Hi @Umesh ,
IPS means Intrusion Prevention System.
This is to protect Intruder from damaging internal network. Thats why its call "intrusion" = incoming.
WAN > DMZ - Protect DMZ from WAN
WAN > LAN - Protect LAN from WAN
LAN > DMZ - Protect DMZ from LAN
IPS commonly apply to policy that hitting servers.
However, IPS also can block botnet&CC if apply on LAN> WAN.