SNMP and friends

1. SNMP andfriends 4 Application Layer Protocols4.1 Device Management Protocolsprotocolos de gestión de dispositivosProtocoles de gestion des appareilsGerätezugangsprotokolle

2. Contents This part treats device remote access in order of increasing complexity 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

3. The classical solution for analogue values 4.1.1 Current Loop Example differential pressure transducer 4..20 mA current loop Reminder: fluid

4. Data over 4..20 mA loops 4.1.2 HART 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

5. The Round card http://www.fint.no/ha-i4012.pdf 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.

6. HART commands summary Master Slave command Indication Request time-out response Response Confirmation

7. network adapter 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 modem adapter adapter 4-20 mA loop for HART 13.32 9.8 0.8

8. Installation point-to-point multidrop universal hand-help terminal taken from: www.hartcomm.org

9. Simple Network Management Protocol for the Internet 4.1.3 SNMP

10. Simple Network Management Protocol • Configuration Management • Keepingtrackofdevicesettings • Fault management • Dealingwithproblemsandemergencies (routerstopsforwarding, server loses power, etc) • Performance Management • Howsmoothlyisnetworkrunning? • Can it handle thecurrentworkload?

11. SNMP - MIB objects MIB managed information base Agent 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 exclusively for communication

12. 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

13. SNMP - Access to Managed Objects User agent manager interface interface object interface MIB managed information base Manager Agent call (request) call (indication) reply (confirm) reply (response) UDP UDP IP IP ISO 8802-2 Type 1 ISO 8802-2 Type 1 ISO 8802-3(Ethernet) Token Ring ATM ISO 8802-3(Ethernet) Token Ring ATM management messages network

14. 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.

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

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

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/snmp4tpc/files/reference/francois/snmp.ppt

18. Manufacturing Messaging Specification (MMS) Named Variable Named Program Variable List Invocation Domain Types Operator Transaction File Station Journal Semaphore Event Event Condition Enrolment Event 4.1.4 MMS Action

19. 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)

20. MMS - Application field schedule robot configuration

21. MMS - Concept MMS (Manufacturing Message Specifications) defines: • A set of standard objects which must exist in every conformant device, on which operations can be executed (example: local variables, read and write) or which can start a transmission spontaneously • A set of standard messages exchanged between a manager and an agent station for 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) 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)

22. MMS - Manufacturing Message Specification device device MMS specifies a set MMS specifies a set (e.g. PLC) (e.g. SCADA) of messages which of objects which allow an MMS client an MMS server is to control an MMS MMS MMS client expected to contain server server remote request response procedure (command) (reply) call interface communication stack communication stack network linking device (example) router

23. MMS - Communication Stack Association Control Service Element, ACSE, ISO 8649/8650, N2526,N2327 “Application” 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 8802-3(Ethernet) ISO 8802-4 MAC (token bus) Physical quite heavy… Boeing decided to drop ISO for TCP/IP ("TOP“).

24. MMS - Basic Communication Principles MMS assumes that the communication stack offers two services: MMS Requester MMS Responder (client) (server) network Request Indication 1) Remote Procedure Call (Call paired with Reply, synchronous, unicast) processing Confirmation Response 2) Event Reporting event (spontaneous messages sent by server) Request Indication 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.

25. 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 DefineEventCondition EventNotification AlterEventCondition AckEventNotification (MMS server) enables/disables event conditions Event Condition Event Enrolment Event Action When? Who? What? event notification and confirmation Events are the most complicated part of MMS

26. MMS - Event triggering MMS client MMS client TriggerEvent EventNotification AckEventNotification MMS Server NETWORK-TRIGGERED Event Condition Event Enrolment Event Action booleanvariable MONITORED cyclic monitoring plant events are triggered by a change in a boolean variable in the server (monitored event) or by an MMS client (trigger event) as an invitation procedure

27. Named Variable Named Program Variable List Invocation Domain Types Operator Transaction File Station Journal Semaphore Event Event Condition Enrolment Event VMD: Virtual Manufacturing Device • 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 robot flow meter cell Virtual Virtual Virtual Device Device Device Application Programming Interface (MMSI = MMS interface) communication presentation stack Action session transport network link physical

28. 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 ?