What's the biggest, fastest LAN switch?

Start-ups have a new take on how to build the 'biggest' ethernet switch

This isn't a trick question, but one with a lot of tricky answers depending on how you define "big" and "fast."

Ethernet switch vendors such as 3Com, Force10, Cisco, Extreme, Foundry and HP ProCurve constantly tussle with claims of the highest performance, density and latency. But keep in mind that what's available right now from such vendors is three-year-old technology, on average. Meanwhile, a host of hungry start-ups such as Raptor Networks and Woven Systems have a new take on how to build the "biggest" Ethernet switch. Their approach diverges from single big-iron chassis, and more resembles clustered supercomputing, or InfiniBand networking topologies.

How fast Ethernet can go is bound by the current 802.3ae standard -- 10Gbps -- so no single port is speedier than that, supposedly. Other ways to measure switch heftiness are by the bandwidth of the switch fabric and the density of ports that the chassis or box supports. Then there's the performance of the ports themselves. Latency -- how long a switch holds onto a packet -- are factors in switch performance, as well as jitter, which is a measure of the amount of variance of latency.

"Everybody does line rate on a per-port basis," says David Newman, president of Network Test and a member of Network World's Test Alliance. "The question then becomes how many ports do you do line rate on before you start dropping packets?"

In terms of published specifications, among the biggest of the core enterprise switches are Force10's E1200, Foundry's RX series, Cisco's Catalyst 6500, and Extreme's BlackDiamond. Comparing published specs, Foundry's RX-16 switch is the highest-capacity switch; it can run 64 10G Ethernet ports at full speed, and up to 192 10G ports in a chassis in an oversubscribed configuration (where the sum bandwidth on all ports exceeds the switches capacity). Force10's E1200 TeraScale switch can run 56 10G ports, or up to 224 10G ports when oversubscribed. Extreme's BlackDiamond 10808 chassis can support 48 non-blocking 10G ports. Cisco's Catalyst 6513 can handle 32 10G Ethernet connections all running at full-duplex.

Some say that what's less important is how a switch handles variables such as jitter and packet loss when the switch is running full blast, as opposed to how the vendors carve up per-slot and overall system bandwidth. "What I think is a more useful metric than throughput is latency." Newman says. "There, I'd say clearly Cisco is the best."

Newman says he has clocked a Cisco Catalyst 4948 at around 3 microseconds at 10G rates, "which is the lowest I've measured," he adds. "Force10 was in the low double digits [in microseconds of delay]. They used to be hundreds of times higher, which would mean thousands of packets outstanding. But they've fixed it some over time."

With Force10's newest switch offering -- the S-series, which Newman says he has not yet tested -- the company claims it delivers latency numbers in the 200 to 300 nanosecond range -- several orders of magnitude faster than 3 microseconds. (This delivery claim is based on a test of the product conducted by network testing firm The Tolly Group and sponsored by Force10.)

Lawrence Berkeley National Laboratory, a U.S. Department of Energy research lab in California, uses both Force10 and Cisco switches in its data center and LAN core. Putting a finger on which of the two products is "fastest" or "best-performing" is difficult, says Mike Bennett, LBNL senior network engineer for the LBLnet Services Group, since the switches are used in different applications.

"[I've] tested a 6500 with 2 ports of 10G and the E1200 with 2 ports of 10G -- and neither of them are over-subscribed, and neither drops packets," says Bennett. "So it's not that one's faster than the other. It's just that they both work as advertised."

When large amounts of 10G ports are needed, Bennett uses the Force10 E1200 for its higher 10G port density. "Typically when you buy Cisco, you buy the kitchen sink when it comes to features," says Bennett. "Force10 is different in that they don't have everything in a particular version of an operating system." This is preferable for applications at the lab that require a high-density, non-block switch that simply moves packets fast. "We try to go with the simplest fastest solution in order to minimize the number of variables to keep operating costs low."

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