I'm not sure, I follow. I believe you describe what is often called equivalent-time sampling. That however obviously works only on strictly periodic signals. UDP packets would be a fairly large waveform, requiring a corresponding large buffer and they would have to be repeated with very precise timing. Further, I don't see the need for such an absurd high sampling rate for signals transmitted at a mere 5Gbps (50GSps - itself a pretty high sampling rate - should be plenty). I sense some confusion.