FAQs on 400G Transceivers and Cables You Need to Know, Pt. 3


As data center networks continue to grow in both size and complexity, the need for higher bandwidth and faster speeds has become increasingly apparent. To meet these demands, a substantial number of 400G transceiver and cable standards have been developed.

In this article, we will answer some more frequently asked questions about 400G transceivers and cables. Read on!

Q7: What Does it Mean When a 400G Electrical or Optical Channel is Referred to as ‘PAM4’?

PAM4 refers to the encoding scheme used by the high-speed electrical interface in the transceiver. PAM4 is a 4-level Pulse Amplitude Modulation that encodes data on a single channel as two bits per symbol. Prior to the advent of 400G interfaces, essentially all optical transceivers utilized an NRZ (Non-Return to Zero) coding scheme. NRZ is a 2-level Pulse Amplitude Modulation (PAM2) that encodes data a single bit per symbol (1 bit per baud).

Most 400G transceiver types use PAM4 not only on the optical side but the electrical side. The electrical interface of a transceiver is what connects the transceiver to the host system. The electrical interface for 400G transceivers is in two standards known as 400GAUI-8 and CEI-56G-VSR-PAM4. The 400GAUI-8 is defined in the IEEE 802.3bx standard and the CEI-56G-VSR-PAM4 standard was defined in the OIF (Optical Internetworking Forum).

Q8: What are the Challenges of Implementing 400G Transceivers and Cables?

Some of the challenges of implementing 400G transceivers and cables include the following:

1. Cost: One of the biggest challenges of implementing 400G transceivers and cables is the cost. 400G transceivers and cables are only one part of these costs. Host switches must typically be upgraded to a new generation that offer QSFP-DD (or OSFP/CFP8) interfaces. 

2. Compatibility: Another challenge of implementing 400G transceivers and cables is compatibility.  For example, most 100G and lower speed interfaces utilize duplex fiber cabling with most transceiver types sporting duplex-LC type connectors. Many 400G interface types require multi-fiber ribbon cables as they are equipped with MPO-12 and even MPO-24 optical connectors.

3. Deployment: A third challenge of implementing 400G transceivers and cables is deployment. These components may be more difficult to deploy, test and commission. Organizations may need to hire specialized personnel to install and maintain them.

Q9: What is the Future of 400G Transceivers and Cables?

The future of 400G transceivers and cables is bright. These components are becoming more affordable, and they are becoming more compatible with existing infrastructure. Additionally, deployment is becoming easier, with expertise increasing as more organizations are adopting these technologies. The future of 400G transceivers and cables is promising as both commercial and enterprise data centers as well as the telecommunications industry accelerate adoption of these technologies.


This guide provides comprehensive information on 400G transceivers and cables, including their key features, benefits, and applications. It also discusses the main considerations when choosing a 400G transceiver or cable, such as compatibility, cost, and performance. This guide will be helpful for anyone who needs to select a 400G transceiver or cable for their data center or other application.

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