APPLICATION BRIEF
25g qsfp cable
A 25g qsfp cable request usually starts as a server or storage port that speaks about 25.78125 Gb/s, and a switch cage that is QSFP28. One QSFP28 socket can break out toward four SFP28 ends. That is a different purchase from a straight 100G lead and from an SFP28-to-SFP28 DAC. Write the ends before you ask for a price.
LinkScope Sourcing 03 is an independent sourcing partner for that brief. The intended use, the aisle length, and the host software belong in the packet so factories answer the same job.
Three ways to buy the same 25G lane, kept on separate lines
Background: a US buyer has a leaf switch with QSFP28 cages and servers with SFP28 ports, quantity still open, destination a US loading dock, timing a stated week in the brief. Process: the desk asks each factory to answer one column below and to mark deviations. Result: no winner is chosen here. The buyer compares after length, coding, and evidence match. Figures are questions, not measurements from this site.
| Question | QSFP28 to 4x SFP28 copper | Active optical breakout | 25G module plus fiber |
|---|---|---|---|
| Data rate | Ask for 25.78125 Gb/s on each leg | Same lane rate, optical conversion inside the ends | SFP28 module rate plus the fiber plant |
| Reach | Often a few meters of twinax; ask the maximum on your host | Longer than passive copper; ask the stated meters | Set by fiber mode and optical budget, not by a twinax AWG |
| Power | Passive copper is a low wattage question | Ask watts per end | Ask module watts, separate from the fiber |
| Wavelength | Not an optical parameter | Ask the wavelength the AOC uses | 850 nm multimode and 1310 nm single-mode are different plants |
| Evidence | Datasheet, AWG, EEPROM identity | Datasheet plus optical test note | Module datasheet plus fiber specification |
Single-mode argues for longer reach when the link is designed for it. Multimode argues for shorter halls when the transceiver and the fiber agree. OEM-coded memory argues for a tighter vendor-support path. A compatible code argues for a wider factory list after the named host accepts it. Both pairs are open until the supplier names the part. An IEEE 802 overview consulted on 2026-10-27 can point at the 25G clause to ask about. It is not a link test.
Documents, stages, and site limits to confirm
- Host model, software release, and whether the QSFP28 port is allowed to break out to four 25G legs.
- Length per leg, AWG if copper, and the bend radius printed for that gauge. A 2 m or 3 m aisle path is a measurement you take, not a default.
- Insertion loss and return loss from the supplier table, with the temperature of the table. Commercial discussion often uses 0 °C to 70 °C until the sheet replaces it.
- Connector mating-cycle note if technicians will reseat leads during turn-up. Impedance note for copper, often discussed near 100 ohm differential.
- Delivery stages: document check, optional sample, incoming length and latch check, then a host link check with FEC as the host requires. This desk does not run those checks.
- Site constraints: rack side, airflow, latch clearance, and the US destination that sets freight. Ingress protection matters for an outdoor tail and is usually irrelevant inside the hall.
A new assembly may show a clearer length mark and warranty path. A surplus lead may cover a legacy cage when condition and EEPROM are stated. Do not convert either sentence into a published claim about a named plant. Inquiry labels stay separate from this application story. Frequency range on a copper lead should be copied from the datasheet rather than inferred from the lane rate alone.
Limits you should expect: passive copper reach shrinks as the lane rate rises, so a length accepted at 10.3125 Gb/s is not evidence for 25.78125 Gb/s. A matching latch is not host compatibility. A family brochure is not the datasheet of the part in the box. Compliance marks, if any, have to name the exact model.
Turn the aisle into a 25G packet
Describe the switch cage, the server port, the breakout or straight choice, quantity, destination, and timing. Add wavelength and optical budget if the column you chose is glass. Currency and per-assembly or whole-order basis can sit in the optional budget fields.
The desk will not treat a lower headline rate on the wrong column as a saving. The contact page explains the reply path. Leave blank any cell the supplier must fill.