Memory I/O bottlenecks have become a battleground as network speeds push into the 10-Gbit/second range, with various companies proposing fast-cycle DRAM, double-data-rate (DDR) SRAM and quad-data-rate (QDR) SRAM as optimum solutions for speeding up the movement of data between packet processing engines and off-chip memory. Agere is putting its weight behind fast-cycle RAMs, and the Network DRAMs jointly developed with Samsung will be compatible with existing FCRAMs

Initially developed by Toshiba Corp. and Fujitsu Ltd., FCRAMs combine DRAM densities with the fast access times of SRAMs. To achieve fast access, FCRAM links a fast memory core with a three-stage-row pipelining scheme. The pipelining scheme delivers a speed improvement in row address cycle times. The core, on the other hand, is segmented into smaller sub-arrays that can be quickly accessed. The result is a faster access time at the pin level, said Robert Munoz, product marketing manager at Agere Systems.

Samsung said it is working on Network DRAMs that deliver 400-MHz DDR performance, providing an aggregate throughput of 800 Mbits/s. These performance levels will be important in networking architectures, which is one reason Agere places such importance on FCRAMs, Munoz said.

Random cycle times are another factor in Agere's support. The company expects FCRAM to achieve a random access cycle time of 25 ns or better, Munoz said. "That's in sharp contrast to DDR SDRAMs, which deliver a random cycle access time of 60 ns or more," he said.

Cost is another factor. In a system handling between one and two million routes, Munoz said designers can perform packet look-ups using two or fewer FCRAMs, leading to an overall cost of less than $50 for the packet lookup function, he said.

On the application front, Munoz said FCRAM can be used in high-end OC-192 box designs as well as in OC-48 and slower boxes. In OC-12 systems, FCRAM can replace existing SRAM solutions, Munoz said. In high-end boxes, FCRAMs can compliment QDR and DDR SRAM, Agere said. For example, a 2.5-Gbit or 10-Gbit networking architecture could use FCRAM for table look-ups while SRAMs handle tasks like policing and statistics, Munoz said.

Increased supply

Agere has been actively working with Toshiba and Fujitsu to define the interface and performance requirements required by FCRAM architectures. The agreement announced Monday extends those efforts to include Samsung's Network DRAM development activities.

Munoz said Agere will benefit from the increased availability of FCRAM products for its customers. By working with three major memory vendors, Agere can guarantee multivendor support when recommending FCRAMs to customers, Munoz said.

Samsung is currently mass producing a 256-Mbit Network DRAM. The 400-MHz parts are expected to hit the market in the third quarter of 2003. Agere's PayloadPlus network processor family, aimed at 2.5-Gbit network designs, will supporting Samsung's memory solutions, the company said. Agere's 10-Gbit network processing architectures will also support Network DRAM solutions, Munoz said.