How have CXP connectors and cables evolved in recent years?

By Ed Cady, Contributing Editor

CXP+ is the 10-16 Gbps per lane mainstream and current volume version of this connector family. This connector was chosen for 12×14 Gbps InfiniBand FDR, 12×16 Gbps FC-ISL and many other IO interface applications. To meet the increased speed rate for medium and long reaches, active copper chips were added to the cable’s PCB plug with options for different signal conditioning, retiming or re-driving requirements. Some OEM systems’ house cables have had EPROM chips on board as well for various system management functionality like identification, closed and secured networked system requirements. Sometimes there has been EPROM handshake inter-compatibility problems between different company products causing headaches for end-users. CXP+ active optical cables have been mostly used for 10+ meter reaches. This is done by having an E/O engine chip on the plug PCB and terminating optical fibered cable to the plug. See SFF-8642 connector and SFF-8417 (cage) CXP+ specifications.

Some OEM systems’ house cables have had EPROM chips on board as well for various system management functionality like identification, closed and secured networked system requirements. Sometimes there has been EPROM handshake inter-compatibility problems between different company products causing headaches for end-users. CXP+ active optical cables have been mostly used for 10+ meter reaches. This is done by having an E/O engine chip on the plug PCB and terminating optical fibered cable to the plug. See SFF-8642 connector and SFF-8417 (cage) CXP+ specifications.

CXP28 is the fairly new 25-32 Gbps per lane version. The Ethernet Alliance and InfiniBand trade association past plug-fest testing events were successful working out the compliance and interoperability issues. It appears the markets are using both active copper and active optical cables for most reach requirements. See the Integrators List at www.infiniband.org for various qualified suppliers. It appears a back-to-back receptacle connector is being developed that would have internal copper twin-axial flat cables or better substrate quality, PCB jumpers extending over the primary, but lower quality substrate main PCB. These internal CXP28 jumpers connect back to the PCB very close to the switch chip or on top of the chip itself. IEEE802.3bj and IEEE802.3bm Ethernet standards make use of CXP28. See the SFF-8648 connection system SFF-8617 mechanical specifications

CXP56 has been the latest developing 50-56-Gbps version. It appears that this would be used for mostly active optical modules, active optical cables and maybe some very short active copper cables applications which may be more expensive and power consuming. It appears that this may be supplanted by use of internal mid-board optical/electrical interconnect flyovers and bulkhead MPO or MXC connectors.

microCXP28 is a newly released 33% smaller package size connector that enables many more ports to be on a standard 1U box bulkhead. The smaller plug PCBs have made for a tighter passive/active component layout and better substrate type usage. Controlling the active chip thermal generation and heat flow thru the interconnect system has been a challenge and will be more so for nascent microCXP56. For more info on this interconnect family see the recently posted ConnectorTips related QSFP and SFP articles.

CFP, common form-factor pluggable, is a competing larger size module, cage and cabling system used primarily in telecom systems and WAN/Metro applications. A new ConnectorTips article will describe the CFP, CFP2, CFP4 and CFP8 interconnect system. It seems that there is also an increase in competition by use of new type of custom cabled backplane connector systems like ExaMax 25/56, Impel+ and Whisper+ that includes external connectivity. I’ll be exploring that more soon.

Some CXP specifications, including SFF-8679, can be found at www.sffcommittee.org. The members of the SFF committee do detailed interconnect specifications for open industry standard groups as well as the originating CXP MSA private consortium.