The Network Layer
The Network layer (Layer 3, typically IP) will receive a segment from the Transport layer (Layer 4, typically TCP or UDP), and will add its own header to it to create a packet. The size of the packet will thus always be the size of the segment plus the Network layer header, the same as when the next layer down (the Data Link layer, layer 2, typically Ethernet) encapsulates the packet into a frame for transmission.
A packet.A packet.A packet.A packet.
The PDU at the Network layer is referred to as a packet. A PDU at the Data Link Layer is referred to as a frame.
Network Layer
The network layer is responsible for addressing nodes in a logical way. It is also responsible for making decisions on routing a packet from one network to another. Without the network layer it would not be possible to send a packet outside of your own local network.
Frames are encapsulating packets. The data link layer makes framing and provide this service to the layer above layer "the network layer".
Network Control Protocol is uses to identify the Network layer protocol used in the packet
Frames are encapsulating packets. The data link layer makes framing and provide this service to the layer above layer "the network layer".
Because ICMP is on the network layer
its depend on which protocol used in transport layer
Network - Always identifies the final destination of a packet