15.3 XON and XOFF

Command: xon

(C-a q, C-a C-q)
Send a ^Q (ASCII XON) to the program in the current window. Redundant if flow control is set to ‘off’ or ‘auto’.

Command: xoff

(C-a s, C-a C-s)
Send a ^S (ASCII XOFF) to the program in the current window.