As bandwidth demands in data centers, metro networks, and 5G transport continue to surge, optical module speeds and form factors are evolving rapidly. From 100G to 400G and even 800G, enterprises face multiple packaging choices such as OSFP, QSFP112, and QDD (QSFP-DD), as well as various transmission distance specifications like VSR4, DR4, LR4, ER4, and ZR4. This article provides a detailed technical breakdown of OSFP/OSFP112-400G-VSR4, QSFP112, QDD, QSFP DD DR4, QSFP56-DD-400G-DR4, QSFP56-DD-400G-VSR4, and the 100G family including QSFP28 LR4/ER4/ZR4, 100KM ultra-long reach, and BIDI 40KM/80KM. This guide offers a professional and practical reference for enterprise network planning.
Today’s 400G optical modules primarily come in OSFP, QSFP112, and QSFP-DD (QDD) packages. Each has distinct advantages in power consumption, port density, and backward compatibility.
OSFP (Octal Small Form Factor Pluggable) was originally designed with 8×50G PAM4 channels to deliver 400G aggregate bandwidth. It is slightly larger than QSFP-DD but offers superior thermal performance, making it suitable for high-power scenarios. The OSFP112-400G-VSR4 is an optimized short-range variant within the OSFP family, typically used for intra-rack or inter-rack copper connections. It leverages 112G PAM4 SerDes technology and supports up to 2km over multimode fiber or direct attach copper (DAC) cables. With typical power consumption below 10W, it is an excellent choice for high-density switch interconnects in hyperscale data centers.
QSFP112 is a 400G module that upgrades the traditional QSFP form factor while retaining the physical dimensions of QSFP28. Its electrical interface is upgraded to 4×112G PAM4. The main advantage is partial compatibility with existing QSFP28 ports (subject to switch support), enabling a smooth migration from 100G to 400G. QSFP112 is mainly used for transmission distances up to 500m over multimode or single-mode fiber, such as 400G-SR4 (100m on OM4) and 400G-DR4 (500m single-mode).
QSFP-DD (Quad Small Form Factor Pluggable Double Density) is currently the most popular 400G package, using 8×50G PAM4 or 4×100G PAM4 architectures. Among them, QSFP DD DR4 is the standard model for 500m transmission over single-mode fiber, utilizing four parallel single-mode lanes at 100G each via an MPO-12 connector. QSFP56-DD-400G-DR4 is essentially the same specification, emphasizing the use of 56G baud PAM4 technology. The QSFP56-DD-400G-VSR4 is designed for very short distances (typically ≤2km) with low-power DSP or direct CDR drive, suitable for campus networks or intra-DCI links.
When selecting 400G modules, transmission distance and fiber type are as critical as form factor. The table below summarizes typical parameters for key 400G models:
OSFP112-400G-VSR4: Multimode/single-mode, 2km, ~9W, ideal for rack-to-rack links.
QSFP56-DD-400G-VSR4: Single-mode, 2km, 10W, suitable for short-reach DCI.
QSFP56-DD-400G-DR4: Single-mode, 500m, ~12W, standard for data center interconnect.
QSFP DD DR4: Same as above, alternative naming.
For 400G links requiring more than 2km, consider 400G-FR4 (2km) or 400G-LR4 (10km), but this article focuses on the listed keyword models.
Despite the rise of 400G, 100G still dominates access and metro networks. Based on the QSFP28 package, the following product family covers distances from 2km to over 100km.
QSFP28 100G LR4 is the most common 10km single-mode solution for data centers and campus networks. It uses LAN-WDM wavelength division multiplexing (4×25G) with typical power consumption of 3.5W. QSFP28 100G ER4 extends reach to 40km, requiring APD receivers and SOA amplifiers, with power around 4.5W – commonly used in metro aggregation. QSFP28 100G ZR4 supports 80km transmission, usually requiring more sensitive optics and FEC, with typical power of 5.5W. For backbone links exceeding 80km, optical amplification and dispersion compensation can be added.
