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Maximizing 10GBase-T connectivity in data centers (Part 2)

Posted: 13 Apr 2012 ?? ?Print Version ?Bookmark and Share

Keywords:10GBase-T? 10Gbps? cable fiber?

When compared with other 10Gbps connectivity solutions, one of the most significant advantages of 10GBase-T is its ability to communicate and interoperate with slower legacy Base-T systems. Most commercially available 10GBase-T transceivers are perfectly capable of reversion to both 1000Base-T (1Gbps) and 100Base-TX (100Mbps) protocols. In this way data centers can future proof their switching architectures. A 10GBase-T switch purchased today can communicate effectively with all legacy 1G and 100M servers, while providing the infrastructure to upgrade to 10G switching when commensurate speed servers are introduced. This also means that data center expenditures can grow incrementally. Rather than a wholesale conversion of all servers and switches to 10G speeds, which would be required with a non-compatible technology such as SFP+ Direct Attach, 10GBase-T switching systems can convert only those links that truly need upgrades to 10G speeds, while maintaining 1G speed on legacy servers that don't require such data rates.

Unlike direct attach twin-ax cabling systems, which constrain full-performance-supported distances to 7m depending on cable thickness, 10GBase-T allows cable spans to reach to the full 100-meter length permitted by structured cabling rules. This extra reach affords data center managers the flexibility of locating switches away from server racks and opens up the data center to architectures that may be more amenable to accommodating legacy configurations that rely on more centralized switching. Heretofore, a lack of economical cabling options for 10G Ethernet beyond a single or adjacent rack has led to the popularity of top-of-rack (ToR) architectures, in which a stack of rack-mounted servers are connected with short cables to a fixed configuration switch in close proximitytypically on top of the server rack. However, such an architecture has the drawback of increased management domains with each rack switch being a unique control plane instance that must be managed and updated.

A more centralized switching approach known as end-of-row (EoR) architecture, in which server ports are routed to a larger switch servicing several racks of servers, can have the benefit of a singular entity for management with commensurate reduction in maintenance costs. Moreover, because larger switches amortize the cost of common elements such as power supplies and cooling fans, the per-port cost of a larger EoR switch still may be lower than the equivalent number of ports in a collection of ToR switches.

Figure 1: 10GBase-T with Cat6A vs. Direct Attach Twin-Ax cabling.

An additional benefit of 10GBase-T is that of a uniform transmission media. The alternative in use today relies on a hodgepodge of cabling types, lengths and connectors: Cat6 for 1000Base-T, twin-ax with SFP+ connectors for short rungs of 10G, optical modules, and multimode fiber for longer runs of 10G. By standardizing on 10GBase-T, the data center manager can focus on only one cabling system for all speeds and all distances. And as luck would have it, that cabling system can be inexpensive Cat6A with familiar, cheap, and easily used and installed RJ45 connectors.

This, of course, leads to another great advantage of 10GBase-T technology: its ability to use ubiquitous and inexpensive cabling and, in many cases, the installed base of cabling that already exists in the data center in support of 1000Base-T systems. Even if a data center does not currently have Cat6 or Cat6A cabling as part of its existing cabling plant, the purchase price of UTP cable is at least three times less expensive than connectorzied twin-ax cable of the same length and up to 10 times less expensive than fiber solutions, when factoring in the necessary optical modules. Figure 1 summarizes some key advantages of 10GBase-T when compared to SFP+ DA cables.

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