200G Optical Transceiver: QSFP56 vs QSFP-DD

With the rapid development of data centers, 200G QSFP56 and 200G QSFP-DD optical transceivers have become the mainstream solution for 200G Ethernet deployments, as 100G optical transceivers are not enough to meet the growing network upgrade requirements and 400G is not yet popular. We will give you a detailed introduction to the 200G QSFP56 vs QSFP-DD on this article.

Form Factor and Density

200G QSFP56 (4x50G)

The 200G QSFP56 (Quad Small Form-factor Pluggable 56) transceiver has a form factor similar to the earlier QSFP transceivers, with a size of 70mm x 18mm x 13mm. It has 4 channels, each capable of transmitting data at a rate of up to 50 Gbps, which results in a total data rate of up to 200 Gbps.

A QSFP56 transceiver can support up to 36 ports per 1RU (rack unit).

200G QSFP-DD (8x25G)

The 200G QSFP-DD (Quad Small Form-factor Pluggable Double Density) transceiver has a larger form factor, with a size of 87mm x 18mm x 13mm. It has 8 channels, each capable of transmitting data at a rate of up to 50 Gbps, which results in a total data rate of up to 400 Gbps.

A QSFP-DD transceiver can support up to 64 ports per 1RU, providing higher port density.

In summary, both transceivers have the same bandwidth, and they are high-speed pluggable transceivers used for data communication applications. However, 200G QSFP-DD has a larger form factor and higher port density compared to 200G QSFP56, which allows it to support a higher total data rate and number of ports per unit of rack space.

Modulation Technology

200G QSFP56 (PAM4 Modulation)

The QSFP56 package has 4 transmit and receive ports, the transmission rate of each channel is up to 56Gbps, and the modulation method is PAM4, which is a common solution for 200Gb/s.

200G QSFP-DD(NRZ Modulation)

QSFP-DD adopts 8 channels, and the rate of each channel is up to 25Gb/s (NRZ modulation) or 50Gb/s (PAM4 modulation), and the aggregation provides solutions up to 200Gb/s or 400Gb/s.


To achieve the same signal transmission capability, the symbol rate of the PAM4(Pulse Amplitude Modulation 4-level) signal only needs to be half that of the NRZ(Non-Return-to-Zero) signal, so the loss caused by the transmission channel is greatly reduced.

Architecture Solution

200G QSFP56 DSP Solution

200G QSFP56 DSP solution uses PAM4 modulation to achieve 4x50G optical interconnect, which allows for higher data rates over the same bandwidth as NRZ. However, PAM4 signals are more sensitive to noise and distortion than NRZ signals, and require digital signal processing (DSP) to recover the original data accurately. While DSP improves performance, it also increases power consumption and cost.

200G QSFP-DD All-Analog Architecture Solution

200G QSFP-DD all-analog architecture solution uses NRZ modulation to achieve 8x25G optical interconnect, which maintains signal integrity without the need for DSP. The delay of the all-analog optical interconnect is only one-thousandth of that of the DSP solution, which is a key advantage in achieving the fastest system and network performance. The simplified design of the all-analog 200G module reduces total component count and avoids the development and implementation costs of DSP, resulting in lower power consumption and cost.

Backward Compatibility

The 200G QSFP-DD is backward compatible with QSFP+, QSFP28 and QSFP56 transceivers, allowing for flexibility and ease of migration between different data rates. This is possible because of the unique double-density design of the QSFP-DD transceiver, which can accommodate both 4-lane and 8-lane configurations.

On the other hand, the 200G QSFP56 supports backward compatibility with QSFP+ and QSFP28 optical transceivers.

Transmission Distances

200G QSFP56

200G QSFP56 optical transceivers are commonly available in 200G QSFP56 SR4, DR4, FR4, LR4, ER4.

200G QSFP56	Interface	Power Consumption	Transmission Distance
SR4	MPO	＜5W	100m
DR4	MPO	＜5.5W	500m
FR4	LC Duplex	＜5.5W	2km
LR4	LC Duplex	＜7.5W	10km
ER4	LC Duplex	＜9W	40km

200G QSFP56 SR4

The 200G QSFP56 SR4 is a 200G Ethernet switch direct connect solution with a 4-channel full duplex transceiver transceiver with an MPO 12-core interface and a central wavelength of 850nm, with a built-in CDR on the transmitter and receiver side, and with multi-mode fibre (MMF) for short distance transmission up to 100m.

