Understanding 128GFC QSFP Transceivers and Reach Options

As Fibre Channel networks move toward higher bandwidth, 128Gb/s connectivity has become an important option for storage environments that need greater throughput without continually increasing the physical footprint of networking hardware. Achieving this bandwidth, however, is not simply a matter of making one optical lane run faster.

The 128GFC architecture uses four 32Gb/s lanes to create an aggregate 128Gb/s Fibre Channel connection. This approach distributes the transmission workload across multiple channels and fits well with the compact QSFP form factor used in high-density optical networking equipment.

The QSFP 128Gb/s Transceiver is built around this multi-lane 128GFC concept and is available in different optical configurations for short, medium, and long-distance Fibre Channel links. Understanding how these versions differ is useful when planning storage networks, selecting replacement modules, or upgrading existing Fibre Channel infrastructure.

Why 128GFC Uses a Four-Lane Architecture

Increasing the total network bandwidth can be approached in several ways, but pushing extremely high data rates through a single electrical and optical lane creates additional engineering challenges.

At higher lane speeds, signal integrity, PCB routing, transmitter performance, receiver sensitivity, bandwidth, and optical design all become more demanding. Dividing the aggregate 128Gb/s rate into four 32Gb/s channels provides a different way to handle the required throughput.

Each lane carries part of the overall data stream, while the four channels operate together as one 128GFC connection. This arrangement also fits naturally within a QSFP module, where multiple transmit and receive paths can be integrated into a relatively compact pluggable package.

For storage equipment designers, this means higher Fibre Channel bandwidth can be supported without relying on a single unusually high-speed optical path.

How 4×32Gb/s Works Inside a QSFP Module

The expression “4×32Gb/s” refers to the architecture of the 128GFC connection rather than four unrelated network links.

On the host side, the data is distributed across four electrical lanes. The transceiver converts the electrical signals into corresponding optical channels for transmission. At the receiving end, the optical signals are detected and recovered as part of the same Fibre Channel connection.

Because several channels are operating simultaneously, consistent performance across the lanes is important. Optical output, receiver sensitivity, electrical signal quality, thermal conditions, and internal optical coupling can all influence the performance of the completed link.

This multi-channel design also allows different optical technologies to be used without changing the fundamental 128GFC bandwidth architecture. The same four-lane concept can therefore be adapted for different physical distances.

Short-Reach 128GFC for Storage Equipment Rooms

Not every Fibre Channel network requires kilometer-level transmission.

Within a data center, storage room, or equipment area, switches, directors, and storage systems may be positioned relatively close to one another. For these applications, short-reach optical modules can provide the required bandwidth without using a long-distance optical architecture.

The QSFP28-128G-SW4 supports a reach of up to 0.1 km, or 100 meters. It uses an 850nm VCSEL transmitter, a PIN receiver, and an MPO connector.

This configuration is intended for short-distance links using compatible multimode fiber infrastructure. It can be considered for connections where Fibre Channel equipment is installed within the same facility and the optical path remains within the specified distance.

For a network with a 100-meter requirement, using a short-reach solution can also simplify the relationship between the transceiver and existing multimode cabling.

When 100 Meters Is Not Enough: eSWL

Some Fibre Channel installations require more reach than a conventional short-reach module can provide while still remaining within a relatively localized network environment.

The QSFP28-128G-eSW4 extends the specified reach to 0.3 km, or 300 meters. Like the SW4 version, it uses an 850nm VCSEL transmitter, a PIN receiver, and an MPO connector.

The difference is primarily the supported optical distance.

This distinction can be useful in larger equipment rooms or data center layouts where 100 meters is insufficient but a single-mode solution designed for several kilometers would be unnecessary.

When comparing the two short-reach configurations, the physical cable distance should therefore be established before selecting the module.

Moving to Single-Mode Fiber for Longer Links

Once the required transmission distance goes beyond the practical range of short-reach multimode deployment, the optical architecture changes.

The QSFP28-128G-LW4 is specified for transmission distances of up to 2 km over single-mode fiber. It uses an LC connector, with the transmitter based on CWDM4 DFB technology covering approximately 1270–1330nm and a PIN receiver.

