Computer Networks Overview

Vocabulary flashcards covering OSI/TCP-IP models, layers, devices, and common protocols described in the notes.

OSI Model

Open Systems Interconnection model; a conceptual 7-layer framework for network communications.

TCP/IP Model

Four-layer model mapping OSI layers to Network Access, Internet, Transport, and Application.

Physical Layer (OSI)

Layer 1; transmits raw bits over physical media; defines cables, signaling, voltages.

Data Link Layer (OSI)

Layer 2; node-to-node delivery; uses MAC addresses; includes LLC and MAC sublayers; error detection with CRC; CSMA/CD in Ethernet.

Network Layer (OSI)

Layer 3; logical addressing and routing between networks; uses IP addresses; supports fragmentation.

Transport Layer (OSI)

Layer 4; end-to-end delivery; segmentation/reassembly; offers reliable TCP or best-effort UDP; flow control.

Session Layer (OSI)

Layer 5; manages sessions between applications; authentication/authorization; dialog control; NetBIOS, RPC, SMB.

Presentation Layer (OSI)

Layer 6; translates/formats data; encryption/decryption; compression; formats like JPEG, TLS conceptually.

Application Layer (OSI)

Layer 7; user-facing services; HTTP/HTTPS, DNS, SMTP, FTP, etc.

Network Access Layer (TCP/IP)

Combines OSI Physical and Data Link layers; handles access to the physical network (Ethernet, Wi‑Fi, ARP, PPP).

Internet Layer (TCP/IP)

Matches OSI Network Layer; handles logical addressing and routing (IPv4/IPv6, ICMP, IGMP; routing protocols).

Transport Layer (TCP/IP)

Same as OSI Transport; end-to-end delivery; TCP, UDP, SCTP.

Application Layer (TCP/IP)

Merges OSI Session/Presentation/Application; handles application processes and protocols (HTTP/HTTPS, DNS, SMTP, etc.).

NAT

Network Address Translation; converts private internal IP addresses to a public IP for Internet communication.

Firewall

Traffic-filtering device or feature that blocks/allows traffic by ports and protocols; can be hardware or software.

Router

Device that forwards packets between networks; uses routing tables; may include NAT and firewall functions.

Switch

Layer 2 device; connects many devices; uses MAC addresses to forward frames; can support VLANs (802.1Q).

Hub

Layer 1 device; repeats signals to all ports; creates shared collision domain; largely replaced by switches.

Bridge

Layer 2 device that connects two network segments and forwards frames between them.

Access Point

Wireless device that provides Wi‑Fi connectivity to a wired network.

NIC

Network Interface Card; hardware component that connects a device to the network.

Ethernet (IEEE 802.3)

Wired LAN standard; defines physical and data link layers; supports MAC addressing.

Wi‑Fi (IEEE 802.11)

Wireless LAN standard; defines PHY/MAC for wireless networks.

MAC Address

Hardware address assigned to a network interface at the data link layer.

IP Address

Logical address assigned to a device for IP networks; used for routing.

ARP

Address Resolution Protocol; maps IP addresses to MAC addresses on local networks.

ICMP

Internet Control Message Protocol; used for diagnostics and error reporting (e.g., ping).

IGMP

Internet Group Management Protocol; manages multicast group membership.

OSPF

Open Shortest Path First; interior gateway routing protocol using a link-state algorithm.

EIGRP

Enhanced Interior Gateway Routing Protocol; Cisco-proprietary routing protocol.

BGP

Border Gateway Protocol; inter-domain routing on the Internet; selects best paths between autonomous systems.

VLAN (802.1Q)

Virtual Local Area Network; logical segmentation of a LAN using tag-based switching.

DHCP Server

Dynamic Host Configuration Protocol server; automatically assigns IP addresses and network settings.

DNS

Domain Name System; resolves domain names to IP addresses.

HTTP/HTTPS

Hypertext Transfer Protocol; web communication; HTTPS adds TLS/SSL for security.

FTP/SFTP

File Transfer Protocol; FTP is insecure; SFTP provides secure file transfer over SSH.

SMTP/IMAP/POP3

Email protocols; SMTP for sending; IMAP/POP3 for receiving.

TLS/SSL

Encryption protocols for securing data in transit (TLS=successor to SSL; used in HTTPS).

Backbone Link

High-speed main connections between network segments (1–100 Gbps).