Packet-Radio-Dictionary

There are many special terms and expressions on the matter of  Packet-Radio, which may confuse the beginner. We tried to explain some of these in a short form dictionary:

AFSK Audio Frequency Shift Keying. Digital data is transmitted ty modulating one of two possible tones via the audio modulator of a radio.

ASCII American Standard Code for Information Interchange. ASCII defines, how the characters are represented by the bit patterns. In most cases, the expression ASCII means the transmission of only printable (readable) characters to distinguish the mode from 'binary' transmission, which allows all 256 possible bytes to be sent.

Asynchronous transfer On the serial interface (RS232) data is transferred asynchroneous, that means, the characters are transmitted one by one with a stop and a start bit as delimiter. Opposite: Synchroneous transfer.

AX.25 Protocol, regulation. Defines, how data is transformed into data packets. AX.25 was derived from the X.25 protocol, which was used by data transmission systems via wire links.

Baud (Baudot was a French scientist) Measure for the speed of digital data transmission. 1 Baud means 1 step per second. With 1200 baud AFSK, every step contains 1 bit iInformation. 1000baud = 1 Kbaud; 1000Kbaud = 1 Mbaud. If the data is binary, 1 baud = 1 bit/s.

baud rate transmission speed (s. baud).

BBS Bulletin Board System. Similar to 'mailbox'. The users of such a system can send bulletins to the system, which can be read by all other users. The information submitted is normally organised into different special boards, e.g. "GENERAL", "IBM", "LINUX", "HARDWARE" etc.

binary transmission data transmission mode which allows to transmit all 256 possible bytes to be transferred. As the Packet-radio controller normally not allow ann bytes (control characters are excluded), binary files have to be converted to ASCII first. (7 plus)

Bit smallest information unit. A bit can be 0 or 1.

Byte a information containing 8 bit. With 1 byte, you can transmit a single character out of an alphabet of 256 characters.

Call Callsign of a Packet-Radio-station. A call may consist of up to 6 characters (uppercase letters or figures), which MUST be unique in a net. (s. SSID)

Connect to establish a data connection (s. disconnect)

Connect-Text (CTEXT) a short message, stored in TNC, which is automatically transmitted as the answer to the station connecting.

Cross-Digipeat (s. digipeater) Dual-port TNC may be configured in a way to retransmit packets comeinf from port 1 on port 2 and vice versa. This makes it possible to establish a link between two stations on different frequencies.

DAMA Protocol to control the access of packet-radio transmitters to the frequency channel they share. The user stations (DAMA-slaves) must transmitt only if they get the permission by the central node (DAMA-master). This makes it possible that all stations controlled by a DAMA master are priviledged equal. DAMA was developed by Nord<>Link for Packet-Radio and is standard in Europe but not in most other countries.

Digipeater (DIGItal rePEATER), a packet-radio station which receives data and re-sends it immediately (data-relay). Retransmission can be done on the same or on an other frequency.

Disconnect  close an existing data connectionin

FSK  Frequency Shift Keying  (s. AFSK): The RF-carrier is shifted in frequency according to the data. One of two possible radio frequencies is transmitted. E.g. the upper of the two frequencies represents the "HI" state, the lower means "LO".

Hayes-mode Telephone modems and computer use 'Hayes-mode' in most cases. Commands begin with  AT, e.g. AT DT 12345 means to dial the phone number 12345. To control a Packet-Radio-controller by use os software which was intended to be used with telephone-modems, the TNC3 or TNC31 has a mode which accepts the basic AT-commands of Hayes-mode. Hayes mode works transparent.

Hostmode When a terminal or a computer with terminal-emulation is used to control a TNC, data is exchanged in so called 'Terminal-Mode'. But there exists various and comfortable programs for Packet-Radio (running on PC, Amiga, Atari) which use a different command-language to communicate with TNC, the so-called Host-Mode. All TNC2 and TNC3 support this Host-Mode and can be operated with such software.

Mail a (personal) message to the user of a mailbox. As soon as the user connects the box, a message as  "You have mail" is returned.

Mailbox programm, which stores mail which can be accessed by other users.

Modem a modem converts digital data into tones, which can be transmitted via a radio link. Every TNC consists of a microprocessor, which generates a serial digital data stream and a modem, which converts the data to tones.

