Industrial Automation Automation Industrielle Industrielle Automation 4Application Layer Protocols...
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Transcript of Industrial Automation Automation Industrielle Industrielle Automation 4Application Layer Protocols...
Industrial AutomationAutomation IndustrielleIndustrielle Automation
4 Application Layer Protocols
4.1 Device Management Protocolsprotocolos de gestión de dispositivosProtocoles de gestion des appareilsGerätezugangsprotokolle
SNMP and friends
Device access protocols 4.1 - 2Industrial Automation 2013
Contents
4.1.1 current loop 4..20 mA
4.1.2 HART
4.1.3 SNMP: Simple Network Management Protocol
4.1.4 MMS: Manufacturing Messaging Specification
This part treats device remote access in order of increasing complexity
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4.1.1 Current Loop
The classical solution for analogue values
Example differential pressure transducer
4..20 mA current loop
fluid
Reminder:
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4.1.2 HART
Data over 4..20 mA loops
Practically all 4..20mA devices come equipped with HART today
About 15 Mio devices are installed worldwide.
more info:
http://www.thehartbook.com/default.htm
http://www.hartcomm.org/
Reminder:
Reminder:
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The Round card
The round card is a standardized printed circuit board that can be mounted in an instrument, containing the modem, a processor, RAM, EPROM and all the logic
and software necessary to execute the HART protocol.
It is round because most hydraulic instruments have a round case.
http://www.fint.no/ha-i4012.pdf
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HART commands summary
Universal Commands Common Practice Commands
Device-Specific Commands(example)
• Read manufacturer and device type
• Read variable and units• Read current output and
percent of range• Read up to four predefined
dynamic variables• Read or write 8-character tag,
16-character descriptor, date• Read or write 32-character
message• Read device range values,
units, and damping time constant
• Read or write final assembly number
• Write polling address
• Read selection of up to four dynamic variables
• Write damping time constant• Write device range values• Calibrate (set zero, set span)• Set fixed output current• Perform self-test• Perform master reset• Trim variable zero• Write variable unit• Trim DAC zero and gain• Write transfer function (square
root/linear)• Write sensor serial number• Read or write dynamic
variable assignments
• Read or write low-flow cut-off• Start, stop, or clear totalizer• Read or write density
calibration factor• Choose variable (mass, flow,
or density)• Read or write materials or
construction information• Trim sensor calibration• enable PID, write PID setpoint• Valve characterization• Valve setpoint• Travel limits• User units• Local display information
Master
Indication
Slave
Request
Confirmation
Response
time-out
command
response
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Device access
type
manufacturer
modemnetworkadapter
device volumetric flow rate
FlowPro
ABB
velocity 13.32 m2/s
diff. pressure 9.8 Pa
density 0.8 kg/l
volumetric flow rate
cross sectional area:
pipe inside diameter
3 cm2
2 cm
13.32 9.8 0.8
field device
hand-held device
networkadapter
SCADA
4-20 mA loop for HART
networkadapter
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Installation
taken from: www.hartcomm.org
point-to-pointmultidrop
universal hand-help terminal
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4.1.3 SNMP
Simple Network Management Protocol for the Internet
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Simple Network Management Protocol
• Configuration Management
Keeping track of device settings
• Fault management
Dealing with problems and emergencies (router stops forwarding, server loses power, etc)
• Performance Management
How smoothly is network running?
Can it handle the current workload?
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SNMP - MIB objects
TCP/UDP/IP (171 objects)NT network (90 objects)DHCP (14 objects)WINS (70 objects)AppletalkNowellIPXDecNet…..CISCO (proprietary)
Mostly parameters, statistics and error counters used exclusively for communication
AgentMIBmanaged
informationbase
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tcpMaxConn OBJECT-TYP SYNTAX Integer32 (-1 | 0..2147483647) MAX-ACCESS read-only STATUS current DESCRIPTION "The limit on the total number of TCP connections the entity can support. In entities where the maximum number of connections is dynamic, this object should contain the value -1." ::= { tcp 4 }
tcpActiveOpens OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times that TCP connections have made a direct transition to the SYN-SENT state from the CLOSED state. Discontinuities in the value of this counter are indicated via discontinuities in the value of sysUpTime." ::= { tcp 5 }
SNMP – ASN.1 Object example
http://net-snmp.sourceforge.net/docs/mibs/TCP-MIB.txt
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SNMP - Access to Managed Objects
call(indication)
call(request)
management messages
object interface manager interface
User
managed informationbase
reply(confirm)
reply(response)
agent interface
MIBManager Agent
network
UDPIP
ISO 8802-2 Type 1ISO 8802-3(Ethernet)
TokenRing
ATM
UDPIP
ISO 8802-2 Type 1ISO 8802-3(Ethernet)
TokenRing
ATM
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SNMP - Operations on objects
Operations (PDU type):Get (read)Set (write)GetNext (transversal reading)GetBulk (optimized GetNext, v2 and v3)Response (variable bindings and acknowledgement)Trap (asynchronous agent notification, priorities)
Since SNMPv1/SNMPv2 do not provide authentication, “Set” commands are normally disabled. Traps are rarely used.
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SNMP - How are objects identified ?
