Streaming video, cloud services, and mobile data are fueling the continuous expansion of global network traffic. To keep up with this growth, network systems must deliver faster line rates and the capability to process millions of packets per second. In such environments, packet arrival order is unpredictable, and each packet requires multiple memory operations for processing. This leads to a demand for hundreds of millions of memory accesses per second to perform lookups or update statistics in the forwarding table.
The packet processing rate directly correlates with the random access rate. Modern network devices need high random access performance (RTR) and wide bandwidth to handle today’s rapidly growing traffic. RTR refers to the number of completely random memory operations—reads or writes—that can be executed per second, regardless of the amount of data processed. It is measured in millions of transactions per second (MT/s).
Current high-performance DRAMs fall short of meeting the random access demands of advanced network systems. QDR-IV SRAM was specifically designed to deliver superior RTR performance, making it ideal for complex tasks like updating statistics, tracking flow status, scheduling packets, and performing table lookups. As shown in Figure 1, QDR-IV outperforms other memory types by a significant margin, offering twice the RTR performance of the next best alternatives. This makes it an excellent choice for high-performance networking applications.
In the first part of this series, we will examine two variants of QDR-IV memory—XP and HP—and explore their clocking, read/write operations, and grouping capabilities.
**Different Types of QDR-IV: XP and HP**
There are two main types of QDR-IV SRAM: HP and XP. The HP variant operates at lower frequencies and does not support grouping operations, while the XP version uses a grouping scheme and runs at higher frequencies, making it suitable for the most demanding applications.
The read and write latency of QDR-IV depends on its operating speed. Table 1 outlines the different operating modes and the corresponding frequency ranges supported by each mode.
**Table 1: Operating Modes**
QDR-IV SRAM features two independent ports—Port A and Port B. This allows for simultaneous read and write operations, maximizing the random transaction rate. Each port uses a double data rate (DDR) address bus, with Port A's address latched on the rising edge of the input clock (CK), and Port B's address latched on either the falling edge of CK or the rising edge of CK#. Control signals (LDA#, LDB#, RWA#, RWB#) operate at a single data rate (SDR) and determine whether a read or write operation is performed. Both data ports (DQA and DQB) use DDR interfaces, supporting a 2-word burst architecture and providing data bus widths of ×18 or ×36.
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