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Packet glossary of terms


ACKMODE - Option in KISS. ACKMODE enables the transmission of 'ACK required' frames. These cause the TNC to send a reply when the frame has been transmitted. This will improve link performance by avoiding the possibility of a retry being sent before the original frame has even left the TNC. This mode should always be used if the TNC support it

AFSK - Audio Frequency Shift Keying. A way of encoding data into audio (for transmission over an audio network e.g. radio or telephone) by converting it into audio frequencies.

ALOHA - Computer networking system developed at the University of Hawaii in the 1970s. The ALOHA random-access protocol is used to resolve collisions on RF networks.

ALOHA limit (18%) - tbc

AXIP - AX.25 over IP. Useful for interconnecting nodes over the internet and private IP links.

AX.25 - Amateur X.25, a variant of the X.25 protocol for amateur radio applications. v2.2 specification


Baud rate - the data rate of a serial link. Measured in bits per second.

BBS - a private mail and/or bulletin board application which typically runs “under” a node

BPQ - the packet node software written by G8BPQ.


bull - Bulletin. Message sent to many rather than one person.



Chat - an IRC-like near-realtime, transient, instant messaging application which typically runs “under” a node


Dire Wolf - - Software AX.25 modem/TNC and APRS encoder/decoder. Sometimes incorrectly written as Direwolf.




FEC - Forward Error Correction

FRACK - FRame ACKnowledge. Acknowledges a received frame.



GPIO - General Purpose Input/Output - A bank of spare input and/or output pins on a computer module which are reserved for user applications. Examples would be the BBC Micro's User Port, or the Raspberry Pi's dual-row 40-pin “GPIO” pins.


IL2P - Improved Layer-2 Protocol - an improved version of the AX.25 layer-2 packet format by which adds forward error correction and packet-synchronous scrambling.



KISS - Keep It Simple (Stupid). A very simple protocol used to interface a TNC to a controlling computer in a stateless manner.


MAXPAC - Formed as a dedicated AX.25 Packet group for the [GB] Midlands. Possibly does not exists anymore (2023)link


MSK - Minimum Shift Keying, A variant of AFSK, where the frequencies used are selected to ensure there is no phase shift at the transition from one bit to the next. This reduces high-frequency harmonics in the transmission.


NET/ROM - NET/ROM (Networking over Radio Operations and Management) is both a network layer (OSI L3) protocol, which allows for the routing of packets between different nodes, and a transport layer (OSI L4) protocol that provides reliable delivery of packets and error correction. It adds reliability and efficiency capabilities such as automatic routing, link quality monitoring, and congestion control. A NET/ROM node user may display a list of other known network nodes; establish a transport-level circuit to a distant node; and connect to another end-user or mailbox in the vicinity of that distant node.


Node - the top level construct representing a single packet radio station, proving some level of node services, e.g. applications like BBS or Chat, or inter-node transports such as NET/ROM.



OFDM - Orthogonal Frequency Division Multiplexing. A method of transmitting large amounts of data in a comparatively small amount of RF spectrum by splitting that block of spectrum into many 'sub channels'. Often implemented with Fast Fourier Transform algorithms.

OSI model - OSI model - Wikipedia

Source: Wikipedia


Packet - a single unit of transmision. An “over”, from the perspective of the radio.






RUH - G3RUH came up with an implementation of 9600 baud packet (vs 1200 baud), and the standard is known as RUH.

RS-232 - the primary standard used to implement serial connections between modems and computers. Some variations of the standard specify fairly large positive and negative voltages.


Scrambling - A means of equalising the average voltage level of a data packet by making it look like random noise. The added transitions make it easier to recover the data clock, even if the input data has long strings of the same voltage level (0 or 1). Bringing the average level close to mid-way also resolves issues with FM transmitters, where the transmit PLL may make it difficult to transmit long streams of repeated '0' or '1' bits.

Serial port - In serial communication data is transferred one bit at a time sequentially. RS-232 and USB are types of “serial port”.

Symbols - A symbol is a discrete “state” of a signal in a slice of time.For binary coding, a symbol is either 0 or 1. For quadrature coding, a symbol is 00, 01, 10, or 01. For binary coding, you can encode 1 bit of information per symbol. For quadrature coding, you can encode 2 bits of information per symbol. BPSK - binary phase shift keying - you get 1 bit per symbol (binary) so baud rate == bits per second. QPSK - quadrature phase shift keying - you get 2 bits per symbol (quadrature) so baud rate (or symbol rate) == half the bits per second.


TARPN - Terrestrial Amateur Radio Packet Network

TCP/IP - Transmission Control Protocol/Internet Protocol. The protocol which underpins much internet traffic. Provides reliable transport (packets arrive in the same order as transmitted) over unreliable links. TCP is the transport layer protocol.

TELNET - provides a standard method for terminal devices and terminal-oriented processes to interface. Telnet is application layer protocol.

TNC - Terminal Node Controller - a hardware device which connects between a radio transceiver and a computer, and implements packet radio protocols. Essentially a packet modem.

TTL Serial - A serial port implemented with TTL (as opposed to RS-232) levels. May be either 0V/5V, 0V/3.3V, or in some cases 0V/1.2V.

TVRG - Thames Valley Repeater Group. Several members are interested in packet and host digipeaters.


UART - Universal Asynchronous Receiver/Transmitter. A device which implements a serial port. Asynchronous means the clock is carried by the data (or generated locally with a baud rate generator), versus synchronous serial (like SPI) which requires a separate clock signal.

UI frame - Unnumbered Information frame, somewhat analogous to UDP, as opposed to I - Information - frames, as used in conencted-mode packet, somewhat analogous to TCP.




packet/glossary.txt · Last modified: 2023/11/11 13:47 by m0lte