200G QSFP56 DR4

The 200G QSFP56 DR4 is a 4-channel full duplex transceiver transceiver that complies with QSFP56 MSA and IEEE 802.3bs 200GBASE-DR4 Ethernet standard. With MPO12 core interface, operating at 1310nm, 50G PAM4 and single-mode parallel technology, the transmission distance is up to 500m over single-mode fibre (SMF) with FEC enabled in the system.

200G QSFP56 LR4

The 200G QSFP56 LR4 is the most common 200G optical transceiver for long-haul DCI interconnects. With dual LC interfaces and an operating wavelength of LDWM4, it can transmit distances of up to 10km/20km over single-mode fibre (SMF) with FEC enabled in the system.

200G QSFP56 ER4

For ultra-long distance transmission, 200GE QSFP56 ER4 optical transceivers with dual LC interfaces and LDWM4 operating wavelength are usually used. 50G PAM4 and LWDM4 technologies are used, and a maximum transmission distance of 40km can be achieved via single-mode fibre (SMF) with FEC on.

200G QSFP-DD

200G QSFP-DD optical transceivers can realize low-cost optical interconnection within data centers, commonly available in 200G QSFP-DD SR8(2SR4), PSM8, and LR4.

200G QSFP-DD	Interface	Power Consumption	Transmission Distance
SR8(2SR4)	MPO	4W	2km
PSM8	MPO	6W(2km)/6.5W(10km)	10km
LR4	LC Duplex	＜7.5W	10km

200G QSFP-DD 2SR4

The 200G QSFP-DD 2SR4 is a short-reach optical transceiver that supports data rates of up to 200Gbps over a multimode fiber (MMF) link. It uses four wavelengths (i.e., 850 nm, 880 nm, 910 nm, and 940 nm) to transmit and receive data over a distance of up to 100 meters. The QSFP-DD 2SR4 is designed for use in short-reach applications within the data center, such as server-to-switch or switch-to-switch connections, where high bandwidth, low power consumption, and low cost are required.

200G QSFP-DD PSM8

The 200G QSFP-DD PSM8 (Parallel Single-Mode 8) is a high-speed optical transceiver that supports data rates of up to 200Gbps over a parallel single-mode fiber (PSMF) link. It uses eight lanes of single-mode fibers to transmit and receive data over a distance of up to 10 km. The QSFP-DD PSM8 is designed for use in data centers and high-performance computing (HPC) applications where high bandwidth, low power consumption, and long reach are required.
The QSFP-DD PSM8 optical transceiver uses eight parallel single-mode fibers to achieve 200Gbps data rate while maintaining low power consumption and high reliability. The PSMF enables easy migration from 100G to 200G network infrastructure without the need for expensive optical components or complex system upgrades.

200G QSFP-DD LR4

The 200G QSFP-DD LR4 is a high-speed optical transceiver that supports data rates of up to 200Gbps over a single-mode fiber (SMF) link. It uses four wavelengths (i.e., 1296.1 nm, 1300.1 nm, 1304.6 nm, and 1308.1 nm) to transmit and receive data over a distance of up to 10 km. The QSFP-DD LR4 is designed for use in long-haul and metro optical networks, as well as in data center interconnect (DCI) applications where high bandwidth, low latency, and long reach are required.

How to Choose a 200G Optical Transceiver?

While the QSFP-DD package is currently the most popular package type in the 400G Ethernet market, this does not mean that the QSFP56 package type is obsolete. For some data centers that don’t have the same high speed requirements as 400G, deploying 200G Ethernet using 200G QSFP56 package optical transceivers is still the ideal solution. If you are considering upgrading to 400G, deploying 200G QSFP-DD package optical transceivers is a more cost effective solution.

NADDOD 200G products include optical transceivers and DAC/AOC. 200G QSFP56 SR4 is suitable for short distance data transmission, such as interconnection between aggregation switch and access switch; 200G QSFP56 FR4 can be used to interconnect data center Leaf switch with Spine switch; 200G QSFP-DD LR8 is usually used for Tier 1 and Tier 2 interconnection, taking up data transmission between core router, core switch and access switch; 200G DAC and AOC are usually deployed between core router, core switch and server.

In the underlying access switch and server interconnection solution, in addition to using direct-connect DAC and AOC, branch DAC and AOC can also be used for different needs. NADDOD’s 200G to 4x50G or 200G to 2X100G DAC and AOC products provide a more flexible solution for data centers.


Related Resources:
Mainstream for 200G Data Centers, 200G QSFP56 or 200G QSFP-DD?