This document discusses PROFINET network design for performance. It provides an overview of PROFINET features such as using switched Ethernet topology, separate channels for IO data and TCP/IP, and full duplex communication. It compares PROFINET Real-Time (RT), Isochronous Real-Time (IRT), and Non-Real Time (NRT) communication and their respective cycle times. It emphasizes the importance of network planning and load simulation to avoid overloads from increasing non-real-time traffic from IT systems merging with industrial networks. Network planning tools can calculate bandwidth utilization across ports and recommend optimizations.

1. Andy Gilbert
PROFINET - designing for performance
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PROFINET - Introduction

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PROFINET features
PROFINET is 100% "switched Ethernet“
(no need for repeater)
 The topology follows the production process
Device diagnostics & network
diagnostics in all PROFINET devices
 Reduction of downtime
Separate channels for IO data and TCP/IP
 No extra network for TCP/IP needed
PROFINET uses full duplex communication
 More applications on one cable
Two-way simultaneous communication PROFINET uses IT standards (IEEE 802.3)
Topology characteristics Integrated diagnostic functions

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One cable does it all 4
The right topology for every system
• Support for star, tree, line or ring topologies
• Various media available for networking: Cat5 copper cable,
glass and plastic fiber-optic cables, and IWLAN
• Access to machines and plants over a secure VPN
connection, e.g. for remote maintenance purposes
Topology based on design
• Smaller cabling overhead and easier commissioning
• Line topology and redundant ring structures possible
without additional network components
• Several controllers can be operated in one network 
simultaneous access to one device with Shared Device and I-
Device
Line
(Redundant) ring
Star
Tree
Wireless communication
(IWLAN)
PROFINET
PROFIsafe
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PROFINET vs. PROFIBUS

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Communication Cycle
Application Cycle Device Cycle
Field DeviceControl Field Device Drive
PROFINET RT?
RT applications are not synchronous:
• Cycle time down to 1ms
• 100Mbit/s bandwidth
• Suitable 80% of all automation applications
• Different non-synchronous cycles
• Application, data transmission and field devices have their own processing cycles
• Slower cycle time and more jitter than IRT
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PROFINET IRT?
Communication CycleApplication Cycle Device Cycle
Field DeviceControl Field Device Drive
IRT is synchronous data transmission
• Cycle time down to 31.25µs
• Application, data transmission and device cycle are synchronous
Cycle time <1ms with jitter accuracy <1µs
• 100Mbit/s bandwidth
• Deterministic data & internet protocol at the same time
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NRT?
NRT is acyclic data transmission
• Runs at same time, albeit with lower priority than RT/IRT
• Unrestricted open TCP/IP data traffic
• Non real-time for an acyclic data transmission (e.g. TCP / IP, UDP / IP)
• 100Mbit/s bandwidth
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Merging of automation and IT-worlds …
… increases network requirements
© 2018
RT / IRT data Other TCP-data Quality gathering data Video
Network load/traffic
Long-term development of plants‘ network load
High data volume through
• Acquisition of quality data
• High resolution videos
• Web services
• Cloud-connection
In parallel to real-time data (RT/IRT)
Poor design can lead to
… overloads on single ports
... lower plant availability
Impact

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Guaranteed PROFINET IO communication
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• … looks after PROFINET time-sensitive IO-Data
transmission
• … does not maintain data traffic consisting of both real-
time and non real-time data (e.g. TCP/IP).
• … does not support devices which are not configured
using it (e.g. standard computers, camera systems, etc.)
PLC engineering suite

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Transparency using a network planning tool
© 2018
• Simulation of the network utilization according to topology
and network participants
• Calculation of the network utilization
• Of cyclic PROFINET IO-Data communication and
• Of acyclic data communication
(Remote Operate Server, cameras, computers, web
server access, …)
• Calculation across projects
• Networks containing non-PROFINET devices
Network planners support …

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Free network load calculation tools
https://www.profibus.com/download/profinet-installation-
guidelines/

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Typical PROFINET planning tool screenshot
© 2018

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Features of a PROFINET planning tool
© 2018
• Import of TIA Portal
and STEP 7 projects
✓
• Port granular simulation ✓
• Validation of the PROFINET
planning guidance
✓
• Online scan function ✓
• Reporting with
detailed results
✓

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Calculation and simulation of the network
utilization
Calculation and simulation
PROFINET IO data (RT/IRT)
Non real-time data (NRT e.g. TCP IP)
Calculation of different scenarios through
selection and deselection of dataflows
Displayed information
Average bandwidth utilization
Queues utilization of the ports
Graphic display in case of a breach of
configured thresholds
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Calculation and simulation of port load and
bandwidth utilization
Real-time data
PROFINET RT / IRT
Cyclic IO-Data
Non real-time data
TCP / IP communication
e.g. IP camera, ...
PN IO Data
TCP/IP Data
Port 1
Port 2
Port 3
Port 4
Queue 1
Queue 2
PN IO Data
NRT Data
PN IO
NRT
PN IONRT
Bandwidth
utilization
Queue / port load
35%

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Data flows & port load
Port 1
Port 2
Port 3
Port 4
Queue 1
Queue 2
PN IO Data
NRT Data
PN IO
NRT
Queue / port load: 100%
NRT
PN IOPN IO
NRT
X
NRT Data
TCP/IP Data
PN IO Data
Real-time data
PROFINET RT / IRT
Cyclic IO-Data
Non real-time data
TCP / IP communication
e.g. IP camera, ...
PN IO

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Benefits
Simulation of existing plant
(e.g. if no project is present)
Calculation of dataflows
(e.g. TCP/IP traffic of computers, cameras, …)
Online functions
Topology scan
Analysis of Pcap files (recorded by a TAP)
Dataflows may be assumed into the current
project or may be stored in the catalog as
templates
Online scan and Pcap analysis
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Recommendations for optimization
© 2018
Shortest path to higher level networks/
high data volume
Be mindful of load caused by standard
(NRT) Ethernet devices
Distribute automation applications across
separate branches

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Avoid ‘topological overlap’
© 2018
Multiple IO controller application
High combined network load caused by
shared path

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Things to avoid!
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Avoid high utilization of bandwidth, and
queue memory

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Line depth
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‘Store and forward ‘‘cut through’
+ 26

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Literature

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Final thought!
“When it comes to ‘Ethernet switches’ there are two types of
people ...
... those who chose to use managed switches ...
... and those who wished they had ...”

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Thank you for your time!
siemens.com/answers
Andy Gilbert
Siemens Applications Specialist
PROFIBUS, PROFINET and IO-Link Seminar comes to
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