1644 IoT Glossary: A-F
Essential IoT Terms from ACL to Frame
This is Part 1 of the IoT Glossary, covering terms A-F. See also:
- IoT Glossary Index - Overview and quick navigation
- Glossary G-P - Gateway through Publisher
- Glossary Q-Z - QoS through 6LoWPAN
1644.1 Learning Objectives
After reviewing this section, you should be able to:
- Define key IoT terms from A to F with technical accuracy
- Distinguish between commonly confused concepts (e.g., ACL vs. RBAC, edge vs. fog computing)
- Use appropriate terminology when discussing IoT protocols, architectures, and security
- Identify related concepts and navigate cross-references effectively
1644.2 A
1644.2.1 ACL (Access Control List)
Definition: A security mechanism that specifies which users, devices, or systems are granted or denied access to particular resources, and what operations they can perform.
In simple terms: A list that says who can do what - like a VIP list for a club that specifies which guests can enter which rooms.
Common confusions: - ACL vs. RBAC (Role-Based Access Control) - ACLs are resource-centric while RBAC is role-centric - ACLs define permissions per resource, not per user globally
Related terms: Authentication, Authorization, OAuth
Synonyms: access list, permission list
1644.2.2 Acknowledgment (ACK)
Definition: A signal or message sent by a receiving device to confirm successful receipt of data, enabling the sender to know transmission was successful.
In simple terms: A “message received” confirmation - like texting “got it” when someone sends you important information.
Common confusions: - ACK vs. response - ACK confirms receipt, response contains actual reply data - Different protocols implement ACKs differently (TCP vs. UDP)
Related terms: QoS, At-least-once, Retry
Synonyms: ACK, confirmation
1644.2.3 Actuator
Definition: A device that converts electrical signals or energy into physical action, enabling IoT systems to affect the physical world through motion, heat, light, or other outputs.
In simple terms: The “muscles” of an IoT system - while sensors are the eyes and ears, actuators are the hands that actually do things like turn on lights or open valves.
Common confusions: - Actuator vs. sensor - sensors read data, actuators perform actions - Not all output devices are actuators (displays show data but don’t perform physical actions)
Related terms: Sensor, GPIO, DAC
Synonyms: effector, output device
1644.2.4 ADC (Analog-to-Digital Converter)
Definition: An electronic circuit that converts continuous analog signals (like voltage from a sensor) into discrete digital values that can be processed by a microcontroller.
In simple terms: A translator that converts real-world measurements (like temperature as voltage) into numbers a computer can understand.
Common confusions: - ADC resolution (bits) determines precision, not accuracy - Sampling rate and resolution are independent specifications
Related terms: DAC, Sensor, GPIO, Sampling
Synonyms: A/D converter, analog-digital converter
1644.2.5 Aggregation
Definition: The process of combining multiple data points into summary statistics (sum, average, min, max, count) to reduce data volume while preserving meaningful information.
In simple terms: Summarizing lots of small measurements into useful totals - like calculating your average daily steps from thousands of individual step counts.
Common confusions: - Aggregation loses individual data points (cannot recover original values) - Different aggregation functions suit different use cases (average vs. sum vs. max)
Related terms: Time Series, Sampling, Telemetry
Synonyms: summarization, rollup
1644.2.6 AMQP (Advanced Message Queuing Protocol)
Definition: An open standard application layer protocol for message-oriented middleware, providing reliable queuing, topic-based publish-subscribe, flexible routing, and transactions.
In simple terms: A sophisticated postal system for software - it ensures messages get delivered reliably with options for different delivery patterns and confirmations.
Common confusions: - AMQP vs. MQTT - AMQP is more feature-rich but heavier; MQTT is simpler and lighter - AMQP 0.9.1 (RabbitMQ) vs. AMQP 1.0 are quite different protocols
Related terms: MQTT, Broker, Publisher, Subscriber
Synonyms: none common
1644.2.7 API (Application Programming Interface)
Definition: A set of defined rules, protocols, and tools that specify how software components should interact, enabling different applications to communicate and share data.
In simple terms: A menu at a restaurant - it tells you what you can order (available functions) and how to order it (required format), without needing to know how the kitchen works.
