Introduction to tcp/IP

Process / Application Layer

The Application layer of the DoD model provides the following key capabilities:

• Enables applications to communicate between each other.
• Provides access to the services of the lower layers of the DoD model.

The Application layer of the DoD model is associated with the Session layer, Presentation layer, and Application layer of the OSI model.

The Host to Host Layer

The Host to Host, or transport layer of the DoD model manages the transportation of data, and establishes the connection between hosts to exchange already formatted data. This layer is associated with the Transport layer of the OSI model. The Host to Host layer is responsible for establishing communication channels between the Application layer and the lower layers.

The main CP/IP protocols that operate at the Transport layer are:

• Transmission Control Protocol (TCP): TCP offers greater reliability when it comes to transporting data than what UDP, the other TCP/IP protocol which works at this level provides. With TCP, the application which sends the data receives acknowledgement or verification that the data was actually received.
• User Datagram Protocol (UDP): UDP does not provide reliable data transport. No acknowledgements are transmitted.

The Internet Layer

The internetworking or Internet layer of the DoD model handles the packaging, addressing, and routing of data. The Internet layer of the DoD model relates to the OSI model's network layer. The Internet layer was initially defined to enable two computers to establish a connection to exchange data. The Internet layer formed the basis for internetworking or communication over the Internet. After the Network Interface layer receives data and translates it to signals on the physical medium, the Internet layer defines packaging, addressing, and routing of the data.

The main TCP/IP protocols that operate at the Internet layer are:

• Address Resolution Protocol (ARP)
• Internet Protocol (IP)
• Internet Control Message Protocol (ICMP)
• Internet Group Management Protocol (IGMP)