40GBASE-SR4 QSFP: Breakout and Aggregation Applications

Straight 40G aggregation

In a straight 40G aggregation design, a QSFP SR4 module at each end of a multimode link carries 40G between distribution and core layers, or between a top-of-rack switch and an aggregation switch. The listed figures for the module on this site are 850nm operation with OM3 fibre at up to 100m and OM4 fibre at up to 150m, and the link length must be measured against the installed fibre grade, not against a generic distance. A straight link that exceeds the grade-specific reach needs a different module family, regardless of any other figure.

Straight aggregation links are the simpler application, because the cable assembly is a standard parallel-optics assembly and the only variables are the fibre grade, the length and the connector. Even here, the connector flag matters: the source pages for this module disagree between an MPO receptacle and a Double LC connector, and the connector must be confirmed in writing before ordering, because the assembly type follows from the connector and an assembly ordered against the wrong connector does not mate.

Breakout to four 10G links

In a breakout design, a single 40G QSFP port feeds four 10G endpoints through a breakout cable assembly, which splits the four parallel lanes into four separate 10G links. That design suits aggregation switches serving 10G servers, where a single 40G port replaces four 10G ports and saves faceplate space while keeping 10G at the server. The breakout application is listed on the product page for this module, and it is the application that most affects ordering, because the breakout cable assembly is a separate item with its own specification.

Breakout ordering needs three items beyond the module: the breakout assembly type, the 10G endpoint connectors, and the length of each breakout leg. The legs are rarely equal in practice, because servers sit at different positions in the rack, and a breakout assembly ordered with equal legs may not reach the farthest server. State the leg lengths and the endpoint connectors in the enquiry alongside the module, so the assembly and the module are confirmed as a combination rather than as separate items that may not fit together.

Fibre grade in breakout designs

Fibre grade affects breakout links exactly as it affects straight links, because the same multimode physics applies to each lane. The OM3 and OM4 distances listed for this module apply per lane, and the longest breakout leg decides whether the design fits: a design where three legs are short and one leg exceeds the grade-specific reach fails on that one leg. Measure the longest leg, not the average leg, and compare it against the reach for the installed grade.

Where the longest leg is close to the reach limit, the margin decision matters as it does for straight links. A leg at the edge of the listed reach leaves no room for additional connectors, for re-routing or for measurement error, and a small change in the rack layout can push it outside specification. In that case the safer choice is a higher-grade fibre run for that leg or a different module family, decided before ordering rather than after installation and testing.

The connector flag, repeated deliberately

The connector conflict on the 40G product page is repeated here deliberately, because it affects both applications and it is easy to miss when reading an application article rather than the product page. The source pages disagree between a single MPO receptacle and a Double LC connector, and this site presents neither as confirmed. A breakout design ordered against the wrong connector assumption fails twice over, because both the module connector and the breakout assembly connector depend on it, so the written confirmation matters more for breakout than for a straight link.

The general lesson extends beyond this module. Any product page on this site that flags a conflict should be read as a whole before ordering, including its application articles, because a conflict flagged on the product page applies to every application of that module. An application article that omitted the flag would mislead a buyer who read only the article, which is why the flag is repeated here rather than left on the product page alone.

Before you send the enquiry

A good enquiry for any topic in this article names the rate, the wavelength, the fibre type, the distance, the connector, the quantity and the application, plus the host platform when compatibility matters and any certification document needed by name. Each item removes a round of questions, and together they usually allow a quotation and a compatibility confirmation without further correspondence. An enquiry that names only a rate, or only a module-style name, will need at least one further round, because none of the other items can be inferred from the rate alone.

Environment and quantity also belong in the first message. Quantity affects the quotation and the delivery schedule, and environment matters because the listed temperature range for a module covers ordinary indoor conditions; links in unconditioned spaces, in roof voids or in outdoor enclosures fall outside that range and should be raised explicitly. Stating the environment when it is not an ordinary indoor data center or wiring closet lets the temperature grade be confirmed as part of the order rather than discovered as a failure in summer or winter.

Finally, check whether the line you need has a product page on this site or only a guide page. A product page carries a listed specification for a specific model, and an enquiry against it can confirm price, stock and compatibility for that model. A guide page explains the line and routes you to an enquiry, because no listed specification exists for that line here. Knowing which of the two you are reading prevents the most common buying mistake on this site, which is treating a guide figure, a title figure or a standard figure as if it were a specification for a specific module.

Frequently asked questions

How do I get a quotation?

Send an enquiry naming the model, the rate, the wavelength, the distance and the quantity you need, plus the application. Quotations are confirmed per order, and specifications are confirmed per model before payment. This site does not list fixed selling figures, and no price is shown for any model.

What certification documents can you provide?

The company states ISO 9001, CE, FC, 3C and RoHS names. Certificates are available upon request. If a buyer needs a certificate for a specific model, name the model in the enquiry so the correct document can be checked. No certificate numbers are published on this site.

Do the specifications on one page apply to the whole range?

No. Specifications are shown per model and must not be read across the whole range. Where a value is not listed for a model, the page says to confirm per model rather than filling in a generic figure, and where the source pages disagree, the page flags the conflict instead of choosing one value as fact.

What are the minimum order quantity and lead time?

At company level both are unavailable on this site and are confirmed per model in the enquiry. A single-model note, where one exists, is marked as applying to that model only and must not be read as a company-wide term.