Common confusions: - API vs. SDK - API defines the interface, SDK provides tools to use it - REST API vs. API - REST is one style of API, not all APIs are RESTful
Related terms: REST, HTTP, Microservices
Synonyms: interface, service endpoint
1644.2.8 At-least-once
Definition: A message delivery guarantee where messages are delivered one or more times, ensuring no message loss but potentially causing duplicates that receivers must handle.
In simple terms: “Better safe than sorry” delivery - the system keeps trying until it’s sure you got the message, even if that means sending it twice.
Common confusions: - At-least-once requires idempotent receivers to handle duplicates properly - More reliable than at-most-once but less than exactly-once
Related terms: QoS, At-most-once, Exactly-once, Idempotency
Synonyms: QoS 1 (in MQTT)
1644.2.9 At-most-once
Definition: A message delivery guarantee where messages are delivered zero or one time, providing best-effort delivery without retries, which may result in message loss.
In simple terms: “Fire and forget” delivery - send the message once and hope it arrives, like shouting across a noisy room.
Common confusions: - At-most-once is not unreliable by design - it’s appropriate for frequent, non-critical data - Often used for high-frequency sensor data where occasional loss is acceptable
Related terms: QoS, At-least-once, Exactly-once
Synonyms: QoS 0 (in MQTT), best-effort delivery
1644.2.10 Authentication
Definition: The process of verifying the identity of a user, device, or system, typically through credentials like passwords, certificates, tokens, or biometrics.
In simple terms: Proving who you are - like showing your ID at a security checkpoint before being allowed in.
Common confusions: - Authentication vs. authorization - authentication proves identity, authorization grants permissions - Strong authentication often requires multiple factors (MFA)
Related terms: Authorization, Certificate, Token, OAuth
Synonyms: identity verification, login
1644.3 B
1644.3.1 Backoff
Definition: A strategy for handling failed operations by waiting increasingly longer periods before retrying, typically using exponential growth to reduce system load during failures.
In simple terms: Being patient when something fails - instead of repeatedly hammering a locked door, wait longer between each attempt to give the system time to recover.
Common confusions: - Exponential backoff vs. linear backoff - exponential grows faster (1s, 2s, 4s, 8s) - Jitter (randomization) is often added to prevent thundering herd problems
Related terms: Retry, Circuit Breaker
Synonyms: exponential backoff, retry delay
1644.3.2 Bandwidth
Definition: The maximum rate of data transfer across a network path, measured in bits per second (bps), kilobits (kbps), megabits (Mbps), or gigabits (Gbps).
In simple terms: The width of a pipe - a wider pipe (more bandwidth) lets more water (data) flow through at once.
Common confusions: - Bandwidth vs. throughput - bandwidth is capacity, throughput is actual achieved rate - Bandwidth vs. latency - bandwidth is how much, latency is how fast
Related terms: Latency, Throughput, Jitter
Synonyms: data rate, capacity, speed
1644.3.3 BLE (Bluetooth Low Energy)
Definition: A wireless personal area network technology designed for short-range communication with minimal power consumption, operating in the 2.4 GHz ISM band with range up to 100m.
In simple terms: Energy-efficient Bluetooth - designed so small devices like fitness trackers can communicate wirelessly while running on tiny batteries for months or years.
Common confusions: - BLE vs. Bluetooth Classic - BLE is optimized for low power, Classic for continuous streaming - BLE is not backward compatible with Bluetooth Classic
Related terms: Zigbee, Thread, Mesh
Synonyms: Bluetooth Smart, Bluetooth 4.0+
1644.3.4 Broker
Definition: A middleware server that receives messages from publishers and routes them to appropriate subscribers based on topics or other criteria in publish-subscribe messaging systems.
In simple terms: A post office for IoT messages - it receives mail (messages) from senders and delivers it to everyone who signed up to receive that type of mail (subscribers).
Common confusions: - Broker vs. queue - broker routes messages, queues store them - Brokers can cluster for high availability and scalability
Related terms: MQTT, Publisher, Subscriber, Topic
Synonyms: message broker, MQTT broker
1644.4 C
1644.4.1 CBOR (Concise Binary Object Representation)
Definition: A binary data serialization format designed to be extremely compact and efficient, based on JSON’s data model but optimized for constrained environments and IoT devices.