ISO defined a world-wide addressing scheme on a hierarchical basis:
MIB objects are identified by a concatenation of numerical identifiers
quite wasteful, but bearable in LANs
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SNMP example of identification
.1.3.111.3.37.238.9999.1.1.2 ==.iso.org.ieee.standards-association-c-series-standards.std-c37.part238.
ieeeC37238TSMib.ieeeC37238Objects.ieeeC37238DefaultDS.ieeeC37238DefaultDSClkIdentity
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SNMP - Assumptions about the underlying communication network
- the network is connectionless (datagrams): only UDP is used (no TCP).
- manager and agent can send messages to each other spontaneously
- all entities must be able to receive and send packets of at least 484 octets
- the network supports broadcast
Further reading: www.wtcs.org/snmp4tpc/files/reference/francois/snmp.ppt
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4.1.4 MMS
Manufacturing Messaging Specification (MMS)
Action
ProgramInvocation
NamedVariable Named
Variable List
File
Types
Semaphore
EventEnrolment
Transaction
Domain
OperatorStation
Journal
EventCondition
Event
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MMS - Manufacturing Message Specification
Developed 1980 for the MAP project (General Motor’s flexible manufacturing initiative)
Reputed for being heavy, complicated and costly (due to poor implementations)
But:• Boeing adopted MMS as TOPs (MMS on Ethernet)• Adopted by the automobile industry and power distribution
Standardized as:
[1] ISO/IEC 9506-1: Industrial Automation systems - Manufacturing Message Specification -Part 1: Service Definition (IS 1990)
[2] ISO/IEC 9506-2: Industrial Automation systems - Manufacturing Message Specification -
Part 2: Protocol Specification (IS 1990)
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MMS - Application field
schedule
robot configuration
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MMS - Concept
• A set of standard messages exchanged between a manager and an agent stationfor the purpose of controlling these objects
• A set of encoding rules for these messages
• A set of rules for exchanging messages between devices (basic protocol)
• A set of standard objects which must exist in every conformant device, on whichoperations can be executed (example: local variables, read and write) or whichcan start a transmission spontaneously
MMS (Manufacturing Message Specifications) defines:
MMS does not specify application-specific operations (e.g. change motor speed).This is covered by application-specific, “companion standards”(e.g. flexible manufacturing, drives, remote meter reading)
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device(e.g. PLC)
MMSserver
communicationstack
MMS - Manufacturing Message Specification
network(example)
request
(command)
response
(reply)
linkingdevice
router
procedure call interface
device(e.g. SCADA)
remote
MMS specifies a set of objects which
MMSclient
an MMS server isexpected to contain
MMS specifies a set of messages which
to control an MMS server
allow an MMS client
communicationstack
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MMS - Communication Stack
Association Control Service Element, ACSE, ISO 8649/8650, N2526,N2327
ISO 8473 connectionless
ISO 8802-3(Ethernet) Physical
Link
Network
Transport
ISO 8802-4
ISO 8073 Class 4
ISO 8326/8327
Abstract syntax notation,ISO 8822/8823, 8824/8825 Presentation
ISO 8802-2 Type 1
MAC
“Application”
Session
quite heavy… Boeing decided to drop ISO for TCP/IP ("TOP“).
(token bus)
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MMS - Basic Communication Principles
Remote Procedure Call(Call paired with Reply,synchronous, unicast)
Event Reporting(spontaneous messages sentby server)
1)
2)
MMS does not specify how to address clients and servers. Messages contain only a communication reference (number which identifies the connection) obtained by unspecified means.
Indication
MMS Responder(server)
Request
Confirmation Response
network
Indication
Request
processing
event
MMS Requester(client)
MMS assumes that the communication stack offers two services:
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MMS - Event services
MMS provides services to:- Event Condition (define the boolean condition that triggers an event and its priority)- Event Enrolment (define the MMS client(s) to notify when an event is triggered)- Event Action (define the MMS confirmed service to be executed when the event occurs)
MMS client MMS client
(MMS server)enables/disables event conditions
event notification and confirmation
AlterEventCondition EventN
otifica
tion
AckEve
ntNotifi
catio
n
EventAction
EventEnrolment
EventCondition
What?Who? When?
DefineEventCondition
Events are the most complicated part of MMS
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MMS - Event triggering
MMS client MMS client
MMS Server
NETWORK-TRIGGERED
plant
EventAction
EventEnrolment
EventCondition
TriggerEvent
EventN
otifica
tion
events are triggered by a change in a boolean variable in the server (monitored event) orby an MMS client (trigger event) as an invitation procedure
cyclic monitoring
AckEve
ntNotifi
catio
n
booleanvariable
MONITORED
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VMD: Virtual Manufacturing Device
ProgramInvocation
NamedVariable Named
Variable List
File
Types
Semaphore
EventEnrolment
Transaction
Domain
OperatorStation
Journal
EventCondition Event
Definition of objects, services, and behavior •Only specifies the network-visible aspects (device / application communication)•Internal implementation details (programming language, operating system, CPU type, input/output (I/O) systems) not specified by MMS
interoperability
Action
flow meterrobot
Application Programming Interface(MMSI = MMS interface)
Virtual Device
Virtual Device
Virtual Device
communication
stack
physicallink
networktransportsession
presentation
cell
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Assessment
What is the purpose of the HART protocol ?
Which communication is used between a hand-help and a field device ?
Which categories of commands do exist ?
What distinguishes Hart from SNMP ?
What distinguishes SNMP from MMS ?
What are the (dis)advantages of MMS ?