By Ed Cady, contributing editor
Now that we’ve delved into the beginnings of CFP connectors, we’re going to look at more modern developments in this technology.
CDFP (CD=400 in Latin) is a four-generation system but the first 16x25G= 400G larger size module and interconnect system. This solution uses one mezzanine connector, two PCBs and a four-row edge receptacle connector in two styles with 120 contacts used in a 29.71 mm wide module. Developing the thermal heat transfer path and larger heatsink design was more challenging to develop and qualify. Cleverly combining heatsink structures with metal cages have provided patent IP value for some interconnect companies. Passive optical cables using 32 OM4 fibers and MPO connectors to support 16 lanes have been deemed too costly for some potential applications. It seems that some custom, inside-the-box usage of the CDFP and CFP connector systems could have solved certain system packaging applications with similar form-factor requirements.
CDFP interconnect design/product verification has utilized SFF-8679 transceiver, SFF-8636 Common Interface Standard, SFF-8472 Diagnostic Monitoring Interface and JESD22A114 ESD specifications.
CDFP developers have targeted using the developing IEEE802.3bs specification for Ethernet 400GBaseSR, 400GBaseLR and 400GBaseER applications. They also targeted InfiniBand EDR hydra cables and 128GFC applications but so far little market segment pick up. It’s possible that some switched SAS 4.0 multi-port Nx24G links have been installed, but not many. CDFP products are also measured to validate electrical signal performance per IEEE802.3bm and OIF CEI-28-VSR with special compliance boards. Some shipments have supported certain MAN, WAN, OTU and ITU based design-ins.
Having 32 copper twin-ax elements contributed to heavy and difficult to build precision cable assemblies. Holding CDFP 16 channels or lanes together relative to the System Layer Stack is much harder and more costly than the more newly developing CFP8. Though relatively new with 2014 and 2015 rev releases, CDFP may be short lived due to the smaller more efficient developing set of CFP8 solutions.
CFP8 is the latest developing 8×50-56G=400-448G form-factor version. Proposal and design/product development has been going on for 9+ months. One proposal using the CFP large module size has not gained much traction. However, there has been interest in a 400GBase-SR16 parallel MMF 16x25G NRZ proposal. Another proposal is the 400GBase-FR8/LR8 duplex SMF 8x50G PAM4 WDM. This would use a 2×26=32 fiber MPO connector and OM4 type fiber.
The most evolutionary proposal is the 400GBaseDR4 4x100G parallel SMF PAM4 signaling technology. This is targeted to fit in the CFP4 21.5-mm width module size, while using 12 (SMF) fibers within a 1×12 MPO optical connector and the host board electrical 56-pin edge connector.
OIF CEI 56G, FC-PI-7, InfiniBand HDR, IEEE802.3bm, IEEE802.3bs and Ethernet single lane 50G link specifications are being used for this effort.
It appears that this would be used for mostly active optical modules, some active optical cables and maybe some very short active copper cables applications that may be more expensive and power consuming. It appears that this may be partially supplanted by use of internal mid-board optical/electrical interconnect flyovers and bulkhead MPO or MXC connectors.
CFP16 is an advanced nascent proposal for a narrower 4x100G module size close to the size of the new microQSFP module and corresponding connectors.
CFPxx is a nascent concept and road-mapping effort focusing on potential 5x200G=1T 2x500G=1T; remarkable of the exponential science, engineering, manufacturing and business effort needed for each new generation of high-speed interconnect network links. Signal and power integrity and test measurement are the biggest parts of the challenge. We’ll look further at these pioneering designs in future blogs.