In simple terms: Compressed JSON - takes the same information as JSON but packs it into a smaller, faster-to-process binary format perfect for devices with limited resources.
Common confusions: - CBOR vs. JSON - CBOR is binary (smaller, faster), JSON is text (human-readable) - CBOR is used with CoAP, while JSON is typically used with HTTP
Related terms: JSON, Protobuf, Serialization, CoAP
Synonyms: none common
1644.4.2 Certificate
Definition: A digital document that uses cryptographic signatures to bind a public key to an identity, enabling secure authentication and encrypted communication in TLS/SSL.
In simple terms: A digital ID card - like a passport that proves your identity, issued by a trusted authority (Certificate Authority) that vouches for who you are.
Common confusions: - Certificate vs. private key - certificate is public, private key must stay secret - Self-signed vs. CA-signed certificates - self-signed aren’t trusted by default
Related terms: TLS, Authentication, Encryption
Synonyms: X.509 certificate, digital certificate, SSL certificate
1644.4.3 Channel
Definition: A logical or physical pathway for communication between devices, which may refer to radio frequency channels, communication ports, or logical message streams.
In simple terms: A TV channel for data - different channels carry different information, and devices tune to specific channels to send or receive data.
Common confusions: - Physical channel (radio frequency) vs. logical channel (message stream) - Channel overlap in Wi-Fi can cause interference
Related terms: Topic, Bandwidth, Frequency
Synonyms: communication channel, frequency band
1644.4.4 Circuit Breaker
Definition: A design pattern that prevents cascading failures by monitoring for failures and temporarily stopping requests to failing services, allowing them time to recover.
In simple terms: A safety switch for software - like an electrical breaker that trips when there’s too much load, it stops sending requests to overwhelmed services to prevent total system collapse.
Common confusions: - Circuit breaker vs. retry - circuit breaker prevents retries during known failures - States: closed (normal), open (failing), half-open (testing recovery)
Related terms: Retry, Backoff, Dead Letter Queue
Synonyms: failure circuit, stability pattern
1644.4.5 Cloud
Definition: Remote computing infrastructure accessed over the internet that provides on-demand computing resources, storage, and services without direct management by the user.
In simple terms: Someone else’s computer that you rent - instead of buying servers, you use shared computing resources over the internet and pay for what you use.
Common confusions: - Cloud vs. edge - cloud is remote/centralized, edge is local/distributed - Public cloud vs. private cloud vs. hybrid cloud architectures
Related terms: Edge Computing, Fog Computing, Platform
Synonyms: cloud computing, cloud services
1644.4.6 CoAP (Constrained Application Protocol)
Definition: A specialized web transfer protocol designed for constrained devices and networks, using UDP for lightweight request/response communication with built-in discovery and multicast support.
In simple terms: HTTP’s smaller sibling - does similar things (GET, PUT, POST) but is designed to work on tiny devices with limited memory and battery over unreliable networks.
Common confusions: - CoAP uses UDP (not TCP like HTTP), making it lighter but requiring application-level reliability - CoAP is request/response while MQTT is publish/subscribe
Related terms: HTTP, MQTT, 6LoWPAN, DTLS
Synonyms: none common
1644.4.7 Compression
Definition: The process of encoding data to reduce its size for storage or transmission, using algorithms that eliminate redundancy while allowing recovery of original data.
In simple terms: Packing a suitcase efficiently - arranging data to take up less space, like vacuum-sealing clothes so you can fit more in your luggage.
Common confusions: - Lossless vs. lossy compression - lossless recovers exact data, lossy discards some - Compression adds CPU overhead - trade-off between bandwidth and processing
Related terms: Payload, CBOR, Serialization
Synonyms: data compression, encoding
1644.5 D
1644.5.1 DAC (Digital-to-Analog Converter)
Definition: An electronic circuit that converts digital values from a microcontroller into continuous analog signals, enabling digital systems to control analog devices.
In simple terms: The reverse of ADC - converts computer numbers back into real-world signals, like turning a volume number into actual sound levels.
