QSA Port Adapters Now Supporting 50G-PAM4

Adapters, Link-X

QSA Port Adapters solve problems linking equipment with different port sizes and speeds



  • DynamixTM QSA56: QSFP-to-SFP Adapter
  • Enables an SFP device to plug into a QSFP port
  • Supports 1G/10G/25G and now 50G-PAM4 line rates
  • Supports BASE-T, DACs, AOCs, multi-mode and single-mode transceivers
  • ½-meter to 10km reaches
  • -10oC to +40oC High Temp versions for QSA+ and QSA28
  • Zero latency, zero power consumption

Bottom line:

QSA Port Adapters are very inexpensive, simple devices every data center needs.


Network Form-factor Problems & Solutions

Problems: You have a 4-channel QSFP port (QSFP+, QSFP28, QSFP56) on a switch or network adapter. But you’ve got a subsystem with single-channel SFP devices you want to connect to the 4-channel port. Maybe you are out of single-channel switch ports (e.g. Mellanox SN2410, SN2010 switch) or maybe you want to connect the fancy new gear to the legacy older equipment running in the 1G/10G “old-world” to the 200G/400G “new-world” using ConnectX-5/6 network adapters.

DynamixTM QSA Port Adapters: Enables Linking Single-Channel SFP Device into 4-Channel QSFP Ports


How to Connect Different Port Types and Speeds Together?

Answers: Get the Mellanox QSA Port Adapters. QSFP-to-SFP Adapter – Available in three different configurations and now supporting both 10G and 25G NRZ and the new 50G-PAM4 line rates!

Sometimes, the simplest things can solve big problems and frustrations. The QSA is one such device and costs less than a dinner for two.

Each speed step seems to bring a flurry of new and confusing buzz words and it’s not about to stop anytime soon! In moving to the next speed step, the industry has to drag along the older legacy equipment and often times have to link it to the new equipment. This is where the problems expand exponentially as mechanical form-factors, line rates, and now modulation schemes add to the matrix.

What is a DynamixTM QSA Port Adapter?

The QSA port adapter is a Mellanox-designed and manufactured mechanical adapter that fits neatly inside any QSFP port and enables plugging in a smaller, single-channel SFP device into a QSFP 4-channel port. Only the one-channel gets passed through even though the mechanical port is 4-channels. The other 3-channels are terminated and not used. The QSA contains a configuration EPROM to tell the host what it is and what speed to run at, reach, FEC, temperature rating, etc. but otherwise does not impact latency, insertion loss or power consumption.

QSA Port Adapters are patented and trademarked products invented by Mellanox.

Don’t be fooled by cheap counterfeits!

 DynamixTM QSA Port Adapter Product Advantages

  • Used in QSFP+, QSFP28, QSFP56, QSFP-DD ports
  • Supports NRZ and/or 50G-PAM4 signaling
  • Supports 1G, 10G, 25G, and 50GbE
  • Backwards compatible supporting SFP+, and SFP28 devices and line rates
  • Supports DACs, AOCs, multi-mode & single-mode transceivers and BASE-T converters
  • Near zero power consumption, latency delay and insertion loss
  • QSA EEPROM ID with SFP device ID pass through
  • Open loop pull tab for efficient airflow and no fluttering in the wind
  • Secure latching mechanism
  • Extended Temp versions -10oC to +85oC for QSA+ and QSA28
  • Registered US patent by Mellanox
  • Extensively tested in all Mellanox Ethernet switches and network adapters
  • Can be used in any IEEE industry standard port
  • QSAs are accepted in QSFP-DD ports, but not OSFP
  • Designed for Ethernet protocol only but can be configured for others as well (e.g. 5G)
  • Availability: GA Q2 2020


What Are the Different QSA Port Adapter Types?

The QSAs are available in several speed 10G, 25G NRZ and now in 50G-PAM4 signaling. Each are backwards compatible to slower speeds all the way to 1G. Also, they support backwards compatible form-factors, e.g. QSA56 supports SFP28 and SFP+ devices. The new QSA56 supports the latest 50G-PAM4 modulation transmitting 2-data bits per clock pulse versus one data bit as with NRZ.

Mellanox DynamiX QSA Port Adapter Product Line

New Signal Modulation Scheme – PAM4?

With the speed jump from 25G to 50G, the IEEE industry standards groups changed the modulation scheme used.  Instead of simple 2 intensity levels for digital 1,0s, (called Non-Return to Zero or NRZ), 50G now uses the new modulations scheme of Pulse Amplitude Modulation with 4-levels – called PAM4. PAM4 is a 4-level “stair step” up instead of just two levels. Think of it as two data bits stacked on top of each other.

This enables keeping the same basic 25G clocking with its low-cost connectors, PCBs, etc. infrastructure, but doubling the bandwidth. As electrical and optical signaling get faster and faster, everything gets more complicated, wires get shorter, noise is greater, more heat and the bottom line – more expensive.  Keeping the 25G base clocking and stacking the data bits on top enables doubling the data rates while keeping the cost down. But this has introduced massive changes and lots of confusing terms and concepts.

