Engineer Mark Kempf's Unsung Innovations Transform Ethernet, Fueling the Rise of Switching

The invention of Ethernet by Robert Metcalfe and David Boggs has significantly impacted the world, leading to the development and advancement of various networking technologies. However, the full story involves the creation of a learning bridge by Mark Kempf in 1983, which revolutionized LAN technology by enabling data store-and-forward switching. This innovation allowed existing Ethernet networks to be upgraded easily and increased their performance, leading to the gradual shift from CSMA/CD-based coaxial cables to dedicated copper and fiber links. Kempf's invention and the subsequent standardization efforts laid the foundation for the widespread adoption and continued evolution of Ethernet, which remains the dominant LAN technology today.

Ethernet's Evolutionary Journey: The Unsung Role of Mark Kempf and the Rise of Switching

Ethernet, a ubiquitous technology that underpins the internet and countless other applications, celebrates its 50th anniversary this year. While the invention of Carrier Sense Multiple Access with Collision Detection (CSMA/CD) by Robert Metcalfe and David Boggs is widely recognized as a pivotal moment in Ethernet's history, the contributions of others who shaped its evolution are often overlooked. Among them, Mark Kempf stands out as a visionary engineer whose innovations transformed Ethernet from a shared media technology to the high-performance, switched network we know today.

The Quest for Speed and the Threat from FDDI

In the 1980s, the limitations of CSMA/CD Ethernet became increasingly apparent as the demand for faster network speeds grew. A coalition of companies, including Digital Equipment Corporation (DEC), embarked on the development of a new standard, Fiber Distributed Data Interface (FDDI), which promised speeds of 100 Mb/s over optical fiber. FDDI seemed poised to supplant Ethernet as the dominant LAN technology.

A New Approach: Store-and-Forward Switching

However, Kempf, a principal engineer at DEC, believed there was a better way. Instead of developing a faster version of Ethernet or adopting FDDI, he proposed a novel approach: store-and-forward switching.

In a store-and-forward switch, each message is received and stored in a buffer before being transmitted to its destination. This eliminates the need for collision detection, enabling higher speeds and eliminating the need for a shared medium.

The Birth of the Learning Bridge

Kempf's idea took shape in a collaboration with Bob Shelly, a software engineer. Together, they developed the concept of a "learning bridge," a device that would connect multiple Ethernet LANs and selectively forward packets based on their destination MAC addresses.

The learning bridge had several advantages. It allowed easy upgrades of existing Ethernet networks, isolated heavy traffic to specific segments, and doubled the effective cable length limit. Most importantly, it removed the performance bottlenecks inherent in shared media access protocols.

Overcoming Obstacles and Gaining Acceptance

Kempf's innovation faced several challenges. One was the risk of packets looping indefinitely in misconfigured networks. However, Radia Perlman, another DEC engineer, provided a solution: the spanning tree protocol, which ensures that bridges form a tree-like topology, preventing loops.

Another challenge was the need for high-performance hardware to process packets at wire speed. Kempf designed a custom hardware engine using programmable array logic (PAL) devices to achieve the required performance.

Despite these challenges, Kempf's bridge technology was groundbreaking. In 1986, DEC introduced the LANBridge 100, the first commercial learning bridge. It allowed existing CSMA/CD coax-based Ethernets to be upgraded to much higher speeds.

The Gradual Migration to Switched Ethernet

Kempf's bridge technology did not replace Ethernet but rather complemented it. By allowing store-and-forward switching between existing Ethernets, bridges paved the way for a gradual migration away from CSMA/CD over coax to the now ubiquitous copper and fiber links between individual computers and a dedicated switch port.

The speed of the links is no longer limited by the constraints of collision detection. Over time, the change completely transformed how people think of Ethernet.

The Impact of Switching Technology

The existence of bridges with increasingly higher performance effectively rendered new shared media LAN access protocols obsolete. FDDI later faded from the marketplace in the face of faster Ethernet versions.

Bridge technology also enabled the development of more advanced networking features, such as virtual LANs (VLANs) and support for multiple network protocols. These enhancements further contributed to Ethernet's longevity and popularity.

The Lasting Legacy of Mark Kempf

Kempf's invention of the learning bridge played a pivotal role in the evolution of Ethernet. It transformed Ethernet from a shared media technology into a switched network, paving the way for the high-speed, reliable, and efficient networks we use today.

Kempf's contributions have not received the widespread recognition they deserve. However, his invention has had a profound impact on the development of the internet and the entire digital landscape.

Ethernet's enduring success is a testament to the power of innovation and the foresight of engineers like Mark Kempf. As we celebrate its 50th anniversary, it is important to remember the unsung heroes who shaped its history and continue to drive its evolution.