OS2 Trunks for DCI and Campus Links: Outdoor Cable, Loss and Ordering
A link between two buildings has three sections: indoor cabling in building A, an outside plant (OSP) cable between the buildings, and indoor cabling in building B. Use OS2 single-mode for all three. The outdoor section needs outdoor-rated cable (water-blocked, UV-resistant, armored or duct-rated as the route requires); the indoor sections need listed indoor cable such as OFNR or OFNP. In the US, unlisted outdoor cable may run only about 15 m (50 ft) inside a building before it transitions to listed cable or enters a raceway. At campus and DCI distances, use duplex WDM optics such as FR4 or LR4, and budget connectors carefully: on a 10 km link, connector grade and the number of patch points decide whether it passes.
Scope of this guide: links between buildings, from a few hundred metres to about 10 km. For OS2 vs multimode inside the data hall see OS2 vs OM3 vs OM4 vs OM5; for indoor jacket ratings see OFNP vs OFNR vs LSZH.
The Three Sections of a Campus or DCI Link
| Section | Cable | Terminations |
|---|---|---|
| Building A: switch to entrance | Indoor OS2 MPO trunk or LC cords, OFNR/OFNP/LSZH | MPO or LC at both ends |
| Between buildings | Outdoor OS2 cable (loose tube, water-blocked; armored, dielectric or aerial as the route needs) | Spliced or pre-terminated at each entrance |
| Building B: entrance to switch | Indoor OS2 MPO trunk or LC cords | MPO or LC at both ends |
The transition happens at an entrance facility: a splice enclosure or patch panel close to where the outdoor cable enters. In the US, the National Electrical Code (NEC Article 770) limits unlisted outside plant cable to about 15 m (50 ft) inside the building unless it runs in a suitable raceway. Check local codes elsewhere.
Which Optics: Parallel or Duplex?
Parallel single-mode optics such as 400G DR4 use MPO and reach 500 m. Beyond that, most links use duplex WDM optics on LC: 400G FR4 to 2 km and 100G LR4 or 400G LR4 to 10 km. That makes the outdoor cable a count of duplex pairs, and it is why an MPO trunk inside the building often ends in an MPO-to-LC cassette or breakout at the entrance. See transceiver cabling map.
Loss Budget: Two Worked Examples
Values used. TIA maximums (ANSI/TIA-568.3-D): outside plant single-mode cable 0.5 dB/km and inside plant cable 1.0 dB/km at 1310 nm; mated connector pair 0.75 dB; splice 0.3 dB. Spec-grade parts: OS2 cable at 0.4 dB/km (the ISO/IEC 11801 OS2 cabled-fiber value; TIA-568.3-D itself allows 0.5 dB/km for outside plant), 0.35 dB per mated pair (Huawellux specification) and 0.1 dB per fusion splice (typical). Each link has 100 m of indoor cable at each end (0.2 km total). Channel limits are the maximum channel insertion loss in IEEE 802.3: 4.0 dB for 400GBASE-FR4 (2 km) and 6.3 dB for 100GBASE-LR4 (10 km). The connections in the transceiver ports are not counted.
400G FR4, 2 km outdoor + 0.2 km indoor, limit 4.0 dB. Four mated pairs (a patch panel and an entrance panel in each building) and two splices (one at each entrance).
| Item | Calculation | Spec-grade parts | TIA maximums |
|---|---|---|---|
| Outdoor fiber | 2 km × 0.4 dB/km (spec) / 2 km × 0.5 dB/km (TIA) | 0.80 dB | 1.00 dB |
| Indoor fiber | 0.2 km × 1.0 dB/km | 0.20 dB | 0.20 dB |
| Mated pairs | 4 × 0.35 / 4 × 0.75 | 1.40 dB | 3.00 dB |
| Splices | 2 × 0.1 / 2 × 0.3 | 0.20 dB | 0.60 dB |
| Total | 2.60 dB, pass (1.40 dB margin) | 4.80 dB, fail (0.80 dB over) |
100G LR4, 10 km outdoor + 0.2 km indoor, limit 6.3 dB. Fiber, spec-grade: 10 × 0.4 + 0.2 × 1.0 = 4.00 + 0.20 = 4.20 dB. Fiber, TIA maximum: 10 × 0.5 + 0.2 × 1.0 = 5.00 + 0.20 = 5.20 dB. Two splices in every case.
| Design | Calculation | Spec-grade parts | TIA maximums |
|---|---|---|---|
| 4 mated pairs, 2 splices | 4.20 + 1.40 + 0.20 / 5.20 + 3.00 + 0.60 | 5.80 dB, pass (0.50 dB margin) | 8.80 dB, fail (2.50 dB over) |
| 2 mated pairs, 2 splices | 4.20 + 0.70 + 0.20 / 5.20 + 1.50 + 0.60 | 5.10 dB, pass (1.20 dB margin) | 7.30 dB, fail (1.00 dB over) |
If the outdoor cable is only guaranteed to the TIA-568.3-D 0.5 dB/km rather than 0.4 dB/km, add 0.1 dB per km to the spec-grade column: +0.2 dB on the FR4 example and +1.0 dB on the LR4 example, which puts the 4-pair spec-grade LR4 design at 6.80 dB, over the limit.
