New forward error correction (FEC) specification lowers total
physical layer latency for engineered network links
SANTA CLARA, Calif.–(BUSINESS WIRE)–The 25 Gigabit Ethernet Consortium, established to develop 25 Gbps and
faster Ethernet specifications, today announced the availability of a
low-latency forward error correction (FEC) specification for 50 Gbps,
100 Gbps and 200 Gbps Ethernet networks.
High latency is a problem for performance-critical networks in
applications such as high-performance computing (HPC), data center
interconnect, machine learning, financial trading and others. The
availability of a low-latency FEC allows high-speed Ethernet to be
better suited for these applications, especially for HPC networks where
other interconnect technologies are more prominent than Ethernet.
“Five years ago, only HPC developers cared about low latency, but today
latency sensitivity has come to many more mainstream applications,” said
Rob Stone, technical working group chair of the 25G Ethernet Consortium.
“With this new specification, the consortium is improving the single
largest source of packet processing latency, which improves the
performance that high-speed Ethernet brings to these applications.”
FEC is a major source of latency in a switched network and the new
specification cuts FEC latency approximately in half. This will have a
significant impact on overall physical layer latency, in particular for
hyperscale datacenter networks comprised of a large number of nodes,
with multiple hops between servers.
The specification allows NEMs to optionally use a shortened codeword FEC
variant – RS (272, 257+1, 7, 10) that replaces the IEEE 802.3cd and
802.3bs standard FEC.
The shortened codeword contains 272 x 10-bit symbols rather than the 544
x 10-bit symbols originally specified. Nothing else changes in the
symbol distribution process from the output of the encoder to the FEC
lanes in the new FEC, but that process is implemented more quickly due
to the shortened codeword.
“The value of having a standard extends to ensuring multi-vendor product
interoperability and ecosystem,” said Tim Lustig, marketing chair of the
25G Ethernet Consortium. “To ensure specification conformance and
interoperability, testing will be held at future plugfests the
consortium regularly conducts at the University of New Hampshire
InterOperability Laboratory (UNH-IOL).”
The original FEC standards are designed to maximize data integrity and
minimize data packet retransmissions due to packets or data that are
lost or corrupted in transmission. In simulations conducted by the
consortium using the new FEC standard, copper cable lengths of up to 2m
and fiber cable lengths up to 30m can be supported. To ensure high data
integrity, the consortium recommends that the new FEC be used only on
engineered data connections.
The specification is now available for implementation by switch chip
manufacturers. The specification is available at https://25gethernet.org/ll-fec-specification.
About the 25 Gigabit Ethernet Consortium
The 25 Gigabit Ethernet Consortium is an open organization of
third-party companies who wish to enable the transmission of Ethernet
frames at 25 or 50 Gigabit per second (Gbps) and to promote the
standardization and improvement of the interfaces for applicable
products. The consortium is open for membership to any organization
willing to help facilitate industry adoption. To become a member, please
David Rodewald, 805-494-9508