What protocol does PPP use to identify the Network layer protocol?

PPP, or Point-to-Point Protocol, utilizes Network Control Protocol (NCP) to identify and manage network layer protocols during its operation. NCP is essential because it allows PPP to support multiple network layer protocols by providing mechanisms for the configuration, enabling, and disabling of these protocols for the connection being established. When a PPP connection is initiated, NCP negotiates the specific network layer protocol that will be utilized, such as IP or IPX.

In the context of the other options:

• ISDN is a digital transmission protocol used in telecommunications, which does not interact specifically with the identification of network layer protocols.

• HDLC, while being a framing protocol that can be used in PPP, mainly deals with the data link layer and does not have a role in identifying network layer protocols.

• LCP stands for Link Control Protocol, which is used in PPP to establish, configure, and test the data link connection but not to identify the protocols at the network layer.

Understanding the distinction between these protocols highlights the role that NCP plays in PPP, confirming that it is indeed the correct answer for identifying network layer protocols.