Transceivers are the components that convert electrical signals from the switch or network adapter into optical (light) signals that travel through the fiber optic cable, and vice versa on the receiving end. Every port on a switch or ConnectX adapter that connects to a fiber cable needs a transceiver plugged into it.
Nokia PoC (Proof of Concept)
Nokia wants to come to your datacenter and test their OSFP transceivers with your B300 servers. Transceivers are vendor-agnostic in theory, but in practice you need to validate that a specific vendor’s transceivers work properly with specific switch and NIC hardware. That’s what a PoC is for — Nokia wants to prove their transceivers are compatible and perform well with the B300 setup before you’d consider buying them at scale.