PROFINET
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
1
Isochronous Real-Time
© PNCC Burgdorf
PROFINET IRT
PROFINET - a modular technology
1
Process
Automation
MES
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
Interbus
Integration
PROFIBUS
Integration
Motion
Control
Decentralized
Periphery
WLAN
Safety
Test +
Certification
WEB
Integration
Train
Application
2
Distributed
Automation
Network
Installation
Network
Management
Real-time
Communication
© PNCC Burgdorf
PROFINET IRT
Security
2
1
Improving Performance in the Communication Stack
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
• The time needed for the provision and processing of the
data is independent of communication
• Improved performance is possible only through optimization of the turnaround times in the communication stack
• The transmission speed on the line can be regarded as
negligible (100 Mb/s)
Producer
Consumer
∆T1
Provide
data
Process
data
∆T2
Process
communication stack
Process
3
communication stack
∆T3
Transmission
© PNCC Burgdorf
PROFINET IRT
3
PROFINET IO and Real-Time
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
PROFINET distinguishes between two Real-Time classes with
differences regarding the performance:
Real-Time (RT):
● Using standard components
● Performance characteristics like field buses today (e.g. PROFIBUS)
● Typical application area: Factory Automation
Isochronous Real-Time (IRT):
● Clock synchronized communication
4
● Hardware support via Switch-ASIC
● Typical application area: drive control in Motion Control applications
© PNCC Burgdorf
PROFINET IRT
4
2
Real-Time Communication
RT
Controller Factory Automation
und HMI
Overview
Motion Control
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
100ms
5 ... 10ms
<1ms
TCP/IP
Real-Time
ƒ RT offers comparable Real-Time-characteristics like
PROFIBUS
5
ƒ Bus cycle times from 10 down to 5 ms are realistic
ƒ PROFINET is fully compatible to the TCP/IP-Standard without
limitations
© PNCC Burgdorf
PROFINET IRT
5
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
IT Applications
e.g.
z HTTP
z SNMP
z DHCP...
Real-Time
RT-Communication Stack
1 Open TCP/IP channel
z Device parameterization
z Reading of diagnostics
data
z Loading of
interconnections
z Negotiation of the
communication channel
for user data
RT
2 Real-Time channel
PROFINET Applications
1
Standard data
Real-Time data
TCP/UDP
IP
2
(RT)
z
Ethernet
z
z
High-performance
transmission
6
Cyclic
data
Event-controlled signals
RT-Communication can be realized with every Ethernet Controller
© PNCC Burgdorf
PROFINET IRT
6
3
Distribution of Refresh Times
n
RT
Overview
TCP/IP
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
15%
100%
7
10 msec
t
100 msec
• RT improvements against standard TCP/IP
•
•
•
Optimization of the absolute transmission time: factor 6-10
Minimization of the variance of the transmission times: factor 5-8
Improved behavior at replacement value: factor 7
© PNCC Burgdorf
PROFINET IRT
7
Isochronous Real-Time Communication
IRT
IRT
Controller Factory Automation
und HMI
Overview
Real-Time (RT)
for Motion Control
IsochronousReal-Time (IRT)
Calculations
100ms
5 ... 10ms
<1ms
TCP/IP
Real-Time
Motion Control Requirements
● Bus cycle less than 1 ms
8
● Clock Synchronization including determinism
● Jitter less than 1µs
● Time scheduled transmission
© PNCC Burgdorf
PROFINET IRT
8
4
IRT-Communication Stack
1 Open TCP/IP channel
z
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
z
IT Applications
e.g.
z HTTP
z SNMP
z DHCP...
PROFINET Applications
z
z
1
Standard data
Real-Time data
Device parameterization
Reading of diagnostics data
Loading of interconnections
Negotiation of the
communication channel for
user data
Calculations
2 Real-Time channel - RT
Real-time
TCP/UDP
IP
Ethernet
2 RT
z
z
z
High-performance transfer
Cyclic data
Event-controlled signals
3 IRT
3 Real-Time channel - IRT
Real-Time
z
Real-Time switch ASIC
z
z
High-performance transfer
Data
9 in isochronous mode
Jitter <1µsec
How can this be distinguished ? Æ
© PNCC Burgdorf
PROFINET IRT
9
IRT Æ “Life on the Fast Lane”
RT
Lane for IRT
RT
TCP/IP
RT
TCP/IP
RT
TCP/IP
TCP/IP
TCP/IP
P/
IP
Calculations
● Reserved Lane (Resources) for RT
● Guaranty for Real-time independent from traffic (Network
load)
● Access with no restrictions (TCP/IP, IT, ….)
