H323 difference between tone ringback alert-no-pi and progress_ind setup?

[webstd.design]

What is the difference between tone ringback alert-no-pi and progress_ind setup?

[Evgeniy.Suvorov]

progress_ind

To set a specific progress indicator (PI) in call setup, progress, or connect messages from an H.323 VoIP gateway, use the progress_ind command in dial-peer configuration mode.

tone ringback alert-no-PI

To generate automatic ringback for the caller when no Progress Indicator (PI) alert has been received over the H.323 network, use the tone ringback alert-no-PI command in dial-peer configuration mode.