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How Much Do You Know About QSFP56?

HowardUpdated at Jan 16th 20221 min read

In recent years, various optical module form factor types have emerged with the growth of new technology and high-speed interconnects. Among them, QSFP56, as a member of the QSFP family, serves as a solution for 200G applications. Wondering about the difference between QSFP56 and other QSFP family form factors? Curious if QSFP56 is the same as QSFP56-DD? If so, this article is for you.
Figure 1: Transceiver form factor
QSFP56—Form Factor of 200G Transceivers
To make clear what QSFP56 is, let’s take a look at the QSFP form factor first. Quad Small Form-Factor Pluggable (QSFP) was developed after SFP, which was originally designed to replace the single-channel SFPs with high-density optical modules. Due to the fact that it denotes four lanes for up to 4 wavelengths, it provides higher bandwidth capacity compared with the SFP modules.
Developed on the basis of QSFP, 40G QSFP+ arose and then 100G QSFP28 came into use for high-density applications. QSFP56, developed after QSFP28, is a Quad 50 Gigabits Small Form-Factor Pluggable transceiver, designed for 200G Ethernet, supporting 4×50~56Gb/s speeds. With the rise of data traffic in data centers and advanced network applications, the market is urgent to achieve higher-speed general availability. There is more addition to QSFP family form factors, such as 200G QSFP56 and 400G QSFP56-DD.
Figure 2:Types of QSFP form factor
Sometimes QSFP56 can also be referred to as 200G QSFP for sake of simplicity. QSFP56 optical modules are similar to QSFP ones in terms of size and form factor. Classified by distance, QSFP56 modules can be divided into QSFP56 CR, SR, DR, FR, LR, which enables different transmission distances over a single mode fiber (SMF) or multimode fiber (MMF).
Generally, two QSFP56 modules can be used with SMF or MMF to establish a 200G link. Additionally, using QSFP56 AOC/DAC allows for a simplified connection process between the QSFP56 ports on two devices to achieve a 200G link. For bridging 200G QSFP56 ports to other speeds, there are 200G QSFP56 to 2x100G QSFP28 breakout cables and 200G QSFP56 to 4x50G SFP56 breakout cables, enabling 2x100G or 4x50G connections.
FS provides a variety of 200G QSFP56 modules, including InfiniBand and Ethernet modules. Mainly the following types:
Technology
Product
Chip
Modulation (Electrical)
Modulation (Optical)
Power Consumption
Connecter
Distance (Max.)
Application
InfiniBand
Marvell
4x 50G PAM4
4x 50G PAM4
≤5W
MPO-12/UPC
100m
NVIDIA QM8700/8790 Devices and ConnectX-6 Adapters
Ethernet
Marvell
4x 50G PAM4
4x 50G PAM4
≤5W
MPO-12/UPC
100m
200G to 200G Link for Switch-to-Switch
4x 50G Breakout to SFP56-SR-50G
Inphi
4x 50G PAM4
4x 50G PAM4
≤6.5W
Duplex LC/UPC
2km
200G to 200G Link for Switch-to-Switch
Inphi
4x 50G PAM4
4x 50G PAM4
≤8W
Duplex LC/UPC
10km
200G to 200G Link for Switch-to-Switch
QSFP56 vs QSFP28 vs QSFP+
Seen from their industry names, QSFP56, QSFP28, and QSFP+ are very similar, as they all share the same QSFP form factor, indicated by their suffixes, and have identical dimensions. However, their data center and connectivity capabilities are different. Below is a table listing the basic parameters of QSFP56, QSFP28, and QSFP+.
Form Factor
Year
original meaning
Channels
Lane rate
Modulation
Speed
QSFP+
2013
Quad Small Form-factor Pluggable Plus
4
10G
NRZ
40G
QSFP28
2016
Quad Small Form-factor Pluggable 28
4
25G
NRZ
100G
QSFP56
2017
Quad 50 Gigabits Small Form-factor Pluggable
4
50G
PAM4
200G
The comparison chart clearly shows that, in contrast to QSFP+ and QSFP28, the QSFP56 form factor offers a higher network speed, supporting 4×50G channels. QSFP+ is an evolution of the QSFP, supporting 4×10G channels for 10G Ethernet, 10G Fiber Channel, or QDR InfiniBand. It introduced the concept of multiplexing 4 lanes to increase bandwidth, allowing it to handle 40Gbps line rates at 10G Baud NRZ per lane. QSFP28 supports 4×25G channels and includes a 4-lane optical transmitter and receiver, similar to QSFP+.
The most significant change from the QSFP+ and QSFP28 to the QSFP56 is that the QSFP56 undergoes a change from NRZ to PAM4 modulation. While QSFP56 still uses 4 lanes like QSFP28, the modulation is increased to 50G per channel, enabling more data transmission over existing fiber and making it more suitable for hyperscale data center networks.
Shift from QSFP56 to QSFP56-DD (400G QSFP-DD)
With data centers undergoing rapid growth, the rising demand for data volume is pushing network components to support higher bandwidth and higher density. The latest iteration of optical module form factor is from QSFP56 to QSFP56-DD, which is also called 400G QSFP-DD. DD here refers to double density, representing reaching 400G (with 50G PAM4) by doubling data lanes of QSFP56, from 4 lanes to 8 lanes.
Though QSFP56-DD has the double density, its size is similar to QSFP56. 400G QSFP56-DD port is backward compatible with the QSFP transceivers which means as long as the switch supports, QSFP56 can work on the QSFP56-DD port. When using a QSFP56 module in an QSFP56-DD port, this port will be configured for a data rate of 200G, instead of 400G.
The QSFP56-DD form factor is now recognized by the 400G market as the 400G form factor that gets the most concern. Despite that nowadays 400G Ethernet is seen as a futureproofing solution for the next-generation data center, there is still a need for 200G QSFP56 for some organizations deploying 200G Ethernet. At present, FS offers 200G QSFP56 transceivers that have undergone rigorous testing on target devices to ensure perfect compatibility and reliability, delivering superior performance. Choose FS QSFP56 transceivers for your 200G network solutions!