These are example calculations; check the module data sheet. On long links, fiber loss dominates, so remove patch points rather than chase lower connector loss. See MPO insertion loss budget.
Choosing the Outdoor Cable
- Duct: dielectric loose-tube cable, water-blocked (gel or dry).
- Direct burial or rodent risk: armored cable, often with an extra jacket.
- Aerial: self-supporting or lashed cable rated for the span.
- Indoor/outdoor: a cable rated for both can run through the building without a transition, if its listing meets the local code.
Bend-insensitive G.657.A1 fiber helps in tight trays and enclosures at each end. See bend-insensitive fiber.
Splice or Pre-Terminate?
Long outdoor cables are usually pulled bare and fusion spliced to pigtails at each entrance, because connectors would not survive the pull. Short campus runs can use pre-terminated cable with a pulling grip. Inside each building, factory-made MPO trunks save time and come with test reports. See preterminated vs field-terminated fiber.
Ordering Checklist
| Item | What to specify |
|---|---|
| Route | Distance per section, duct, burial or aerial |
| Optics | DR4, FR4 or LR4; this sets fiber count and connector type |
| Fiber count | Duplex pairs needed, plus spares |
| Indoor sections | MPO or LC, polarity, gender, length, jacket rating |
| Transition | Splice enclosure or patch panel at each entrance |
| Testing | OTDR on the outdoor cable; insertion loss on each indoor assembly |
Very high fiber counts: for 1,728 to 6,912 fibers in one outdoor cable, see rollable ribbon fiber cable.
Frequently Asked Questions
Can I use indoor OS2 trunk cable between buildings?
No. Outdoor runs need outdoor-rated cable that is water-blocked and UV-resistant. Indoor cable is not built for moisture or temperature swings.
How far can outdoor fiber cable run inside a building?
In the US, NEC Article 770 allows unlisted outside plant cable about 15 m (50 ft) inside the building before it transitions to listed cable, unless it runs in a suitable raceway.
What optics are used for campus and DCI links?
Parallel DR4 reaches 500 m on MPO. Longer links usually use duplex FR4 (2 km) or LR4 (10 km) on LC connectors.
How many patch panels can a 10 km LR4 link have?
In the example, OS2 fiber at 0.4 dB/km (ISO/IEC 11801) uses 4.2 dB of the 6.3 dB budget, and four mated pairs pass at 5.80 dB with 0.35 dB connectors. At TIA-568.3-D maximums (0.5 dB/km outside plant, 0.75 dB per pair) fiber uses 5.2 dB and the link fails at 8.80 dB with four pairs or 7.30 dB with two. Use low-loss connectors and as few patch points as possible.
Should the outdoor cable be spliced or pre-terminated?
Long cables are usually spliced to pigtails at each entrance. Short runs can be pre-terminated with a pulling grip.
Does Huawellux supply outdoor OS2 cable?
Yes. Huawellux supplies outdoor OS2 single-mode cable for campus and DCI routes, together with the indoor assemblies. Send the route details (fiber count, length, installation method) and the cable construction is confirmed in the quotation.
Huawellux Outdoor OS2 Cable and Indoor Assemblies
Huawellux supplies outdoor OS2 single-mode cable for the outside plant section, and makes OS2 G.657.A1 MPO trunks, MPO-to-LC breakouts, harnesses and LC patch cords for the indoor sections of campus and DCI links, with polarity, gender, length and labels confirmed before production. For the outdoor section, send the route details (fiber count, length, installation method) and we confirm the cable construction in the quotation.
Huawellux's specification for MPO and MTP® assemblies (identical for both) is insertion loss ≤0.35 dB for single-mode and multimode, with return loss >60 dB single-mode (OS2, APC) and >30 dB multimode (OM3/OM4/OM5). LC and SC patch cords are listed at insertion loss ≤0.35 dB and return loss ≥50 dB (single-mode UPC), ≥60 dB (single-mode APC) and >30 dB (multimode). Every Huawellux product receives end-face visual inspection under a 400x video microscope and is tested for insertion loss (IL) and return loss (RL) before it ships. Interferometric end-face geometry (fiber height, coplanarity, end-face angle and radius) is checked by sample-based testing in standard production, and 100% interferometer testing of a batch is available on request. Dust caps are fitted on every connector, and a formal test report is available on request.
Huawellux replies to inquiries within 24 hours. Custom orders typically take 1–5 business days to complete production, with final timing confirmed case by case in the quotation. For special/custom requirements, MOQ is 2 km of fiber length. Standard listed patch cords have no formal MOQ. The sample fee is credited against the bulk order.
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