Link Layer¶

icspacket.proto.dnp3.link.LPDU_HEADER_MIN_LENGTH = 5¶: Minimum number of bytes required to represent an LPDU header.

icspacket.proto.dnp3.link.LPDU_HEADER_MAX_LENGTH = 255¶: Maximum possible size of an LPDU header in bytes.

icspacket.proto.dnp3.link.LPDU_USER_DATA_MAX_LENGTH = 250¶: Maximum user data size (250 bytes) that a single LPDU can contain.

class icspacket.proto.dnp3.link.LinkDirection(*values)[source]¶

Direction indicator bit for the DNP3 link layer (DIR field).

(See DNP3 Specification, Section 9.2.4.1.3.1)

MASTER = 1¶: Indicates a frame sent from a Master device.

OUTSTATION = 0¶: Indicates a frame sent from an Outstation device.

class icspacket.proto.dnp3.link.LinkPrimaryFunctionCode(*values)[source]¶

Primary-to-Secondary function codes for the Link Layer.

These codes are valid when the PRM bit is set (PRM = 1). (See DNP3 Specification, Table 9-1)

RESET_LINK_STATES = 0¶: Reset link states.

TEST_LINK_STATES = 2¶: Test link states.

CONFIRMED_USER_DATA = 3¶: Confirmed user data transfer.

UNCONFIRMED_USER_DATA = 4¶: Unconfirmed user data transfer.

REQUEST_LINK_STATUS = 9¶: Request link status.

class icspacket.proto.dnp3.link.LinkSecondaryFunctionCode(*values)[source]¶

Secondary-to-Primary function codes for the Link Layer.

These codes are valid when the PRM bit is clear (PRM = 0). (See DNP3 Specification, Table 9-2)

ACK = 0¶: Acknowledgement.

NACK = 1¶: Negative acknowledgement.

LINK_STATUS = 11¶: Report link status.

NOT_SUPPORTED = 15¶: Function code not supported.

class icspacket.proto.dnp3.link.LinkControl(direction: LinkDirection = LinkDirection.MASTER, primary_message: bool = False, frame_count_bit: bool = False, frame_count_valid: bool = False, function_code: int = 0)[source]¶

Control field of the Link Layer Protocol Data Unit (LPDU).

Stores metadata about the frame direction, initiator, error handling, and function code. (See DNP3 Specification, Section 9.2.4.1.3)

direction: LinkDirection = 1¶: DIR bit. Indicates the physical origin of the frame (Master/Outstation).

primary_message: bool = False¶

PRM bit.

True Frame initiates a transaction.
False Frame completes a transaction.

frame_count_bit: bool = False¶: FCB bit. Used in primary-to-secondary frames to detect loss or duplication.

frame_count_valid: bool = False¶: FCV bit. Specifies whether the secondary station must examine the FCB.

function_code: int = 0¶: Function code field identifying the service or command type.

property data_flow_control: bool¶

Report data flow availability (DFC bit).

Indicates insufficient Data Link Layer buffer capacity.

Returns:: True if buffer space is insufficient, False otherwise.
Return type:: bool

property pri2sec_code: LinkPrimaryFunctionCode¶

Interpret the function code for Primary-to-Secondary frames.

Returns:: Link layer function code for PRM = 1.
Return type:: LinkPrimaryFunctionCode

property sec2pri_code: LinkSecondaryFunctionCode¶

Interpret the function code for Secondary-to-Primary frames.

Returns:: Link layer function code for PRM = 0.
Return type:: LinkSecondaryFunctionCode

class icspacket.proto.dnp3.link.LPDU(start: bytes = b'\x05d', length: int = 0, control: LinkControl = None, destination: int = 0, source: int = 0, crc16: int = 0, user_data: bytes = b'')[source]¶

Link-layer Protocol Data Unit (LPDU).

Each LPDU consists of a fixed header block and a variable-length sequence of data blocks, each terminated by a 16-bit CRC. (See DNP3 Specification, Section 9.2.4)

start: bytes = b'\x05d'¶: Sync bytes marking the start of every LPDU (0x05, 0x64).

length: int = 0¶: Length field. Number of non-CRC bytes following the header. Includes CONTROL, DESTINATION, SOURCE, and USER DATA fields.

control: LinkControl = None¶: Control field containing direction, function, and status flags.

destination: int = 0¶: Destination address of the data link frame.

source: int = 0¶: Source address of the data link frame.

crc16: int = 0¶: CRC checksum for the LPDU header block.

user_data: bytes = b''¶: Payload data field containing one or more user data chunks.

build() → bytes[source]¶

Construct a serialized LPDU with correct length.

Returns:: Encoded LPDU bytes.
Return type:: bytes

static from_octets(data: bytes) → LPDU[source]¶

Parse an LPDU from a raw byte sequence.

Changed in version 0.2.0: Renamed from from_bytes to from_octets

Parameters:: data (bytes) – Encoded LPDU bytes.
Returns:: Decoded LPDU instance.
Return type:: LPDU

property apdu: APDU¶: Parse the APDU contained in the TPDU.

property tpdu: TPDU¶: The TPDU contained in the LPDU.