New MSA to enable four-lambda 400-gigabit modules
Tuesday, September 12, 2017 at 4:57PM
Roy Rubenstein in 100G Lambda MSA, 100G-FR, 100G-LR, 400G-FR4, COBO, IEEE, Mark Nowell, OSFP, QSFP-DD, optical transceivers

A new 100-gigabit single-wavelength multi-source agreement (MSA) has been created to provide the industry with 2km and 10km 100-gigabit and 400-gigabit four-wavelength interfaces.

Mark NowellThe MSA is backed by 22 founding companies including Microsoft, Alibaba and Cisco Systems.

The initiative started work two months ago and a draft specification is expected before the year end.

“Twenty-two companies is a very large MSA at this stage, which shows the strong interest in this technology,” says Mark Nowell, distinguished engineer, data centre switching at Cisco Systems and co-chair of the 100G Lambda MSA. “It is clear this is going to be the workhorse technology for the industry for quite a while.”

 

Phased approach

The 100G Lambda MSA is a phased project. In the first phase, three single-mode fibre optical interfaces will be specified: a 100-gigabit 2km link (100G-FR), a 100-gigabit 10km link (100G-LR), and a 2km 400-gigabit coarse wavelength-division multiplexed (CWDM) design, known as the 400G-FR4. A 10km version of the 400-gigabit CWDM design (400G-LR4) will be developed in the second phase.

For the specifications, the MSA will use work already done by the IEEE that has defined two 100-gigabit-per-wavelength specifications. The IEEE 802.3bs 400 Gigabit Ethernet Task Force has defined a 400-gigabit parallel fibre interface over 500m, referred to as DR4 (400GBASE-DR4). The second, the work of the IEEE 802.3cd 50, 100 and 200 Gigabit Ethernet Task Force, defines the DR (100GBASE-DR), a 100-gigabit single lane specification for 500m.

 

Twenty-two companies is a very large MSA at this stage, which shows the strong interest in this technology

 

“The data rate is known, the type of forward-error correction is the same, and we have a starting point with the DR specs - we know what their transmit levels and receive levels are,” says Nowell. The new MSA will need to contend with the extra signal loss to extend the link distances to 2km and 10km.

With the 2km 400G-FR4 specification, not only does the design involve longer distances but also loss introduced using an optical multiplexer and demultiplexer to combine and separate the four wavelengths transmitted over the single-mode fibre.

“It is really a technical problem, one of partitioning the specifications to account for the extra loss of the link channel,” says Nowell.  

One way to address the additional loss is to increase the transmitter’s laser power but that raises the design’s overall power consumption. And since the industry continually improves receiver performance - its sensitivity - over time, any decision to raise the transmitter power needs careful consideration. “There is always a trade off,” says Nowell. “You don't want to put too much power on the transmitter because you can’t change that specification.” 

The MSA will need to decide whether the transmitter power is increased or is kept the same and then the focus will turn to the receiver technology. “This is where a lot of the hard work occurs,” he says.

 

Origins

The MSA came about after the IEEE 802.3bs 400 Gigabit Ethernet Task Force defined 2km (400GBASE-FR8) and 10km (400GBASE-LR8 interfaces based on eight 50 gigabit-per-second wavelengths. “There was concern or skepticism that some of the IEEE specification for 2km and 10km at 400 gigabits were going to be the lowest cost,” says Nowell. Issues include fitting eight wavelengths within the modules as well as the cost of eight lasers. Many of the large cloud players wanted a four-wavelength solution and they wanted it specified.  

The debate then turned to whether to get the work done within the IEEE or to create an MSA. Given the urgency that the industry wanted such a specification, there was a concern that it might take too long to get the project started and completed using an IEEE framework, so the decision was made to create the MSA.

“The aim is to write these specifications as quickly as we can but with the assumption that the IEEE will pick up the challenge of taking on the same scope,” says Nowell. “So the specs are planned to be written following IEEE methodology.” That way, when the IEEE does address this, it will have work it can reference.

“We are not saying that the MSA spec will go into the IEEE,” says Nowell. “We are just making it so that the IEEE, if they chose, can quickly and easily have a very good starting point.”        

 

Form factors

The MSA specification does not dictate the modules to be used when implementing the 100-gigabit-based wavelength designs. An obvious candidate for the single-wavelength 2km and 10km designs is the SFP-DD. And Nowell says the OSFP and the QSFP-DD pluggable optical modules as well as COBO, the embedded optics specification, will be used to implement 400G-FR4. “From Cisco’s point of view, we believe the QSFP-DD is where it is going to get most of its traction,” says Nowell, who is also co-chair of the QSFP-DD MSA.

Nowell points out that the industry knows how to build systems using the QSFP form factors: how the systems are cooled and how the high-speed tracks are laid down. The development of the QSFP-DD enables the industry to reuse this experience to build new high-density systems.

“And the backward compatibility of the QSFP-DD is massively important,” he says. A QSFP-DD port also supports the QSFP28 and QSFP modules. Nowell says there are customers that buy the latest 100-gigabit switches but use lower-speed 40-gigabit QSFP modules until their network needs 100 gigabits. “We have customers that say they want to do the same thing with 100 and 400 gigabits,” says Nowell. “That is what motivated us to solve that backward-compatibility problem.”

 

Roadmap

A draft specification of the phase one work will be published by the 22 founding companies this year. Once published, other companies - ‘contributors’ - will join and add their comments and requirements. Further refinement will then be needed before the final MSA specification, expected by mid-2018. Meanwhile, the development of the 10km 400G-LR4 interface will start during the first half of 2018.       

The MSA work is focussed on developing the 100-gigabit and 400-gigabit specifications. But Nowell says the work will help set up what comes next after 400 gigabits, whether that is 800 gigabits, one terabit or whatever.

“Once a technology gets widely adopted, you get a lot of maturity around it,” he says. “A lot of knowledge about where and how it can be extended.”

There are now optical module makers building eight-wavelength optical solutions while in the IEEE there are developments to start 100-gigabit electrical interfaces, he says: “There are a lot of pieces out there that are lining up.” 

The 22 founding members of the 100G Lambda MSA Group are: Alibaba, Arista Networks, Broadcom, Ciena, Cisco, Finisar, Foxconn Interconnect Technology, Inphi, Intel, Juniper Networks, Lumentum, Luxtera, MACOM, MaxLinear, Microsoft, Molex, NeoPhotonics, Nokia, Oclaro, Semtech, Source Photonics and Sumitomo Electric.

Article originally appeared on Gazettabyte (http://www.gazettabyte.com/).
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