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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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)

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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

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Ethernet Evolution - VLANs

Slide 6

Ethernet Evolution - Redundancy

Spanning Tree? No, Industrial Redundancy!

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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

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I/ODensity

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I/ODensity

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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

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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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