| OSI Model | ||||
|---|---|---|---|---|
| Layer | Protocol data unit (PDU) | Function | Examples | |
| Host layers | 7. Application | Data | Human-computer interaction layer, where applications can access the network services. High-level APIs, including resource sharing, remote file access, directory services and virtual terminals. |
|
| 6. Presentation | Data | Ensures that data is in a usable format and is where data encryption occurs. Translation of data between a networking service and an application; including character encoding, data compression and encryption/decryption. |
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| 5. Session | Data | Maintains connections and is responsible for controlling ports and sessions. Managing communication sessions, i.e. continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes. |
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| 4. Transport | Segment (TCP) /
Datagram (UDP) |
Transmits data using transmission protocols including TCP and UDP. Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing. |
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| Media layers | 3. Network | Packet | Decides which physical path the data will take. Structuring and managing a multi-node network, including addressing, routing and traffic control. |
|
| 2. Data link | Frame | Defines the format of data on the network. Reliable transmission of data frames between two nodes connected by a physical layer. |
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| 1. Physical | Bit | Transmits raw bit stream over the physical medium. Transmission and reception of raw bit streams over a physical medium. |
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