Mark Filer

Elastic optical networking in the microsoft cloud [Invited]

To keep pace with the tremendous bandwidth growth in cloud networking, web-scale providers, such as Microsoft, have been quick to adopt elastic features of modern optical networks. In particular, colorless flexible-grid reconfigurable optical add-drop multiplexers, bandwidth-variable transceivers, and the ability to choose a variety of optical source types are integral for cloud network operators to improve network efficiency while supporting a variety of service types. We take an in-depth look at Microsofts deployed network infrastructure and discuss the impact of elasticity on network capacity and flexibility. As a proof-of-concept, a new elastic open line system (OLS), in which the line system components and the signal sources are disaggregated, was assembled in a laboratory environment, and 4000 km of propagation over primarily nonzero dispersion-shifted fiber using multiple source types is demonstrated. Finally, the long-term goal of unifying the control plane of the OLS, DWDM signal sources, routers, and Ethernet switches under a single software-defined network controller is briefly addressed.

Run, Walk, Crawl: Towards Dynamic Link Capacities

Fiber optic cables are the workhorses of todays Internet services. Operators spend millions of dollars to purchase, lease and maintain their optical backbone, making the efficiency of fiber essential to their business. In this work, we make a case for adapting the capacity of optical links based on their signal-to-noise ratio (SNR). We show two immediate benefits of this by analyzing the SNR of over 2000 links in an optical backbone over a period of 2.5 years. First, the capacity of 80% of IP links can be augmented by 75% or more, leading to an overall capacity gain of 145 Tbps in a large optical backbone in North America. Second, at least 25% of link failures are caused by SNR degradation, not complete loss-of-light, highlighting the opportunity to replace link failures by link flaps wherein the capacity is adjusted according to the new SNR. Given these benefits, we identify the disconnect between current optical and networking infrastructure which hinders the deployment of dynamic capacity links in wide area networks (WANs). To bridge this gap, we propose a graph abstraction that enables existing traffic engineering algorithms to benefit from dynamic link capacities. We evaluate the feasibility of dynamic link capacities using a small testbed and simulate the throughput gains from deploying our approach.

RADWAN: rate adaptive wide area network

Fiber optic cables connecting data centers are an expensive but important resource for large organizations. Their importance has driven a conservative deployment approach, with redundancy and reliability baked in at multiple layers. In this work, we take a more aggressive approach and argue for adapting the capacity of fiber optic links based on their signal-to-noise ratio (SNR). We investigate this idea by analyzing the SNR of over 8,000 links in an optical backbone for a period of three years. We show that the capacity of 64% of 100 Gbps IP links can be augmented by at least 75 Gbps, leading to an overall capacity gain of over 134 Tbps. Moreover, adapting link capacity to a lower rate can prevent up to 25% of link failures. Our analysis shows that using the same links, we get higher capacity, better availability, and 32% lower cost per gigabit per second. To accomplish this, we propose RADWAN, a traffic engineering system that allows optical links to adapt their rate based on the observed SNR to achieve higher throughput and availability while minimizing the churn during capacity reconfigurations. We evaluate RADWAN using a testbed consisting of 1,540 km fiber with 16 amplifiers and attenuators. We then simulate the throughput gains of RADWAN at scale and compare them to the gains of state-of-the-art traffic engineering systems. Our data-driven simulations show that RADWAN improves the overall network throughput by 40% while also improving the average link availability.

Transmission of Nyquist-shaped 32 GBaud PM-QPSK over a production flex-grid open line system

Nyquist PM-QPSK signals are sent over 4000 km of fiber through an open line system employing colorless flex-grid ROADMs. The signal source is a layer 2/3 modular switch with embedded coherent ASICs and CFP2-ACO optics.

Beyond Binary Failures in Networks

Fiber optic cables are the workhorses of todays Internet services, but they are an expensive resource and require significant monetary investment. Their importance has driven a conservative deployment approach with redundancy baked into multiple layers of the network under the assumption that links have a constant reliability status and operate at a fixed capacity. In this work, we take an unconventional approach and argue that link failures should not be always considered binary events; this approach enables the foundation of a framework for network links with dynamic capacity and reliability. We investigated this idea by conducting the first ever large-scale study of operational optical signals, analyzing over 2,000 channels in a wide-area network for a period of three years. Our analysis uncovered several findings that enable cross-layer optimizations and smart algorithms to improve traffic engineering, increase capacity, and reduce cost. For instance, we show the capacity of over 90% of wide-area links can be augmented by at least 50 Gbps, leading to an overall capacity gain of more than 100 Tbps. This means we get higher capacity and better availability using the same links. Based on work published at [1] Rachee Singh, Monia Ghobadi, Klaus-Tycho Foerster, Mark Filer, and Phillipa Gill. 2017. Run, Walk, Crawl: Towards Dynamic Link Capacities. In Proceedings of the 16th ACM Workshop on Hot Topics in Networks (HotNets-XVI). ACM Press, Palo Alto, CA, 143--149. DOI:https://doi.org/10.1145/3152434.3152451

Analog Coherent Optics for Long Haul Datacenter Regional Networks

We review key aspects of analog coherent optics adoption in long haul datacenter regional networks. We discuss the main advantages and drawbacks of this approach and present potential improvements for next generation 60 + Gbaud long haul analog 8/16QAM systems. Finally, specificities of the 120 km datacenter interconnect (DCI) use case are also considered in the context of the ongoing OIF 400ZR standard effort.

Interoperation of layer-2/3 modular switches with 8QAM/16QAM integrated coherent optics over 2000 km open line system

Arista, Cisco, and Junipers layer-2/3 modular switches with integrated coherent optics are interoperated over 2000 km at 150G 8QAM and 1000 km at 200G 16QAM on Microsofts open line system.