Simultaneous substitution
（重定向自Signal replacement）
Simultaneous substitution (also known as simsubbing or signal substitution) is a practice mandated by the Canadian Radio-television and Telecommunications Commission (CRTC) requiring cable television, direct broadcast satellite (DBS), IPTV and MMDS television distribution companies in Canada to distribute the signal of a local or regional over-the-air station in place of the signal of a foreign or non-local television station, when the two stations are broadcasting identical programming simultaneously.