Be Ready for CPO: Integrating and Enhancing CPO Switches with SONiC

Author: Wataru Ishida, Software Engineer, NTT Devices; Yuki Arikawa, NTT Collection: 2024 OCP Global Summit - Networking

Summary

NTT presents the software challenges of supporting Co-Packaged Optics (CPO) switches in SONiC, drawing from their experience building an OIF IA-compliant CPO switch prototype. CPO switches place optical engines (OEs) directly around the switch ASIC rather than using pluggable front-panel transceivers, offering power savings through shorter electrical traces, a future-proof path beyond 200G/lane serdes rates, and potentially higher reliability via redundant external laser sources. However, CPO introduces significant NOS (Network Operating System) challenges that are not merely hardware issues -- they require fundamental changes to how SONiC manages transceivers.

The presentation identifies four key software challenges: (1) SPI support replacing I2C for optical engine management, requiring new CPLD kernel modules instead of the existing optoe module; (2) CMIS 3D addressing with bank switching for optical engines with 32+ lanes, which SONiC currently does not support since optoe only handles bank 0 for 8-lane transceivers; (3) OE-ELSFP coordination where the NOS must manage the physical fiber mapping between external laser sources and optical engines, handle shared laser channels across multiple ports, and take over transceiver firmware functions like laser activation during CMIS state machine transitions; and (4) the need for virtualized development environments, which NTT addressed by enabling xcvrd (the transceiver daemon) in the SONiC virtual switch environment for the first time.