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--- packet_radio [2026/10/02 16:22] – Organise Wikiham as an encyclopedia of individual articles 127.0.0.1
+++ packet_radio [2026/10/02 21:06] (current) – Add technical encyclopedia coverage, formulas, examples and primary references admin
@@ Line 1: / Line 1: @@
 ====== Packet radio ======
-**Packet radio** is data communication over radio in which information is organised into packets. It is used for a range of amateur radio networking applications.
+**Packet radio** transfers data over radio in discrete frames or packets. In amateur radio, traditional systems often use **AX.25**, a link-layer protocol with station addressing, framing and error detection. Packet radio is a networking method, not one fixed modulation mode.
-===== Networks =====
+===== AX.25 frames =====
-A packet system can include radio links, computers, interfaces and routing or application software. The protocols and equipment depend on the particular network.
+An AX.25 frame includes boundary flags, source and destination addresses, control information and a frame-check sequence. Some frame types also carry a protocol identifier and information field. Addresses encode station callsigns with an SSID to distinguish station functions.
-Amateur radio IP networking, including [[44net]], may use radio links as part of a wider path. An IP address alone does not establish whether the transport is radio, wired or tunnelled.
+Connected operation supports acknowledgements and retransmission. **Unnumbered information (UI)** frames send data without first establishing a connected session; [[aprs|APRS]] commonly uses this approach.
-===== See also =====
+The frame-check sequence detects many transmission errors. It does not itself reconstruct damaged data: retransmission or an additional coding scheme is needed for recovery.
+===== Modems and interfaces =====
+A traditional terminal node controller (TNC) combines modem and protocol functions. A software modem can perform part of the same work using a computer's audio interface. KISS is an interface between a host and TNC; it is not the RF waveform itself.
+Common VHF implementations use 1200-bit/s AFSK through FM. Faster systems may need direct access to a radio's data path because microphone and speaker filtering can alter the modem waveform.
+===== Throughput and channel sharing =====
+<code>
+Useful throughput = delivered payload bits / elapsed time
+</code>
+Sending 100 payload bytes at a nominal 1200 bit/s takes at least 0.667 s for those bits alone. Addresses, flags, bit stuffing, channel access, key-up delay and retries increase elapsed time. Raw modem rate therefore overstates application throughput.
+Stations typically share a half-duplex channel. Carrier sensing and suitable access delays reduce collisions, but hidden stations and interference can still cause losses. More retries or digipeater hops consume additional airtime.
+===== Networks =====
-  * [[digital_mode|Digital mode]]
+Applications include messaging, telemetry, bulletin boards and IP networking. [[44net|44net]] can use radio links within a wider network; a 44net address by itself does not establish whether a path is radio, wired or tunnelled.
-  * [[44net]]
-===== Further reading =====
+===== References =====
-  * [[https://www.ardc.net/|Amateur Radio Digital Communications]]
+  * [[https://web.tapr.org/tech_docs/AX25/AX25.2.2.pdf|TAPR: AX.25 Link Access Protocol, version 2.2]].
-  * [[https://www.aprs.org/|APRS information]]
+  * [[https://files.tapr.org/meetings/DCC_2014/DCC2014-Amateur-Bell-202-Modem-W6KWF-and-Bridget-Benson.pdf|TAPR DCC: an amateur Bell 202 modem]].
+  * [[https://www.aprs.org/|APRS project documentation]].
+  * [[https://www.ardc.net/|Amateur Radio Digital Communications]].