History of Channel Operating Margin (COM)
Earlier this year I met with one of Samtec’s exceptional engineers, Rich Mellitz, who started telling me he was in the “room where it happened” when people realized there was a need for a metric to evaluate high-speed data channels. Today, channel operating margin (COM) is a well-established IEEE methodology that has effectively guided interconnect design and specification since its formal adoption in 2014. I asked Rich to tell me the story of the origins of COM.
The result of my conversations with Rich is the Samtec “Origins of COM” white paper, which captures his recollections of the origins of COM, including how COM came to be, how it evolved over time, and where it may be headed next. (Note that this white paper does not explain COM’s technical mechanics, those are well documented in the IEEE standards and related references.)
Setting the Stage
Rich served as one of COM’s principal architects, and begins his COM story in the 1990s, when the needs of PCI Express®, InfiniBand™, and 10 Gb/s Ethernet required semiconductor companies to specify electrical channels that use separate differential pairs for transmit and receive. As the challenges intensified, the typical test methods of the day, such as setup and hold timing verification, began to give way to eye diagrams for compliance testing and frequency domain limit masks. As cabling lengths grew, there became no easy way to budget between insertion loss, crosstalk, return loss, and transceiver capability. This need paved the way for COM.
Learning Required
The engineers working on the challenges of high-speed data rates in the 1990s and early 2000s needed a better understanding of loss, crosstalk, reflections, and modulation schemes. The work during this time period also led to significant advancements in simulation.
Since its inception in the IEEE 802.3bj project, COM has undergone many revisions in response to industry needs and evolving market demands. It has been adopted in multiple IEEE projects including IEEE Std 802.3bm-2015, 802.3by-2016, 802.3bs-2017, 802.3cd-2018, 802.3ck-2022, 802.3df-2024, and P802.3dj. Additionally, COM has influenced related efforts in OIF and InfiniBand that align with IEEE Ethernet development.
Please take a look at the entire white paper in PDF form, Origins of Channel Operating Margin, to follow along with Rich on the evolution of COM, and how the hurdles the developers overcame helped shape the industry.
More Information
GEEk SpEEk: IEEE COM for Channel Analysis
Channel Operating Margin: An In-Context Channel Compliance Method – The Samtec Blog
COM: A Link Designer’s Field Guide | Signal Integrity Journal
