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Blog • • 5 minute read

Coherent QSFP28 Is Finally Here

The release of 100G ZR coherent QSFP28 transceivers from Nokia, Cisco and others promises to accelerate the already rapid shift from traditional core network designs to optical and packet converged architectures.

In this blog

  1. The converged story so far
  2. A new chapter in the story
  3. Blending 100G and 400G across a core network
  4. How to learn more

 The converged story so far

There's no doubt that  optical and packet convergencehas gone mainstream over the last several years, but so far, the technology has been weighed down by a major burden: the requirement for organizations to purchase new routers in order to deploy optical and packet convergence in their core network.

This requirement stems from the fact that converged transport requires the use of DWDM-coherent transceivers, and so far these transceivers have only been available in two form factors;

  • The C form-factor pluggable (CFP2), which is bulky and draws a lot of power, limiting its port density and scale capabilities
  • The Quad Small Form-factor Pluggable (QSFP-DD), which has become much more popular than CFP2 because it provides backward compatibility with the highly adopted QSFP28 (100G) form factor.

Both of these port types (CFP2 and QSFP-DD) were fairly uncommon until recently, meaning that the vast majority of organizations need to purchase new routers or new router line cards to use these form factors to implement optical and packet convergence.

Until recently, there has not been a compelling way to use existing port form factors, most notably QSFP28, to achieve optical and packet convergence in the core network.

 A new chapter in the story

In 2022, Adtran Networks (at the time operating as Adva) released the industry's first 100ZR QSFP28 coherent transceiver.  By the time the solution was showcased at OFC 2023, the major router vendors like Cisco and Nokia had begun developing their own coherent transceivers that use ZR technology out of a QSFP28 port.  Those second-generation developments are finally here, and they promise a big shift in how optical+packet converged networks are architected because now we can leverage existing investments in QSFP28 port density when overhauling the core network.

These coherent transceivers may vary slightly between vendors, but they all have some key features in common:

  • Compliance with the 100GBASE-ZR standard defined in IEEE 802.3-2022(key for interoperability)
  • C-band tunable
  • ~80km unamplified reach
  • ~120km+ amplified reach
  • QSFP28 form factor

The main differences between vendors will revolve around the transmit power of the transceiver.   The higher the transmit power, the more power the transceiver will draw.  The more power it draws, the more heat it will generate, and the more difficult it will be for the router to dissipate that heat.  On the other hand, reduced power will cause a lower optical output level, meaning an overall reduction in distance that the signal can reach. These tradeoffs have led some vendors to release two different 100G QSFP28 ZR pluggables: a higher power dissipation (~6W) version and a lower power dissipation (~5W) version.  The higher power pluggables are C-temp or E-temp rated, while the lower power pluggables are E-temp or I-temp rated.  There are other vendors that are starting out by producing one pluggable that simply aims for the middle ground (~5.5W).

Another variation between vendors will be in how the transceivers' wavelengths get configured.  Generally speaking, the current way to configure the wavelength on a CFP2 or QSFP-DD port that uses ZR/ZR+ technology is to hard code the specific wavelength using the router's operating system.  As this 100GBASE-ZR standard draws in third-party optic vendors, they have a need for automatic wavelength detection and tuning that ensures their transceiver will work autonomously on a Cisco, Nokia or Juniper router.  

 Blending 100G and 400G across a core network

In September, Cisco showcased their new C-band tunable QSFP28 ZR pluggable at their annual Packet Optical Networking Conference (PONC).  They successfully demonstrated this plug being used in an NCS 540 router to send a 100G wave over 100km distance to a BrightZR+ optic running at 400G in a Cisco 8201 router.  This demo is particularly interesting for showing how optical & packet convergence can be used in a variety of ways--it doesn't always have to be matching coherent pluggables on both sides of a link.  In this case, the 400G BrightZR+ signal was split into 4 lanes of 100G, allowing for the connectivity to the QSFP28 coherent pluggable on the other side.  This opens the door to many new and compelling architectural capabilities when rolling out converged core networks.

 How to learn more

The easiest way to learn more about this exciting development is to request a briefing or workshop on the topic with us so that we can share the latest developments with you and discuss your individual needs.  Speaking with us directly will be the best way to get an up-to-date snapshot of the landscape and developments surrounding QSFP28 coherent pluggables.

Here are a few available solutions that you can learn more about directly from the vendor's documentation:

Technologies