Some vendors offer QSFP28 100G 100KM solutions, often based on coherent optics or high-sensitivity APD + SOA + pre-amplifier. For example, a CFP2-DCO coherent module combined with EDFA can achieve 100~120km unrepeatered transmission. Due to size and power constraints, a true non-coherent 100km QSFP28 is challenging. The mainstream approach uses CFP2 or QSFP-DD coherent modules, but enhanced non-coherent QSFP28 products exist for specific links (e.g., high-power launch and advanced FEC). Enterprises should verify link loss budget and dispersion tolerance when selecting such modules.
BIDI (Bi-Directional) modules use two different wavelengths on a single fiber for transmit and receive, saving 50% of fiber resources. For 100G BIDI, 2-wavelength (e.g., 1270nm/1330nm) or 4-wavelength schemes are used. QSFP28 100G BIDI 40KM employs two 50G PAM4 or four 25G NRZ lanes with high-sensitivity receivers to achieve 40km. QSFP28 100G BIDI 80KM further adopts stronger FEC and optical amplification, ideal for fiber-constrained long-haul links. Compared to traditional dual-fiber LR4/ER4, BIDI significantly reduces fiber leasing costs, especially for carriers and metro edge nodes.
Based on the above technical parameters, enterprises can quickly match their network architecture:
Inside data center (≤500m): Prefer QSFP DD DR4 or QSFP112 400G-DR4 for optimal power and cost. For legacy 100G access, use QSFP28 100G LR4 (10km) or SR4 (100m).
Data center interconnect (2km): OSFP112-400G-VSR4 or QSFP56-DD-400G-VSR4 provide cost-effective solutions without expensive optical amplifiers.
Metro aggregation (40km–80km): QSFP28 100G ER4 (40km) or ZR4 (80km) are standard. If fiber is scarce, use QSFP28 100G BIDI 80KM.
Long-haul backbone (100km+): Evaluate QSFP28 100G 100KM (if link loss permits) or upgrade to 400G coherent solutions.
In real-world environments, the following factors are often overlooked but critical:
Power and thermal management: 400G VSR4 modules consume<10W, while DR4 may exceed 12W. Ensure switch port cooling design meets requirements.
Fiber type and connectors: DR4 uses MPO-12 (APC or UPC); LR4/ER4 use duplex LC. BIDI also uses LC but requires correct wavelength pairing.
FEC compatibility: Long-haul modules (especially 100KM and BIDI 80KM) rely on host FEC capabilities. Verify RS-FEC or FC-FEC support with switch/router vendors.
Dispersion penalty: For links beyond 80km, standard NRZ or PAM4 modules may require DSP CDR compensation. Use enhanced modules with integrated CDR.
A: No, they have different electrical interfaces (OSFP vs. QSFP-DD) and are physically incompatible. However, if a switch provides both port types and optical parameters match, they can be used for the same link on different ports.
A: No. LR4 is designed for a maximum of 10km (dispersion tolerance ~2dB). A 40km link has excessive loss and dispersion – you must use ER4 or repeaters with amplification.
A: Only one single-mode fiber core, because BIDI uses different wavelengths for bidirectional transmission on the same fiber. Traditional LR4 requires two cores (one transmit, one receive).
A: Yes. Both refer to the QSFP-DD package, 400G speed, and DR4 interface (500m). The QSFP56-DD naming emphasizes 56GBaud PAM4 technology, but the specification is identical.
A: Standard QSFP28 modules cannot reach 100km. Options include coherent QSFP28-ZR (often in CFP2 form factor) or using EDFA optical amplifiers with high-sensitivity modules. Some vendors offer enhanced non-coherent modules, but verify link budget (typically total loss<25dB).
A: Some VSR4 modules support breakout mode – using a one-to-four fanout cable to split one 400G port into four 100G ports. This requires switch chip support for port splitting.
From 100G to 400G, the variety of packages and transmission schemes offers flexible networking options but increases selection complexity. Correctly matching OSFP/OSFP112-400G-VSR4, QSFP112, QSFP DD DR4, QSFP56-DD-400G-VSR4, as well as 100G long-haul and BIDI series, can significantly reduce total cost of ownership and ensure network reliability.
For detailed solution design tailored to your specific link distance, switch model, and budget, please contact our optical module technical team. We provide full support from sample testing to mass deployment, and can customize special distances (e.g., non-standard 100KM) and BIDI wavelength plans upon request. Reach out today for professional selection advice and pricing.
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