Glossary

Radio and air protocol

NPR — New Packet Radio. Open data-radio protocol designed by Guillaume F4HDK for amateur 70 cm use. Carries IPv4 over a master-controlled TDMA channel on SI4463-class radios. PacketRF is one implementation of NPR; the original F4HDK firmware is another.

Master — the central NPR station that controls timing on the channel, publishes the slot allocation, and admits clients. There is exactly one master per NPR network.

Slave / client — an NPR station connected to a master. There can be several clients per master (today, up to seven; the protocol roadmap allows more).

Radio network ID — the NPR equivalent of CTCSS. A short identifier that lets two networks share a frequency without listening to each other. Use a different ID for any two networks that are physically near each other.

TDD — time division duplex. Master and clients transmit on the same frequency, taking turns. NPR uses TDD by default; an optional FDD-style operation exists in the original specification for special cases.

TDMA — time division multiple access. The mechanism by which several clients share one channel by transmitting in distinct time slots. NPR's TDMA is managed — the master allocates the slots explicitly rather than letting clients self-schedule.

TDMA frame — one full cycle of the schedule. Duration depends on the modulation profile (≈ 80 ms to ≈ 560 ms in the standard set).

Microslot — the smallest unit of allocation inside a TDMA frame. Each TDMA frame has a short reduced microslot at the start (for the allocation frame) plus seventeen regular microslots that the master hands out to clients.

Timeslot (slot) — one contiguous block of microslots assigned to one client.

Allocation frame — the short broadcast at the start of every TDMA frame in which the master publishes the current schedule. NPR protocol ID 0x1F, broadcast destination client ID 0x7F.

Fast mode — the master is giving this client at least one transmit opportunity per TDMA frame. The mode you want for interactive use.

Slow mode — the master is only giving this client a slot on the multiframe cadence, by default once every eight TDMA frames (x8). The client is fully connected; airtime is just sparse.

Multiframe — sparse scheduling for low-demand clients. Keeps the client connected and synchronized, but the uplink opportunity arrives only every N TDMA frames.

TOP — synchronization marker carried in the TDMA byte. Clients lock to the master's timing through it.

TA / Timing advance — the master's correction of a client's perceived slot start, applied so uplink bursts from far-away clients arrive in the right place despite propagation delay.

WHO — periodic broadcast in which the master (and connected clients) advertise callsigns and a small amount of identifying information. Required by amateur regulations and used by PacketRF as the basis of the neighbor cache.

Modulation profile — one of the standardized NPR settings (11 through 14 in 2GFSK, 20 through 24 in 4GFSK) that simultaneously selects symbol rate, modulation, raw bitrate, channel bandwidth and TDMA frame length. See Modulation Profiles.

Segmentation boundary — the IP packet size at which NPR has to split a packet into more than one radio frame, currently 252/253 bytes. Crossing this boundary roughly doubles per-packet airtime.

IP and addressing

Pseudo-bridge — the design choice that all NPR modems on one network behave like one big Ethernet switch from the IP point of view. Implemented through proxy ARP rather than through actual Ethernet broadcast. See Interface and Addressing Model and the uart.cz article.

Proxy ARP / PARP — the technique where a modem answers ARP requests on behalf of remote hosts, so the local host can keep treating the NPR subnet as one flat segment. Standardized as RFC 1027.

Pool — a named, configured IPv4 range inside PacketRF. The pool manager is the single source of address assignment for USB, PPP, master-side NPR allocation, and (in the future) DHCP. Pools are either static (range configured directly) or dynamic (range published at runtime by a source interface, typically np2 on a slave).

Interface mode — how an interface gets its address. Currently static, dhcp, from-pool, or disabled.

**np2** — runtime name of the NPR-facing IPv4 interface. Configured by the npr1 section.

**us0** — runtime name of the USB CDC-NCM service interface. Default factory address: 192.168.42.1.

**et1** — runtime name of the optional W5500 Ethernet interface.

Management plane

Bootstrap mode — the state a freshly flashed device is in until the first admin key has been installed. Only a tiny set of management endpoints is reachable in this state, and the device displays a short bootstrap code (on UART log and on the LEDs of RFBB-A) used during the bootstrap-install handshake.

Admin key — an Ed25519 keypair held on the operator side. The public key gets installed into the device's keyring with the admin flag during bootstrap; the private key signs control writes afterwards. There can be more than one admin key on a device.

Trusted key — a public key the device is willing to verify against. Admin keys are also trusted; not all trusted keys are admin.

Nonce — short rotating value the device publishes through /system/nonce. Signed control writes have to carry the current nonce in the COSE protected headers; this prevents replay of an old captured request after the nonce has rotated.

COSE_Sign1 — the standard CBOR signed-message envelope used for PacketRF management traffic. PacketRF uses Ed25519 (alg = -8) and embedded payload form. See the COSE module.

**prf-mgmt** — the host-side Python CLI used to talk to PacketRF nodes, both during bootstrap and afterwards. See the Management CLI guide.

Control endpoint — an inner management path under /mgmt, e.g. /system/status or /interface/np2/status. The same paths are reachable over CoAP and over the USB serial framing.

Hardware

RP2350 / RP2350B — the dual Cortex-M33 microcontroller from Raspberry Pi that PacketRF currently targets.

SI4463 — the Silicon Labs sub-GHz radio transceiver that NPR uses on air. Same chip as in the original F4HDK design.

RF Baseboard Rev A / RFBB-A — the custom PacketRF main board with RP2350B, two radio module slots, USB-C, W5500, 16 MB flash and optional PSRAM. Engineering prototype as of writing.

W5500 — Ethernet MAC+PHY chip with an SPI interface, used by the optional et1 interface.