AX.25 v2.0 is responsible for establishing link layer connections, transferring data encapsulated in frames between nodes, and detecting errors introduced by the communications channel.
[2] Stations can automatically negotiate payload sizes larger than the previous limitation of 256 bytes.
Digipeaters act as simplex repeaters, receiving, decoding and retransmitting packets from local stations.
Traditionally, amateur radio operators have connected to AX.25 networks through the use of a terminal node controller, which contains a microprocessor and an implementation of the protocol in firmware.
The computers can also interconnect to other computers or be bridged or routed to TNCs and transceivers located elsewhere using BPQ over Ethernet framing, which is also natively supported by the Linux kernel to facilitate more modern setups with the actual transceivers directly placed under or in the antenna mast, creating a 'low loss', shorter RF wiring need, and replacing expensive and long and thick coax cables and amplifiers with cheap fiber (RFI (both ways)/EMP/lightning resistant) or copper Ethernet wiring.
BPQ Ethernet framing allows connecting entire stacks of TNC+transceiver pairs to any existing network of computers which then can all access all radio links offered simultaneously (transparently bridged), communicate with each other internally over AX.25, or with filtered routing select specific TNCs/radio frequencies.
It can function as a digital repeater, GPS tracker, and APRS Internet Gateway (IGate) without any additional software.
AX.25 is often used with a TNC that implements the KISS[7] framing as a low-cost alternative to using expensive and uncommon HDLC controller cards.
It merely serves to encapsulate the protocol frames in a way that can successfully pass over a serial link to the TNC.
[8] AX.25 has most frequently been used to establish direct, point-to-point links between packet radio stations, without any additional network layers.
This is sufficient for keyboard-to-keyboard contacts between stations and for accessing local bulletin board systems and DX clusters.
Some amateurs, notably Phil Karn KA9Q, have argued that AX.25 is not well-suited to operation over noisy, limited-bandwidth radio links, citing its lack of forward error correction (FEC) and automatic data compression.
Likely reasons may include: Despite these limitations, an extension to the AX.25 protocol, supporting forward error correction, has been created by the TAPR.
However, in recent years, the ability to receive as well as send using cheap microcontrollers (such as the Atmel AVR or the Motorola 68HC08 families) has been demonstrated.