10
TC
IsochronousReal-Time (IRT)
HOV lane
RT
Real-Time (RT)
RT
Overview
© PNCC Burgdorf
PROFINET IRT
TCP/IP
TCP/IP
Tr
af
fic
Ja
m
10
5
PROFINET and IRT
What does IRT require ?
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
„
Segmentation Æ only possible within 1 segment
„
Time Scheduled Communication Æ reserved bandwidth
„
Time Synchronisation Æ acc to IEEE 1588
11
© PNCC Burgdorf
PROFINET IRT
11
Real-Time Ethernet with Isochronous Mode
Communication system scheduling
Overview
Real-Time (RT)
●Exact cycle synchronization
●Separate time domains for Real-Time and non Real-Time
IsochronousReal-Time (IRT)
Calculations
IRT
channel
Open
channel
(TCP/IP)
Cycle 1
Open
channel
(TCP/IP)
IRT
channel
Cycle 2
Cycle n
E.g. 1 ms position control cycle
Synchronization
Deterministic communication
IRT data
© PNCC Burgdorf
12
Open communication
RT and TCP/IP data
PROFINET IRT
12
6
Synchronised Real-Time Scheduling
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
Tsendclock
Tsendclock+1
Calculations
iRT
Time scheduled
communication
RT aRT
NRT
iRT
RT aRT
Address based
communication
NRT
13
© PNCC Burgdorf
PROFINET IRT
13
Time Scheduling with PROFINET
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
cycle time e.g. 1 ms
green interval
Calculations
red interval
reserved IRT-area
red interval
...
green/red
border
green/red
border
green frame shall
complete here
14
© PNCC Burgdorf
PROFINET IRT
14
7
Behavior of Real-Time Switches
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
RT
RT
RT
RT
NRT
NRT
SRT-Weiche
Calculations
NRT-Weiche
RT-Phase
NRT-Phase
RT-Phase
15 NRT-Phase
Switch
Switch
NRT
RT
RT
RT
RT
NRT
RT-Weiche
NRT-Weiche
Switch
Switch
Cycle Synchronization
© PNCC Burgdorf
PROFINET IRT
15
Processing of the Data in an IRT-Switch
Overview
Real-Time (RT)
ƒ If the frame cannot be clearly identified (CRC different) at the
receive point of time a diagnosis information is created and the
frame is forwarded in any case (Transfer_status<>0)
IsochronousReal-Time (IRT)
3,6 µs
Calculations
FrameChecker
(CRC)
CRC different ?
Status good/bad
…….
CRC
……
CRC
Switch
Switch
16
The Schedule has to be fulfilled in any case
© PNCC Burgdorf
PROFINET IRT
16
8
Simultaneous Communication
IRTDevice
IRTDevice
Overview
Real-Time (RT)
1
IsochronousReal-Time (IRT)
Calculations
1
IRT- 1
Device
IRTDevice
IRT- 2
Device
IRTDevice
3
IRTDevice
IRTDevice
4
17
The complete Communication
can take place at the same time
1 …5
IRT- 5
Device
Forwarding information is stored
(independent from MAC-addresses)
© PNCC Burgdorf
IRT- Frames in Ascending Order
IsochronousReal-Time (IRT)
IRTDevice
Frame 2
Recv.Port3
Send Port1
Calculations
IRTDevice
PROFINET IRT
17
Frame 1
Recv.Port1
Send Port3,t
Overview
Real-Time (RT)
IRTDevice
1
IRTDevice
IRTDevice
IRTDevice
IRTDevice
2
Frame 1
Recv.Port 2
Send Port 3,t
IRTDevice
18
Frame 1
Recv.Port 1
Send -------Frame 2
Recv.Port4
Send Port1,t
Frame 2
Recv.Port2
Send ----
© PNCC Burgdorf
PROFINET IRT
18
9
Time Synchronization: Based on IEEE1588
Sync-Master
Sync-Slave
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
12:00
T1
Calculations
Sync.Req
ld
T2
FollowUp.
Req ( T1
=
12:05
12:00)
12:15
T3
eq
Delay.R
T4= e.g..
20 sec
Delay.Rsp
(T4=
12:00 20
)
19
12:55
1.
