Choosing a 400G QSFP-DD Transceiver

How 400G is built

A 400G QSFP-DD module reaches its rate by combining eight electrical lanes at 53.125 gigabits per second each with four optical channels at 100G each, using PAM4 signalling on each channel. The doubling from QSFP to QSFP-DD is electrical as well as optical: the module needs a QSFP-DD host port, it does not fit a QSFP port, and a QSFP module in a QSFP-DD port does not deliver 400G. The host port is therefore the first selection item, before any optical figure is considered.

The optical side of the DR4 module on this site runs four parallel channels at 1310nm over single-mode fibre, with an MPO-12 connector carrying the parallel channels. Parallel optics means the fibre assembly matters as much as the module: the MPO polarity, the fibre type and the connector count all affect whether the link works, and a module ordered without checking the mating assembly is an incomplete order. Name the assembly type in the enquiry alongside the module.

Reach and error correction at 400G

The DR4 module on this site is listed at up to 500m on single-mode fibre with forward error correction, and that pairing of distance and error correction is part of the design rather than an optional extra. A host that cannot support the required error correction will not achieve the listed reach, and a link whose loss budget exceeds the design will not achieve it either, even at 500m. Both items should be confirmed before ordering: the host error correction support and the link loss estimate.

Reach within 400G divides into shorter parallel-optics lines for data center interconnects and longer lines for inter-site links, and the DR4 line sits at the shorter end, suited to in-data-center and between-building interconnects rather than metro links. A requirement beyond 500m needs a different 400G family with a different listed reach, and no such family carries a listed specification on this site, so a longer 400G requirement should be sent as an enquiry with the measured length and loss budget.

Power and cooling at 400G

Power is a first-class selection item at 400G, because a 400G module draws materially more power than a 100G module and the host must supply and cool that power across all populated ports. The DR4 module on this site lists 12W, and a fully populated switch faceplate multiplies that figure across every port, which is why power and cooling are checked at the switch level rather than per module. Confirm the per-module power and the host power budget together in the enquiry, especially for a full-faceplate deployment.

Cooling follows power: a module that the host can power but cannot cool will throttle or fail, and a deployment planned on power alone without a cooling check is incomplete. State the deployment density, the ambient environment and the host cooling design in the enquiry when the deployment is dense or the environment is not a conditioned data center, so the combination can be checked rather than assumed.

Statements on the product page that need per-order confirmation

Two statements on the 400G product page need per-order confirmation, and this article repeats the flags so they are not missed. The first is stock: a source-page question mentions a large stocked quantity, but that general statement does not commit a quantity, a version or a delivery date for a specific order, and stock must be confirmed per order. The second is compatibility: the page names compatibility only as a source-page statement for one host platform family and does not publish a longer brand list, so compatibility for a specific platform must be confirmed per order.

Those flags are not footnotes; they are part of the specification discipline of this site. A product page that published a stock figure as a guarantee, or a brand list as a compatibility catalogue, would mislead buyers about what is actually committed. The per-order confirmation route is slower than reading a guarantee, but it produces an answer tied to a specific order, which is the only answer that can be relied upon.

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.