RealTime IT News

RDMA Completes Spec to Combat Latency

The Remote Direct Memory Access Consortium (RDMA) -- the group responsible for creating architectural specifications for products that combat data latency for TCP/IP networks -- Wednesday said it has completed the inaugural version of its spec.

The Chicago-based RDMA, working as a complementary group to the Internet Engineering Task Force (IETF), was launched in May to accommodate demands for increased networking bandwidth and speeds.

Specifically, RDMA helps eliminate cumbersome data copy operations and reduces latencies by allowing one computer to directly place information in another computer's memory with few demands on memory bus bandwidth and CPU processing overhead. Simply, RDMA smooths the passage of network data, and improves communications in the process.

The RDMA over TCP protocol, it follows, reduces the overhead burden on processors and memory. This frees up ultra-taxed processors for other duties, such as user applications. The RDMA said another opportunity is the ability to converge functions in the data center over fewer types of interconnects. This makes the infrastructure less complex and easier to manage.

The RDMA was born out of concern for the future of network data interchange, as the future moves closer to 10 gigabit Ethernet and data centers get challenged: right now, the ratio of CPU power to network speeds are closing on one another fast, which will mean more pesky latency. The group also argues that current proprietary RDMA products are unsatisfactory and that an interoperable standard is needed.

John Gromala, Manager of Technology Strategy & Marketing for HP Industry Standard Servers and HP's spokesman on behalf of SDMA, called the RDMA technology the IP fabric that improve the utliization of the data center as a valuable tool to house data for businesses.

"Over time, this will open up new server designs that feature less interconnect," Gromala told "This will lower operating costs for the businesses. In the end, IP fabric ends up being the single unifying piece."

Gromala, who expects first generation RDMA products to see the light of day in 2004, said the RDMA technology improves the end-to-end efficiency and scaling in those networks, as well as communication between servers.

"From an IP consolidation perspective, we like to compare this technology to the reason why people are buying SUVs," Gromala said. "RDMA has fewer interconnects, reduces complexity and lowers cost.

Those that think RDMA doesn't sound much different than the problems addressed by InfiniBand or VI Architecture would be correct. All three architectures specified a form of RDMA and have strong similarities. While VI Architecture's goal was to was to specify RDMA capabilities without specifying the underlying transport, InfiniBand improved upon the RDMA capabilities of VI and specified an underlying transport and physical layer that are optimized for data-center class traffic. RDMA over TCP/IP will specify an RDMA layer that will interoperate over a standard TCP/IP transport layer. RDMA over TCP does not specify a physical layer; it will work over Ethernet, wide area networks (WAN) or any other network where TCP/IP is used.

RDMA, whose founding members include Adaptec, Broadcom, HP, IBM, Intel, Microsoft and Network Appliance, said version 1.0 of the wire protocol specs are suitable for first generation industry implementations of the RDMA over TCP protocol and have been forwarded to IETF working groups as Internet Drafts for their consideration. RDMA is also working on companion specs, which are expected to roll out in the first quarter of 2003.

For technical treatments of the consortium's goals and motivations, please see this white paper.