Electronic Design

ICs Drive Down The Cost Of Connectivity For Gigbit Ethernet Over Copper

An end-to-end solution is expected to bring ultra-fast networking right to the desktop.

Until now, end-to-end connectivity for Gigabit Ethernet over copper has been a costly proposition. But, that's about to change thanks to the development of two new ICs from Broadcom: an integrated switch, the BCM5680, and a PHY (physical-layer interface), the BCM5401. Together, these chips promise to drive the per-port system cost of a Gigabit Ethernet switch below the $50 mark for OEMs.

A glance at the block diagram of the BCM5680 shows that eight Gigabit Ethernet ports have been integrated onto the chip (Fig. 1). It's a triple-speed switch—10/100/1000 Mbits/s—which gives it flexibility. It can be used in gigabit backbone applications and also has the ability to connect to 10/100 network-interface cards (NICs) on the desktop. Both copper and fiber are supported on each port.

The company has accelerated the switch fabric to be able to accommodate the gigabit ports. A few other minor enhancements have been made as well, but essentially the device has layer 2 through 7 functionality, similar to Broadcom's BCM5600 StrataSwitch.

One major change from its earlier models is an on-chip packet buffer. According to the company, putting the memory on the chip, 512 kbytes in this case, alleviates many I/O bottlenecks, and reduces cost. In addition, integrated onto the chip are address-resolution logic tables and a rules engine. The rules engine can look into a packet, up through layer 7 filtering.

The rules engine lets users set rules based upon different fields within the packet. A rule might forward the packet to the CPU, drop it, or do various other functions. The engine can support up to 128 rules at any given time. The chip doesn't do layer 4 through 7 switching, because that requires a different level of functionality. Still, it does do filtering.

The chip can process 8K-media-access-control (MAC) addresses and 2000 layer 3 IP addresses at full line rate. Layer 2 only, layer 3 only, or layer 4 through 7 filtering can all be done at line rate.

Further, the chip contains four class-of-service (CoS) queues. Thus, the chip can classify traffic, for example, as voice, video, web traffic, e-mail, and so forth. The filter engine can look into the packet for socket IDs and other information to figure out what CoS queue to use.

For very high-performance systems, a PCI bus interface is on the chip. Typically, this is the interface used by the company's customers. Additionally, there's an I2C serial interface. In Broadcom's view, this opens the door for a new class of product—a low-cost, unmanaged 8-port switch.

The BCM5680 is stackable too. The company says it could fit very well with the StrataSwitch stacking-compatible interface, as a gigabit member of the family. Presently, the company has a large group of customers writing software around the StrataSwitch. These customers can take full advantage of that software for this gigabit switch. The company considers this a significant time-to-market benefit.

Essentially, the application programming interface (API) for this new chip and the API of the older version are the same. The only difference is that the user has to program the drivers for eight gigabit ports in the new chip instead of two. And, some recompilation of software is required.

Improved Bit-Error Rate
Providing the other half of this solution is the BCM5401 PHY (Fig. 2). Like the 5680, it works at three speeds—10/100/1000 Mbits/s. As a second-generation device, the 5401's bit-error rate has improved to be well below 10-12. Other new features include enhanced echo cancellation, the ability to work over longer distances, and improved tolerance to cable variations.

The 5401 offers a number of plug-and-play features. Automatic MDI crossover determination eliminates the need for crossover cables and ensures operation over the existing cable plant. Also, the chip automatically detects and corrects pair swaps, skew, and polarity. It supports both GMII and 10-bit physical medium-attachment (PMA) interfaces.

The 5401 has the same proven DSP technology that's available on the company's 5400 PHY. Like its predecessor, the new chip employs a DSP with a variety of filter coefficients. These ultimately end up characterizing a cable, so data can be transmitted across it. In other words, the chip has a built-in cable tester.

To further enhance this feature, the company includes software code that uses the coefficients to supply information about the cable. The data tells users how long the cable is, if there is a break in it, and about 30 other useful characteristics of the cable. The net effect is a kind of green light that indicates if the cable is gigabit ready.

In addition, the company has de-creased the overall power consumption of the 5401. Because a fan or heat sink is no longer necessary, this should open-up new applications, like NIC cards or very small switches.

Both chips are 0.25-µm CMOS designs. The 5680 is packaged in a 400-pin tape ball-grid array—a very low-cost package. The key for Broadcom is to drive the system cost to less than $50 per port. This includes chassis, power supply, and so forth, making it possible to build an 8-port standalone system at an OEM cost of less than $400.

Price & Availability
Sample quantities of the BCM5680 are available now for $240 each and of the BCM5401 for $70 each. For very high-volume pricing—greater than 50K units for a complete 8-port switch—a set of chips, which includes one BCM5680 and eight BCM5401s, will cost less than $300.

Broadcom Corp., 16215 Alton Parkway, P.O. Box 57013, Irvine, CA 92619-7013; phone (949) 450-8700; fax (949) 450-8710; www.broadcom.com.

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