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400 Gigabit Ethernet Transceiver Form Factors and Protocols

The online data needs of businesses and consumers are increasing, and telecommunications networks must be able to handle the load. Consumers are demanding faster access and more data for applications including video and audio streaming, cloud computing, and the increase in mobile-connected devices.


One way that telecom providers can meet that need is through installing or upgrading their data networks to support 400 Gigabit Ethernet. The IEEE, MSA, and other standards bodies are introducing new protocols and pluggable form factors to meet various requirements. These needs come from telecom network providers, enterprise LAN, datacenters, mobile, cable operators, and other stakeholders.


It’s difficult to keep up with the various form factors and protocols, together with the best uses for each one. We put together this quick introduction to give you some insight into the various 400G options, so you can decide on the right configuration to meet your optical and electrical network signalling needs.


Advantages of the Move to the 400G IEEE 802.3 Ethernet Protocol


There are several major advantages provided by the IEEE 802.3 400G ethernet protocol. Here are the main benefits:


  • Four times faster than the previous ethernet standard, 100G.
  • Allows for denser port configurations and greater economies of scale.
  • Reduces the footprint required for higher speeds.
  • Better cost control
  • Forward Error Correction (FEC) as standard, for better compatibility and signal integrity.
  • Reduces energy needs due to efficient form factors and consumption.
  • Reduces testing times for interoperability with other telecoms network infrastructure.


Areas to Consider for 400G Form Factors and Protocols


Each of the following areas will influence the right form factor for your telecommunications network:


  • Density — how many transceivers and ports you can fit into a rack unit.
  • Integrity — the quality and strength of the transceiver signal.
  • Compatibility — backwards compatibility with existing infrastructure and applications.
  • Cost — the capital and operational expenses for moving to 400G.
  • Cooling — the need to cool tightly-packed transceivers and dissipate heat.
  • Footprint — the size of each transceiver and how that impacts network location space.
  • Maintenance — the ease of repairing or replacing transceivers.


There are three main pluggable 400G ethernet transceiver form factors — CFP8, OSFP and QSFP-DD. We’ll cover each of them below.

CFP8 400G Transceiver Form Factor


The C Form-Factor Pluggable 8 (CFP8) (Figure 1) provides first-to-market advantages for telecommunications network providers:

  • 16x25G electrical interface.
  • A strong addition to the existing CFP standard of transceivers.
  • Electrical and optical signalling available using 50Gb/s or 25Gb/s components.
  • Good thermal and cooling management due to a larger footprint.
  • Low port density due to the large size of the CFP8 form factor.
  • Requires a larger enclosure, around the size of a CFP2.


CFP8 form factors include:


  • 400GBASE-SR16
  • 400GBASE-FR8/LR8
  • 400GBASE-DR4

Figure 1: CFP8 Transceiver

Find more information on CFP8 standards, protocols, and form factors at the CFP-MSA website.

OSFP 400G Transceiver Form Factor


The Octal Small Form Factor Pluggable (OSFP) (Figure 2) form factor is a smaller device designed for maximum performance. It uses 8 lanes at 50-Gb/s each to provide a total of 400G.

  • Uses eight electrical lanes to provide 400G.
  • A small form factor that’s easily pluggable.
  • Fits up to 36 ports in a standard rack unit.
  • 14Tb/s from one rack unit fully-installed with OSFP 400G.
  • Designed to work exclusively with 50Gb/s signalling.
  • Does not provide legacy application support or backwards compatibility.
  • Excellent electrical and signal integrity performance.
  • Thermal and cooling management heat sinks are built directly into OSFP.
  • Requires an adapter for backwards compatibility.


OSFP form factors include:


  • 400GBASE-SR8
  • 400GBASE-DR4
  • 400GBASE-FR4
  • 400G Active Optica Cables

Figure 2: OSFP Transceiver

Find more information on OSFP standards, protocols, and form factors at the OSFPMSA website

QSFP-DD 400G Transceiver Form Factor


The Quad Small Form Factor Pluggable Double Density (QSFP-DD) form factor is designed for good backwards compatibility. QSFP-DD takes advantage of a similar design to 40G QSFP and 100G QSFP28 but with a higher electrical contact density. It uses 8 lanes at 50-Gbps per second each to provide a total of 400G.

  • A well-known form factor familiar to engineers who work with 40 and 100GbE networks.
  • Uses an eight-lane electrical interface.
  • QSFP-DD can be plugged into the same racks and cages as standard QSFP modules.
  • Consumes less power than comparable form factors, resulting in lower operational costs.
  • A good form factor if you need strong backwards compatibility with other network infrastructure.
  • Limited expansion for new 400G electrical and optical components.


OSFP form factors include:


  • 400GBASE-SR8
  • 400GBASE-DR4
  • 400GBASE-FR4
  • 400GBASE-LR8
  • 400G Active Optica Cables

Figure 3: QSFP-DD Transceiver

Find more information on QSFP-DD standards, protocols, and form factors at the  QSFP-DD website.

What is the Best 400G Ethernet Form Factor Module for Your Network Needs?


There isn’t a “best” type of 400G Ethernet module for all configurations and applications. The form factors you choose will depend on the unique needs of your telecommunications network.


You might choose CFP8 if you want a standardized and well-established next-generation form factor. CFP8 allows for 25Gb/s and 50Gb/s components combined with good cooling and thermal management. It is limited by its large size, which means a lower port density.


You might choose OSFP if you need a smaller device with excellent signal integrity and performance. The main issue with the OSFP is the lack of backward compatibility that will require adapters to work with some other network components. It allows for a very high port density with built-in cooling.


You might choose QSFP-DD if backwards compatibility is important and your engineers already have experience with 40 and 100GbE QSFP networks. This form factor can be plugged into the same racks and cages as standard QSFP modules, lowering your capital upgrade costs.


Regardless of the 400G form factor you choose, all will support standard industry optical and electrical interfaces to ensure interoperability with other compatible parts of the network infrastructure. If you need advice on choosing, buying, installing, or upgrading your 400G ethernet network, get in touch. We’re experts at helping you to keep costs down and providing the technical and engineering support you need. Contact us


This is just the first of our guides to the exciting world of 400G. Check back for more insight into 400G networking, protocols, and form factors.


Technology Evangelist