This is the first in a series of blog posts that offer technical and industry insights from Dr. Paul Brooks, who has been involved in R&D and product management for high speed electronic and photonic test equipment for over 20 years. Dr. Brooks holds several patents related to measurement in high speed test equipment and is also actively involved with industry standards including the IEEE 802.3 group.

Modern pluggable optics are a marvel of high-speed electronics, DSP, photonics, mechanical, thermal management and a lot of firmware to hold it all together.  Up to 100G, these modules have been managed over their control interface (for QSFP based around I^2C) using a basic memory mapped command system – SFF 8636. However, as the speeds have increased, this historical system has struggled to keep up.

Because of the substantial increase in complexity required to manage 400G class modules—including PAM-4 interfaces requiring complex equalization—the industry worked hard to develop a module command management system fit for 400G and beyond. The result was the CMIS 4.0, which was released early in 2018 and is starting to be found in QSFP-DD modules and the appropriate network elements. Before CMIS, we had a multitude of older MSAs which often had glaring omissions and gaps. CMIS will now offer a solid, robust and clearly defined standard.

The Common Management Interface Specification (CMIS) is a generic management interface together with a generic management interaction protocol between hosts and modules. It is developed to allow host and module software implementers to utilize a common code base across a variety of form factors. CMIS compliant pluggable modules include form factors such as QSFP-DD, OSFP, COBO, QSFP and SFP-DD.

One key point is that many network elements will also have to support legacy modules using SFF-8636, so adding to S/W and F/W complexity. At this point you may be asking yourself, “Why should I bother getting familiar with CMIS 4.0?” The answer: Because it will grow and evolve to be the management and control system for pluggables.  This includes the upcoming pluggable coherent modules for DCI and 400ZR application. It is also far more challenging to debug and validate than legacy SFF as you need tight coupling between stateful commands, pin & power states and the data path activity.

To find out more about CMIS 4.0 visit http://www.qsfp-dd.com/specification/

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