Hilscher: PROFINET IRT with Hilscher's netX technology

Why do I need PROFINET IRT?

Industrial communication protocols such as PROFINET, EtherCAT and Ethernet/IP are classified as real-time communication protocols. These protocols can already achieve cycle times as low as 1 millisecond and jitter between 10 and 100 microseconds.

In some cases, however, even this level of performance isn’t enough. The fact of the matter is: it takes time to transmit and process data. In certain applications, it is critical that this time be precisely synchronized to ensure that production steps are performed correctly.

This is particularly true in motion control, where the demands for speed and performance in data communication have increased to the point where the cycle times of standard real-time PROFINET are no longer fast enough, and other key metrics such as jitter and determinism no longer meet the required standards.

For example, a robotic arm must be in a precisely defined position at a specific time to pick up or process a part. If the arm is even slightly early or late, the process can be severely disrupted. In such cases, the transmission and processing of data must be both fast and reliable.

PROFINET IRT is used wherever standard real-time communication reaches its limits and extremely accurate synchronization at exceptionally high speeds in data communication are required.

How Does PROFINET IRT Work?

PROFINET IRT requires strict determinism in the transmission of specific data packets within the network. This means that data must be received, processed, and forwarded in a precise sequence within a predetermined time frame, without being affected by delays such as network collisions or jitter.

To do this, a PROFINET IRT network allocates specific time slots for handling time-critical data. For instance, if 20% of the network traffic is reserved for IRT communication, i.e., PROFINET IRT, the network traffic is divided into five time segments:

One segment is dedicated to IRT communication
The remaining four segments are reserved for regular real-time communication

In this case, the network operates as a standard PROFINET network 80% of the time. During the remaining 20%, only PROFINET IRT-relevant data packets are processed, ensuring synchronized and deterministic transmission. While IRT communication is taking place, regular PROFINET data packets are buffered and processed when the IRT time segment is complete.

A picture with numerous columns lined up in it. Every fifth column is labeled IRT, while the rest is labeled RT.

For this system to work effectively, a PROFINET IRT network must meet two essential requirements:

Synchronization across all IRT devices

A consistent synchronization cycle must be maintained across all PROFINET IRT devices. This is managed by a high-precision clock that is shared by all devices. This and additional mechanisms such as the Precision Time Protocol (PTP) are defined in the IEEE 1588 standard. PROFINET IRT extends this standard with the Precision Transparent Clock Protocol (PTCP). PTCP not only maintains a shared clock between PROFINET IRT devices, but also calculates delays between network switches and the associated wiring.

Buffering capabilities

Additional circuitry within the network switch is required to buffer any non-IRT Ethernet traffic received during the designated IRT communication time.

PROFINET IRT with Hilscher & netX

In order to meet the requirements of such time-critical data communication, it is necessary to intervene on layer 1 and layer 2 of the OSI model, in particular on the MAC layer. This is necessary so that the network devices can provide the IRT time segments during which the Ethernet communication is converted to a TDMA (Time Division Multiple Access) medium. The rest of the time, during regular PROFINET communication, the data transmission works as a standard CSMA-CD (Carrier Sense Multiple Access - Collision Detect) medium.

Hilscher is one of the few suppliers worldwide to offer PROFINET IRT for controller applications. This is made possible by Hilscher’s netX communication controllers, which are developed together with the corresponding protocol software.

netX enables PROFINET IRT

Hilscher addresses this challenge with its netX technology. The netX controllers feature a unique xC structure on OSI layers 1 and 2. Using these programmable microcontrollers and Hilscher’s PROFINET protocol stack, the behavior of a PROFINET network can be defined on the first two OSI layers.

A graphical representation of the netX Basic technology switch architecture 100Mbit.

Flexible microcode from Hilscher

A key feature of netX is that this behavior isn’t hardcoded, but can be flexibly adjusted via microcode. With the microcode provided by Hilscher, users have access to the interface between layer 2 and layer 3.

If you already have a PROFINET solution in place, the first step is to check whether your hardware is IRT-capable. In most cases, it is not, as both hardware and software must meet specific requirements to transmit data according to the IRT standard. These requirements go beyond what is needed for most industrial applications and are typically only needed in high-performance systems, such as those used in motion control or robotics. Unfortunately, many PROFINET-enabled devices are not compatible with PROFINET IRT. In the worst case, a PROFINET IRT network will have to be treated and developed completely separate from your existing installations.

PROFINET and PROFINET IRT with netX

netX technology makes the transition much easier. The necessary PROFINET IRT configurations are already integrated in our standard PROFINET stack, and every netX communication controller comes with the required xC structure. You don’t need to make any changes to either your hardware or software. All you need to do is configure your network.

The same also applies to other network technologies such as EtherCAT. Thanks to the multiprotocol capability of netX, the same hardware can also support EtherCAT.

Different cable lengths introduce additional jitter, a physical property that is unavoidable and requires special attention when implementing a PROFINET IRT network.

For example, a data packet sent over a 10-cm cable will have a shorter transmission time than one sent over a 100-meter cable. These different cable lengths and the resulting jitter during data packet transmission must be taken into account in a PROFINET IRT network to ensure that the controller can properly manage the devices on the network.

Hilscher provides a handy tool called the Topology Editor that allows users to map their plant layout and account for the cable lengths connecting their devices.

What devices are suitable for PROFINET IRT?

Devices that meet the requirements for PROFINET IRT are classified as Conformance Class C (CC-C) as part of the PROFINET certification process. This class covers clocked communication with cycle times as low as 32.5 microseconds. CC-C is the most advanced and demanding conformance class for PROFINET. There are other conformance classes as well: CC-A, the basic class, supports “normal” real-time communication, acyclic real-time transmission, and standard TCP-IP Ethernet. CC-B builds on CC-A by adding support for the Simple Network Management (SNMP) protocol. The classes are cumulative, i.e., CC-C not only supports IRT communication, but also includes all features of CC-A and CC-B.

Hilscher’s netX technology is fully compliant with Conformance Class C, as our PROFINET stack already includes all necessary software functions. On the hardware side, our netX communication controllers are also equipped for IRT applications as standard.

PROFINET conformity class	A	B	C
Real-time data exchange with cycle times of up to 1 ms
Alarm and diagnostic functions
Support for network topology
SNMP support
Real-time data exchange with cycle times down to 31.25µs