Message Sequence Charts - PowerPoint by garrickWilliams

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									International Telecommunication Union




Message Sequence
     Charts
       Clive Jervis
     Rapporteur Z.120



  ITU-T Bangalore Workshop, 30-31st August 2001
             Message Sequence Charts
               ITU-T Standard Z.120
Topics:                                        Current Version:         MSC 2000
• Overview                                     Previous Version:        MSC ‟96
• Uses                                         Next Version:            MSC 2004
• Language                                     Standard consists of:
• Future                                       • graphical grammar
• Summary                                      • ASCII grammar
                                               • static & dynamic semantics
                                               • formal semantics, Annex B
                                               • examples

             UK

                  air_in
                            USA         RMTR
                                               MSC is:
                                               • used widely in industry
                              taxi_in



                              taxi_out


                  air_out

                                               • has good tool support
                                               • strong ties to other ITU languages
                            ITU-T - Bangalore Workshop, 30-31st August 2001           2
19.08.2009
                                              Overview
               msc call_set_up

                 mobile_1        base_1          network          base_2         mobile_2
                      up_call_req
                                       up_call_req
                                                       down_req
                                                                      down_req
                                            call_ack
                            call_ack                                  up_call_resp
                                                       up_call_resp
                                         down_resp
                         down_resp




             • Intuitive, widespread informal use
             • Focuses on external interactions rather than internal behaviour
             • Only notation that shows complete system interactions
             • Good for partial specifications - i.e. scenarios
             • Can be used independently of other languages
             • Universal data language interface
                             ITU-T - Bangalore Workshop, 30-31st August 2001                3
19.08.2009
                UK    USA       RMTR
                                                                                            MSCs in the Lifecycle
                 air_in



                                            MSCs Used Formally Throughout Lifecycle
                           taxi_in

                           taxi_out

                 air_out




        ITU, ETSI Standards                                                                                                                                                                                                                                                    System/Integration
                                                                                                                                                                                                                                                                                    Testing
                                       UK    USA       RMTR
                                                                                                                                                                                                   UK    USA                RMTR
                                        air_in
                                                  taxi_in                                                                                                                                           air_in
                                                                                                                                                                                                              taxi_in                  START
                                                                                                                                                                                                                                       MEETING



                                                  taxi_out                                                                                                                                                                             PRESENT        always takes




                                                                                                           Test Generation
                                                                                                                                                                                                                                       ARGUMENTS      too long


                                                                                                                                                                                                              taxi_out    COMPANY X
                                                                                                                                                                                                                          OPINION
                                                                                                                                                                                                                                                   COMPANY Y
                                                                                                                                                                                                                                                   OPINION
                                        air_out
                                                                                                                                                                                                                                 MOTOROLA OPINION

                                                                                                                                                                                                    air_out     THROW OUT
                                                                                                                                                                                                                                        SUPERIOR
                                                                                                                                                                                                                                        ARGUMENT
                                                                                                                                                                                                                                                                    AGREE
                                                                                                                                                                                                                                                                    WITH
                                                                                                                                                                                                                                                                    MOTOROLA
                                                                                                                                                                                                                   IDEA


                                                                                                                                                                                                                                        COFFEE         where the real
                                                                                                                                                                                                                     -                                 work is done
                                                                                                                                                                                                                                        BREAK


                                                                                                                                                                                                                                       PROPOSE
                                                                                                                                                                                                                                       DECISION


                                                                                                                                                                                                                                         MEETING
                                                                                                                                                                                                                                         AGREES


                                                                                                                                                                                                                                                       well
                                                                                                                                                                                                                                        LUNCH          deserved




             System Requirements
                                                                                                                                                                                                   TTCN
Automation                                                                        START
                                                                                  MEETING
                                                                                                                                                                                                   UK    USA
                                                                                                                                                                                                    air_in
                                                                                                                                                                                                              taxi_in
                                                                                                                                                                                                                            RMTR




                                                                                                                                                                                                                                                                                        Box
                                                                                  PRESENT            always takes
                                                                                  ARGUMENTS          too long
                                                             UK           USA          RMTR


Requires
                                                                                                                                                                                                                                      START
                                                                      COMPANY X                 COMPANY Y                                                                                                                             MEETING
                                                                      OPINION                   OPINION

                                                                air_in                                                                                                                                        taxi_out


