OSI Open Systems Interconnection. A model used to
describe how network communication functions are
divided into layers.
OSI Model A layered conceptual framework that standardizes
how systems communicate across a network.
Layered model A design approach that separates complex
communication into smaller functional layers.
Seven layers The OSI Model has seven layers: Physical, Data
Link, Network, Transport, Session, Presentation, and
Application.
Physical Layer Layer 1. Converts data into physical signals and
transmits raw bits over media such as cable, fiber, or
radio.
Data Link Layer Layer 2. Provides local node-to-node delivery using
frames and MAC addressing.
Network Layer Layer 3. Provides logical addressing and routing
between networks.
Transport Layer Layer 4. Provides end-to-end communication
between hosts, including segmentation, reliability,
and flow control when required.
Session Layer Layer 5. Establishes, maintains, manages,
synchronizes, and terminates sessions between
applications.
Presentation Layer Layer 6. Formats, translates, encrypts, decrypts, and
compresses data so systems can understand it.
Application Layer Layer 7. Provides network services directly to user
applications.
, OSI & TCP/IP Networking Layers and Protocols | Complete Practice Questions & Verified Answers
Protocol Data Unit (PDU) The unit of data handled at a specific OSI layer.
Troubleshooting by layer A method of isolating network problems by
determining which OSI layer is failing.
Hardware independence The OSI Model describes communication functions
without depending on one vendor or hardware type.
Conceptual model The OSI Model explains functions. It does not
prescribe the physical layout of a LAN.
Application Layer vs End-user The OSI Application Layer provides network services
application to applications; it is not the application itself.
Layer order bottom-to-top Bottom-to-top is Physical through Application.
Layer order top-to-bottom Top-to-bottom is Application through Physical.
PDU vs Protocol A PDU is the data unit at a layer. A protocol is the rule
set that governs communication.
Network Layer vs Transport Layer Network chooses paths between networks. Transport
manages end-to-end delivery between hosts.
Presentation Layer vs Session Layer Presentation handles format/encryption/compression.
Session manages conversations and checkpoints.
Layer recognition Students must identify the seven OSI layers, their
order, their functions, and their associated data units.