How to Determine Core Size of Fiber Run

Main difference: Singlemode fiber has a lower power loss characteristic than multimode fiber, which means light can travel longer distances through it than it can through multimode fiber. Not surprising, the optics required to drive singlemode fiber are way more expensive, especially considering any varying circumstances.

When to use each: Both singlemode and modern multimode fiber can handle 10G speeds. The most important thing to consider is the distance requirement. Within a data center, it's typical to use multimode which can get you 300-400 meters. If you have very long runs or are connecting over longer distance, single mode can get you 10km, 40km, 80km, and even farther - you just need to use the appropriate optic for the distance required, and again, the prices go up accordingly.

Compatibility issues: They are not compatible. You cannot mix multimode and singlemode fiber between two endpoints. The optics are not compatible either.

There's a lot more to say about fiber, in general, but I hope this answers your immediate question.

No, the numbers are right (Page 46). If I can reword your question, it's "Why should I use fiber if the propagation delay is worse than copper?" You are assuming that propagation delay is an important characteristic. In fact (as you'll see a few pages later), it rarely is.

Fiber has three characteristics that make it superior to copper in many (but not all) scenarios.

1. Higher bandwidth. Because fiber uses light, it can be modulated at a much higher frequency than electrical signals on copper wire, giving you a much higher bandwidth. Also the maximum modulation frequency on copper wire is highly dependent on the length -- inductance and capacitance increase with length, reducing the maximum modulation frequency.

2. Longer distance. Light over fiber can travel tens of kilometers with little attenuation, which makes it ideal for long distance connections.

3. Less interference. Because fiber uses light, it is impervious to electromagnetic interference. That makes it best for "noisy" electromagnetic environments.

4. Electrical isolation. Fiber does not conduct electricity, so it can electrically isolate devices.

But fiber has drawbacks too.

1. Expense. The optical transmitters and receivers can be expensive ($100's) and have more stringent environmental requirements than copper wire.

2. Fiber optic cable is more fragile than wire. If you bend it too sharply, it will fracture. Copper wire is much more tolerant of movement and bending.

3. Difficult to terminate. Placing a connector on a optical fiber strand requires precision tools, technique, and expertise. Fiber cables are usually terminated by trained specialists. In comparison, you can terminate a copper cable in seconds with little or no training.