Function open_session 

async fn open_session(
    link: MeshFrameLink,
    phy: UlcpDeviceConfig,
    target: PublicKey,
    greeting: Greeting,
) -> Result<Session>

Open the device handle at the far end of link.

Opening costs nothing on the air — the binding needs no session and the device is told nothing — so the only exchange here is the name, and only when one was asked for.