What Is QSFP28?
QSFP28 (Quad Small Form-factor Pluggable 28) is a high-density, hot-pluggable fiber optic transceiver standard designed for modern data communication networks. It is an evolution of the QSFP+ standard, offering higher data rates and port densities.
How QSFP28 Works
QSFP28 (Quad Small Form-factor Pluggable) transceivers operate on the principle of parallel optics, utilizing four independent full-duplex channels, each capable of transmitting data at a rate of 25 Gbps. The four channels are combined to achieve an aggregate data rate of up to 100 Gbps (4 x 25 Gbps) .
The key technologies employed in QSFP28 transceivers include:
- Parallel Optics: QSFP28 modules leverage parallel optics by integrating four separate optical channels within a single transceiver package. This allows for higher data rates while maintaining a compact form factor.
- Vertical-Cavity Surface-Emitting Lasers (VCSELs): VCSELs are commonly used as the light source in QSFP28 transceivers due to their low power consumption, high bandwidth, and cost-effectiveness.
- Pulse Amplitude Modulation (PAM4): To achieve higher data rates, QSFP28 transceivers often employ PAM4 modulation, which transmits two bits per symbol, doubling the data rate compared to traditional non-return-to-zero (NRZ) modulation.
- Integrated Circuits: Advanced integrated circuits, such as laser drivers, transimpedance amplifiers (TIAs), and clock and data recovery (CDR) circuits, are used to enable high-speed data transmission and reception.
Key Features of QSFP28
- Data Rates and Channels: QSFP28 supports four independent transmit and receive channels, each capable of operating at up to 28 Gbps, enabling an aggregate data rate of 100 Gbps (4 x 28 Gbps). This meets the requirements for 100 Gigabit Ethernet (100GbE) and 100 Gbps InfiniBand Enhanced Data Rate (EDR) applications.
- Form Factor and Port Density: The compact QSFP28 form factor allows for high port densities on network switches and routers, enabling more interconnections within a given space. The form factor also limits the size and power consumption of internal components like lasers, imposing design constraints.
- Reach and Fiber Types: QSFP28 transceivers can typically support reaches of up to 1 km over multi-mode fiber (MMF) and up to 10 km over single-mode fiber (SMF). However, with advanced modulation techniques like PAM4, reaches of up to 120 km over SMF have been demonstrated.
Types of QSFP28 Modules
Optical Modules
- 100G QSFP28 SR4: Designed for short-reach (up to 100m over OM4 MMF) 100GbE applications. Utilizes 850nm VCSELs and MPO connectors. Key specifications: 25.78Gbps per channel, 4 channels, low power consumption (<2.5W).
- 100G QSFP28 LR4: For long-reach (10km) 100GbE applications over SMF. Leverages EML or DML laser sources and duplex LC connectors.
- 100G QSFP28 CWDM4: Supports 4 CWDM wavelengths for 100GbE over SMF up to 2km. Employs EML or DFB laser sources.
Active Optical Cables (AOCs)
- 100G QSFP28 AOC: Integrates QSFP28 optical transceivers at each end connected by parallel OM3/OM4 MMF cables. Offers a low-cost, low-power, and high-density interconnect solution for short reaches (up to 100m).
- QSFP28 to SFP28 AOC Breakout Cables: Fans out a QSFP28 interface into 4x SFP28 ports, enabling interconnection with SFP28 optics/DACs.
Direct Attach Copper (DAC) Cables
- Passive QSFP28 DACs: Offer a low-cost, low-power, and high-density copper interconnect for short reaches (up to 5m).
- Active QSFP28 DACs: Integrate re-driver ICs to extend the reach up to 10-15m while maintaining signal integrity.
Advantages of QSFP28
- High Bandwidth Density: By integrating four channels into a single module, QSFP28 transceivers provide a high bandwidth density, enabling higher port densities on network switches and routers.
- Low Power Consumption: QSFP28 modules typically consume less than 3.5W of power, significantly lower than other 100G transceiver form factors like CFP and CFP4, which can consume up to 24W.
- Cost-Effective: The use of parallel optics and VCSELs, along with the compact form factor, makes QSFP28 transceivers a cost-effective solution for high-speed data transmission.
- Reach Extension: With the adoption of PAM4 modulation, QSFP28 transceivers can achieve extended reach, enabling transmission distances of up to 40 km over single-mode fiber (SMF).
- Compatibility and Upgradability: QSFP28 modules are designed to be backward-compatible with existing QSFP+ infrastructure, allowing for a seamless upgrade path from 40G to 100G networks.
QSFP28 vs QSFP+
Data Rate Capabilities
- QSFP28 supports 4 channels, each operating at up to 28 Gbps, enabling an aggregate data rate of 100 Gbps (4 x 25 Gbps). This meets the requirements for 100 Gigabit Ethernet and 100 Gbps InfiniBand Enhanced Data Rate (EDR).
