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Transport

Low-level async UDP transport for the Icom LAN protocol. Most users should use IcomRadio instead.

Class: IcomTransport

from icom_lan import IcomTransport

Handles:

  • UDP socket management via asyncio.DatagramProtocol
  • Discovery handshake (Are You There → I Am Here → Are You Ready)
  • Keep-alive ping loop (500ms interval)
  • Sequence number tracking
  • Retransmit request handling
  • Packet queueing for consumers

Constructor

IcomTransport()

No parameters — the transport is configured via connect().

Methods

connect()

async def connect(self, host: str, port: int) -> None

Open UDP connection and perform discovery handshake.

Parameter Type Description
host str Radio IP address
port int UDP port number

Raises: TimeoutError if discovery fails after 10 attempts.

disconnect()

async def disconnect(self) -> None

Close the UDP connection and stop background tasks (ping, retransmit).

send_tracked()

async def send_tracked(self, data: bytes) -> None

Send a packet with automatic sequence number assignment and tracking for retransmission.

receive_packet()

async def receive_packet(self, timeout: float = 5.0) -> bytes

Wait for the next incoming packet.

Raises: asyncio.TimeoutError if no packet arrives within timeout.

start_ping_loop()

def start_ping_loop(self) -> None

Start the background ping task (500ms interval).

start_retransmit_loop()

def start_retransmit_loop(self) -> None

Start the background retransmit request task (100ms interval).

Attributes

Attribute Type Description
state ConnectionState Current connection state
my_id int Local connection identifier
remote_id int Remote (radio) connection identifier
send_seq int Next outgoing tracked sequence number
ping_seq int Next outgoing ping sequence number
tx_buffer dict[int, bytes] Sent packets buffer (for retransmit)

Enum: ConnectionState

from icom_lan import ConnectionState
Value Description
DISCONNECTED Not connected
CONNECTING Handshake in progress
CONNECTED Ready for communication

Internal Protocol Details

Packet Handling

When a packet arrives, the transport:

  1. Checks if it's a retransmit request → resends buffered packet
  2. Checks if it's a ping → sends pong reply
  3. Tracks sequence numbers for gap detection
  4. Queues the packet for receive_packet() consumers

Retransmit Logic

  • Missing sequence numbers are detected by gaps in incoming seq numbers
  • Retransmit requests are sent every 100ms
  • After 4 failed retransmit attempts, the missing packet is abandoned
  • Buffer holds up to 500 sent packets