1.Transport: provides reliable or unreliable delivery and error recovery and flow control.
2. Network: provides logical addressing used by routers for path determination. Logical addressing is used to identify a host on a network (for example, by its IP address).
3. Data Link: combines packets into bytes and bytes into frames. Each frame has a header and a trailer. A header contains the source and destination MAC address. A trailer contains the Frame Check Sequence field, used for errors detection. The Data Link layer is divided into two sublayers:
Logical Link Control – used for flow control and error detection and
Media Access Control – used for hardware addressing and controlling the access method.
4. Physical: defines how to move bits from one device to another. It deals with the physical characteristics of the transmission medium, describing connectors, pins, cables, connectors, and network interface cards.