The OSI Model defines seven layers that data must pass through to travel from one device to another over a network. Layer 1 is the Physical layer defining hardware connections and signals. Layer 2 is the Data Link layer which assigns protocols and transmits frames between nodes. Layer 3, the Network layer, determines how data will be sent to the recipient. The remaining layers establish communication sessions, handle error checking and data flow, convert data to standard formats, and enable applications to transfer files and messages.

1. The OSI Model
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2. What is the OSI Model
• OSI – Open System Interconnection
• A set of seven layers that define the
different stages that data must go through
to travel from one device to another over a
network.

4. The Layers
• Layer 7: Application - This is the layer
that actually interacts with the operating
system or application whenever the user
chooses to transfer files, read messages
or perform other network-related activities.
• Layer 6: Presentation - Layer 6 takes the
data provided by the Application layer and
converts it into a standard format that the
other layers can understand.

5. The Layers (cont.)
• Layer 5: Session - Layer 5 establishes,
maintains and ends communication with
the receiving device.
• Layer 4: Transport - This layer maintains
flow control of data and provides for error
checking and recovery of data between
the devices.

6. The Layers (cont.)
• Layer 3: Network - The way that the data
will be sent to the recipient device is
determined in this layer.
• Layer 2: Data Link - In this layer, the
appropriate physical protocol is assigned
to the data. Also, the frames are
transmitted from node to node based on
station address.

7. The Layers (cont.)
• Layer 1: Physical - This is the level of the
actual hardware. It defines the physical
characteristics of the network such as
connections, voltage levels and timing.