Overview
The 40G QSFP+ (Quad Small Form-factor Pluggable Plus) transceiver is a compact, hot-pluggable module used for 40 Gigabit Ethernet data communications. It was a pivotal technology that enabled the mass adoption of 40GbE by significantly increasing port density and reducing power consumption compared to previous solutions. The core of the QSFP+ standard is its four-lane architecture, transmitting and receiving four parallel 10Gbps streams for an aggregate data rate of 40Gbps.
This 4x10G architecture is the QSFP+’s most powerful feature, enabling not only a native 40G connection but also a “breakout mode.” This allows a single 40G QSFP+ port to be connected to four separate 10G SFP+ ports, providing unparalleled flexibility and density for network architects, especially in Top-of-Rack (ToR) data center switching.
Key Features & Common Variants
- High Density: The compact QSFP+ form factor allows for high port density on switches and line cards.
- 4x10G Breakout Capability: Enables a single 40G port to function as four independent 10G ports, maximizing hardware investment.
- Versatility: Supports a wide range of applications and distances with various module types.
- Low Power Consumption: More energy-efficient than using four individual 10G SFP+ transceivers.
- Hot-Pluggable: Can be installed or removed from a host device without interrupting system operation.
The most common variants are distinguished by the distance they support and the type of fiber and connector they use:
- 40GBASE-SR4: The most popular choice for short-reach data center applications. It uses four parallel lanes over multi-mode fiber (OM3/OM4) and terminates with an MTP/MPO connector to achieve distances up to 150 meters. Ideal for breakout applications.
- 40GBASE-LR4: Designed for long-reach applications up to 10 kilometers over single-mode fiber. It uses WDM (Wavelength Division Multiplexing) to combine four 10G wavelengths onto a single fiber pair, terminating with a standard Duplex LC connector.
- 40GBASE-ER4: An extended-reach version of LR4, capable of transmitting up to 40 kilometers over single-mode fiber, also using a Duplex LC connector.
Applications
40G QSFP+ transceivers are deployed in a variety of high-speed networking environments:
- Data Center Networks: Used extensively in spine-and-leaf architectures for interconnecting Top-of-Rack (ToR) switches to leaf switches, or for links between leaf and spine switches.
- Enterprise Core & Distribution: Provides high-capacity uplinks from access/distribution switches to the enterprise network core.
- High-Performance Computing (HPC): Connects servers and storage clusters that require high-bandwidth, low-latency communication.
- Service Provider Networks: Used for aggregation and metro network links.
Specifications
| Parameter | Value |
|---|---|
| Form Factor | QSFP+ |
| Data Rate | 41.25 Gbps (4 x 10.3125 Gbps) |
| Common Variants | 40GBASE-SR4, 40GBASE-LR4, 40GBASE-ER4 |
| Connector Types | MTP/MPO-12 (for SR4), Duplex LC (for LR4/ER4) |
| Fiber Types | Multi-Mode Fiber (MMF) for SR4, Single-Mode Fiber (SMF) for LR4/ER4 |
| Compliance | QSFP+ MSA, IEEE 802.3ba |
FAQ (Technical & product category Questions)
1. What does QSFP+ stand for?
QSFP+ stands for Quad Small Form-factor Pluggable Plus. “Quad” refers to its four data channels, and “Plus” indicates its support for 10Gbps per channel, distinguishing it from the older QSFP standard which supported 1Gbps per channel.
2. What is the main difference between 40GBASE-SR4 and 40GBASE-LR4?
The key differences are application, technology, and hardware. SR4 is for short distances (up to 150m) over multi-mode fiber using an MTP/MPO connector. LR4 is for long distances (up to 10km) over single-mode fiber using a Duplex LC connector and WDM technology to multiplex the four channels.
3. What is 40G breakout mode?
Breakout mode allows a 40G QSFP+ port, typically using an SR4 module, to be split into four independent 10G links. This is achieved using an MTP-to-4xLC breakout cable, which connects the single MTP port on the QSFP+ to four separate SFP+ modules with LC ports.
4. Can I use a 40G QSFP+ module in a 100G QSFP28 port?
Yes, in most modern network equipment, a 100G QSFP28 port is backward compatible with 40G QSFP+ modules. The port will automatically detect the QSFP+ module and operate at 40Gbps.
5. What happens if I plug a QSFP+ module into an SFP+ port?
This is physically impossible. The QSFP+ module is wider and has a different form factor than an SFP+ module. They are not mechanically or electrically compatible.
6. What cable do I need for a 40GBASE-SR4 connection?
For a native 40G to 40G link, you need a multi-mode fiber patch cable with MTP/MPO-12 connectors at both ends (Type B, female-female). For breakout mode, you need an MTP-to-4xLC breakout cable.
7. Is 40G QSFP+ still a relevant technology?
Absolutely. While new hyperscale data centers are deploying 100G and higher speeds, 40G remains a highly cost-effective and powerful solution for many enterprise networks, smaller data centers, and specific roles within larger networks. It offers a significant performance upgrade from 10G and is supported by a vast ecosystem of hardware.
