Fiber Channel Cables And Connectors - IBM System Storage DS3500 Introduction And Implementation Manual

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Figure 3-5 Four host servers attached to a DS3500 subsystem with iSCSI

3.2.4 Fiber Channel cables and connectors

In this section, we discuss various essential characteristics of fiber cables and connectors.
This information can help you understand the options you have for connecting and cabling the
DS3500 Storage System.
Cable types (shortwave or longwave)
Fiber cables are basically available in multi-mode fiber (MMF) or single-mode fiber (SMF).
Multi-mode fiber allows light to disperse in the fiber so that it takes many paths, bouncing off
the edge of the fiber repeatedly to finally get to the other end (multi-mode means multiple
paths for the light). The light taking these various paths gets to the other end of the cable at
slightly separate times (separate paths, separate distances, and separate times). The
receiver has to determine which incoming signals go together.
The maximum distance is limited by how "blurry" the original signal has become. The thinner
the glass, the less the signals "spread out," and the further you can go and still determine
what is what on the receiving end. This dispersion (called modal dispersion) is the critical
factor in determining the maximum distance a high-speed signal can travel. It is more relevant
than the attenuation of the signal (from an engineering standpoint, it is easy enough to
increase the power level of the transmitter or the sensitivity of your receiver, or both, but too
much dispersion cannot be decoded no matter how strong the incoming signals are).
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IBM System Storage DS3500: Introduction and Implementation Guide
Draft Document for Review March 28, 2011 12:24 pm