                                                                                                                           Test Generation
                                                                                                                                                                                                                                      PRESENT        always takes
                                                                            MOTOROLA       OPINION
                                                                                                                                                                                                                                      ARGUMENTS      too long
                                                                                                                AGREE
                                                              THROW OUT
                                                                 IDEA
                                                                             taxi_in
                                                                                   SUPERIOR
                                                                                   ARGUMENT
                                                                                                                WITH
                                                                                                                MOTOROLA
                                                                                                                                                                                                                         COMPANY X                 COMPANY Y

                                                                                  COFFEE              where the real
                                                                                                                                                                                                    air_out              OPINION                   OPINION
                                                                  -




                                                                                                                                                                                                                                                                                       Testing
                                                                                  BREAK               work is done
                                                                                                                                                                                                                               MOTOROLA OPINION

                                                                            taxi_out
                                                                                  PROPOSE
                                                                                  DECISION
                                                                                                                                                                                                              THROW OUT
                                                                                                                                                                                                                                       SUPERIOR
                                                                                                                                                                                                                                       ARGUMENT
                                                                                                                                                                                                                                                                  AGREE
                                                                                                                                                                                                                                                                  WITH
                                                                                                                                                                                                                                                                  MOTOROLA
                                                                                                                                                                                                                 IDEA




Formal
                                                                                    MEETING                                                                                                                                           COFFEE          where the real
                                                              air_out               AGREES                                                                                                                       -
                                                                                                                                                                                                                                      BREAK           work is done

                                                                                                     well
                                                                                   LUNCH                                                                                                                                              PROPOSE
                                                                                                     deserved
                                                                                                                                                                                                                                      DECISION


                                                                                                                                                                                                                                        MEETING
                                                                                                                                                                                                                                        AGREES


                                                                                                                                                                                                                                                     well
                                                                                                                                                                                                                                       LUNCH         deserved




Languages                            Box Requirements                                                                                                                                              TTCN
                                                                                                                                                                                         Code Generation
                                                                                                                                               START
                                                                                                                                               MEETING


                                                                                                                                               PRESENT       always takes
                                                                                                                                               ARGUMENTS     too l ong




   ASN.1                               SDL Design                                                                           THROW OUT
                                                                                                                              IDEA


                                                                                                                               -
                                                                                                                                   COMPANY X
                                                                                                                                   OPINION


                                                                                                                                         MOTORO LA OPINION
                                                                                                                                                SUPERIOR
                                                                                                                                                ARGUMENT


                                                                                                                                               COFFEE
                                                                                                                                               BREAK
                                                                                                                                                           COMPANY Y
                                                                                                                                                           OPINION



                                                                                                                                                                            AGREE
                                                                                                                                                                            WITH
                                                                                                                                                                            MOTORO LA


                                                                                                                                                              wher e the r eal
                                                                                                                                                              wor k i s done            Code Generation                                                                            Code
 Everywhere!                                                                                                                                   PROPOSE
                                                                                                                                               DECISION


                                                                                                                                                 MEETING
                                                                                                                                                 AGREES



                                                                                                                                                LUNCH
                                                                                                                                                             well
                                                                                                                                                             deserved




                                                                            ITU-T - Bangalore Workshop, 30-31st August 2001                                                                                                                                                                         4
19.08.2009
                                                                                                                                                                   MSC Uses
                                                                                Formality Enables Useful Tool Support
                                                                                                                                                                    Verification & Validation:
                                                                                                                                                                        • feature interactions
                UK               USA               RMTR
                      air_in
                                         taxi_in




                    air_out
                                     taxi_out
                                                                              Requirements V&V                                                                          • race conditions
                                                                                                                                                                        • tracing

                                                                                                UK                USA                  RMTR
                                                                                                                                                                    Tracing:
                                                                                                                                                                        • model validation
                                START
                                MEETING
                                                                                                         air_in
                                PRESENT       always takes
                                ARGUMENTS     too l ong
                                                                                                                          taxi_in
                    COMPANY X               COMPANY Y




                                                                          SDL Tracing
                    OPINION                 OPINION




                                                                                                                                                                        • application code validation
                          MOTORO LA OPINION

             THROW OUT
                                 SUPERIOR
                                 ARGUMENT
                                                             AGREE
                                                             WITH
                                                                                                                      taxi_out
               IDEA                                          MOTORO LA


