Nicole Faubert is the Data Center Infrastructure Solutions Lead at Keysight Technologies.
Data center operators need to evolve their networks from 100GE to 400GE to support the bandwidth and response times required by emerging technologies such as fifth-generation wireless (5G), artificial intelligence (AI), virtual reality (VR), Internet of Things (IoT), and autonomous vehicles. In less than 15 years, data center speeds have evolved from 10GE to 100GE. Data center 100GE implementations began in 2014, yet full build-outs only became cost-effective over the last couple of years thanks to the availability of more affordable optical transceiver modules. Meanwhile, research and development for 400GE transceivers is well underway and is expected to reach mature pricing within a year of introduction.
Next-generation 400GE optical transceivers need to use less power per gigabit, be less expensive per gigabit, and operate at four times the speed of 100GE transceivers. Modern hyperscale data centers house more than 50,000 fibers with an optical transceiver at each end. Transceiver designers need to find a way to simultaneously increase channel capacity, guarantee quality and interoperability, and reduce the cost of new 400GE transceivers.
Increase Channel Capacity
The move from 100GE to 400GE is revolutionary, not evolutionary. Non-return-to-zero (NRZ) and four-level pulse amplitude modulation (PAM4) are two modulation technologies that can enable 400GE. Each comes with its own unique set of challenges. As speeds of NRZ designs increase above 28 Gb/s, channel loss of the transmission medium becomes a limiting factor. New multilevel signal modulation techniques, such as PAM4, are needed to overcome this limitation. However, PAM4 designs are far more susceptible to noise.
In PAM4 designs, the signal to noise ratio (SNR) is lower and analyzing noise in transceiver designs becomes a critical test factor. PAM4 uses forward error correction (FEC) to work around the lower SNR. FEC is an advanced coding technique that sends the required information to correct errors through the link along with the payload data. Physical layer testing of PAM4 signals must accommodate new test challenges introduced by FEC.
Guarantee Quality and Interoperability
The nature of pluggable modules necessitates that any new transceiver technology is thoroughly tested to comply with specifications to ensure quality and seamless interoperability before insertion into the network. Optical transceiver manufacturers must ensure their transceivers have strict compliance with defined specifications and are interoperable with network components and transceivers from different vendors. Network downtime due to faulty transceivers is not an option for data center operators which have guaranteed service level agreements (SLAs) with users.
Fortunately, several standards organizations, such as the Institute of Electrical and Electronics Engineers (IEEE), International Committee for Information Technology Standards (INCITS) and the Optical Internetworking Forum (OIF), govern optical transceiver specifications and define test procedures to ensure compliance to standards and interoperability with other vendors. There are different sets of optical and electrical tests for transmitters and receivers, and the effects of the channel between them also need to be considered. The faster and more complex the system, the more time-consuming and challenging characterization and compliance testing becomes. Data center operators can guarantee the quality and compatibility of their next-generation transceivers by selecting one that has successfully passed all physical Layer 1 characterization and compliance tests defined by industry standards.
Reduce Test Time and Cost
The cost of transceivers is directly proportional to the complexity of the design and the number of optical components. Test time is also significant and contributes to the overall cost of the transceiver. The need to measure complex specifications per defined standards complicates the design and validation process and requires a steep learning curve for test engineers.
Several techniques can significantly reduce test time, and the overall cost of transceivers from design simulation, to device characterization and compliance, and finally manufacturing. Using innovative simulation technologies in the design phase ensures first pass success and high yields. Powerful software simulation tools simplify the design process and enable post-processing and data analysis without rerunning simulations. With software simulation, it is possible to pinpoint problems early in the design cycle and avoid costly manufacturing issues later.
Engineers still struggle with how to efficiently test PAM4 modules in manufacturing production. However, once 400GE transceivers reach the manufacturing phase, real-time analysis and monitoring of data can drive manufacturing improvements and efficiencies, mitigating risks of failure and downtime. Fast containment of operational or product quality issues increases productivity and asset utilization, reducing test time and cost.
The Next Test Challenge — Traffic Loading
Many data center operators are shifting to virtualized networks using software-defined networking (SDN) and network functions virtualization (NFV). SDN is a network architecture that enables software programmable network control of a virtualized network infrastructure. NFV is an architectural concept that automates entire classes of network node functions into building blocks that can be connected to create communication services. Once data center operators shift to a virtualized network, they need to make sure that data flows through it as expected. Complete network test of Layers 2-7, including SDN/NFV validation and traffic loading, becomes the next hurdle to overcome.
Preparing for 5G and IoT
400GE transceiver technology is squarely on the horizon and will soon become a reality in data centers. With IoT introducing billions of new devices to the internet, and 5G enabling new data intensive applications with ultra-fast response times, data center operators upgrading their networks to 400GE will be ready to support them. Ensuring that 400GE transceivers meet all required standards, using test solutions specifically developed to validate them, is the best way to ensure seamless migration from 100GE to 400GE.
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