OSI Model – Core Vocabulary

30 English vocabulary flashcards covering key terms and concepts from the OSI Model lecture.

OSI Model

A seven-layer conceptual framework created by ISO in 1984 to standardize network communication functions.

International Organization for Standardization (ISO)

The standards body that developed the OSI model.

Application Layer (Layer 7)

Top OSI layer that provides network services directly to end-user applications (e.g., HTTP, FTP, SMTP).

Presentation Layer (Layer 6)

Handles data translation, encryption, and compression so the Application layer can understand incoming data.

Session Layer (Layer 5)

Establishes, manages, and terminates sessions between applications, providing dialogue control and synchronization.

Transport Layer (Layer 4)

Provides reliable or best-effort end-to-end data delivery, segmentation, flow and error control (e.g., TCP, UDP).

Network Layer (Layer 3)

Performs logical addressing and routing of packets across networks (e.g., IP, OSPF, BGP).

Data Link Layer (Layer 2)

Ensures reliable data transfer across a physical link; uses MAC addresses and framing (e.g., Ethernet, Wi-Fi).

Physical Layer (Layer 1)

Defines electrical, mechanical, and signaling specifications for transmitting raw bit streams over the medium.

Encapsulation

Process in which each OSI layer adds its header (and trailer, if applicable) to the data from the layer above.

Decapsulation

Reverse process of stripping headers/trailers as data ascends the OSI layers at the receiving host.

Protocol Data Unit (PDU)

Layer-specific data unit created after encapsulation (e.g., Segment, Packet, Frame).

Segment

Transport-layer PDU generated by TCP after adding its header to data.

Packet

Network-layer PDU formed when the IP header is added to a segment or datagram.

Frame

Data Link-layer PDU consisting of a packet plus link-layer header and trailer.

Bit

Smallest unit of data; the Physical layer transmits raw bits over the medium.

TCP (Transmission Control Protocol)

Connection-oriented, reliable Transport-layer protocol providing sequencing, acknowledgment, and flow control.

UDP (User Datagram Protocol)

Connectionless, best-effort Transport-layer protocol that offers low-latency delivery without reliability guarantees.

IP (Internet Protocol)

Network-layer protocol responsible for logical addressing and packet routing across interconnected networks.

MAC Address

Unique physical address assigned to a network interface card, used at the Data Link layer.

Router

Layer 3 device that forwards packets between networks based on IP addresses.

Switch

Layer 2 device that forwards frames within a local network based on MAC addresses.

Hub

Layer 1 device that broadcasts incoming bits to all connected ports without filtering.

Repeater

Layer 1 device that regenerates and amplifies signals to extend the physical network range.

Flow Control

Technique (e.g., sliding window) used mainly at the Transport layer to manage data transmission rate between hosts.

Congestion Control

Transport-layer mechanisms (e.g., TCP slow start) that reduce network congestion by adjusting send rates.

Logical Addressing

Use of IP addresses at the Network layer to uniquely identify hosts across networks.

Routing

Process of selecting a path for traffic across one or more networks, handled by the Network layer.

TCP/IP Model

Four-layer practical model (Application, Transport, Internet, Network Access) that dominates real-world networking.

Layered Troubleshooting

Diagnostic approach that isolates network problems by testing each OSI layer in sequence.