                                COFFEE         wher e the r eal
                -
                                BREAK          wor k i s done
                                                                                                     air_out
                                PROPOSE
                                DECISION




                                                                                                                                                                        • test validation
                                  MEETING
                                  AGREES


                                              well
                                 LUNCH        deserved




                UK
                      air_in
                                 USA               RMTR                                                              START
                                                                                                                     MEETING


                                                                                                                     PRESENT
                                                                                                                     ARGUMENTS
                                                                                                                                        always takes
                                                                                                                                        too l ong
                                                                                                                                                                    Design Verification:
                                                                                                                                                                       • model checking
                                         taxi_in                                                         COMPANY X
                                                                                                         OPINION
                                                                                                                                     COMPANY Y
                                                                                                                                     OPINION




                                                                          SDL Verification
                                                                                                                MOTORO LA OPINION
                                                                                                                      SUPERIOR                         AGREE
                                                                                                 THROW OUT                                             WITH
                                     taxi_out                                                      IDEA
                                                                                                                      ARGUMENT                         MOTORO LA


                                                                                                                     COFFEE              wher e the r eal
                                                                                                     -                                   wor k i s done
                                                                                                                     BREAK




                                                                                                                                                                       • SDL upholds MSCs
                    air_out                                                                                          PROPOSE
                                                                                                                     DECISION


                                                                                                                         MEETING
                                                                                                                         AGREES


                                                                                                                                         well
                                                                                                                      LUNCH              deserved




                                                                                                                                                                    Test Generation:
                                                                                                                                                                        • conformance testing
                UK               USA               RMTR                                                          START
                                                                                                                 MEETING



                      air_in                                                                                    PRESENT
                                                                                                                ARGUMENTS
                                                                                                                                   always takes
                                                                                                                                   too long


                                         taxi_in                                                    COMPANY X                  COMPANY Y
                                                                                                    OPINION                    OPINION




                    air_out
                                     taxi_out
                                                                         TTCN Generation     THROW OUT
                                                                                                IDEA


                                                                                                -
                                                                                                             MOTOROLA OPINION
                                                                                                                 SUPERIOR
                                                                                                                 ARGUMENT


                                                                                                                 COFFEE
                                                                                                                 BREAK


                                                                                                                 PROPOSE
                                                                                                                                               AGREE
                                                                                                                                               WITH
                                                                                                                                               MOTOROLA


                                                                                                                                    where the real
                                                                                                                                    work is done

                                                                                                                                                                        • test purposes (one-2- many)
                                                                                                                 DECISION




                                                                                                                                                                        • test specification (one-2-one)
                                                                                                                   MEETING
                                                                                                                   AGREES


                                                                                                                                   well
                                                                                                                 LUNCH             deserved




                                                                                     ITU-T - Bangalore Workshop, 30-31st August 2001                                                                       5
19.08.2009
                                       Basic Features
                   msc call_expiration
                                base          network      manager
   Time
                                   initiate
Progresses                                                                     handler
                   wait(5)                                ready
Downwards
                                                                               „handle
    • No linearity                                call_set_up                    call‟
    • No synchronicity
                                   expired
    • Interleaving
                                                  terminate




                   • instance            • create                    msc call_set_up
                   • message             • reference
                                                                               network
                   • timer               • local action
                   • co-region           • stop
                             ITU-T - Bangalore Workshop, 30-31st August 2001             6
19.08.2009
                                           Semantics
                       • Single MSC defines a set of event traces
                       • Events interleaved
                       • Timing constraints can reduce possible traces

                                       msc call_expiration
         A message consists of:
                                            mobile          base              network
         • a send event
         • a receive event                            identify
                                                                 initialise
         Semantics prescribes
         no buffering mechanism


                                                       send initialise        receive initialise
                                   receive identify
       Three
                  send identify                       receive identify        receive initialise
      traces!
                                   send initialise
                                                      receive initialise       receive identify
                             ITU-T - Bangalore Workshop, 30-31st August 2001                       7
19.08.2009
                                        High-Level MSCs
                        Structuring MSCs             msc call_blocking

                        References can be to
                        • basic MSCs or                             initiate_call
                        • high-level MSCs

                        • start point
                        • end point                       call_set_up         call_refused
                        • reference
                        • branching
                        • looping
                                                        call_proceeding
                        • parallel (not shown)
                        • guards (not shown)

