The role of fiber-optic connectivity and management in data centers is central to cloud computing operations.
By Jose Gutierrez, Clearfield Inc.
Technology has evolved almost immeasurably in the past several decades. I remember being a young man watching an AT&T commercial that discussed optical fiber. It went something like this: “AT&T has fiber that can carry 24 phone calls on a fiber as thin as a human hair.” Using a standard calculation that a single phone call is 64 kbits/sec (64,000 bits per second), a total of 24 phone calls would be 1.54 Mbits/sec (1.54 million bits per second)—or the equivalent of a Digital Signal 1 (DS1).
Let’s jump to current day. We now have fiber carrying Terabits—one trillion bits per second. That is an enormous amount of information passing at the speed of light through this one strand of fiber the size of a human hair.
With this as a frame of reference, let’s now take a look at the impact of fiber in a data center environment. Data centers of the past were copper-based with multiple DS1 and Digital Signal 3 (DS3, approximate transmission rate of 45 Mbits/sec) lines handling the load of servers to an Optical Carrier 3 (OC3) with a transmission rate of 155 Mbits/sec. This OC3 would connect the servers to the network cloud or outside world. Copper dominated in a data center environment and the only fiber installed was that single line connecting the servers to the network cloud. All DS1 and DS3 connections were on copper panels, possibly with a digital access and crossconnect system (DACS).
Now in 2012, video (iTunes, Netflix, Hulu and others) and cloud computing/hosted servers, backup and storage, Microsoft CRM, hosted private branch exchanges (PBXs), web analysis tools and web hosting are driving enormous growth in data center server deployments. Data centers are offering rates at DS1, DS3, 5 Mbits/sec, 10 Mbits/sec, 20 Mbits/sec and up to an OC3, all connecting to the outside world via 10-Gbit Ethernet or 100-Gbit Ethernet connections from multiple providers. Today fiber is heavily deployed, placing a large concentration of revenue-generating traffic in a small place. To alleviate risk, the data center architecture is evolving away from the previous copper DS1 and DS3 panels, to fiber panels with multiple connections to the client and to the cloud for redundancy.
|When Telcordia established a 0.4-dB loss limit for optical patch cords, many manufacturers responded by saying their cords’ “typical” rather than “guaranteed” performance was 0.4 dB. Today users can find cords with guaranteed 0.2-dB loss.|
Fiber connectivity, management
Historically, fiber in the data center was not protected with the same level of sophistication as was provided by telecommunications service providers. There were two standards—the high-end product lines that were used by the telco provider to ensure the ultimate in reliability, and the low-end solutions used in the data center. However, the line between data and telco have become blurred, and as a result, the sophisticated standards deployed by the telco provider are now being implemented in the data center. Fortunately, this does not equate to a huge increase in cost. In fact, choosing a fiber-management architecture that delivers reliability, modularity and scalability, without giving up density, will actually reduce the cost of fiber deployment. Choosing a modular fiber panel ensures that additional fiber connections can be added, on an as-needed basis, thus lowering the ongoing cost per port.
For maintaining a fiber connection, proper handling techniques like cleaning the fiber are now brought to the forefront. Some copper connections can be wiped clean simply; not so with fiber. A dirty fiber connection can cause a completely blocked signal or introduce attenuation, thus limiting the distance of the signal. Equipment such as a fiber microscope is used to look at a fiber to see how clean the connection is. (Note: Never look into a fiber that is connected to a system.) Cleaning the fiber can be performed with specialty products available on the market, used in adherence to industry cleaning standards. These specifications are good references.
- IEC 61300-3-35, Fibre Optic Interconnecting Devices and Passive Components – Basic Test and Measurement Procedures
- IPC 8497-1, Cleaning Methods and Contamination Assessment for Optical Assembly
- IEC 62627 (DTR), Fibre Optic Interconnecting Devices and Passive Components – Fibre Optic Connector Cleaning Methods
Ensuring minimal insertion loss is key to performance of the network. In recent years, Telcordia has established that the standard for loss should be no more than 0.4 dB. When Telcordia re-set the standard to 0.4 dB of loss, most patch cord vendors reported performance “typical” of the Telcordia standard. As “typical,” the process to build the patch cord was capable of delivering 0.4-dB performance, but each individual cord that came off the line may or may not meet the standard—did 51 percent of the cords match the standard? 75 percent?
Few patch cord vendors were “guaranteeing” the 0.4-dB loss, as it required extensive quality-control measures in their production process and very tight tolerances in their test metrics. These tightened performance specifications were perceived by the vendor as expensive and cost-prohibitive. Achieving a “guaranteed” performance level was expected to result in extensive production-floor “scrap” as patch cords that did not meet the guaranteed number were either set aside as “seconds” or repolished to achieve the desired results. Because there were no guarantees, network designers needed to allow for variation in patch cord performance. As a result, their network designs did not fully benefit from the reported performance enhancements.
Performance of the fiber, guaranteed for immediate and ongoing performance for the life of the network, is critical to delivering the user experience that cloud computing promises. Not only should you demand guaranteed (rather than typical) performance of your fiber, but 0.4 dB should not be good enough in today’s demanding world. Vendors that have built their data centers for optimal performance are delivering guaranteed 0.2-dB loss.
Entering the 21st century, we have seen a significant increase in the use of data centers. As a telco guy by heritage, I have grown up with the central office as the core of a telco network and have seen an incredible amount of evolution over the years. Today there is even talk of data centers being the central offices of the future. With fiber being tested and verified by telco service providers over the past 20 years, the data center manager has some great practical wisdom to follow. We find ourselves at a time of great opportunity as we learn from the past to continue to create an exciting future. The best is yet to come.
Jose Gutierrez is applications engineer with Clearfield Inc. (www.clearfieldconnection.com). He has more than 20 years’ experience in the field of telecom applications engineering and sales support.