This configuration provides a significant increase in reach compared with the 100-meter and 300-meter SWL options.

The move from an 850nm VCSEL-based multimode solution to a CWDM4 DFB-based single-mode design also means that the cabling infrastructure must be considered during procurement. An LC-based SMF connection cannot simply be treated as a direct replacement for an MPO-based MMF installation.

For Fibre Channel system integrators, the fiber type and connector should therefore be confirmed together with the required transmission distance.

10 km Fibre Channel Links With LR4

Some storage networks connect equipment over substantially longer distances. For these applications, the QSFP28-128G-LR4 supports transmission of up to 10 km.

The LR4 version uses approximately 1295–1310nm LAN WDM DFB technology, a PIN receiver, and an LC connector.

The longer reach makes this configuration suitable for Fibre Channel links where a 2 km LWL module does not provide enough coverage.

At this distance, however, the optical link cannot be evaluated only by its nominal reach. Fiber attenuation, connector insertion loss, patching, splicing, and other passive components contribute to the total loss of the transmission path.

A proper link budget should therefore be considered before deploying LR4, particularly when the actual distance approaches the maximum specified range.

ER4 for Extended 40 km Transmission

For Fibre Channel connections requiring considerably more optical distance, the QSFP28-128G-ER4 provides a specified reach of up to 40 km.

The ER4 configuration uses LAN WDM EML technology on the transmitter side and an APD receiver. It also uses an LC connector and operates over single-mode fiber.

The use of different transmitter and receiver technologies reflects the greater optical requirements of long-distance transmission. At 40 km, receiver sensitivity and available optical margin become increasingly important, and the complete transmission path needs to be evaluated.

ER4 can therefore be considered for extended Fibre Channel interconnection scenarios where a 10 km LR4 configuration cannot provide the required reach.

Comparing the Main 128GFC Optical Versions

The main configurations can be summarized according to their reach and optical architecture:

Module	Reach	Optical Technology	Connector
SW4	0.1 km	850nm VCSEL + PIN	MPO
eSW4	0.3 km	850nm VCSEL + PIN	MPO
LW4	2 km	CWDM4 DFB + PIN	LC
LR4	10 km	LAN WDM DFB + PIN	LC
ER4	40 km	LAN WDM EML + APD	LC

The important point is that these modules are not differentiated only by their maximum distance. The fiber type, connector, wavelength arrangement, transmitter technology, and receiver architecture also change as the required reach increases.

What Network Designers Should Check Besides Reach

Transmission distance is an important starting point, but it is not the only specification that determines compatibility.

The 128GFC modules use a 4×32Gb/s Fibre Channel architecture and are designed for integration into compatible QSFP equipment. They use a single 3.3V power supply and support hot-pluggable installation.

The modules are QSFP MSA compliant and RoHS compliant. Their standard operating case temperature is specified from -5°C to 75°C.

They also use IEC 60825-1 Class 1/CDRH Class 1 eye-safe laser specifications, while digital diagnostic functions are provided according to SFF-8472.

For equipment manufacturers and network integrators, these details can be important when determining whether an optical module will operate correctly in the intended host platform.

Fiber Infrastructure Can Determine the Module Choice

An optical transceiver should always be considered together with the cabling system.

For example, SW4 and eSW4 use 850nm optics and MPO interfaces for short-reach multimode applications. LW4, LR4, and ER4 use LC interfaces and single-mode fiber for longer connections.

If a storage network is being upgraded from one optical generation to another, the existing cabling should be documented before purchasing replacement modules.

Changing from an MPO-based multimode architecture to an LC-based single-mode architecture may involve additional changes to fiber trunks, patch panels, adapters, polarity, and connection arrangements.

This is why a module that appears suitable based on bandwidth and distance can still be incompatible with the installed network.

Optical Budget Becomes More Important as Distance Grows

Long-distance Fibre Channel connections require closer attention to the optical budget.

Every section of the optical path can contribute to signal loss. Fiber attenuation, connectors, splices, adapters, patch panels, and other passive components should be included when calculating the expected link loss.

