The rise of photonic switching in the datacenter

Plexxi Photonic Switching
Mike Bushong, Plexxi

There is a lot of industry inertia around two major datacenter networking trends: white box switching and software-defined networking (SDN). The primary driver behind both is cost. The former is about commoditizing physical switches to reduce overall capital expenses (CapEx).

The latter is about simplifying management to reduce operating expenses (OpEx). Think of this as an effort to commoditize control over the network in distributed, heterogeneous environments.

Networking costs, however, are not limited to just traffic forwarding and network management.

Physical switching costs

Physical switching costs are already coming down due in part to industry convergence on a narrow set of merchant silicon and an increasingly competitive switching landscape. As switching costs continue their downward descent, the cost of interconnecting those switches will begin to play a larger role in the design, purchase and maintenance of datacenter networks.

Currently, more than 80 percent of all traffic in the datacenter is east to west. That means that the dominant path for packets in the datacenter is between servers, not up and out of the datacenter itself, and this number is growing.

The dependence on the interconnect between switches is even more profound for Big Data applications such as Hadoop and Cassandra, which require high volumes of traffic to store and retrieve data.

This dependence creates tremendous demand for low-latency bandwidth between servers, leading to the question: How will this scale?

Does photonic scale?

Today, the most common datacenter switching architectures feature high numbers of interconnect links. In a small, 6-switch leaf-spine architecture that supports 432 access ports, there are a whopping 288 interconnect ports requiring 144 cables. This means that 40 percent of the total switch ports in the entire deployment are dedicated solely to interconnecting switches.

Without factoring in the operational costs associated with cabling (especially during expansion), the sheer volume of cables and ports is becoming a significant contributor to overall cost. If the major trends in networking are all cost-related, there will need to be an emergent trend beyond just the switch hardware and management. The interconnect itself will need to go through the same commoditization evolution.

Fortunately, high-speed, low-latency links are not unique to datacenters. Large service providers have been providing high-capacity links for ages, leveraging optical equipment for transport. Photonic switching hasn’t caught on in the datacenter though, not due to the technology’s capabilities but rather the cost. When used across a small number of devices, the costs are fairly reasonable, but when the implementation is scaled to span an entire datacenter the cost can become prohibitively expensive.

Fortunately, advances in technology are changing that.

In recent years, manufacturing has gone through an evolution that has brought the costs of photonic switching nearly in line with its electronic counterpart. The same technology that makes high-speed transport possible in carrier environments can be applied to the growing needs of the datacenter.

The benefit of this technological shift is that the introduction of photonic switching doesn’t just commoditize the interconnect. It also introduces some of the optical features that make dynamic pathing possible in carrier networks today. Effectively, this allows network architects to provide dynamic bandwidth on a static infrastructure.

Imagine allocating dedicated, high-bandwidth, single-hop paths to applications when and where they are needed. For example, during a Big Data job, the infrastructure could temporarily provide a network bypass that guarantees the fastest connection between two servers. The result is a much more flexible network that works in collaboration with the very applications it supports. And it does so all at the same or lower costs than common networks today.

Ultimately, the future of networking simply has to scale in terms of both performance and cost. And it has to scale across all three - switching, management, and the interconnect. Photonic switching will undoubtedly be the third leg of the commoditization stool.

  • Michael Bushong is the vice president of marketing at Plexxi.