Application Layer: The application layer protocol defines a common specification of the Internet communications application. Each application layer protocol defines a client which requests the image server can send, in response to which the server can be returned to the client, the request packet and response packet field which has, for each field to achieve what function each meaning the value represented by a variety of fields.
Transport Layer: TCP and UDP transport layer protocol, the TCP protocol is a reliable transmission, retransmits the packet loss; unreliable UDP transmission, packet loss does not check.
Network Layer: The network layer protocol is responsible for forwarding packets different network segments and then choose the best path forward to packet network router forwards packets at different segments, select the path for the packet forwarding, so we called routers work in Network layer.
The data link layer: The data link layer protocol is responsible for transmitting data packets from one end to the other end of the link. Network devices connected by a cable or cables, connected to this network device is called a cable or a cable link. There are different mechanisms and methods on different uplink transmission data, which is different from the data link layer protocol, such as Ethernet using CSMA / CD protocol, point to point link using the PPP protocol.
Physical Layer: The physical layer defines the Network Device Interface Some characteristics related, standardized, such as shape, size, number and arrangement of pins, fixed and predetermined locking means, respective lines appearing interface cable interface, such as a voltage range, It can be considered a physical layer protocol.