ARQ

ARQ stands for Automatic Repeat reQuest and is a mechanism for requesting retransmission of lost or corrupted data. It is used across different network layers: at the network access/link layer (for example in wireless standards like 802.11) and at higher layers (for example TCP at the transport layer) to ensure reliability. For students in Audio/Video, Maker, and Web, ARQ is important because it affects how media and file data are reliably delivered — in some real-time A/V use cases ARQ can introduce latency, in maker/embedded contexts ARQ is used on serial or radio links to recover packets, and on the web retransmission is implemented by protocols (TCP/HTTP or application-level ARQ for custom transports).

Imagine you build an IoT camera (Maker) that streams live video to a web server (Web) and also uploads recorded clips for on-demand playback (Audio/Video). For live streaming you often choose UDP/RTP and avoid heavy ARQ because retransmissions create visible glitches; instead you may use FEC or selective NACKs for brief recovery. For uploading recorded video files you use TCP or an application-layer ARQ so every packet is guaranteed to arrive; if the camera connects over Wi‑Fi, the 802.11 link layer also performs ARQ (ACK and retry), while on wired Ethernet retransmissions are typically handled at higher layers. In a maker project where a microcontroller sends sensor data and thumbnails over a lossy radio or serial link (e.g., LoRa or UART), you implement a simple ARQ (ACK/NACK and resend) to ensure data integrity, balancing the extra latency and energy cost.