DNP3.0 (IEEE 1815) vs IEC 60870‑5‑104 Key Differences

• DNP3.0 is the mainstream SCADA protocol for North‑American power systems. IEC 60870‑5‑104 is an IEC international standard and the predominant telecontrol protocol in China and Europe. Both protocols implement four‑remote functions (remote indication, remote measurement, remote control, remote adjustment) and support TCP/IP Ethernet communication. However, they differ significantly in protocol architecture, data model, message frame structure and engineering practices.

Standard Background & Application Regions

Layer Definition & Message Frame Structure

DNP3.0

• It fully defines link layer + transport layer + application layer, with native support for serial FT3, TCP and UDP. The link layer adopts CRC‑16‑ANSI checksum; frame header is 0x05 0x64. Maximum link‑layer frame size is 292 bytes, and large messages are automatically fragmented and reassembled.
• Message structure: Frame header (0x0564) + Length + Control Octet + Source/Destination Address + CRC + Transport Layer + Application Layer (Object‑Variation‑Qualifier).

IEC 60870‑5‑104

• There is no independent link layer. It maps the application layer of IEC 101 (serial FT1.2) directly onto TCP/IP. A 6‑byte APCI header is introduced for flow control and heartbeat supervision, with start character 0x68. Transmission reliability is guaranteed by TCP, and no CRC check is implemented at link layer.
• Message structure: 6‑byte APCI header + ASDU (Application Service Data Unit). Frames are classified into I‑frames (information), S‑frames (confirmation), U‑frames (link control). A complete set of timeout parameters t0/t1/t2/t3 are defined.

Data Model (Most Essential Difference)

DNP3.0: Object‑Oriented Model — Group‑Variation‑Qualifier

• Data is organized into object groups: binary inputs, analog inputs, counters and control commands each correspond to an independent Group. Variation defines data format and timestamp availability; the qualifier specifies the range of point addresses.
• Timestamp is a built‑in attribute of the object. A single binary point can be reported with or without millisecond timestamp flexibly. The outstation maintains an internal event buffer pool for historical SOE (Sequence‑of‑Event) records. The master can read historical SOE at any time; buffered events can be resumed after communication recovery. This feature is highly suitable for wireless, narrow‑band and unstable communication channels.
• Point address range in DNP3.0: 0‑65535, supports 1‑byte or 2‑byte point addresses.

IEC 60870‑5‑104: ASDU + Information Object Address Model

• Message types are distinguished by Type‑ID. Binary points without timestamp and binary points with 7‑byte timestamp belong to two separate ASDUs. The timestamp is an attached field of the information object, not an inherent attribute of the data point.
• No built‑in event buffer is available. Only changed points are transmitted in spontaneous reporting. Historical events will not be automatically resumed after link re‑establishment; full data shall be retrieved by master station via General Interrogation (GI).
• Information object address is fixed at 3 bytes; combined with Common Address of ASDU (typically 1‑2 bytes, depending on specific ASDU type) and Cause of Transmission (COT).

Remote Control Modes

DNP3.0

• Two control modes are supported:
• Select‑Before‑Operate (SBO): Safe two‑step control sequence
• Direct Operate: One‑step command, widely adopted in field engineering

IEC 60870‑5‑104

• Both Direct Operate and SBO are defined in the protocol specification. Power dispatching industry specifications mandate the 3‑step Select‑Before‑Operate‑Confirm workflow. Direct‑operate mode is practically prohibited in Chinese‑domestic power projects.

Communication Mechanism & Reliability

DNP3.0

• Link‑layer acknowledgement and re‑transmission mechanism; transport layer handles fragmentation and reassembly
• Outstation supports Unsolicited Response (spontaneous reporting), and master‑initiated polling is also available
• Natively supports multiple master stations accessing one single outstation
• Well‑suited for microwave, 4G‑wireless and poor‑quality communication channels
• Optional Secure Authentication (SA); TLS encryption is supported in newer versions
• Event queue: Outstation caches SOE events; buffered events can be uploaded after communication recovery
• Note: Event buffering is a standard capability of DNP3.0. The actual buffer depth (maximum record count) depends on RTU vendor implementation. Buffer capacity shall be verified during equipment selection according to on‑site SOE volume requirements.

IEC 60870‑5‑104

• Reliability relies on TCP; APCI implements sliding‑window flow control
• Supports spontaneous reporting, General Interrogation (GI) and group interrogation
• The protocol itself does not allow one outstation to connect to multiple masters simultaneously; multi‑master access requires gateway forwarding
• No link‑layer CRC check; no local event buffer
• No native security authentication in the protocol; security is realized by external firewalls and network isolation

Time Synchronization

• DNP3.0: Dedicated application‑layer time‑synchronization object, propagation delay compensation is available, millisecond‑resolution timestamp; each event object carries its own timestamp.
• IEC 60870‑5‑104: Time synchronization is performed via time‑tagged ASDU. SOE messages adopt the dedicated 7‑byte time‑tag ASDU type (CP56Time2a).

Engineering Characteristics

DNP3.0

• Advantages: Robust performance over wireless / narrow‑band / jitter‑prone links; event buffering & post‑recovery event resume; flexible timestamp configuration per point; native multi‑master support; mandatory for North‑American and certain overseas projects.
• Disadvantages: Rarely used in Chinese domestic dispatching systems; complex protocol stack implementation; limited debugging tools and experienced engineers in China.

IEC 60870‑5‑104

• Advantages: Standard protocol for Chinese power grid and new‑energy grid‑connection; mature tool chains; widespread engineer familiarity; stable and reliable over Ethernet.
• Disadvantages: No link‑layer retransmission for poor‑quality channels such as microwave; no local event buffer, events generated during link outage will be lost; multi‑master station is not supported.

Selection Guidelines

• Domestic power grid, new‑energy grid‑connection and domestic substations: Prioritize IEC 60870‑5‑104.
• Projects for North‑America, Latin‑America, parts of Africa with RTU and narrow‑band wireless links: Adopt DNP3.0.
• For protocol inter‑working: Protocol gateway is required. Key considerations include point‑list mapping, SOE timestamp conversion, SBO / Direct Operate mode matching and event‑buffer handling.

• Selection Mnemonic: Use 104 for domestic grids, DNP for overseas wireless sites. DNP features built‑in event buffer while IEC‑104 relies on master GI. DNP supports multi‑master, IEC‑104 is single‑master oriented.