               Single telecom. feature                  terminate_call
             may have >100 basic MSCs
             structured through 3 levels
                 of high-level MSCs
                                 ITU-T - Bangalore Workshop, 30-31st August 2001             8
19.08.2009
                          In-Line Expressions
                Structuring event behaviour within an MSC
                              msc MyLife

 In-line expressions:                     infra              mobile_1     mobile_2
 • alternative                                call_req
 • parallel                   t(5)
 • optional
 • loop                             alt
                                                            when idle
 • exceptional
                                                         call_ack
 Operands:                      t            call_accept
 • non-deterministic choice
 • may be guarded                                           otherwise
 • events interleaved with      t
   those outside expression                  req_refused



                        ITU-T - Bangalore Workshop, 30-31st August 2001              9
19.08.2009
                             Time Constraints/Data
                        • Real-Time Constraints    • Message Contents
                        • Data Dependent Behaviour • Parameterisation
   Time Constraints:
      • absolute (tracing)              msc call_expiration(time_out: time)
      • relative (specification)
      • single point, intervals             base           network      manager
      • constrain regions                       initiate
                                                                                  @10:00
   Data:                                                              ready
   • static variables
        - parameterises MSC              x := f(_, 5)
        - global to MSC                                    set_up(time_out + 3)    [5, 10]
        - also instances, etc.
   • dynamic variables                         expired
        - local to instance                    (“z1”, _, x)     terminate
        - assigned in actions
        - declared MSC Document
   • underspecification
        - “don‟t care” values
                             ITU-T - Bangalore Workshop, 30-31st August 2001                 10
19.08.2009
                        Instance Decomposition
                 Splitting an Instance Into Constituent Processes
                   msc call               network
                                      decomposed as
                        base            network_call           manager

                          initiate
                                                             ready

                                               set_up


   • Hierarchical view of processes     msc network_call
                                           base_handler         manager_handler
   • Instance structure defined
                                        initiate                                 ready
      in enclosing MSC Document
                                                    initiate_set_up
   • Internal messages hidden in
                                                                            set_up
     upper view
                          ITU-T - Bangalore Workshop, 30-31st August 2001                11
19.08.2009
                                     Other Features
                 MSC: a Comprehensive Specification Language
                                          mscdocument network_manager
    MSC Document
                                          inst base_handler(x : integer);
    • module encapsulation                inst call_controller;
    • all declarations
                                          msg initiate(integer, integer, bool);
    • definition of data interface
    • inheritance/decomposition               call_set_up     call_proceeding     terminate_call


                                 msc call
    Control Flow
    • alignment with UML             mobile           base_1            network        base_2
    • method calls                      call initiate
    • suspension regions                                    set_up
                                                                         g
                                                                              call_set_up
                                                                         h
    Gates                                                       done
    • connecting messages
      across boundaries
                            ITU-T - Bangalore Workshop, 30-31st August 2001                        12
19.08.2009
                                 Future Features
                                          Z.120 MSC 2004
                          • Message Channels
                              - superseding gates
                              - organising messages through channels
                              - buffering semantics

                          • Presentation Formats
                               - TTCN Graphical presentation format, Z.142
                               - semantic restrictions, e.g. tracing
        Plenty to do
     Please Contribute!   • Formal Semantics, Z.120 Annex B
                              - Currently compliant only with MSC ‟96

                          • Instantiations of Universal Data Interface
                               - SDL interface scheduled 2002, Z.121
                               - ASN.1 interface?
                               - TTCN-3 interface?

                          • UML alignment
                              - OMG UML v2.0 sequence diagrams

                          ITU-T - Bangalore Workshop, 30-31st August 2001    13
19.08.2009
                                        Summary
                                     MSC is a rich language
                                        • suitable for requirements specification
Topics:      UK
              air_in
                    USA       RMTR


                        taxi_in         • many uses across lifecycle
• Overview    air_out
                        taxi_out
                                        • „engineer friendly‟ language
• Uses                                  • used in telecom standards

• Language                           Good tool support
• Future                                • getting more sophisticated
• Summary                               • industrial use
                                        • integrated with SDL, TTCN tools

                                     Standardisation Continues
                                         • interesting problems to work on
                                         • good forum for insight, new ideas
                                         • learn latest methods/technology

             • Improved productivity comes through
               automating manual processes
             • Automation requires formal languages
             ITU-T - Bangalore Workshop, 30-31st August 2001                        14
19.08.2009

								
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