Telecoms embraces 400ZR optics for IP-over-DWDM

Verizon Media has trialled 400-gigabit coherent pluggable optics to improve the delivery of video content to subscribers.

Tomas Maj

Verizon Media added a 400ZR QSFP-DD module from Inphi to a switch already using 100-gigabit optics.

Adding dense wavelength-division multiplexing (DWDM) optics to a switch enables it to send IP traffic (IP-over-DWDM) directly without needing a separate DWDM data centre interconnect box and additional client-side optics to link the two platforms (see diagram).

“Verizon Media, showing leadership outside the hyperscalers, is moving to IP-over-DWDM,” says Tomas Maj, senior director, marketing, optical interconnect at Inphi. “It shows the maturity of the ecosystem and the confidence of more and more operators in IP-over-DWDM and 400ZR.”

Content distribution network

Inphi cites three applications driving traffic growth between data centres: cloud network virtualisation, content distribution and edge analytics, and data mirroring and backup.

The primary users of these applications are the hyperscalers - it is the hyperscalers that spurred the creation of the OIF’s 120km 400ZR standard - but these applications increasingly apply to the telcos.

Verizon Media uses its content delivery network to share and back-up video between its data centres dubbed super PoPs (points-of-presence). Video is also sent to smaller outlying sites, closer to subscribers, where the most popular content is hosted.

ColorZ II

Verizon Media’s network uses Inphi’s existing 100-gigabit ColorZ QSFP28 pluggable optics.

The ColorZ is a direct-detect module that uses 4-level pulse amplitude modulation (PAM-4) to convert 4x25-gigabit electrical signals to two 50-gigabit PAM-4 optical wavelengths that fit within a 100GHz channel.

The ColorZ module, of which Inphi has now shipped over 100,000 units, has an 80km reach.

Inphi’s second-generation ColorZ II uses the OIF’s 400ZR coherent standard. Both generations employ an silicon photonics chip to implement the optics.

“As you go up in PAM-4 speed, you are taking hits in optical signal-to-noise ratio and receiver sensitivity and the design becomes costly,” says Maj. “At some point, you look at coherent and you have better yield and optical performance.”

Source: Inphi

For Verizon Media’s trial, the ColorZ II 400ZR QSFP-DD was added to switches from Arista Networks. Using ColorZ II optics in the same 100GHz channels quadruples fibre capacity from 4 to 16 terabits while halving the transmission cost-per-bit.

Nitin Batta, principal infrastructure architect at Verizon Media, said in a press release that the ColorZ II was chosen to enable it to “rapidly, easily and cost-effectively add terabits of capacity in response to customer demand.”

The 400ZR standard ensures interoperability and gives customers confidence by having several module companies to choose from, says Maj. Adopting the module also provides important diagnostic information regarding a link’s performance.

All the elements for a 400-gigabit ecosystem are coming together, says Inphi.

Four-hundred-gigabit client-side optical modules are leading the way and now 400-gigabit coherent pluggables are at the testing and validation stage before volume deployment.

The ColorZ II will be generally available at the year’s end.