Calculation line delay:
2. Adjust time
time in Follow up+ line delay +
local Timer from the time T2
Tld = ( (T 4 – T1) – (T3 – T2) ) / 2
© PNCC Burgdorf
PROFINET IRT
19
Isochronous Real-Time Communication
Overview
time x+ 9 µs
time x+ 13,5 µs
time x+ 4,5 µs
time x+ 9 µs
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
time x *)
1
2
3
Switch
1
Always a max. length of 100 m between 2 Switches is assumed = 0,5 µs run time
2
For safety reasons 0,5 µs is added per line
3
The throughput time of a frame within a switch is app 3,6 µs
20
*) the time synchronisation is done separately. The values are estimated values
© PNCC Burgdorf
PROFINET IRT
20
10
IRT- Calculation (Facts)
Assumption: bus cycle time is 1ms Æ 250 µs for RT and 750 µs for NRT
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
Calculation for RT-communication.
1 min. frame for RT-communication is
64 Bytes Standard Ethernet
8 Bytes Preamble and SFD
12 Bytes idle time
= 84 bytes in total
1 byte takes 80 ns at 100 Mb/s
1 min. frame takes app. 6,7 µs for one node
21
Calculation for TCP/IP frames:
1 complete Ethernet frame is app. 1500 bytes Æ 120 µs
1 kbyte Æ 82 µs Æ in 750 µs app. 9 Megabytes can be transferred
© PNCC Burgdorf
PROFINET IRT
21
Optimized Communication with PROFINET (IRT-Principle)
Outputs:
Overview
Real-Time (RT)
time
#1
t4
IsochronousReal-Time (IRT)
t3
Calculations
t2
#3
#2
#2
#3
#3
#4
#4
#4
#4
t1
IRT-
IRTDevice
Control
ler
#1
Inputs:
IRTDevice
IRTDevice
#2
#3
IRTDevice
#4
time
#1
t1
t2
t3
t4
22
#2
#2
#3
#3
#4
#3
#4
#4
#4
© PNCC Burgdorf
PROFINET IRT
22
11
Calculation without considering of the Jitter
Devices
Overview
IRTController
IRTDevice
Real-Time (RT)
IRTDevice
IRTDevice
IRTDevice
IsochronousReal-Time (IRT)
0 µs
Calculations
O,5 µs
7 µs
14 µs
7,5 µs
Time
21 µs
28 µs
Frame
1
3,5 µs
4µs
7µs
7,5µs
10,5 µs
Frame
2
11 µs
14 µs
Frame
3
23
Frame
4
*) the switchthrough time of a switch is considered to be about 3 µs
© PNCC Burgdorf
PROFINET IRT
23
Calculation with considering of the Jitter
IRTDevice
Overview
Real-Time (RT)
IsochronousReal-Time (IRT)
*)
Calculations
IRTDevice
IRTDevice
#1
IRTDevice
IRTDevice
#2
#xx
1 µs Jitter permits ca. 20 hops from the first to 24the last Device
*) 1 Hop = sending a frame from switch to switch Æ 40 ns
© PNCC Burgdorf
PROFINET IRT
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12
Example with considering of the Jitter
Backbone
Overview
HMI
HMI
HMI
HMI
MC
MC
MC
MC
..
..
..
..
HMI
HMI
HMI
HMI
MC
MC
MC
MC
MC
..
..
..
..
..
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
1
10
25
Machine module
Motion-Controller Drive
with ERTEC 400 withERTEC 200
© PNCC Burgdorf
The longest distance is18
PROFINET IRT
25
Distribution of updating times
n
Overview
IRT
RT
TCP/ IP - DCOM
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
15%
0.25...1.0
msec
10
msec
100%
26
t
100
msec
© PNCC Burgdorf
PROFINET IRT
26
13
Performance Parameters of IRT
Overview
Cycle Time
1 msec
250 µsec
Jitter
<1 µsec
<1 µsec
Real-Time (RT)
IsochronousReal-Time (IRT)
Calculations
Number of
Nodes/Axes
Simultaneously
transferable
TCP/IP data *)
*)
70
35
150
9
6
MB/sec
MB/sec
27
6
MB/sec
Standard length of the TCP/IP data packets from 64 to 1536 bytes
Max. data transmission rate on Fast Ethernet: 12 MB/sec
© PNCC Burgdorf
PROFINET IRT
27
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