How far will it go?
A designer wants a 10 Gbit/s link between two buildings 350 metres apart. The cable is OM3 multi-mode. Will it work?
The answer sits in a table. It joins the speed, the colour of light and the fibre grade to a longest distance. Learn to read it and you can answer in seconds.
Key words
| Word | What it means |
|---|---|
| Wavelength | the colour of the light, measured in nanometres (nm) |
| Reach | the longest run a link can have and still work |
| OM3 and OM4 | grades of multi-mode fibre made for lasers |
| OS1 and OS2 | grades of single mode fibre |
| SX | short wavelength: about 850 nm, on multi-mode fibre only |
| LX | long wavelength: about 1310 nm, on single mode or multi-mode fibre |
| Nanometre | one millionth of a millimetre |
| Ethernet | the common way to join wired devices in an office |
| Gbit/s | thousands of millions of bits each second |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can read a fibre table, say what SX and LX mean, and tell whether a fibre grade reaches a given distance.
Starter: fibre grades
Have a go
Starter: fibre grades
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Wavelength and the names SX and LX
Light for fibre is infrared, so you cannot see it. Two wavelengths are common. 850 nm is cheap and suits short, multi-mode runs. 1310 nm suits longer runs and single mode.
In the Ethernet names, SX is short wavelength (multi-mode only) and LX is long wavelength (single mode, and multi-mode too).
Longest run for each grade, about
| Ethernet name | Speed | Light | OM3 | OM4 | OS1 and OS2 |
|---|---|---|---|---|---|
| 1000BASE-SX | 1 Gbit/s | 850 nm | 550 m | 550 m | Not used |
| 1000BASE-LX | 1 Gbit/s | 1310 nm | 550 m | 550 m | 5 km |
| 10GBASE-SR | 10 Gbit/s | 850 nm | 300 m | 400 m | Not used |
| 10GBASE-LR | 10 Gbit/s | 1310 nm | Not used | Not used | 10 km |
| 40GBASE-SR4 | 40 Gbit/s | 850 nm | 100 m | 150 m | Not used |
The cells students fill in are left blank in this preview.
How to read the table
Find the row for the speed you want. Pick the column for your grade. Compare the run with the figure. Longer than the figure and the link will fail or run with many errors.
For our 350 metre, 10 Gbit/s link: OM3 reaches 300 metres, so it fails. OM4 reaches 400 metres, so it works.