Today’s Gigabit Ethernet is fully exploited in the datacenter. Since Gigabit Ethernet (GE) began appearing in datacenters a decade ago, performance demands and computing strategies have changed dramatically. Server performance has increased 100-fold through higher clock speeds, more efficient and compact processor designs, and the use of multicore processors. Virtualization has become a key strategy for server management, demanding higher server I/O performance to support multiple Virtual Machines (VMs) per server. In addition, the concept of converged I/O has moved storage onto existing Ethernet pipes, further increasing the demand for bandwidth. These demands began to fill existing GE links years ago, and the unmet demand for bandwidth has begun to impact datacenter performance.

The obvious answer is to extend 10-Gigabit connectivity at the edge, between servers and their corresponding switch downlinks. However, 10-Gigabit connectivity for servers is materializing more slowly than desired, because optical 10-Gigabit Ethernet adapters are too expensive and too complex for use in the high volume environment needed for servers. The expectations and requirements at the edge of the network are not the same as they are for inter-switch links.

Short-term solutions exist for the bandwidth squeeze at the edge of the network. The first step to satisfying this bandwidth demand was link aggregation, where multiple GE links are set up between the server and switch, only incrementally increasing the overall available bandwidth. On the other hand, some users have sufficient bandwidth demand to deploy 10GE at the edge today utilizing XFP or SFP+ optical modules, and are willing to accept the cost and complexity inherent with such optical solutions.

10GBASE-T: High-Volume 10-Gigabit Ethernet

What the market is calling for is an implementation of 10-Gigabit Ethernet which is as simple and cost-effective as Gigabit Ethernet is today, with plug-and-play simplicity via familiar unshielded twisted pair (UTP) copper cabling and RJ45 connectors. Vendors of edge-connected datacenter equipment are eager to see dual-port NICs with servers connecting to aggregation switches, starting in the near future at the 16- to 24-port density.

The 10GBASE-T standard (802.3an, ratified by the IEEE in June 2006) provides this solution. 10GBASE-T leverages a couple of attributes inherent in silicon-based technology. Moore’s Law applies, delivering the benefit of continued process shrinks.

Integration is the other benefit delivered by Moore’s Law. The path to higher integration in servers will deliver LAN-on-Motherboard (LOM), in which 10GBASE-T appears as a standard feature, not as an option. Higher integration in switches will combine with dual-PHYs, which will be followed by quads and higher integration as process and circuit advances permit. On the way to this destination, 10GBASE-T PHYs will also be making progress on a number of vectors.

Power: The limitations for device power are derived from the requirements of the target platforms. PCIe Network Interface Cards (NICs) are limited to 25W, with pressure to see them come in at power of 18W or less. New generation 10GBASE-T (in conjunction with state-of-the-art controllers) meets this objective. Ethernet switches will aggregate this edge traffic.

First generation 10GBASE-T switches will be scaled to meet the demands of the datacenter. Densities of 16 to 24 ports are initially required, balancing switch fabric densities and desired oversubscription rates. These switch densities become feasible once 10GBASE-T achieves the low power required to fit within such a platform.

Over time, power will continue to be a key requirement. Servers will move 10GBASE-T on the motherboard, and switches will drive densities of 48 ports and higher. These improvements will be enabled as advances in semiconductor processes permit continued reductions in per-port power.

Costs: Copper PHY solutions provide the lowest total cost. 10GBASE-T leverages silicon rules, which will drive down costs. Perhaps more important is the nature of how copper PHYs are configured within equipment. It is difficult to conceptualize a server with anything other than a pair of RJ45s on the back panel. Similarly, Ethernet switches represent completely different cost profiles between copper and optics: line cards with RJ45s have no incremental costs as the capacity is utilized. Optics will not only require the selection and purchase of the correct module, but since the module is purchased retail, margin stacking will be present in the final customer cost.

Cabling Environment: Datacenters utilize “structured cabling,” which defines a cabling implementation where the racks and cabling are part of the “structure,” and the servers and switches can be placed (and moved) with great flexibility. Cross connects with patch cords provide the flexibility to connect any server to any switch. 10GBASE-T is defined for 100 meters, but as importantly, this includes 4 connectors, permitting a cross connect on both ends of the horizontal cabling. It is easy to visualize the benefit of using a cabling like UTP, which can be easily field-terminated.

Rate Flexibility: Customers expect connections over an RJ45 to always work. The standard defines auto-negotiation, which permits ports to link at the maximum possible speed, but most importantly, to always link. 10GBASE-T will coexist with 1000BASE-T (and 100BASE-T) for a number of years, and the triple speed capability of 100/1000/10GBASE-T PHYs translate to network operational savings because UTP links will always come up.

Green Initiatives: Low power may not be what comes to mind for most people when thinking about first generation 10GBASE-T devices. However, we will we see significant power savings for those with innovative architectures and through adoption of finer geometry processes. Further, there are a number of initiatives underway that will drive down system power. Most interesting among these is the work underway in IEEE802.3az, or Energy Efficient Ethernet (EEE). EEE promises to permit copper PHYs to see drastically reduced power under reduced traffic, but also to permit the benefits of lower power to extend within the server or system. Such new techniques are in addition to current green strategies that have been well proven with copper PHYs, such as wake-on-LAN (WOL). A 10GBASE-T link, which shifts down to the 100Mb/s speed, can enter a sleep state and use WOL to exit the sleep state via a network command.

A Marathon, Not a Sprint

New copper-based networking technology always follows a development curve that begins with making it work, advances to making it economically feasible for commercial deployment, and then drives on toward ever-greater deployment and ever-declining costs. We are now at the point with 10GBASE-T where technical feasibility is rapidly advancing toward commercially viable manufacturing and deployment. Semiconductor producers that win in the marketplace will be those that design their products to meet not only the key market and technical requirements for initial deployments, but to scale and improve as the market grows.

About the Author

Bill Woodruff is vice president of Marketing and Business Development at Aquantia Corp. (www.aquantia.com). Bill has identified and driven multiple generations of leading-edge interconnect technologies. He led Velio’s penetration of the grooming switch market. Earlier positions include GiGA (acquired by Intel), Vitesse and Mostek. He holds a BSEE from the University of Missouri and an MBA from SMU.