slide 1 ethernet evolution - switching switched ethernet with full duplex communication now there...
Post on 18-Dec-2015
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Slide 1
Ethernet Evolution - Switching
Switched Ethernet with full duplex communication
Now there are no collision domains and hence no collisions!
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F6
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F1
Slide 2
Original Ethernet standards Maximum frame size – 1518 bytes
Recent change to allow Prioritisation Maximum frame size – 1522 bytes (increase of 4 bytes)
Ethernet Evolution – Prioritisation (QoS)
Preamble SFDDestination-
AddressSourceAddress FCSData
Length/Type
Preamble SFDDestination-
AddressSourceAddress FCSData
Length/TypeTAG
TPID TCI TPID = Tag Protocol Identifier
TCI = Tag Control Information
CFI = Canonical Format Indicator
Tag Protocol ID UserPriority
CFI VLAN ID
16 bit 3 bit 1 bit 12 bit
64 byte - 1518 byte
Slide 3
Ethernet Evolution – Prioritisation (QoS)
File
Video
Voice
Email+
Attach
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3
0
Voice
Video
File
Priority
Slide 4
Ethernet Evolution - VLANs
Part of the same development as Prioritisation was VLANs or Virtual Local Area Networks.
DTE can be tagged as belonging to a virtual LAN.
Any traffic for something outside of that VLAN will not be accepted by the DTE.
Switches too can monitor VLAN traffic and will not pass on frames that are not for that VLAN.
Slide 5
SCADA Server
Sales Server
IT Server
Manufacturing
Sales
IT
Ethernet Evolution - VLANs
Slide 6
Ethernet Evolution - Redundancy
Spanning Tree? No, Industrial Redundancy!
a b
Windows NT, 2000 etc
Slide 7
Bringing it all together
By combining all the recent developments of Ethernet together, data throughput is greatly increased.
10Mbit/s shared
10Mbit/s switched full duplex
100Mbit/s switched
10Mbit/s switched
100Mbit/s shared
100Mbit/s switched full duplex
4Mbit/s4Mbit/s
10Mbit/s10Mbit/s
20Mbit/s20Mbit/s
200Mbit/s200Mbit/s
40Mbit/s40Mbit/s
100Mbit/s100Mbit/s
Slide 8
Real-Time Ethernet
So is Ethernet a real-time control network?
Consider our original definition of real-time
Adjective :(computer science) of a system, in which data-processing occurs as the data is generated.
No, Ethernet cannot be considered a real-time control network, a control network definitely, but not a real-time one.
BUT, what about a deterministic one??
Slide 9
Deterministic Ethernet
Consider this typical RS485 bus network
Bus Termination Bus Termination
MasterController
I/ODensity
site
I/ODensity
site
I/ODensity
site
I/ODensity
site
500m 500m
500m
I/O 31I/O 1
Slide 10
M=Master; S= Slave; SW= Switch RS1
Application with one Master, 31 Slaves and 4 RS1-Switches
100 Mbit/s 100 Mbit/s100 Mbit/s
M S7 S8
SW1 SW2 SW3 SW4
S1 S8 S15 S16 S23 S24 S31
10 Mbit/s 10 Mbit/s 10 Mbit/s 10 Mbit/s
M
10 Mbit/s
Cascading of 10/100 Switches
Slide 11
Multicast from Master to all Slaves:
Send packet from Master to SW1: 57.6µsLatency in SW1: 4.0µsReceive packet in Slave 1: 57.6µsSend packet S1 to SW2: 5.76µsTransmit time SW1 to SW2 : 2.5µsLatency in SW2: 4.0µsSend packet SW2 to SW3: 5.76µsTransmit time SW2 to SW3 2.5µsLatency in SW3: 4.0µsSend packet SW3 to SW4: 5.76µsTransmit time SW3 to SW4 2.5µsLatency in SW4: 4.0µsReceive packet in Slave 31: 57.6µs
Total time: 155.98µs
Receive packet
at slave 1
Receive packet
at slave 31
This time is called:Receive variance
Cascading of 10/100 Switches
Slide 12
All Slaves sending response to Master:
Send packet Slaves 24-31 to SW4: 57.6µsLatency in SW4: 4.0µsSend packet from SW4 to SW3: 52.8µsTransmit time SW4 to SW3: 2.5µsLatency in SW3: 4.0µs Send packet SW3 to SW2: 52.8µsTransmit time SW3 to SW2 2.5µs Latency in SW2: 4.0µsSend packet SW2 to SW1: 52.8µsTransmit time SW2 to SW1 2.5µsLatency in SW1: 4.0µsSend packet SW1 to Master: 528.0µs
Total time: 767.5µs
Cascading of 10/100 switches
Slide 13
100 Mbit/s
100 Mbit/s 100 Mbit/s100 Mbit/s
M
M = Master; S = Slave; SW = Switch RS2
Application with one Master, 31 Slaves and 4 RS2-Switches
SW1 SW2 SW3 SW4
S1 S8 S15 S16 S23 S24 S31
100 Mbit/s 100 Mbit/s 100 Mbit/s 100 Mbit/s
Upgrading all links to 100Mbps
Slide 14
Multicast from Master to all Slaves:
Send packet from Master to SW1: 5.76µsLatency in SW1: 4.0µsReceive packet in Slave 1: 5.76µsSend packet S1 to SW2: 5.76µsTransmit time SW1 to SW2 : 2.5µsLatency in SW2: 4.0µsSend packet SW2 to SW3: 5.76µsTransmit time SW2 to SW3 2.5µsLatency in SW3: 4.0µsSend packet SW3 to SW4: 5.76µsTransmit time SW3 to SW4 2.5µsLatency in SW4: 4.0µsReceive packet in Slave 31: 5.76µs
Total time taken: 52.3µs
Receive packet
at slave 1
Receive packet
at slave 31
This time is called:Receive variance
Upgrading all links to 100Mbps
Slide 15
All Slaves sending response to Master:
Send packet Slaves 24-31 to SW4: 5.76µsLatency in SW4: 4.0µsSend packet from SW4 to SW3: 52.8µsTransmit time SW4 to SW3: 2.5µsLatency in SW3: 4.0µs Send packet SW3 to SW2: 52.8µsTransmit time SW3 to SW2 2.5µs Latency in SW2: 4.0µsSend packet SW2 to SW1: 52.8µsTransmit time SW2 to SW1 2.5µsLatency in SW1: 4.0µsSend packet SW1 to Master: 52.8µs
Total time: 240.46µs
Upgrading all links to 100Mbps
Slide 16
Scan Times
Scan time of a 10Mbps network
312 µs + 2193µs = 2505 µs
Scan time of 10Mbps network with 100Mbps links between switches
156 µs + 768 µs = 924 µs
Scan time of 100Mbps network
52 µs + 240µs = 292 µs
Slide 17
Real-Time, Determinism and Ethernet
So can Ethernet cope with the demands of a real-time control network?
Scan times are as quick if not quicker than contemporary bus systems. Deterministic? Definitely in a controlled traffic network.
Worldwide, open standards means all vendors support Ethernet.
Flexibility means it already supports such things as remote video monitoring.
Evolutionary history means it can only get better!
Slide 18
The Future
How many disparate networks do you need between the information and device layers?
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