Tau Touts Cheap Switch Fabric
Aimed at enterprise and metro networks, the T64 switch fabric chipset scales linearly from 2.5 to 640 Gbit/s of full-duplex bandwidth, giving it a maximum capacity of 64 10-Gbit/s ports. It comprises two chips: the TL2410 line interface on the line card, and the TX6410 crossbar/scheduler on the switch card. No surprises there.
What may come as a surprise to some is Tau's marketing of the chip. It's making a huge song and dance about the price.
According to Tau, the main reason systems vendors continue to develop their own switch fabric solutions rather than buying from merchant silicon vendors is simply because off-the-shelf parts are too expensive. Performance may have been an issue in the past, but that certainly isn't the case any more. Price is now the main concern.
That's where Tau believes it can make an impact. "Charging $500 to $600 a chip is a non-starter," says the startup's VP of marketing Dave Gampell. "[Our design] allows us to set the price where it needs to be." Tau is projecting a price of $250 to $350 per 10-Gbit/s port, depending on the system configuration.
One reason switch chips are so expensive, he contends, is because they are physically very large. Large chips mean fewer chips per wafer, which doesn't lead to good economies of scale. "The wisdom in the semiconductor industry is," says Gampell, "You could sell 1,000 chips at $1,000 apiece for a total of $1 million, but you'd be better off selling 10,000 chips at $100." Even though the cheaper chips bring in the same total amount of revenue, the margin on manufacturing them is higher.
To this end, Tau claims to have shrunk its chips and their packaging. For starters, it's optimised the layout of the traces inside the chip by custom designing the layout where necessary. Place-and-route tools, which automate this process, don't always come up with the most compact solution, Gampell contends. Tau also claims to have shrunk the BGA (ball grid array) packages by using fewer solder bump connections, but without sacrificing any features.
Analysts don't buy the story completely. "I'm surprised they promoted cost so significantly," says Jeremy Donovan, chief analyst at Gartner/Dataquest. "In my view, there are only three ways to cut prices: large volumes, efficient design, and low margins."
Tau certainly isn't selling large volumes at present, and Donovan doesn't believe that anyone can make the design so efficient it will cut price by 50 percent. "From where I sit, the only way Tau can achieve very low prices is with low margins," he says.
But, he adds, there are so many switch fabric vendors around today, that price may be one of the only ways left to compete successfully.
Putting price on one side, however, analysts do seem to be impressed with the features of Tau's chip. "It's not lagging behind in anything: power, price, or performance," says Donovan.
He particularly likes the number of classes of flows it can support. More flows translates as an improved ability to regulate and monitor quality of service to customers.
Tau claims that the T64 can monitor flows down to the OC3 (155 Mbit/s) level, and offers 16 levels of service per flow. Doing the math, that means each TX6410 crossbar/scheduler on the switch card can support 65,536 flows. For comparison, Agere Systems (NYSE: AGR/A) says its PI-40 chipset can support flows down to the OC12 (622 Mbit/s) level, meaning it supports only one quarter the total number of flows or less (see Agere Announces Products, Contracts).
Jag Bolaria, senior analyst at The Linley Group concurs with Donovan's view, adding that another strength of Tau's switch fabric is the scheduling algorithms, which eliminate the need for a lot of external memory -- another big cost saver for the customer.
"You might imagine that with all these flows, we need a huge amount of memory," says Tau's Gampell. Rather than holding one queue per flow, which is the usual way, Tau has a developed patent-pending queue management scheme that allows it to "juggle" queues without using much memory.
Furthermore, he says, if a flow gets blocked, the crossbar doesn't need memory to store the buildup of data. "Our logic was that the network processor also needs loads of memory to function, so why don't we use that." If one flow is misbehaving, then the crossbar simply sends a message back to the network processor to say "don't send us any more data."
Working against Tau is the fact that other switch fabrics are more established. Agere's PI-40, for instance, is in volume production right now, the company claims. Tau's chips, on the other hand, have only just come back from the foundry, and are still being tested.
Founded in October 2000, Tau Networks has been funded entirely by VenGlobal Capital. Gampell didn't disclose the total amount of funding, but did note that it was in the single-digit millions. "In my 15 years in the semiconductor industry I must say I've never seen so much done with so little."
— Pauline Rigby, Senior Editor, Light Reading