| Layer | Name | Common Protocols |
|---|---|---|
| 7 | Application | SSH, telnet, FTP |
| 6 | Presentation | HTTP, SMTP, SNMP |
| 5 | Session | RPC, Named Pipes, NETBIOS |
| 4 | Transport | TCP, UDP |
| 3 | Network | IP |
| 2 | Data Link | Ethernet |
| 1 | Physical | Cat-5 |
The functions of the seven layers of the OSI model are:
Layer Seven of the OSI Model
The Application Layer of the OSI model is responsible for providing end-user services, such as file transfers, electronic messaging, e-mail, virtual terminal access, and network management. This is the layer with which the user interacts.
Layer Six of the OSI Model
The Presentation Layer of the OSI model is responsible for defining the syntax which two network hosts use to communicate. Encryption and compression should be Presentation Layer functions.
Layer Five of the OSI Model
The Session Layer of the OSI model is responsible for establishing process-to-process commnunications between networked hosts.
Layer Four of the OSI Model
The Transport Layer of the OSI model is responsible for delivering messages between networked hosts. The Transport Layer should be responsible for fragmentation and reassembly.
Layer Three of the OSI Model
The Network Layer of the OSI model is responsible for establishing paths for data transfer through the network. Routers operate at the Network Layer.
Layer Two of the OSI Model
The Data Link Layer of the OSI model is responsible for communications between adjacent network nodes. Hubs and switches operate at the Data Link Layer.
Layer One of the OSI Model
The Physical Layer of the OSI model is responsible for bit-level transmission between network nodes. The Physical Layer defines items such as: connector types, cable types, voltages, and pin-outs.
