DoD model
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The DoD model (DoD, Department of Defense) is a layered abstract description for communications and computer network protocol design. It was created in the 1970s by DARPA for use in developing the Internet's protocols, and the structure of the Internet is still closely reflected by the DoD model.
The DoD model has four layers:
- Layer 4 - Process Layer or Application Layer - This is where the "higher level" protocols such as SMTP, FTP, SSH, HTTP, etc. operate.
- Layer 3 - Host-To-Host (Transport) - This is where flow-control and connection protocols exist, such as TCP. This layer deals with opening and maintaining connections, ensuring that packets are in fact received.
- Layer 2 - Internet or Internetworking Layer - This layer defines IP numbers, with many routing schemes for navigating packets from one IP address to another.
- Layer 1 - Network Access - This layer describes the physical equipment necessary for communications, for example the MAC addresses of the network cards in an Ethernet.