IEC 62412: Real-time Ethernet P-NET on IP – Fieldbus Communication over IP Networks

1. Introduction to P-NET on IP

IEC PAS 62412 defines P-NET on IP, an adaptation of the P-NET fieldbus (IEC 61158 Type 4) that encapsulates P-NET communication in UDP/IP packets for routing through IP networks while preserving real-time characteristics.

P-NET on IP enables integration of fieldbus segments into plant-wide IP networks for remote monitoring and cross-site data exchange.

2. Protocol Architecture

2.1 Protocol Stack

Layer	Protocol
Application	P-NET (IEC 61158-5 Type 4)
Data Link	P-NET on IP
Transport	UDP (RFC 768)
Network	IP (RFC 791)
Physical	ISO/IEC 8802-3

2.2 Address Translation

An IPNetTable maps IPNetID to IP addresses and UDP ports. P-NET clients access servers on IP networks without knowing IP addresses.

Existing P-NET software needs no modification to run over IP networks.

3. Data Link Extensions

3.1 DLPDU Types

Type	Route Format	Use Case
Confirmed	IP	Request with acknowledgment
Unconfirmed	IP	Broadcast
Acknowledge	Immediate	Link-level ACK

3.2 UDP Ports

Normal port 34378 and Secure port 34379 (IANA-registered).

Configure ports 34378 and 34379 in network security policies when deploying across network boundaries.

4. Engineering Design Insights

P-NET on IP eliminates long-distance dedicated fieldbus cabling. Full-duplex supports 125 Data Link Entities without token arbitration. Dynamic client support enables flexible configurations.

5. Frequently Asked Questions

Q: Can it route through multiple subnets?
A: Yes, IPNetTable enables routing via multiple IP networks.

Q: Compatible with existing P-NET?
A: Yes, application-layer interface is unchanged.

Q: What is the Secure port for?
A: Port 34379 for sensitive operations with separate firewall rules.

Q: How is congestion handled?
A: Queue prioritisation, retry, and full-duplex eliminating token arbitration.