Raman amplification in ­enterprise storage networking

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Enterprise requirements for business continuity and disaster recovery continue to grow more demanding. An example can be found in the drive to lengthen the distances between primary and secondary data centers. Seeking greater protection for a widening range of disasters, enterprises have pushed technology vendors to support increasingly longer distances-as much as 200 km, in some cases.

All-optical Raman amplification supports network architectures that meet these enterprise requirements while lowering network capital and operations expenses. It’s a new role for the technology. Raman amplification is compatible with the enterprise’s or managed service provider’s already installed base of singlemode fiber and supports superior transmission characteristics and longer span lengths than erbium-doped amplifier technologies.

Once primarily used to address cost in service provider long-haul and submarine networks, today Raman amplification can be cost-effectively deployed to support single-span transmission at 10 Gbits/sec over distances of 200 km in enterprise networks. Depending on the length of a given fiber span, this technology can eliminate or at least reduce the need for huts to house in-line amplifiers, as well as the maintenance burden and security concerns that are associated with such facilities.

support single-span transmission at 10 Gbits/sec over distances of 200 km in enterprise networks. Depending on the length of a given fiber span, this technology can eliminate or at least reduce the need for huts to house in-line amplifiers, as well as the maintenance burden and security concerns that are associated with such ­facilities.

Raman amplification offers enterprises as well as service providers significant savings across capital expenditures (capex); engineering, furnishing, installation, and testing (EFI&T); and operations, administration, and maintenance (OAM). Most important in regard to SAN services, a reduction in the number of amplifiers heightens network availability and lessens an enterprise’s exposure to disasters and other events that threaten network survivability.

A greater awareness of the cost of network downtime and a need for more flexible operational models have driven a wider array of enterprises than ever to implement sophisticated storage services. But perhaps the biggest driver of all is regulatory pressure. Government regulations such as the Health Insurance Portability and Accountability Act of 1996 (HIPAA) and the U.S. Security and Exchange Commission’s rule on Retention of Records Relevant to Audits and Reviews have stipulated precisely how enterprises across a variety of industries archive and safeguard data.

In the most demanding scenarios, enterprises require synchronous applications such as continuous data protection (CDP). In this emerging application, disk technologies steadily record data updates in real time. Data is simultaneously written to disk at primary and secondary data centers and time-stamped. In this way, CDP delivers the unprecedented capability for an enterprise to revert to data at any point in time, instead of a snapshot of data recorded on a preset interval (every four hours, for example).Th 208468

Figure 1. Increasing span lengths allows network owners to minimize or even entirely eliminate in-line amplifiers and the facilities that house them.

WDM-enhanced fiber-optic networks-delivering protocol-agnostic, robust connectivity and reliable service-have emerged as the standard medium for CDP and other types of synchronous business-continuity and disaster-recovery services. The rollout of DWDM, CWDM, and hybrid CWDM/DWDM platforms has made it cost-effective for more enterprises to implement sophisticated storage capabilities. These innovations enable the enterprise to deploy only the capabilities it requires for its current recovery-time and recovery-point objectives (RTOs and RPOs), and affordably add traffic channels and bandwidth as new needs arise.

Similarly, there are important innovations taking place in the area of optical-network amplification that also can simultaneously reduce enterprise costs and deliver enhanced service benefits. Optical networks support data transmission over thousands of kilometers, but amplification is necessary along the fiber path. Enterprises have typically deployed in-line erbium-doped fiber amplifiers (EDFAs) in their networks for this job. But locating EDFAs along an optical link introduces security concerns as well as capex, EFI&T, and OAM expenses with each hut that must be constructed to house them.Th 208471

Figure 2. Pump-induced Raman scattering provides amplification of the data-carrying signal in new and already installed transmission fiber, boosting performance beyond that achievable with conventional erbium amplifier technology.

Eliminating-or, at least, reducing the number of-amplifier sites would not only cut an enterprise’s costs, it also would greatly enhance the enterprise’s disaster-recovery and business-continuity capabilities (see Figure 1). By enabling longer fiber spans, the enterprise would be able to locate primary and backup data centers farther apart and still support bandwidth-intensive, real-time services such as synchronous data mirroring. The survivability of the data mirror in the event of a business-threatening event would be increased.

Service providers have relied on all-optical Raman amplification for years, especially in submarine systems. Today, the technology has matured to the point that enterprises, too, can cost-effectively employ Raman amplification. And the benefits are particularly compelling in the context of synchronous storage applications.

In Raman amplification, the fiber is used as the medium for amplification. An optical beam, or “pump wave,” is launched at an appropriate wavelength into the fiber. The data signal propagating across that wavelength is amplified as the optical beam releases its energy in a process called “Raman scattering.” In this technique, amplification is distributed over the length of the fiber strand, as opposed to being limited to discrete amplifier sites in the case of erbium-based amplification (see Figure 2).

With Raman amplification, synchronous storage applications can be supported across distances of 200 km at data rates of 10 Gbits/sec. Because it relies on properties inherent in optical fiber as a medium for amplification, Raman technology can be applied to an enterprise’s or managed service provider’s already installed base of singlemode fiber. And eliminating the amplifier sites necessary with EDFAs slashes costs, improves transmission characteristics, reduces security concerns, and increases the survivability of a data mirror by allowing longer optical links between storage data vaults.

Amplification also can be based on a combination of Raman scattering and in-line EDFAs. High-performance, hybrid Raman/erbium amplifiers are emerging that enable asynchronous storage applications to be supported over even longer distances. Fewer amplifier huts are needed than if erbium-based amplification alone were used, and the enterprise’s capex, EFI&T, and OAM costs are cut accordingly.

The cost savings realized by reducing or eliminating amplifier hut sites should not be underestimated. The capex, EFI&T, and OAM burdens have already been discussed. Consider, too, that leased office space may run an enterprise as much as $1,000 to $2,000 per month when power and air conditioning are included. Elimination of just a single mid-span amplification site along a 200-km link could save the enterprise up to $100,000 over a five-year period. The economic argument for Raman amplification in enterprise networking is strong.

In the context of storage services, the ability to lengthen the distance between data vaults rates has an even more compelling benefit. To gain the protection they want (and governments more and more frequently require), enterprises must be able to put more distance between their primary and backup data centers. Raman amplification cost-effectively delivers that capability.

Per B. Hansen is director, business development, optical solutions, with ADVA Optical Networking (Mahwah, NJ; www.advaoptical.com). As a research scientist for Bell Labs in the late 1990s, Hansen developed Raman amplification techniques to overcome capacity and reach limitations of installed fiber infrastructures-techniques that today are widely used by a variety of optical systems manufacturers. He holds 18 patents.

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