OSI (Open System Interconnection) is one of computer network architecture developed by International Standard Organization (ISO). This model idea is dividing computer network components into 7 layers. Each layer performs a subset of the required communication function and relies on the next lower layer to perform more primitive function. Hence, the lower layer provides services to the next higher layer. Changes in one layer should not require changes in other layer (each layer has an independent function).
Here are the layers from the highest to the lowest:
1. Application Layer
Means for application to access OSI environment hence all network resources can be accessed by the computer applications.
2. Presentation Layer
Performs data formatting, coding, compression, and encryption.
3. Session Layer
Controls of dialogues between application (session), maintain dialogue discipline, grouping, and recovery.
4. Transport Layer
Performs exchange of data between end system (process-to-process message delivery) and maintain quality of data service. The data should be error free, in sequence, no losses, no duplicates.
5. Network Layer
Transports of information so the higher layers do not need to know about underlying technology (Not need on direct links). Move packets from source to destination.
6. Data Link Layer
Performs activating, maintaining, and deactivating a reliable link (hop-to-hop delivery). Provide an error detection control in data transfer so the higher layers may assume the error free transmission. Data Link also organizing the on-out bits into frames.
7. Physical Layer
Represents an interface between computer and network devices. Performs such these functions:
- Mechanical
- Electrical
- Functional
- Procedural
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