What is 400ZR?
While widely used in long-haul telecommunications networks, coherent optical technology has been cost prohibitive and impractical for use in shorter distances such as data center interconnects (DCI). The Optical Internetworking Forum (OIF) and the Institute of Electrical and Electronics Engineers (IEEE) are working on new standards, 400ZR, 100GBASE-ZR, and 400GBASE-ZR, that will enable 100G and 400G speeds to reach up to 80 km.
The OIF is developing the 400ZR networking implementation agreement (IA) for pluggable digital coherent optical (DCO) modules. The 400ZR standard will enable the transmission of multiple 400 gigabit Ethernet (GE) payloads over DCI links up to 80 km using dense wavelength division multiplexing (DWDM) and higher-order modulation. The intent is to ensure an affordable and long-term implementation based on single-carrier 400G using dual-polarization 16-state quadrature amplitude modulation (16 QAM) at approximately 60 gigabaud (Gbaud). This is only possible using coherent detection and advanced digital signal processing (DSP). The 400ZR IA will reduce the cost and complexity of high-bandwidth data center interconnects and promote interoperability among optical module manufacturers.
On the host-side, 400ZR uses the 400GAUI-8 interface. The 400ZR IA details the full data path from this interface to the coherent optical signal on the line side. This also includes the full definition of a concatenated forward-error correction (FEC) scheme, which consists of a hard-decision (HD) outer FEC and a soft-decision (SD) inner FEC.
There is a strong interest by data center operators to use the 400ZR coherent interface to link distributed data centers, which are up to 80 km apart. While the IA does not target a specific form factor, the specifications are written such that the use of QSPFDD, OSFP, or COBO modules are possible. This allows to directly connect to data center switches just like client-side optics and will remove the need for costly and bulky transport networking equipment inside the data centers. Also, the telecommunications industry wants to use 400ZR for residential backhaul traffic of 200 Gb/s streams using 64 Gbaud signaling and quadrature phase shift keying (QPSK).
What is 400GBASE-ZR and 100GBASE-ZR?
In 2018, the IEEE approved the 802.3ct project. IEEE 802.3ct will leverage the OIF’s 400ZR IA to create the 400GBASE-ZR standard for 400 Gb/s transmission on a single wavelength up to 80 km in a DWDM system. A DWDM system involves multiplexing data signals from different transceivers using a single optical fiber.
For 100GBASE-ZR, the IEEE leverages the International Telecommunication Network’s (ITU’s) work for a 100 Gb/s transmission standard that uses a dual-polarization differential quadrature phase shift keying (DP-DQPSK) modulation scheme, as well as CableLabs full duplex coherent optics specification.
Although 400ZR technology is in its infancy, it is expected to significantly impact a number of industries once rolled out:
Hyperscale Data Centers/Cloud Service Providers
A large part of the demand for high-speed data center networking comes from hyperscale data centers owned by companies such as Google, Amazon, Microsoft, and Facebook, as well as Baidu, Tencent, and Alibaba. These massive data centers need to increase connection speeds to accommodate the exponential growth in cloud services, IoT devices, streaming video, and more. Developments in DCI and networking technology help cloud and hyperscale data centers adapt to the ever-increasing network need for more bandwidth.
Distributed Campuses and Metropolitan Areas
For many organizations, building a hyperscale data center is not feasible. This is especially true for distributed campuses and metropolitan areas, where managing multiple data centers is the new norm because of space constraints and disaster recovery requirements. Distributed data centers need to communicate with each other to share data, balance workloads, provide backups, and scale data center capacity when needed. 400ZR technology will enable high bandwidth interconnects essential to connect distributed data centers.
Telecommunications Providers
Like data centers, telecommunications companies grapple with the explosive growth in networking traffic, as consumers demand higher connectivity at home, in the office, and soon from 5G mobile. Applications such as streaming video, online video games, video conferencing, and online backup services will benefit from 400 Gb/s speeds enabled by 400ZR.
The 400ZR standard will allow telecommunications companies to backhaul residential traffic. When operating at 200 Gb/s, using 64 Gbaud signaling and QPSK modulation, 400ZR increases the reach of high-loss spans. For 5G networks, 400ZR offers mobile backhaul by aggregating multiple 25 Gb/s streams.
The Future of Data Center Interconnects
With networks reaching new levels of data traffic each year, 400G coherent optical technology promises to provide faster data flow between data centers. 400G solutions, enabled by new standards such as 400ZR and 400GBASE-ZR, provide many advantages and the flexibility needed to address growing data demands. These new standards substantially increase the bandwidth capacity and reduce operating costs (fewer transceivers), footprint, and power consumption. 400ZR and 400GBASEZR will allow hyperscale data centers, physically separated data centers, and metro telecommunications networks to provide the 400G interconnect speeds emerging technologies require.
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