How Ethernet becomes industrial Prof. Bernard Jouga - Supélec, Rennes – France...

How Ethernet becomes industrial

Prof. Bernard Jouga - Supélec, Rennes – [email protected]

Workshop : Ethernet as a fieldbusGenève – Friday 28th September 2001

Friday 28th September 2001

CERN Workshop Ethernet 2

You said Ethernet…Ethernet offers A level 1 specification : cabling systems,

physical layer… in several versions A level 2 specification : Medium Access

Control… in several versions

So many differences between vintage Ethernetand future Ethernet !



… What do you mean ?

Ethernet doesn’t offer A complete stack up to applications, neither for the

office nor for the plant ! One standard solution for determinism and QoS

issues (not yet ?) One standard solution for connecting in industrial

environment (not yet ?) One standard solution for redundancy

management A satisfying solution for accurate stations

synchronization

As many Ethernet solutions as network vendors ?



The everlasting confusion

"I need Ethernet if I need a network ableto support TCP/IP applications"



AgendaDeterminism and Qos with Ethernet "Vintage" Ethernet Switched Ethernet

Which QoS implementation ?

An overview of vendors proposals Fieldbus interconnection with Ethernet/TCP/IP Fieldbus protocols over Ethernet/TCP/IP IDA proposal

Just one word about securityWhat are the real cost parametersConclusion



Vintage Ethernet

Frame broadcasting Along coaxial cables (10 BAS 5, 10 BAS 2) Through multiports hubs (10 BAS T, 100 BAS T)

Collision occurrences Function of the network size, the traffic load,

the average frame size 20% traffic load : 0,1% collisions 40% traffic load : 5% collisions

Non deterministic packet loss and packet delays



Switched Ethernet

10 Mbps, 100 Mbps, 1 Gbps 10 Gbps in the labs !

Frame switching on dedicated ports On the fly / Store and forward Half duplex /Full duplex



Level 2Back Pressure

Operates in half duplex mode A saturated port sends jam patterns (busy

indicator) to the connected equipment, enforcing the station to Listen Before Talk

No traffic discrimination

STOP



Level 2802.3x Flow Control

Operates in full duplex mode A saturated port sends PAUSE packets

to the connected equipment No traffic discrimination

PAUSE



Level 2802.1p CoS

Operates in half or full duplex modes IEEE 802.1Q defines the general architecture for Virtual

LANs and the VLAN protocol. IEEE 802.1p defines Classes of Services

Not supported by end-stations adaptersMost switches will not manage the 8 Cos (2 or 4)



Level 3DiffServ

Differenciated Services End points managed Uses IPv4 ToS or IPv6 priority field 64 possible levels Needs for adequate switches/routers

and adapted applications



TCP/IPIntServ

Integrated Services Routers managed Based on application identification

(IPv4 sockets or IPv6 Data Flow Id) 3 levels of services Uses RSVP Resource reserVation

Protocol to mark a path of reserved ressources for an application flow



Conclusion on QoS Management

So many strategies to avoidor minimize packets loss

IEEE 802.1p : a transient solution ? DiffServ bind to IPv6 deployment ? No future for IntServ ? Products are just coming on the

market



Switched Ethernet:a case study (1/2)

6 stations, cyclically generating realtime 200 bytes packets, "tagged" high priority

100 Mbps full duplex links One store & forward switch with an average 10 s

nominal latency Coexistence with low priority traffic

Compute the worst case total latency for a RT packet

Ethernet Switch

Station Station Station StationStationStation



Switched Ethernet:a case study (2/2)

16 s store & forward 10 s nominal switch latency 122 s flushing (the station can be at

this moment transmitting a low priority max size frame)

80 s queue emptying (5 RT packets already in queue)

TOTAL = 228 s



Transmission delays

Yet an another issue ! In complex architectures, end-to-end

delays may be lengthened by Gateways Proxys …

An argument for small/average size network domains



Vendors proposalfirst scheme (1/2)

"I offer solutions to interconnect my fieldbus and Ethernet"

A good idea … Profinet (Siemens) WorldFIP …



Vendors proposalfirst scheme (2/2)

But not so simple… Can I support IP applications on the fieldbus,

without disturbing real time traffic ? Can I forward fieldbus protocol messages

through Ethernet segments ? Can I have an integrated solution for the

networks management ? Delays introduced by proxies and gateway

The vendor must offer a complete solution !



Vendors proposalssecond scheme (1/3)

"I take my classic Fieldbus protocol and carry it on Ethernet with TCP or UDP"

A good idea … Modbus/TCP (Schneider) Ethernet/IP (Rockwell, IAONA) HSE (Fieldbus Foundation) WorldFIP EtherFIP …




But not so simple… TCP/IP protocol stack is designed for

Client/server application, not for 1 producer/N Consumers exchanges

Needs switched Ethernet to insure determinism Needs QoS management if mixed traffic with

other IP applications is needed How manage full redundancy if needed ? How manage station synchronization if needed

?

The protocol encapsulation specification is not

enough !




For sure not the cheapest solution ! Needs for industrial packaged Ethernet

products Needs engineering skill if hard real

time constraints

What is the value added for the end user ?

All this stuff doesn't make the initial fieldbus protocol better !



IDA proposal (1/2)

Interface for Distributed Automation NDDS, Network Data Delivery Service

Middleware Covering OSI layers 4 to 7 Producer/Consumer Model Broadcast and Multicast Adapted to real time traffic



IDA Proposal (2/2)

EthernetIP

TCPUDP

SN

MP (T)F

TP S

MT

P HTT

PND

DS

ParametrizationEventAlarm Download DiagnosticsProcess

Image

IDA Object Model

Syst

em

M

anagem

en

t

Programming Interface



Conclusion on Proposals

Various solutions… For various uses ? Most of them not yet mature What future for IEEE 1451 ?



Security IssuesDo not mistake Ethernet and Internet ! Consider the plant floor network as an Intranet Networks manufacturers & designers have the

know-how There are solutions to secure private IP networks (I hope that) plant floor networks (will) make use of

them

Do not mistake Security and safety ! Fieldbus manufacturers have the know-how Mechanisms used to provide safety in classic

fieldbus have to be implemented in Ethernet solutions



Cost parameters (1/3)

Engineering costs Components standardization Well-known design rules

Equipement costs Off-the-shelf components / Customs

components Proprietary protocols / open standards

Installation costs Number of different networks Number of cabling systems



Cost parameters (2/3)Commissioning costs Operators training System testing Proven technology & solid design

Maintenance costs Various components resellers Automatic discovery of new components Avaibility of remote configuration & testing

devices



Cost parameters (3/3)

Operating costs Minimization of operating HMIs Automatic cold & warm start

Evolution Costs



So, Why Ethernet ?Alternative vs. The "Fieldbus War" ? Guarantee of durability Multiple vendors could decrease costs

Seamless data paths From the plant-floor to the office For controllers, PLCs and ERP Systems

One network type One technical expertise A global network management



One Network fits all : an utopia ?

The market today : proprietary solutions Specific network hardware Specific protocols More or less compatible devices Vendors differences based on technical

performances

A challenge for setting a new market ? COTS network hardware One standard protocol for RT applications A large range of Ethernet devices Vendors differences based on value added services A new space for systems integrators ?



Questions ?

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