- QSFP+, on the other hand, supports 4 channels at 10 Gbps each, enabling an aggregate data rate of 40 Gbps.
Form Factor and Physical Dimensions
- QSFP28 and QSFP+ share a similar compact form factor, but QSFP28 is slightly larger to accommodate the higher-speed electronics.
- QSFP28 modules are designed to be hot-pluggable and have a locking mechanism to secure them in the host port.
Applications and Compatibility
- QSFP28 is optimized for 100G applications in data centers, high-performance computing, and high-density networking.
- QSFP+ is widely used in 40G Ethernet and InfiniBand applications, but can also be used in 100G systems with QSFP28 ports by utilizing only a single channel.
- QSFP28 transceivers can be used in SFP28 ports at reduced speeds (25 Gbps), providing a migration path from 10G to 100G networks .
Optical and Electrical Interfaces
- QSFP28 modules can support various optical interfaces, including single-lambda 100G PAM4 for 80 km transmission over single-mode fiber.
- Both QSFP28 and QSFP+ can be implemented with copper or active optical cable (AOC) assemblies for short-reach applications.
Applications of QSFP28
Data Center Applications
QSFP28 transceivers are widely adopted in data centers for high-speed interconnects between servers, switches, and storage systems. Their ability to support 4x25Gbps channels enables cost-effective 100Gbps Ethernet connectivity, simplifying cabling infrastructure and reducing costs. Key data center use cases include:
- Top-of-Rack (ToR) switches to server connectivity
- Leaf-Spine network architectures for East-West traffic
- Storage Area Network (SAN) connectivity
Telecommunications Infrastructure
With the growing bandwidth demands from mobile networks and broadband services, QSFP28 transceivers are increasingly deployed in telecom infrastructure for high-speed backhaul and aggregation links. Some applications include:
- Mobile backhaul from cell sites to core network
- Broadband access aggregation in service provider networks
- Metro Ethernet and Optical Transport Network (OTN) links
High-Performance Computing (HPC)
The high-density and low-power characteristics of QSFP28 make it suitable for high-performance computing clusters and supercomputers. QSFP28 is used for inter-node connectivity within HPC systems, enabling efficient scaling of compute resources.
Emerging Applications
As bandwidth requirements continue to grow, QSFP28 is expected to find new applications beyond its current focus areas:
- 5G infrastructure for fronthaul and midhaul links
- Autonomous vehicle connectivity and sensor data aggregation
- Industrial automation and machine vision systems
Latest Technical Innovations in QSFP28
High-Speed Data Transmission
QSFP28 is a high-speed fiber optic transceiver module widely used in modern communication networks. It adopts an embedded interface structure that supports up to 28 channels of data transmission, with each channel capable of reaching 25 Gbit/s, enabling a total transmission rate of up to 700 Gbit/s. This high-speed data transmission capability is a key innovation in QSFP28 modules.
Compact Form Factor
Compared to other 100G module forms like CFP/CFP2/CFP4 and CXP, QSFP28 modules have a smaller form factor, enabling higher port density and lower power consumption and cost. The compact size is achieved through highly optimized and power-efficient components designed to fit within the QSFP28 form factor constraints.
PCIe Interface Integration
To overcome the incompatibility between QSFP28 interfaces and the PCIe protocol, leading to low data transmission efficiency and resource waste, a novel high-speed optical communication connector QSFP28-PCIe has been developed. It integrates QSFP28 with PCIe, enabling the host device to generate module low-speed signals (MODSEL, reset) or clock signals (CLK_N, CLK_P) for seamless PCIe connectivity.
Parallel Testing System
A parallel testing system for QSFP28 modules has been proposed to address the high testing cost associated with using multiple bit error rate testers (BERTs) for each module. It comprises a signal transmission unit, a splitter unit with multiple output ports, and multiple measurement routes connected to the splitter outputs, enabling parallel testing of multiple QSFP28 modules simultaneously.
Compact Packaging Design
Innovations in QSFP28 module packaging design have been made to securely house the optoelectronic devices, functional circuits, and optical interfaces within the module cavity. The design also includes locking mechanisms for secure integration with host devices and unlocking mechanisms for easy removal.
FAQs
- What is the primary purpose of QSFP28 transceivers?
QSFP28 supports high-speed data transmission, primarily for 100G Ethernet in data centers and enterprise networks. - Can QSFP28 modules be used for 40G networks?
Yes, QSFP28 modules are backward-compatible with QSFP+ to support 40G networks if needed. - What’s the maximum distance supported by QSFP28 modules?
Depending on the type, QSFP28 modules can support distances from 100m (SR4) to 40km (ER4). - How does QSFP28 improve energy efficiency in networks?
QSFP28 uses optimized circuitry to deliver lower power consumption per gigabit compared to older transceivers. - Are QSFP28 modules backward-compatible with older standards?
Yes, QSFP28 modules can work with existing QSFP+ ports and hardware, ensuring a smooth upgrade path.
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