1.1 - Understanding the OSI Model: Professor Messer

Vocabulary flashcards covering OSI model concepts, layer functions, and common networking terms.

OSI model

Open Systems Interconnection reference model used to describe how data traverses a network; not a protocol suite, but applicable to many protocols (including TCP/IP).

Layer 7 – Application layer

Layer where user-facing applications operate; examples include HTTP, HTTPS, FTP, DNS, and POP3.

Layer 6 – Presentation layer

Layer responsible for data formatting, encryption/decryption, and character encoding; often discussed with layer 7.

Layer 5 – Session layer

Layer that manages sessions between devices, including initiation, maintenance, and termination of communication.

Layer 4 – Transport layer

Layer that transfers data between devices; protocols include TCP (reliable) and UDP (connectionless).

Layer 3 – Network layer

Layer that handles routing and forwarding using IP addresses, and can perform fragmentation of packets.

Layer 2 – Data Link layer

Layer that deals with MAC addresses and switching; frames are formed and forwarded based on MAC addresses.

Layer 1 – Physical layer

Layer that concerns the actual physical signals and transmission media (cables, fiber, air); no protocols at this layer.

Mnemonic: All People Seem To Need Data Processing

A phrase to memorize the OSI layer order from Application down to Physical (A, P, S, T, N, D, P).

MAC address

Media Access Control address; the hardware address of a network interface used by switches to forward frames.

DLC (Data Link Control)

The concept at Layer 2 associated with MAC addressing and the data link processes.

EUI-48 / EUI-64

Formats of hardware addresses (48-bit or 64-bit) used for MAC addresses.

Switching layer

Layer 2; switches forward traffic based on destination MAC addresses.

IP address

Layer 3 address used to route packets; supports IPv4 and IPv6.

Subnet mask

Defines the network portion of an IP address to determine the size of the destination network.

TCP

Transmission Control Protocol; reliable, connection-oriented transport at Layer 4.

UDP

User Datagram Protocol; connectionless, best-effort transport at Layer 4.

SSL/TLS

Encryption protocols used at the presentation layer (Layer 6) to secure data in transit.

HTTPS

HTTP over TLS/SSL; secure web traffic.

DNS

Domain Name System; translates human-readable domain names to IP addresses.

Wireshark

Network protocol analyzer that captures and decodes traffic, presenting data in layered views (frame, details, hex/ASCII).