2-Gbit/s Fibre Channel Repeater Doubles Throughput, Halves Power

Storage systems are the heart of the Internet and enterprise networks. But with the increasing amount of data passing to and fro at an exponential rate, these are quickly creating a bottleneck in the drive to maximize throughput in the networks they serve. As a result, the 1-Gbit Fibre Channel connections that have sufficed in popular systems like the storage area network (SAN), the redundant array of independent disks (RAID), and just a bunch of disks (JBOD), are quickly becoming obsolete in terms of throughput, the quality of that throughput, and power consumption.

Well aware of this bottleneck and the need to eliminate it, BitBlitz Communications Inc., Milpitas, Calif., has introduced a double-speed, four-channel Fibre Channel repeater and port-bypass device. It can handle data rates at up to 2.125 Gbits/s per channel (Fig. 1). Dubbed the BBT2020, the device incorporates the company's patent-pending CoolPHYer architecture to achieve a low power consumption of 300 mW at full speed. The full-speed operation is achieved without resorting to parallelism. Plus, a configurable clock-and-data recovery (CDR) unit resets the jitter budget during data transfers to ensure data accuracy.

At the core of the BBT2020 chip, the CoolPHYer architecture is the nomenclature for the company's large-amplitude, differential-logic (LADL) technology that's used in the port multiplexers. The multiplexers in port bypasses use a very different logic style and aren't easy to make at 2.125 Gbits/s—especially considering the data-dependent jitter. A one-zero, one-zero sequence is very different from five ones and five zeros, because of the need to make sure that all positions cross at exactly the same time.

To date, only two approaches are typically employed. The first approach involves using common-mode logic (CML) with a differential pair—and its associated high power consumption. The second method implements standard rail-to-rail CMOS, but that has a lot of deterministic jitter at high speed.

BitBlitz's LADL technology takes a patent-pending hybrid approach, which addresses the jitter problem and keeps the power consumption down to 300 mW at a data rate of 2.125 Gbits/s. This compares favorably with current solutions that consume 700 mW of power while running data at only 1 Gbit/s. The fact that the LADL technology is scalable to data rates of 10 Gbits/s is important for making the power savings even more advantageous with the potential of four-, eight- or 16-port, 10-Gbit/s Fibre Channel, OC-192, or 10-Gbit Ethernet chips in a single system.

The CDR is a digital phase-locked loop (PLL). In the repeater mode, its output is synchronized to the recovered clock (Fig. 2). In the bypass mode, the CDR is unused. While the CDR can be applied to all active ports, it also can be configured for operation only on selected ports.

Those ports are connected to older-technology drives with poor jitter performance. The ports themselves are connected in a daisy-chain style, and can be enabled or disabled using the port bypass controller. When disabled, the incoming data is sent directly to the next port.

Multiple BBT2020s can be cascaded. The total number of required cascaded devices depends on the jitter requirements and the level of redundancy that's implemented.

The device is fully compliant with the ANSI X3T11 Fibre Channel specification. It features user-controlled, dual-speed operation back to 1-Gbit/s operation.

Key specifications of the BBT2020 include a data jitter accumulation of 80 ps (max), which is an improvement over the 96-ps (maximum) requirement of the Fibre Channel MJS-10 document, and a propagation delay (with all circuits bypassed) of 4.0 ns. Jitter tolerance for proper eye opening is specified as 0.21 unit intervals, in accordance with the MJS-10 specification.

The device is made on a 0.25-µm CMOS process. It's specified to operate from 3.3 V, and has an operating temperature range of 0° to 70°C. In addition, the BBT2020 is a pin-compatible, drop-in replacement for existing 1.06-Gbit/s Fibre Channel repeater devices.

BitBlitz Communications Inc., 830 Hillview Ct., Suite 290, Milpitas, CA 95035; Contact Leo Wong at (408) 586-9886, ext. 204; fax (408) 586-9884; or through e-mail at: [email protected]. Or, visit the company's web site at www.bitblitzcom.com.