To answer this question, you need to understand what a network protocol is. A network protocol is a set of rules that governs the communication between devices in a network.
Let's go through each option to understand why it is correct or incorrect:
Option A) HTTP - This option is a network protocol. HTTP stands for Hypertext Transfer Protocol, and it is used for transmitting hypertext over the internet.
Option B) RIP - This option is a network protocol. RIP stands for Routing Information Protocol, and it is used for exchanging routing information between routers in a network.
Option C) PIM - This option is a network protocol. PIM stands for Protocol Independent Multicast, and it is used for efficient multicast routing in a network.
Option D) PSI - This option is not a network protocol. PSI does not stand for any commonly known network protocol. Therefore, it is not a valid network protocol.
The correct answer is option D) PSI. This option is not a network protocol because it does not represent any commonly known network protocol.