-numbered ports were bound to the second interface. Should one of the interfaces fail, the switch automatically moves the clients over to the remaining interface. In our tests, it to
ok about 25 seconds for the switch to realize that a connection was lost, and then move it to the remaining segment. The advantage of FORE's implementation is that when a connection is restored, the switch can redistribute the VCs across both interfaces with minimal interruption.
Another big difference between the FORE ES-3810 and its competition is its internal architecture. The ES-3810 is a frame switch, as opposed to a cell switch. To the user, this means the box is bounded by its frame-processing power rather than by its SAR speed. The ES-3810 is capable of converting about 107,000 frames per second, whether they are 64-byte or 1,518-byte packets.
For small packets, this means reduced performance, but for large-packet environments, it is not an issue. FORE argues that network testers like the SmartBits, which generate wire-speed 64-byte packets, don't represent real-world traffic. We tend to agree, based on what we found on the network at the University of Wisconsin (see "Frames and Cells: What'
s the Difference," on page 87). Our benchmarks confirmed what FORE revealed--the ES-3810 topped out at 106,960 packets per second (pps) with 20 wire-speed 64-byte streams (about 36 percent of the frames sent into the switch), but handled the full 20 wire-speed str
eams at 1,518 bytes, or 16,260 pps.
On the high end, the 100-Mbps adapter in the ES-3810 is top-rate. With eight streams of unidirectional traffic, we obtained 264 Mbps of throughput across the dual ATM link, or roughly 98.6 percent efficiency. In a bidirectional environment, we were able to push 330 Mbps over the dual OC-3 uplink.
Configuring the ES-3810 is not as easy as we would have liked. The interface is simple; a VT-100 interface provides simple-to-navigate menus, but quick changes are tedious due to numerous menu redraws. In addition, the software we tested the ES-3810 under was in late beta, and several features, such as group changes, were not yet implemented. This same beta software prevented the ES-3810 from interoperating with
the Centillion 100 switch we were testing. FORE promised to have the issue resolved before the new module shipped.
Joel Conover can be reached at jconover@nwc.com.
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