Computer Networks: Transport Layer and Network Layer

The Internet's Protocol Layers

• The Internet is a network of networks, and it has multiple layers, including the application layer, transport layer, network layer, and link layer.

Transport Layer

• The transport layer transports application-layer messages between application endpoints.
• There are two transport protocols in the Internet: TCP and UDP.
• TCP provides a connection-oriented service to its applications.
• TCP's service includes guaranteed delivery of application-layer messages to the destination and flow control (sender/receiver speed matching).
• UDP provides a connectionless service to its applications.
• UDP's service has no reliability, no flow control, and no congestion control.

Network Layer

• The Internet's network layer is responsible for moving network-layer packets (datagrams) from one host to another.
• The Internet's network layer includes the IP protocol, which defines the fields in the datagram and how the end systems and routers act on these fields.
• The Internet's network layer also contains routing protocols that determine the routes that datagrams take between sources and destinations.
• There is only one IP protocol, and all Internet components that have a network layer must run the IP protocol.

Link Layer

• The link layer moves packets from one node (host or router) to the next node in the route.

Internet Standards

• Internet standards are developed by the Internet Engineering Task Force (IETF).
• IETF standards documents are called requests for comments (RFCs).
• RFCs define protocols such as TCP, IP, HTTP, and SMTP.

Application Layer

• The application layer is where network applications and their application-layer protocols reside.
• The Internet's application layer includes many protocols, such as HTTP, SMTP, and FTP.
• The application layer also includes protocols that provide specific network functions, such as the domain name system (DNS).