Common confusions: - DAC vs. PWM - DAC produces true analog, PWM simulates analog through fast switching - DAC resolution affects output precision
Related terms: ADC, Actuator, GPIO
Synonyms: D/A converter, digital-analog converter
1644.5.2 Data Lake
Definition: A centralized repository that stores vast amounts of raw data in native format until needed, supporting diverse data types and enabling flexible analysis without predefined schemas.
In simple terms: A massive storage pool - dump all your data in its original form, figure out how to use it later, like keeping everything in a warehouse rather than organizing it into specific shelves.
Common confusions: - Data lake vs. data warehouse - lakes store raw data, warehouses store processed/structured data - Data lakes can become “data swamps” without proper governance
Related terms: ETL, TSDB, Telemetry
Synonyms: raw data repository
1644.5.3 DDS (Data Distribution Service)
Definition: A middleware protocol and API standard for real-time publish-subscribe communication, providing fine-grained QoS policies and designed for mission-critical systems.
In simple terms: Industrial-strength messaging - designed for systems where milliseconds matter and failures aren’t an option, like autonomous vehicles or medical devices.
Common confusions: - DDS vs. MQTT - DDS offers more QoS options and is broker-optional - DDS is peer-to-peer capable, MQTT requires a broker
Related terms: MQTT, AMQP, QoS, Publisher
Synonyms: OMG DDS
1644.5.4 Dead Letter Queue
Definition: A service queue that stores messages that cannot be delivered or processed successfully, allowing later analysis, reprocessing, or manual intervention for failed messages.
In simple terms: A “lost and found” for messages - when a message can’t be delivered, it goes here instead of disappearing, so you can investigate what went wrong.
Common confusions: - DLQ vs. retry queue - DLQ holds permanently failed messages, retry queue holds temporary failures - Messages in DLQ need manual intervention or automated remediation
Related terms: Retry, Circuit Breaker, Broker
Synonyms: DLQ, poison queue, error queue
1644.5.5 Digital Twin
Definition: A virtual representation of a physical device, system, or process that mirrors real-world behavior through synchronized sensor data, enabling simulation, analysis, and optimization.
In simple terms: A virtual clone - a digital copy of a real thing that updates in real-time, letting you test changes or predict problems without touching the actual device.
Common confusions: - Digital twin vs. simulation - twins sync with real data, simulations use models - Digital twins require continuous data connection to their physical counterpart
Related terms: Telemetry, Platform, Edge Computing
Synonyms: virtual twin, device shadow (AWS)
1644.5.6 DTLS (Datagram Transport Layer Security)
Definition: A security protocol providing TLS-equivalent encryption and authentication for datagram protocols like UDP, designed to protect CoAP and other UDP-based IoT communications.
In simple terms: Security for UDP - since TLS only works with TCP, DTLS was created to provide the same protection for connectionless protocols used by many IoT devices.
Common confusions: - DTLS vs. TLS - DTLS works with UDP, TLS requires TCP - DTLS handles packet loss and reordering that UDP doesn’t prevent
Related terms: TLS, CoAP, Encryption, Certificate
Synonyms: none common
1644.6 E
1644.6.1 Edge Computing
Definition: A distributed computing paradigm that processes data near the source of generation rather than in a centralized data center, reducing latency and bandwidth requirements.
In simple terms: Computing at the source - instead of sending all data to a distant cloud, process it locally where it’s created, like having a smart assistant in each room rather than one in a faraway call center.
Common confusions: - Edge vs. fog - edge is at devices, fog is between edge and cloud - Edge doesn’t eliminate cloud, it complements it
Related terms: Fog Computing, Cloud, Gateway, Latency
Synonyms: edge processing, local computing
1644.6.2 Encryption
Definition: The process of encoding data using cryptographic algorithms so that only authorized parties with the correct decryption key can access the original information.
In simple terms: A secret code - scrambles your message so only someone with the right key can read it, like a lockbox that only opens with your key.
Common confusions: - Encryption at rest vs. in transit - different protection for stored vs. moving data - Symmetric vs. asymmetric encryption serve different purposes
Related terms: TLS, DTLS, Certificate, Authentication
Synonyms: encoding, ciphering
1644.6.3 ETL (Extract, Transform, Load)
Definition: A data integration process that extracts data from sources, transforms it to fit operational needs (cleaning, formatting, aggregating), and loads it into a destination database.
