Written by Ray Nering, Product Manager, Transceiver Modules Group, Cisco
Global IP traffic has been forecasted to grow at a 24% CAGR over the next 5 years according to Cisco’s VNI analysis, but traffic within the data center, according to Google, is doubling year over year. Data centers that generate and manage this traffic will need equipment that operate at higher speeds, higher densities and of course need to be more efficient in both power and cost.
On Tuesday, September 12th, 2017, a new Multi-Source Agreement (MSA) called the “100G Lambda MSA” was announced. The 100G Lambda MSA group is an industry consortium with a common focus to provide a new set of optical interface specifications, developed around an optical channel data rate of 100Gb/s. These specifications are targeted for use at 100GE and 400GE applications to be used as a cost-effective solution for high density multi-Terabit switching, routing and transport networks. Cisco is one of 22 founding members of the MSA along with Alibaba, Arista Networks, Broadcom, Ciena, Finisar, Foxconn Interconnect Technology, Inphi, Intel, Juniper Networks, Lumentum, Luxtera, MACOM, MaxLinear, Microsoft, Molex, NeoPhotonics, Nokia, Oclaro, Semtech, Source Photonics, and Sumitomo Electric.
Today the cost of deploying and connecting Ethernet switches with 100GE ports can be impacted significantly by the cost of the optical modules. The need for simpler, more cost-effective pluggable optical modules will be key to enabling the market as traffic continues to grow. According to the Dell’Oro Data Center Ethernet Switch report, more than 35 million 100GE ports will be deployed in data centers by the end of 2019.
A large portion of the cost of 100GE pluggable optical modules can be wrapped up in the optical complexity of the modules themselves. Optical components in the modules can contribute more than 60% of the cost. Most modules today, operating at 100Gb/s, consist of four sets of transmitters and receivers operating in parallel lanes of 25Gb/s. Typically four electrical lanes at the input of the module are routed through re-timers, then drive discrete optical components at 25G. Those four optical signals are coupled either through parallel fibers or are optically multiplexed to a single fiber for transport. The optical signals can be coupled or de-multiplexed into four optical lanes to four receivers and re-timers at the other end of the link. This is the case for 100GBASE-LR4, 100G-CWDM4, 100G-PSM4 and 100GBASE-SR4 modules commonly used in the market. As volumes increase, the electronic ICs in these modules can scale cost with volume as any CMOS technology scales with volume, driving down cost.
Optical components generally do not scale to the same degree since they usually consist of an assembly of discrete components. As the volume of these modules grows with demand, costs eventually will be dominated by optical component content. The fewer the discrete optical components used in the design, the lower the cost as volumes ramp. The IEEE recently acknowledged that the ability of the industry to support 100GE per lambda (wavelength) was near, and also recognized that the cost of a 100GE optical signal could be at least 40% lower with a single optical lane.
To realize this cost advantage, the IEEE utilized 100G PAM4 signalling instead of NRZ for 100G per wavelength standards. This decreased the optical complexity by reducing the number of optical transmitters and receivers from 4 to 1, but increased the complexity of the optical signalling which is handled by the electronics around the optical components. As a result, the high-complexity element is driven to CMOS silicon technology where cost can follow the CMOS experience cost curve, while the cost associated with the optics has been reduced to the bare minimum.
The IEEE quickly developed the standard for 100GBASE-DR and 400GBASE-DR4 for 500m applications. Since these applications were limited to reaches of 500m, the 100G Lambda MSA was formed to extend the reach of the IEEE standards to 2km and 10km utilizing the same signalling approach. This provides a lower cost alternative to 100GBASE-LR4, CWDM4 and PSM4 for service provider and data center applications at 100GE. The MSA will also address 400GE applications using 100G PAM4 signalling per lambda for 2km and 10km applications.
In January 2018, the 100G Lambda MSA published the first set of specifications for 100G-FR and 100G-LR for 2km and 10km applications, respectively, and for 400G-FR4 for 400GE 2km applications
The MSA specifications are available on their website WWW.100glambda.com.