storage distance extension

Storage distance extension can be accomplished by any of the following methods: In metropolitan area networks (MANs), wavelength division multiplexing (WDM) can extend the distance between the storage source and destination to approximately 600 kilometers (km). In wide area networks (WANs), a technique called Generic Framing Procedure (GFP) can extend distances to about 4000 km. Using GFP, buffer credits limit the number of unacknowledged frames that accumulate, reducing problems that occur because of latency. Optical repeaters receive signals from an optical fiber, convert the signals to electronic form, amplify them, convert them back to optical form, and then send them along another length of optical fiber. (A device called an erbium amplifier acts as an optical repeater that amplifies optical signals directly.) An extended-wavelength gigabit interface converter (GBIC) or extended-wavelength small form-factor pluggable (SFP) can counteract the "blurring" that otherwise takes place over long spans because light of different wavelengths travels through optical fibers at different speeds.

In addition to the aforementioned methods, automatic repeat request (ARQ) or forward error correction (FEC) can be used to reduce the error rate at the cost of some throughput. These methods can be useful in systems where the spans of cable are near the maximum limits obtainable with other technologies.

Storage area networks that employ storage distance extension are expected to become increasingly common as the demand for long-distance, high-volume, high-speed offsite storage increases.

Learn more about Remote and offsite data storage

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More resources from around the web: - Nortel Networks has published a white paper on the subject of storage distance extension. - SearchStorage.com discusses Fibre Channel SANs in a paper by Simon Gordon.

FILE EXTENSION AND FILE FORMAT LIST File Extension and File Format List: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

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