Offline Protocol Learning Center
Learn how mesh networks, Bluetooth Low Energy, offline sync, end-to-end encryption and device identity work. Other sections cover store-and-forward delivery, edge telemetry, location, embedded devices, and network outages.
Mesh networking
Mesh topologies, routing protocols, relays, hop limits, and phone meshes.
All 25 articles What is a mesh network?Devices that connect to their neighbours and relay for each other, with no single centre.→Mesh vs peer-to-peer vs client-serverA central server, direct links between equals, or peers that also relay.→Full mesh vs partial meshEvery node linked to every other, or each node linked to a few and relaying the rest.→What is a mobile ad hoc network (MANET)?Mobile devices that route for each other, with no fixed infrastructure.→Wireless mesh network vs mesh Wi-Fi at homeAccess points meshing for coverage, or devices relaying for each other.→
Bluetooth Low Energy
Advertising, GATT, MTU, range, battery, and platform rules on iOS and Android.
All 22 articles How does Bluetooth Low Energy work?The radio, advertising and scanning, connections, roles and GATT.→Bluetooth Classic vs Bluetooth Low EnergyTwo radios in one standard, and why phone-to-phone apps use the low energy one.→What is a BLE beacon?A one-way Bluetooth LE broadcast of an identifier, and what phones do with it.→BLE vs NFC vs UWBDiscovery and data, tap to share, or precise ranging, and how the three combine.→What is BLE advertising?The small broadcast packets that let Bluetooth LE devices find each other.→
Offline-first and sync
Offline sync, conflict resolution, consistency models, and sync engines.
All 20 articles How do apps work without internet?Local data, queued writes, sync on reconnect, and talking to nearby devices directly.→Offline-first vs local-firstTwo approaches to working offline, and where each keeps the source of truth.→How do you design an offline-first architecture?Local store first, a write strategy per action, a sync layer, and a clear authority.→Offline vs partitioned: what is the difference?No connection at all, or a network split into groups. Why apps should treat them apart.→What happens to a write made offline?The path of an offline change, from the local database to accepted or rejected.→
Local-first data
CRDTs, replicated documents, on-device storage, sharing, and deletion.
All 16 articles What is local-first software?Software that keeps your data on your devices first, and syncs as a helper.→What are the seven ideals of local-first software?The essay's seven goals for software that keeps your data yours, one by one.→What does "the device is the source of truth" mean?Why local-first apps treat the device copy as primary, and what servers do instead.→Local-first vs cloud-firstWhether the server or the device holds the copy that counts, and what follows.→Can local-first apps still have a backend?What servers are for in a local-first app, and how to keep the app working without them.→
Encryption and identity
Public keys, signatures, MLS, forward secrecy, and metadata.
All 23 articles What is end-to-end encryption?Only the sender and recipients hold the keys, whoever carries the message.→What are public and private keys?Two related keys, one shared and one secret, behind signatures and key agreement.→Encryption at rest vs in transitProtecting data on the move and data in storage, and what falls between.→What is a digital signature?Proof of who signed something and that it has not changed, and its limits.→How does end-to-end encryption work when there is no server?Key pairs, direct key exchange, and verifying keys when no directory exists.→
Offline authentication
Signed credentials, challenge-response, trust on first use, and revocation.
All 16 articles What is offline authentication?Verifying people and devices with no server, and what that can and cannot prove.→How can you verify someone with no internet?Keys and signed credentials set up in advance, a fresh challenge, and what stays unknown.→When is trust on first use (TOFU) safe?The one window TOFU leaves open, when that risk is acceptable, and how to close it.→Offline authentication vs offline authorizationWho someone is versus what they may do, and how each holds up with no server.→Does self-sovereign identity work offline?Which parts of a self-sovereign identity check work offline, and which do not.→
Delivery and store-and-forward
Outboxes, acknowledgments, retries, deduplication, relays, and receipts.
All 20 articles How does store-and-forward messaging work?Accept, store, wait for a path, hand over: the cycle behind email, brokers and meshes.→How does delay-tolerant networking (DTN) work?Bundles, contacts, convergence layers and custody: DTN from the specifications.→What is an outbox?Write first, send later: the durable queue that keeps unsent messages safe.→What is an acknowledgment (ACK)?How a receiver's confirmation drives retries, and why it is not the end of the story.→How does opportunistic networking move data?Store, carry, forward, and the rules for who gets a copy at each meeting.→
Telemetry and edge data
Edge telemetry, buffering, batching, MQTT, backhaul, and clock drift.
All 16 articles What is edge telemetry?Device-side events, metrics and logs, and how they get home through gaps.→What is edge computing?Doing the work near the data, from on-device code to computing in the access network.→What is backhaul?The link from a cell site, gateway or collector back to the core network.→Edge data vs cloud dataEdge data works offline and stays private; cloud data spans the fleet.→What is a telemetry event?The name, timestamp, attributes and source behind each record a device sends.→
Location and proof of location
GNSS, spoofing and jamming, indoor positioning, and proof of location.
All 16 articles How does GPS work?Satellites broadcast position and time; a receiver turns signal travel time into a fix.→What is GNSS?The family name for GPS, Galileo, GLONASS, BeiDou and the regional systems.→How do phones find their location without GPS?Wi-Fi, cell towers, beacons, Wi-Fi RTT and sensors, fused into one estimate.→What is indoor positioning?Finding a device inside a building with Wi-Fi, Bluetooth and UWB instead of satellites.→What is a geohash?A short string for a rectangle on the map, more precise with every character.→
Embedded and IoT
Microcontrollers, firmware, LoRa, Thread, Matter, Zigbee, and radio rules.
All 20 articles What is a microcontroller?A whole small computer on one chip, built to run one program inside a device.→What is firmware?The software stored in a chip that starts the device and runs its hardware.→What is a constrained device?Tight limits on memory, code, energy and links, and the IETF classes that describe them.→What is an ESP32?Espressif's family of microcontrollers with built-in Wi-Fi and Bluetooth radios.→What is an IoT gateway?The device that connects local sensors and controllers to an IP network or the cloud.→
Connectivity resilience
Direct links, outages, failover, congestion, Reticulum, and Nostr.
All 20 articles How does Wi-Fi Direct work?Discovery, choosing a group owner, and sockets, with no access point in between.→How does Wi-Fi Aware work?Clusters, publish and subscribe, then a direct data path with no access point.→What is Apple Multipeer Connectivity?Apple's framework for linking nearby Apple devices, deprecated in Xcode 27.→How does direct-to-phone satellite messaging work?Phone to satellite to ground gateway, and why it needs open sky and patience.→Can an iPhone and an Android phone connect directly without internet?Which radios an iPhone and an Android phone share, and which stay on one platform.→
Industry problems
Field operations, venues, machines, and evaluating offline software.
All 18 articles How do field teams communicate without coverage?Two-way radio, repeaters, satellite, deployable cell sites, and phone-to-phone data.→How do mines communicate underground?Leaky feeder, node-based mesh, MF and through-the-earth radio, and MINER Act tracking.→How do ships communicate at sea?GMDSS sea areas, VHF and satellite, AIS, and the records crews pass on board.→How do farms connect machines without cell coverage?ISOBUS on the machine, telematics off it, and what happens when the field has no signal.→How do warehouses and yards handle dead zones?More coverage, private cellular, and scan records that survive the gap.→