In simple terms: Data processing pipeline - grab raw data, clean it up and reshape it, then store it where it’s needed, like sorting mail, organizing it by category, and delivering to the right mailboxes.
Common confusions: - ETL vs. ELT - ETL transforms before loading, ELT loads raw then transforms - ETL is batch-oriented, streaming alternatives exist for real-time needs
Related terms: Data Lake, TSDB, Aggregation
Synonyms: data pipeline, data integration
1644.6.4 Exactly-once
Definition: A message delivery guarantee ensuring each message is processed exactly one time - never lost and never duplicated - requiring sophisticated coordination between systems.
In simple terms: Perfect delivery - the message arrives once and only once, like registered mail with confirmation that prevents both loss and duplicate delivery.
Common confusions: - True exactly-once is extremely difficult and often impossible across distributed systems - Most “exactly-once” implementations are actually at-least-once with deduplication
Related terms: QoS, At-least-once, At-most-once, Idempotency
Synonyms: QoS 2 (in MQTT), exactly-once semantics
1644.7 F
1644.7.1 Filter
Definition: A mechanism that selectively passes or blocks messages based on specified criteria such as topic patterns, content attributes, or metadata properties.
In simple terms: A message sieve - only lets through messages you care about, like email filters that sort important messages from spam.
Common confusions: - Topic filters vs. content filters - topic filters match message routing, content filters inspect payload - Filter syntax varies by protocol (MQTT wildcards vs. AMQP routing keys)
Related terms: Topic, Subscription, Wildcard
Synonyms: message filter, selector
1644.7.2 Firewall
Definition: A network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules, creating a barrier between trusted and untrusted networks.
In simple terms: A security guard for your network - checks everyone trying to enter or leave and only allows those who meet the rules to pass through.
Common confusions: - Firewall vs. NAT - firewall filters traffic, NAT translates addresses (though often combined) - Hardware vs. software firewalls serve different deployment needs
Related terms: ACL, Encryption, TLS
Synonyms: network firewall, packet filter
1644.7.3 Fog Computing
Definition: A decentralized computing infrastructure extending cloud capabilities to the network edge, providing intermediate processing, storage, and networking between IoT devices and centralized cloud.
In simple terms: A middle layer between devices and cloud - like regional distribution centers between factories and central warehouses, processing some things locally without going all the way to headquarters.
Common confusions: - Fog vs. edge - fog is in network infrastructure (routers, gateways), edge is at end devices - Fog computing was coined by Cisco, edge computing is more general
Related terms: Edge Computing, Cloud, Gateway
Synonyms: fog networking, edge-cloud continuum
1644.7.4 Frame
Definition: A data unit at the data link layer (Layer 2) containing header information, payload data, and error-checking trailer used for transmitting packets across physical network segments.
In simple terms: An envelope for network data - wraps the actual message (packet) with addressing and error-checking information needed for local network delivery.
Common confusions: - Frame vs. packet - frames are Layer 2 (local network), packets are Layer 3 (routed network) - Frame size limits (MTU) affect how packets are fragmented
Related terms: Packet, Payload, MTU
Synonyms: data frame, Layer 2 PDU
1644.8 Summary
This section covered 32 essential IoT terms from A through F:
| Category | Terms | Examples |
|---|---|---|
| Security | 8 | ACL, Authentication, Authorization, Certificate, Encryption, Firewall |
| Protocols | 6 | AMQP, CoAP, BLE, DDS, DTLS |
| Architecture | 5 | Broker, Cloud, Edge Computing, Fog Computing, Digital Twin |
| Data | 5 | Aggregation, CBOR, Compression, Data Lake, ETL |
| Reliability | 5 | ACK, At-least-once, At-most-once, Exactly-once, Backoff, Circuit Breaker |
| Hardware | 3 | Actuator, ADC, DAC |
| Networking | 4 | Bandwidth, Channel, Filter, Frame |
1644.9 What’s Next
Continue to Glossary G-P for terms from Gateway through Publisher, including key protocols (HTTP, MQTT), hardware interfaces (GPIO, I2C, SPI), and networking concepts (Jitter, Latency, Mesh).