By Christian Urricariet, Finisar Corp.
The continuous increase in bandwidth demand is rapidly pushing cloud data centers and network operators to significantly increase their data traffic capacity. The deployment of 400G Ethernet which is expected to start in the 2019/2020 timeframe will play a key role in this effort, and as with past network upgrades it requires the creation of a multi-sourced interoperable optical ecosystem. Various types of 400G Ethernet (“client-side”) optical interfaces have been or are being in the process of being standardized by the IEEE and MSAs. They include single-mode and multimode options, as well as interfaces running over parallel optics or over duplex optics (using WDM technology).
Additionally, the Optical Internetworking Forum (OIF) has been working on standardizing a 400G coherent (“line-side”) DWDM interface for DCI and other metro/access applications. Recent IEEE efforts are heading in that direction as well.
This white paper presents a summary of these activities.
IEEE 802.3bs Task Force
This Task Force has completed its work and these standards have already been ratified as part of IEEE 802.3 in December 2017. The work included standardizing the 400G electrical interface from the optical transceiver to the host system (400GAUI-8), a well as the 400G optical interfaces which are expected to be deployed initially by the hyperscale cloud service providers and telecom carriers, using single mode fiber:
400G FR8, LR8 and DR4 transceivers in both the QSFP-DD or the OSFP form factors have been widely demonstrated publicly and are already shipping/sampling by Finisar and other optical vendors.
This MSA was announced in September 2017 and was created to standardize additional interfaces which were not covered by the IEEE activities. It currently has 42 member-companies. Finisar is a member of the 100GLambda MSA.
The 400G interfaces it is standardizing are the following:
These FR4 and LR4 interfaces use only 4 lasers instead of 8 lasers (like FR8 and LR8), also optically multiplexing them into one fiber in each direction. This entails using 100G PAM4 (50 GBaud) technology instead of 50G PAM4 (25 GBaud), which may add complexity, risk and cost in the short term, especially for LR4 (10km reach). However, using a lower number of lasers is always desirable from the cost standpoint in the long term, for very high volumes. It is likely that these interfaces will also be standardized by the IEEE soon.
IEEE P802.3cm Task Force
This Task Force was created in May 2018 with the aim of standardizing more cost-effective, shorter-reach 400G interfaces using multimode fiber with a lower fiber count than 400GBASE-SR16. Its primary adopters are expected to be certain hyperscale cloud service providers in North America and China. The Task Force is focusing on the following 400G interfaces:
These standards are currently expected to be ratified in December 2019.
The 400G BiDi MSA announced in July 2018 is also standardizing an interface similar to 400GBASE-SR4.2 called 400G-BD4.2. Finisar is a member of this MSA.
IEEE P802.3cn/ct Task Forces
The P802.3cn Task Force was created in September 2018 with the aim of standardizing high-speed (50G, 100G, 200G and 400G) interfaces beyond 10km. In late 2018, a proposal was put forward at the IEEE to split this Task Force into two more focused efforts (as shown below for 400G only). This proposal to split the Task Force has been approved by the IEEE Standards Board.
These standards are currently expected to be ratified in Q3 CY2020.
OIF 400ZR Implementation Agreement (IA)
The OIF is working on standardizing an interoperable, multi-source 400G coherent (single wavelength) DWDM interface called 400ZR to support Data Center Interconnect (DCI) and other metro/access (“line-side”) applications with links of up to 80km. The expectation is for this optical interface to be implemented in small 400G transceiver form factors such as QSFP-DD or OSFP, although early implementations using CFP2 or CFP8 could possibly appear in the market. The interface is only specified up to a reach of 80km, effectively trading performance for lower power dissipation, physical size and cost. As already stated, the IEEE P802.3ct Task Force is also working on standardizing an 80km 400G coherent interface. It would presumably use the work already done by the 400ZR IA as a baseline.
400G Coherent DWDM technology will also support other line-side applications with up to hundreds of kilometers of reach, but without multi-vendor interoperability for now. The performance requirements for these transceivers, especially if they include a DSP chip inside, may only make them feasible in the CFP2 or CFP8 pluggable form factors in the short/medium term. Earlier implementations may use coherent components on system line cards instead of pluggable transceivers.