Internet Protocol layering and their service model

In order to provide a structure for the design of network protocols, network designers organize the protocols and the network hardware and software to implement these protocols in a layered (layer) way. Protocol layering is somewhat conceptual and structured. However, one potential disadvantage of layering is that a layer may repeat its lower level of functionality. For example, many protocol stacks provide error recovery based on both link and end-to-end scenarios. The second potential disadvantage is that a layer's functionality may require information that appears only on other layers (such as timestamps), which violates the goal of hierarchical separation.

Combining these together, all the protocols in each layer are called protocol stacks. The protocol stack of Internet consists of 5 layers: Physical layer, link layer, network layer, Transport layer and application layer.

　　

1. Application Layer

The application layer is where the network application and its application layer protocols persist. The application layer of the Internet includes many protocols, such as HTTP, SMTP, FTP, DNS, and so on. Application-layer protocols are distributed across multiple end systems, and applications in one-end systems use protocols that are grouped with application-switched information from another end system. We group this information in the application layer into messages.

2. Transport Layer

The Transport layer provides services that transfer application beginning between application (process) endpoints. In the Internet, there are two transport layer protocols, TCP and UDP. TCP provides connectivity-oriented services to its applications, providing reliability and traffic control. TCP also divides long messages into short messages and provides congestion control mechanisms. The UDP protocol provides no-connection services to its applications, provides no reliability, no traffic control, and congestion control. We call the transport layer grouped into message segments.

3. Network layer

The network layer is responsible for moving datagrams (Network layer groupings) from one host to another. The Transport layer protocol in the source host submits the transport beginning and destination addresses to the network layer. The network layer includes a well-known IP protocol that defines the fields in the datagram and how the end systems and routers act on those fields. There is only one IP protocol, so Internet components with a network layer must run the IP protocol. The network layer of the Internet also includes routing protocols that determine routes, which are transmitted from the source to the destination according to the route. Although the network layer includes the IP protocol and some routing protocols, it is often referred to only as the IP layer.

4. Link Layer

The network layer of the Internet sends packets between the source and destination through a series of routers. In order to move the grouping from one node (host or router) to the next node on the path, the network layer must rely on the service at the link layer. Especially at each node, the network layer passes the datagram down to the link layer, and the link layer routes the datagram to the next node along the path. At the next node, the link layer passes the datagram to the network layer. The services provided by the link layer depend on the specific link-layer protocol that is applied to the link. A link-layer grouping is called a frame.

5. Physical Layer

The task of the link layer is to move the entire frame from one network element to the neighboring network element, while the physical layer's task is to move one bit of the frame from one node to the next, whose protocol is related to the actual transmission medium.

Internet Protocol layering and their service model