4 Application Layer Protocols Device Management Protocols - PowerPoint PPT Presentation

EPFL, Spring 2017 4 Application Layer Protocols

Device Management Protocols Application layer protocols offering remote services for large networks of devices: - Monitoring (health of devices and network, get current state) - Management (deployment, configuration, change settings) • current loop 4..20 mA • HART • SNMP: Simple Network Management Protocol • MMS: Manufacturing Messaging Specification Industrial Automation | 2017 2

Current Loop The classical solution for analogue values Example differential pressure transducer 4..20 mA current loop Reminder: fluid Industrial Automation | 2017 3

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. Reminder: Reminder: more info: http://www.hartcomm.org/ http://www.thehartbook.com/default.htm Industrial Automation | 2017 4

The Round card http://www.fint.no/ha-i4012.pdf Standardized printed circuit board - can be mounted in instrument - contains modem, processor, RAM, EPROM… necessary to execute the HART protocol. Why round? Most hydraulic instruments have a round case. Industrial Automation | 2017 5

HART commands summary Universal Commands Common Practice Commands Device-Specific Commands (example) • Read manufacturer and device type • Read selection of up to four dynamic • Read or write low -flow cut-off • Read variable and units variables • Start, stop, or clear totalizer • Read current output and percent of • Write damping time constant • Read or write density calibration range • Write device range values factor • Read up to four predefined dynamic • Calibrate (set zero, set span) • Choose variable (mass, flow, or variables • Set fixed output current density) • Read/write tag, descriptor, date • Perform self -test • Read or write materials or • Read/write 32 -character message • Perform master reset construction information • Read device range values, units, and • Trim variable zero • Trim sensor calibration damping time constant • Write variable unit • enable PID, write PID setpoint • Read or write final assembly number • Trim DAC zero and gain • Valve characterization • Write polling address • Write transfer function (square • Valve setpoint root/linear) • Travel limits • Write sensor serial number • User units • Read or write dynamic variable • Local display information assignments Industrial Automation | 2017 6

Device access device volumetric flow rate type FlowPro manufacturer ABB volumetric flow rate field device SCADA 3 cm2 cross sectional area: 2 cm pipe inside diameter velocity 13.32 m2/s diff. pressure 9.8 Pa density 0.8 kg/l hand-held device network network network modem adapter adaper adapter 4-20 mA loop for HART 13.32 9.8 0.8 Industrial Automation | 2017 7

SNMP:Simple Network Management Protocol Industrial Automation | 2017 8

Simple Network Management Protocol IETF (Internet standard) protocol for device and network management (widely supported, especially by routers, switches, servers, workstations, printers…). 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? Industrial Automation | 2017 9

SNMP - MIB objects networked MIB Device contains MIB device Agent (managed information base) and an agent to access MIB TCP/UDP/IP (171 objects) NT network (90 objects) DHCP (14 objects) WINS (70 objects) Appletalk Nowell IPX DecNet ….. CISCO (proprietary) Mostly parameters, statistics and error counters used for communication Industrial Automation | 2017 10

SNMP – ASN.1 Object example 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 } http://net-snmp.sourceforge.net/docs/mibs/TCP-MIB.txt Industrial Automation | 2017 11

Example SNPM Network Industrial Automation | 2017 12

SNMP - Access to Managed Objects User object interface MIB managed Manager Agent information base call call reply reply (request) (indication) (confirm) (response) UDP UDP IP IP ISO 8802-2 Type 1 ISO 8802-2 Type 1 ISO 8802-3 ISO 8802-3 management (Ethernet) (Ethernet) messages network Industrial Automation | 2017 13

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. Industrial Automation | 2017 14

Example Network and Queries Industrial Automation | 2017 15

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 Industrial Automation | 2017 16

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 Industrial Automation | 2017 17

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/ snmp 4tpc/files/reference/ francois / snmp .ppt Industrial Automation | 2017 18

Manufacturing Messaging Specification (MMS) schedule Named Variable Named Program Variable List Invocation robot Domain Types configuration Operator Transaction File Station Journal Semaphore Event Event Condition Enrolment Event Action Industrial Automation | 2017 19

Interaction between Operator Workplace and field equipment SCADA (client) (any technology) network (any) controller (server) (any technology) represents automation objects, i.e. a collection of PLC 1 variables manufacturing devices represent pieces of equipment MMS: access all controllers, regardless of the manufacturer, in the same way. Industrial Automation | 2017 20

The basic MMS idea: read a variable client (any technology) request read variable name response value status network (any) server I / O devices basic MMS idea: read and write equipment variables using standard messages. Industrial Automation | 2017 21

MMS - Manufacturing Message Specification Developed 1980 for General Motor’s flexible manufacturing initiative Reputation: heavy, complicated and costly (due to poor implementation) But: • Boeing adopted 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) Industrial Automation | 2017 22

MMS - Manufacturing Message Specification MMS does not specify the application interface device device Application Application MMS specifies a set of messages which MMS specifies a set allow an MMS client to control an MMS of objects an MMS MMS MMS server server contains client server request response (command) (reply) communication communication stack stack network linking MMS specifies how device messages are router encoded for transmission Industrial Automation | 2017 23

MMS - Communication Stack MMS Application Association Control Service Element, ACSE, ISO 8649/8650, N2526,N2327 Abstract syntax notation,ISO 8822/8823, 8824/8825 Presentation ISO 8326/8327 Session ISO 8073 Class 4 Transport ISO 8473 connectionless Network ISO 8802-2 Type 1 Link ISO 8802-4 MAC ISO 8802-3 (Ethernet) (token bus) Physical quite heavy… Boeing decided to drop ISO for TCP/IP ("TOP“). Industrial Automation | 2017 24