100GBASEKR4

100GBASEKR4 is a 100 Gigabit Ethernet physical layer specification defined by IEEE 802.3 for high‑speed data transmission over copper backplanes. The “K” in KR4 denotes a backplane medium, and the “R4” indicates four parallel lanes that together carry 100 Gbps of payload.

The standard specifies four differential signal lanes that run concurrently over copper backplane interconnects, enabling 100 Gbps by aggregating the lanes. The backplane or midplane medium used with KR4 is typically compact and designed for short‑reach interconnects within equipment racks or between adjacent line cards in a switch chassis. As a copper backplane solution, KR4 supports fixed, predictably short distances rather than long‑haul links.

Electrical signaling, framing, and error handling requirements are defined in the IEEE 802.3 specification for 100GBASE‑KR4. Implementations are expected to meet performance criteria such as eye safety, dispersion, and cross‑talk, with the PMA layer handling link training and error detection. KR4 is part of the broader family of 100GBASE standards, including 100GBASE‑CR4 (copper twinax), and fiber variants such as 100GBASE‑SR4 and 100GBASE‑LR4.

In practice, KR4 devices are used in data‑center environments to connect switching modules and line cards within a chassis or between adjacent units in a rack, where short‑reach copper interconnects are suitable. The standard emphasizes compatibility and interoperability through IEEE 802.3 compliance, while vendors may extend performance with implementation‑specific features.

See also: 100GBASE‑CR4, 100GBASE‑SR4, 100GBASE‑LR4, IEEE 802.3ba.