The CDFP 400 Gig module
- The CDFP will be a 400 Gig short reach module
- Module will enable 4 Terabit line cards
- Specification will be completed in the next year
A CDFP pluggable multi-source agreement (MSA) has been created to develop a 400 Gigabit module for use in the data centre. "It is a pluggable interface, very similar to the QSFP and CXP [modules]," says Scott Sommers, group product manager at Molex, one of the CDFP MSA members.
Scott Sommers, MolexThe CDFP name stands for 400 (CD in Roman numerals) Form factor Pluggable. The MSA will define the module's mechanical properties and its medium dependent interface (MDI) linking the module to the physical medium. The CDFP will support passive and active copper cable, active optical cable and multi-mode fibre.
"The [MSA member] companies realised the need for a low cost, high density 400 Gig solution and they wanted to get that solution out near term," says Sommers. Avago Technologies, Brocade Communications Systems, IBM, JDSU, Juniper Networks, TE Connectivity along with Molex are the founding members of the MSA.
Specification
Samples of the 400 Gig MSA form factor have already been shown at the ECOC 2013 exhibition held in September 2013, as were some mock active optical cable plugs.
"The width of the receptacle - the width of the active optical cable that plugs into it - is slightly larger than a QSFP, and about the same width as the CFP4," says Sommers. This places the width of the CDFP at around 22mm. The CDFP however will use 16, 25 Gigabit electrical lanes instead of the CFP4's four.
"We anticipate a pitch-to-pitch such that we could get 11 [pluggables] on one side of a printed circuit board, and there is nothing to prohibit someone doing belly-to-belly," says Sommers. Belly-to-belly refers to a double-mount PCB design; modules mounted double sidedly. Here, 22 CDFPs would achieve a capacity of 8.8 Terabits.
The MSA group has yet to detail the full dimensions of the form factor nor has it specified the power consumption the form factor will accommodate. "The target applications are switch-to-switch connections so we are not targeting the long reach market that require bigger, hotter modules," says Sommers. This suggests a form factor for distances up to 100m and maybe several hundred meters.
The MSA members are working on a single module design and there is no suggestion of future additional CDFP form factors as this stage.
"The aim is to get this [MSA draft specification] out soon, so that people can take this work and expand upon it, maybe at the IEEE or Infiniband," says Sommers. "Within a year, this specification will be out and in the public domain."
Meanwhile, companies are already active on designs using these building blocks. "In a complex MSA like this, there are pieces such as silicon and connectors that all have to work together," says Sommers.
OIF demonstrates its 25 Gig interfaces are ready for use
The Open Internetworking Forum (OIF) has demonstrated its specified 25 and 28 Gigabit-per-second (Gbps) electrical interfaces working across various vendors' 100 Gigabit modules and ICs.
"The infrastructure over the backplane is maturing to the point of 25 Gig; you don't need special optical backplanes" John Monson, Mosys
"The ecosystem is maturing," says John Monson, vice president of marketing at Mosys, one of the 11 firms participating in the demonstrations. "The demos are not just showing the electrical OIF interfaces but their functioning between multiple vendors, with optical standards running across them at 100 Gig."
The demonstrations - using the CFP2, QSFP and CPAK optical modules and the 28Gbps CEI-28G-VSR module-to-chip electrical interface - set the stage for higher density 400 and 800 Gigabit line cards, says Monson. The CEI-28G-VSR is specified for up to 10dB of signal loss, equating to some 4 to 6 inches of trace on a high-quality material printed circuit board.
Higher density system backplanes are also ready using the OIF's CEI-25G-LR interface. "Until I get backplanes capable of high rates, there are just too many pins at 10 Gig to support 800 Gig and Terabit [line card] solutions," says Monson.
The ECOC demonstrations include two 100Gbps modules linked over fibre. "You have two CFP2 modules, from different vendors, running at 4x28Gbps OTN [Optical Transport Network] rates over 10km," says Monson.
On the host side, the CEI-28G-VSR interface sits between a retimer inside the CFP2 module and a gearbox chip that translates between 25Gbps and the 10Gbps lanes that link a framer or a MAC IC on the line card.
The demonstrations cover different vendors' gearbox ICs talking to different optical module makers' CFP2s as well as Cisco's CPAK. "We are mixing and matching quite a bit in these demos," says Monson.
The OIF has already started work for the next-generation electrical interfaces that follow the 25 and 28 Gigabit ones
There is also a demo of a QSFP+ module driving active copper cable and one involving two 100 Gigabit SR10 modules and a gearbox IC. Three further demos involve the CEI-25G-LR backplane interface. Lastly, there is a demo involving the thermal modelling of a line card hosting eight slots of the CDFP 400Gbps optical module MSA.
The OIF's CEI-25G-LR is specificed for up to 25dB of loss. The IEEE P802.3bj 100 Gbps Backplane and Copper Cable Task Force is specifying an enhanced backplane electrical interface that supports 35dB of loss using techniques such as forward error correction.
"What the demos say is that the electrical interfaces, at 25 Gig, can be used not just for a 4-6 inch trace, but also high-density backplanes," says Monson. As a result line card density will increase using the smaller form factor 100Gbps optical modules. It also sets the stage for 400 Gig individual optics, says Monson: "The infrastructure over the backplane is maturing to the point of 25 Gig; you don't need special optical backplanes."
Meanwhile, standards work for 400 Gigabit Ethernet is still at an early stage, but proposals for 56Gbps links have been submitted for consideration. "Such a rate would double capacity and reduce the number of pins required on the ASSPs and ASICs," says Monson.
As to how the electrical interface for 400 Gigabit Ethernet will be implemented, it could be 16x25Gbps or 8x50Gbps lanes and will also be influenced by the chosen optical implementation. The OIF has already started work for the next-generation electrical interfaces that follow the 25 and 28 Gigabit ones.
The 11 companies and the two test and measurement companies taking part, as well as the demonstrations, are detailed in an OIF White Paper, click here.