OS1 vs OS2: Same Glass, Different Cable
Quick answer / TL;DR: Short answer: use OS1 indoors where the cable is protected, and OS2 outdoors, in ducts or over long distances. OS2 has a tighter attenuation limit, about 0.4 dB per km at 1310 nm versus 1.0 dB for OS1, which matters over kilometres. Both use the same 9 micron core and the same connectors.
Single-mode patch cords: yellow jacket, LC/UPC, OS2 9/125.OS1 and OS2 are both single mode. The difference is cable construction and attenuation grade: OS1 is tight-buffered for indoor runs, OS2 is loose-tube for outdoor and long-haul.
Specifying the wrong one creates either a fragile outdoor cable or an over-specified indoor one.
Comparison
| Property | OS1 | OS2 |
|---|
| Construction | Tight buffered | Loose tube |
| Typical use | Indoor | Outdoor, duct, long haul |
| Attenuation at 1310 nm | 1.0 dB per km | 0.4 dB per km |
| Water blocking | Not usually | Yes |
The construction difference is what makes OS2 survive moisture and temperature cycling in a duct.
Selection Rules
- Indoor riser: OS1
- Outdoor or buried: OS2
- Long campus runs: OS2
- Hybrid routes: transition at the building entry
- Never rely on indoor cable outdoors
The transition point matters: the outdoor cable should stop at the entry box, with indoor cable from there.
Real-World Applications
A building-to-building link of 800 m uses OS2 in duct with water-blocking, terminating at an entry enclosure. A rack-to-rack link inside the same room uses OS1 patch cable, where tight buffering is easier to handle.
Standards and Verification
| Reference | Relevance |
|---|
| ITU-T G.652 | Single mode fibre |
| IEC 60793-2-50 | Single mode fibre |
| IEC 60794 | Optical cable |
Measured attenuation for a specific cable is not provided in the knowledge base. Require per-reel data.
References
- ITU-T G.652, Characteristics of a single-mode optical fibre cable
- IEC 60793-2-50, Single-mode fibres
- IEC 60794, Optical fibre cables
Practical Notes
Record attenuation in both directions. A link that passes one way can fail the other if a bend is tight.
Related reading: fiber cable — blogs/news/fiber-cable
Related reading: cat6 vs fiber cable — blogs/news/cat6-vs-fiber-cable
Related reading: multimode vs single mode fiber — blogs/news/multimode-vs-single-mode-fiber
Frequently Asked Questions
Are OS1 and OS2 both single mode?
Yes. Both use a 9 micron core.
Which is for outdoors?
OS2, because of loose-tube construction.
Does attenuation differ?
Yes, 1.0 versus 0.4 dB per km at 1310 nm.
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