Monitor-Mode A TNC is able to monitor all data traffic on the receiver frequency. Monitor mode may be permanently disabled or (normal mode) disabled as soon as a connect is established.

MH-Liste  TNC can store a list of stations and the time of their appearance. The stations heard last appear at the beginning of the list. The length of the lost (10...50 or more entries) may ve configured.

Node Packet-Radio-station, which receives packets and forwards them immediately. The node uses lists which help to decide, which way and which channel is best to transfer every packet through the network.  (Routing). The node collects information about the state of the net and the quality of the links between all other nodes in the net and uses it to permanently update the routing tables.

Packet  data packet, consisting of a header, which contains info on sbsender, receiver and the path of the packet, the information itself and a checksum. Norlally, the length of a AX.25 data packet is 128 or 256 byte.

Permanent A connect is normally opened, data is transferred and connection is closed again. With some firmwares, the state of a connect may be set to 'permanent'. Then, a disconnect is no more possible. After a interruption of the link (e.g. if one of the stations is switched off), the connection is re-established automatically after power-on. With TNC3/31, a script file may contain connands, which automatically open a connection after power-on.

Protocol  definition, how data packets are set together. With Packet-Radio, the protocol is called  'AX.25'.

Retry  packets which are not or negative acknowledged are repeated. Usually, the number of 'retries' is limited to 10 before the data link is closed (aborted).

Routing The ability of a node in a data net to decide, in which direction packets are forwarded to get as fast through the net as possible, is called routing. Normally, the decision is based on tables, which are self-configuring (autorouting). If a node in the net fails, the routers react by re-routing the data via alternative routes.

Serial interface data is exchanged between computer and TNC via the serial interface (RS232 or V.24). THe baud rate is 9600, 19200 or faster (up to 115200 baud usually), parity is normally NO and number of stop bits is 1. Other settimgs may be selected. To connect a TNC to a computer, a 3-pire cable with the signals TxD, RxD and ground will do.

Spy  When a frequency is used by more than one stations, it is not easy for a monitoring station to distinguish the different dialogs. Some terminal programs support a 'spy'-function, which separates the data packets. It stores and displays every connection on a different screen window.

SSID Secondary Station Identifier (callsign expansion). If more than one TNC has to be operated by the same station, the callsign may be expanded by appending a dash and a figure. Allowed are the figures 1 to 15, omitting the figure means SSID -0. Mailboxes are usually adressed with the SSID  -8.

Stamp (Timestamp) Important messages from the TNC are time-spamped and displayed. If there is no computer connected, the following message may be stored in TNC and appears later on the PC screen:

* (1) CONNECTED to XYZ - 22/09/00 14:10:34 *

Synchroneous data transfer serial data is transmitted without separation between bytes. The receiver needs a circuit which converts the continuous bit-stream in separate bits and bytes. Advantage: no time is wasted to transmit start and stop bits. Approx. 20% more data per time can be exchanged.

Terminal A terminal is a device, which converts all keyboard entries to a serial (RS232) data signal to e.g. a TNC. The terminal screen displays all data which is received by the serial interface (from TNC). In most cases, a terminal-emulation software is used with a PC, which makes the PC a terminal.

TheNet / ThreeNet / X-Net Adjacent nodes exchange information about the state of the network and about the capability of the data links between nodes. The protocol used for this information interchange is normally called TNN=TheNetNode or Net-ROM. X-Net (former ThreeNet) is a software, which makes a TNC3/31 a net-node with the capability to process TheNet, Net-ROM, Flexnet and TCP/IP network protocol types.

TNC Terminal Node Controller. converts data received by a radio receiver to computer data and vice versa. The TNC adds the protocol information (header, frame, checksum) to every packet without intervention by PC.

Transparent with Packet-Radio, almost every characters may be transmitted, but some (control-characters) are reserved for controlling the TNC. As binary files may contain all 256 possible characters, this kind of data cannot be exchanged by TNC directly. If the TNC is switched to transparent mode (only possible with TNC2 using TAPR-software or TNC3/31 with  Hayes-mode), all characters may be transmitted without exception. Transparent mode can be exited only with special BREAK-commands or with a special combination of characters (+++ and 1 second wait time). In transparent mode, a packet-radio link behaves like a serial data cable, i.e. totally transparent.