For a short 100-meter SW4 connection, the optical path may be relatively simple. For a 10 km LR4 or 40 km ER4 deployment, the engineering requirements are considerably more involved.

The nominal reach of a transceiver should therefore be treated as one reference point rather than a guarantee that every link of that length will operate under all conditions.

Why QSFP Is Practical for High-Density Fibre Channel

The compact QSFP form factor is particularly useful where many high-speed ports must be installed in a limited amount of rack space.

A four-lane architecture allows 128Gb/s aggregate Fibre Channel connectivity to be delivered through a compact pluggable module. This approach helps balance bandwidth, module density, optical complexity, and equipment design.

For storage networking equipment, this can be relevant when expanding port capacity without dramatically increasing the physical footprint of the optical interface.

The flexibility of the architecture is also useful because the same 128GFC generation can be implemented with different optical solutions depending on the required physical distance.

Selecting the Right 128GFC Module

A practical selection process can begin with the optical distance:

• Up to 100 meters: investigate the SW4 short-reach configuration.

• Up to 300 meters: consider the eSW4 option.

• Up to 2 km: the LW4 single-mode configuration provides longer reach.

• Up to 10 km: LR4 is designed for extended Fibre Channel links.

• Up to 40 km: ER4 addresses substantially longer optical paths.

The fiber infrastructure and connector should be checked at the same time.

A 100-meter requirement does not automatically mean SW4 is suitable if the network uses single-mode fiber. Likewise, a 2 km requirement does not mean LW4 can be installed without confirming the LC cabling and host equipment.

The host platform, operating temperature, optical budget, power supply, and applicable Fibre Channel requirements should also be verified before deployment.

Sourcing 128GFC Transceivers for Different Network Environments

For system integrators and storage equipment buyers, procurement can become more complicated when a project involves several transmission distances.

Working with a supplier that offers multiple optical configurations can make it easier to compare short-reach and long-reach modules within the same product family.

Infinol Technology (shenzhen) Co., Ltd develops and supplies optical communication products for Fibre Channel, Ethernet, InfiniBand, data centers, cloud storage, telecommunications, and related networking applications. Its portfolio includes active and passive optical communication products, with OEM and ODM services available for different project requirements.

For buyers managing multiple storage or data center deployments, access to different form factors and optical reach options can also simplify technical coordination during network expansion.

A Practical Checklist Before Ordering

Before selecting a 128GFC QSFP module, buyers and engineers can review several basic questions:

• What is the actual optical distance?

• Is the installed infrastructure multimode or single-mode?

• Is the connection based on MPO or LC?

• Does the selected module provide sufficient optical margin?

• Is the host equipment compatible with the required QSFP interface?

• Does the module meet the applicable Fibre Channel requirements?

• Is the operating temperature within the specified range?

• Are power and hot-plugging requirements compatible with the platform?

• Has the total optical link loss been calculated?

• Will the selected module work with the existing cabling architecture?

Checking these points before procurement can reduce compatibility issues during installation and commissioning.

Final Thoughts

The move to 128Gb/s Fibre Channel is not simply about increasing the headline bandwidth. The way that bandwidth is distributed across four 32Gb/s lanes, combined with the choice of optical technology, determines how the connection can be deployed in a real storage network.

Short-reach SW4 and eSW4 configurations are designed around 850nm multimode applications, while LW4, LR4, and ER4 use single-mode optical architectures for progressively longer transmission distances. Each option addresses a different combination of network distance and optical infrastructure.

For storage networking teams, equipment manufacturers, and system integrators, the QSFP 128Gb/s Transceiver provides a flexible platform for 128GFC connectivity across different physical link requirements.

The key is to select the optical implementation based on the complete network path rather than the 128Gb/s data rate alone. Fiber type, connector, distance, optical budget, host compatibility, operating environment, and module specifications should all be considered before deployment. With those factors aligned, QSFP 128Gb/s Transceiver technology can provide a compact approach to high-bandwidth Fibre Channel connectivity across short equipment-room links and much longer single-mode optical networks.

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