Testing 800G Pluggable Modules – What's All This Orchestrated Test Stuff?
The creation of the 800G ecosystem has begun. Alpha samples of 800G OSFP modules have been demonstrated and we will likely see alpha QSFP-DD800 in a few months. Although 800G modules leverage a lot of the technology from 400G pluggables, the envelope has been pushed a little bit more. The host to module electrical interface (AUI-8) now runs at 100G electrical lanes speeds – using PAM-4 53Gbaud signaling. With this jump, the electrical interface becomes even more challenging to troubleshoot, debug and validate. Now with signal integrated, link performance and reliable & robust equalization deeply interwoven with the host and module SERDES, the module SERDES is closely bound to the DSP and the firmware.
The complex and highly integrated photonics is directly impacted by the DSP and, again, is all intimately linked to the firmware. The module is no longer a lose collection of domains. The electrical, the photonics, the firmware and the module management are now a closely orchestrated system.
VIAVI have been involved with module test and development for over 20 years. As part of this, Viavi have always innovated and enhanced to ensure the ecosystem can be ready to accelerate development, debugging, validation and integration of pluggable optical modules. Late last year, we used our 100G electrical adapters to bring up the first samples of 800G modules and validate performance with live traffic, giving insight into error profiles – individual lane bit errors through bursts and even bit slips. Such insight is critical in ensuring the equalization and SI is optimal and this in turn is deeply linked with the DSP and module firmware.
The ONT family uniquely integrates a powerful range of integrated applications that allow close orchestration of the module control, high speed interface and photonic domains. Indeed, our ability to manage, manipulate and control the photonic signal is handled by our MAP product for both direct detect (PAM-4 – used in client optics) and coherent (used in ZR, ZR+ etc) modules.
Taking the complete approach, coupled with unique applications like dynamic skew, mean the module can be treated as an integrated optical system. Examples of where this is a must include optical power disruption (sometimes called service disruption). A running optical link has the optical signal disrupted triggering an LOS in the module. The module behavior during LOS can be validated (and debugged if required). As the optical signal is reasserted, does the module come correct out of the LOS state and how long does it take? Does it correctly bring up the data interface again? Can it self-recover? Or does it need external host management? All of this and more can be addressed by the ONT and MAP in an orchestrated manner.
Viavi have moved from the isolated test islands used at 100G and below – a separate BERT to test the host interface, an I^2C dongle to debug the firmware and an attenuator with fiber to validate the photonic interface to a deeply integrated approach required for the DSP based modules use at 400G and above.
MCS Test are the approved UK partner for Viavi
Content Source: Testing 800G Pluggable Modules – What’s All This Orchestrated Test Stuff? - VIAVI Perspectives (viavisolutions.com)