QSA Port Adapter – NRZ and PAM4 Modulation


Important Area of Confusion: Modulation and Line Rates

The NRZ and PAM4 signaling devices are NOT compatible with each other. (Warning: This is about where you’re your head will explode!) NRZ is one data bit per clock band PAM4 is two bits per clock.  Mellanox switches and ConnectX network adapters will automatically sense and convert to the type of device inserted (NRZ or PAM4) and run with that format (host reads the device EPROM). The switches and network adapters do the PAM4/NRZ conversion – not the cable or transceiver!

For example, inserting a 25G SR transceiver into a SN3000 series switch based on 50G PAM4, the switch will read the device ID and slows the speed to 25G NRZ and does the modulation conversion. This is called “Backwards Compatibility”. However, it does not work in reverse by inserting a new 50G PAM4 device into an older SN2000 series 25G-based switch – won’t work as the older device cannot recognize PAM4 and probably not the device ID either.

Mixing NRZ and PAM4 modulation schemes with cables and transceivers does not work. NRZ/PAM4 are sort of two different languages.

However, mixing line rates does work. One can link a Mellanox 25G transceiver to a 10G transceivers and the link will come up as Mellanox has a unique “Auto-Sense” feature that will slow the 25G transceiver to 10G. 100G SR4 can run at 40G. Beware this does not work for every type or manufacture’s transceivers. But since Mellanox designs and builds it own transceiver ICs and transceivers, as well as switches and network adapters, thin unique “end-to-end” advantage yield a lot of customer benefits.

Additionally, the same type of cable or transceiver must be used on both ends. One cannot insert a 50G PAM4 transceiver in a 50G PAM4 switch linked to a 25G transceiver in a 25G NRZ network. adapter. These are two different languages talking on the same wire/fiber. Unlike with 25G transceivers that can autosense line rate speeds and down shift, crossing the NRZ-PAM4 modulation schemes doesn’t work. A special converter IC is needed called a gearbox that would have to be inside the cable or transceiver.

The QSA is simply a pass-through device and does not make any speed or modulation changes or conversions.  All that happens in the switch or network adapter.


What SFP Devices Do QSA Port Adapters Support?

The QSAs are essentially passive devices. They do contain an EPROM that is used to tell the switch or NIC what it is, speed, power, reach, etc. But other than that, it stays out of the data path. Since, the QSA can support multiple device types, it simply passes through the EPROM codes for the device inserted into the QSA to the switch or NIC for only one channel. The other unused lanes are simply terminated 3 in a QSFP56 or 7 in QSFP-DD port

The QSAs will support BASE-T converters, DAC and AOC cables and both multi-mode and single-mode transceivers with reaches from ½-meter DACs to 10km LR transceivers.

Also, -10oC -to- +40oC high temp versionsare available to support high-temp SFP devices used in say 25G SFP28 in hot servers with network adapter applications or 5G cell towers. The QSA is optimized for the Mellanox switches & network adapters but works in any unlocked IEEE compliant port.


Mellanox QSA56 for SFP56-based Base-T, DAC, AOC Cables & SR, LR Transceiver


New QSA56 Port Adapter Supports Wide Range of SFP Devices

The new 50G DACs, AOCs and SR multi-mode and LR single-mode transceivers are now becoming available in the SFP56 form-factor and are supported in the new QSA56. This enables the new QSA56s to support even 1G-BASE-T SFP converters, DAC cables from 1/2-meter to 7 meters and out to 10km (6.2 miles) using LR transceivers in a single QSA device. Additionally, the QSAs are line rate backwards compatible to 1G, 10G and 25G NRZ and are accepted in QSFP56 and QSFP-DD 400G ports.

Mellanox DynamixTM QSA56 Port Adapter Supported SFP Products



Not everything in the world runs or needs to run at 50Gb/s so the QSA is a neat way to link slower 1G, 10G or 25G sub-systems to new high-speed Mellanox 200G/400G 50G-PAM4-based Spectrum SN3000/4000-series switches and ConnectX-6 network adapters.

Order by Mellanox Part Number:

QSFP+ (10G)            MAM31Q00A-QSA              SFP+ Adapter           1x10GbE NRZ

QSA28 (25G)            MAM1Q00A-QSA28            SFP28 Adapter         1x25GbE NRZ

QSA56 (50G)            MAM1Q00A-QSA56            SFP56 Adapter         1x50GbE PAM4



More Information:  

Contact your Mellanox sales representative for availability and pricing options and stay tuned to my blog more interconnect news and tips.


About Brad Smith

Brad is the Director of Marketing at Mellanox, based in Silicon Valley for the LinkX cables and transceivers business focusing on hyperscale, Web 2.0, enterprise, storage and telco markets. Recently, Brad was Product Line Manager for Intel’s Silicon Photonics group for CWDM4/CLR4 and QSFP28 product lines and ran the 100G CLR4 Alliance. Director of Marketing & BusDev at OpSIS MPW Silicon Photonics foundry. President/COO of LuxSonar Semiconductors ( Cirrus Logic) and co-founder & Director of Product Marketing of NexGen, a X86-compatible CPU company sold to AMD - now the X86 product line. Brad also has ~15 years in technology market research as Vice president of the Computer Systems group at Dataquest/Gartner; VP/Chief Analyst at RHK and Light Counting networking research firms. Brad started his career at Digital Equipment near Boston with the VAX 11/780 and has served as CEO, president/COO and on the board-of-directors of three start-up companies. Brad has a BSEE degree from the University of Massachusetts; MBA from University of Phoenix and holds 2 optical patents

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