By George Zimmerman and David Chalupsky
Until recently, twisted-pair, or BASE-T Ethernet, has been viewed as the one-size-fits-all solution for in-building mass-market Ethernet data transfer. From 10 to 100 to 1000BASE-T, general purpose wired Ethernet progressed regularly as the preferred port in data center, enterprise, home, and even industrial applications with a single PHY used in all segments. Under all use cases, one hundred meter reach in category cabling was the norm. Each next speed fit neatly into the use cases and applications of the last, and it was only a matter of time before cost and power moved to the point where port speed increased in all use cases. As a result, new speeds were introduced one at a time and in a steady progression across almost all in-building networks.
However, recent standard efforts have seen multiple new speeds of BASE-T Ethernet being offered into the marketplace more or less simultaneously. While 10GBASE-T is beginning to slowly ramp up in the market, it coexists with a continually growing 1000BASE-T, new offerings at 2.5 and 5 Gbits/sec, and new standards developments for 25G and 40GBASE-T. An exploration of how each of the 4-pair BASE-T speeds play out in the application’s space, and how performance niches are diversifying the BASE-T Ethernet PHY universe beyond its traditional one-size-fits-all approach, provides some useful insight on where BASE-T is today, and where it’s headed for the future.
10/100BASE-T: Default connection on the enterprise floor, data center management workhorse
Application needs at individual nodes, cost, poser, limited I/O capabilities of single user endpoints, and support for Category 5e cabling, which remains the lowest common denominator of LAN wiring common today, still make 100/1000BASE-T the universal connection on the enterprise floor for PCs, printers, and wireless access points. All other enterprise BASE-T Ethernet PHYs emulate it and provide improvements. Each has 100-meter reach, but each increases speed with increased demands on the cabling, serving applications that demand higher speeds.
In the data center 1000BASE-T is still a workhorse, but often more for managing devices in the control plane than for data plane server and storage-access networking. Lower performance legacy devices may use 1000BASE-T. Massive arrays of micro servers (resulting in high port growth) may be individually connected at speeds of 1 Gbit/sec. However, highly scalable cloud data centers have long since shifted to 10 Gbits/sec, and even enterprise and smaller business server links are now migrating to 10 Gbits/sec with the emergence of 10GBASE-T.
2.5 and 5GBASE-T: Emerging role in the enterprise
2.5G and 5GBASE-T fill the void between 1 Gbit/sec and 10 Gbits/sec in the application space. With two new PHYs users can make optimal use of their installed cabling, which may stretch to 100-meter reach. However, when used with cabling types older than Category 6A, there may be variable interference between links according to the particular installation’s capability. The IEEE P802.3bz objectives call these “use cases,” referring mainly to the ratio of cable length and interference and, in the case of Category 5e, high-frequency performance of the cable plant. These scenarios for 2.5G and 5GBASE-T are influenced by cabling topologies, quality, and installation practices.
Both speeds support 100-meter reach on installed Category 5e and Category 6 cabling, although there are broader use cases for the lower speed. And, since both 2.5G and 5GBASE-T are expected to work at 100 meters without restriction on Category 6A cabling, these new PHYs offer a bridge to higher speed for existing 100-meter BASE-T networks, and intermediate speed operation on newer networks. While these new speeds will initially serve multi-user nodes, such as wireless access points demanding aggregated speed, it is expected that the speed jump from 1 Gbit/sec to 2.5 Gbits/sec will beign the long-delayed speed migration of single-user end stations up from 1000BASE-T on the enterprise floor.
10GBASE-T: High-end for enterprises, emerging in enterprise and smaller data centers
10GBASE-T was intended to follow 1000BASE-T in the normal succession of speeds in the one-size-fits-all paradigm that used to rule BASE-T Ethernet. Today, 10GBASE-T is available for the highest-speed needs on the enterprise floor. Like 1000BASE-T, it supports 100-meter reach, using newer Category 6A cabling to guarantee the distance, running for shorter distances on Category 6 cabling. 10GBASE-T serves enterprise floor applications that need its speed and that will continue to grow. However, in the enterprise environment there is a lot of room for solutions between 1 Gbit/sec and 10 Gbits/sec, and the mature installed base of cabling is a valuable asset with a long lifetime.
The shift of cloud data centers to 10 Gbits/sec preceded the commercial deployment of 10GBASE-T. As recently as 2011, many declared BASE-T as finished in the data center for all but management and low-speed applications. Yet today, 10GBASE-T is shipping in servers and access switches, and is emerging on the enterprise and smaller data center space as a cost-effective solution for those still migrating to 10-Gbit/sec speeds. Using Category 6 and 6A cabling, 10GBASE-T bridges nicely from emerging enterprise floor applications and provides an entry point to 10-Gbit/sec networking. Most 10GBASE-T PHYs save significant power operating at the reduced distances found in data centers, such as 30 meters, making them even more attractive as data center reaches decrease. As the broader market of smaller data centers moves to 10-Gbit/sec, BASE-T fills that space with 10GBASE-T.
25 and 40GBASE-T: Higher-speed server access
The IEEE P802.3bq Task Force is advancing a standard for 25G and 40GBASE-T PHYs as the cloud data center begins to move to 25-Gbit/sec server access.
25GBASE-T is expected to develop on a fast track due to work already done to define 40GBASE-T and, because of its lower complexity, emerge at a competitive cost/power point. 25GBASE-T will be developed concurrently with the 25-Gbit/sec single-lane twinax standards effort (IEEE P802.3by) to complement applications of 25-Gbit/sec Ethernet by additionally enabling flexible end-of-row and top-of-rack server interconnections.
40GBASE-T is geared toward the higher-performance server market in similar data center architectures, and is expected to have a more delayed and specialized development than 25GBASE-T. Much of its application is dependent on the directions 40-Gbit/sec Ethernet takes in the access network.
The cabling infrastructure for both 25GBASE-T and 40GBASE-T PHYs is expected to use “link segments” with a 30-meter distance for structured end-of-row applications, but with a 5-meter “direct attach” specification within rack applications. The cabling industry has responded in advance, developing Category 8 cabling and components (and ISO Class I/Class II channels) characterized to 2 GHz for applications beyond 10 Gbits/sec. As a result, the data center infrastructure has completed its migration to an application space differentiated from that on the enterprise floor, enabling data center designers to plan for at least a quad speed (1G, 10G, 25G and 40G) infrastructure and possible support of 50 Gbits/sec in the future.
Conclusions
The diversity in the BASE-T world represents a healthy market segmentation that moves beyond the previous conventional wisdom of 10x exponential speed steps to serve each market segment. This better fits the demands of end stations, maturing legacy infrastructure, and bandwidth needs of access networking. On the enterprise floor, where 100-meter reach is a necessity, the use of 1000BASE-T continues to grow but is now augmented by 2.5G, 5G and 10GBASE-T on cabling categories from 5e up to 6A. Meanwhile, many data centers are converging on a rack- or row-based architecture up to 30 meters, using newer cabling categories from 6A to 8. This topology supports BASE-T speeds from 10 Gbits/sec to 25 Gbits/sec and 40 Gbits/sec in development now, and a possible 50G not far behind. BASE-T technologies will continue to adapt and evolve to fill diverse spaces as Ethernets continue to add new markets.
George Zimmerman (left) is Technical Committee Chair of the Ethernet Alliance and President of CME Consulting. David Chalupsky (right) is BASE-T Subcommittee Chair of the Ethernet Alliance and Principal Engineer with Intel.