Packet.Axudp 0.27.0

Packet.Axudp

AX.25-over-IP: UDP-encapsulated AX.25 frames, RFC 1226 style.

AxudpSocket is a bidirectional AXUDP endpoint — UDP encapsulation of AX.25 frames per the RFC 1226 "AX.25 over IP" convention. The UDP payload is the bare AX.25 frame body followed by the 2-octet AX.25 FCS, exactly as every real AXIP/AXUDP peer (LinBPQ's BPQAXIP, XRouter, ax25ipd, JNOS) speaks it. Part of Packet.NET, a .NET amateur-radio / AX.25 packet stack.

Install

dotnet add package Packet.Axudp

Quick start

using System.Net;
using Packet.Ax25;
using Packet.Axudp;

using var receiver = new AxudpSocket(localPort: 0);   // 0 = any free ephemeral port
using var sender = new AxudpSocket(localPort: 0);

var frame = Ax25Frame.Ui(
    destination: new Callsign("Q0PDN", 0),
    source: new Callsign("N0CALL", 7),
    info: "hello"u8);

// SendAsync always appends the 2-octet AX.25 FCS (CRC-16-CCITT, low byte first).
await sender.SendAsync(new IPEndPoint(IPAddress.Loopback, receiver.LocalPort), frame);

// ReceiveAsync strips + validates the FCS, dropping any bad-CRC datagram, then
// returns the sender endpoint, the bare frame body, and a best-effort decode.
AxudpReceiveResult result = await receiver.ReceiveAsync();
Console.WriteLine(result.DecodedFrame?.Source.Callsign);   // N0CALL-7

The FCS is part of the AXUDP wire format and is unconditional: there is no FCS-less form. The decode on receive is best-effort at modulo-8 (this transport layer holds no session context); a modulo-128 / extended link must re-parse RawFrame at its negotiated modulo before trusting N(S)/N(R)/PID/info.

Key types

• AxudpSocket — the bidirectional AXUDP endpoint: SendAsync (appends FCS), ReceiveAsync (strips + validates FCS), SendRawAsync (verbatim escape hatch for replaying captures), LocalPort, Dispose.
• AxudpReceiveResult — one received datagram after FCS strip/validation: From (sender IPEndPoint), RawFrame (bare AX.25 body), DecodedFrame (parsed Ax25Frame, or null if the body didn't decode).

See also

• Source & issues
• Packet.Ax25 — the AX.25 frame model (Ax25Frame, Callsign) that AXUDP carries
• Packet.Core — shared primitives, including the Crc16Ccitt FCS

AGPL-3.0-licensed. Part of the Packet.NET stack.