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Synthesis of Protocol Converter Using Timed Petri-Nets

Synthesis of Protocol Converter Using Timed Petri-Nets. Presented by:. Anh Dang Balaji Krishnamoorthy Manoj Iyer. Motivation. Heterogeneous, distributed networks Protocol converters allow communication among incompatible network protocols

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Synthesis of Protocol Converter Using Timed Petri-Nets

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  1. Synthesis of Protocol Converter Using Timed Petri-Nets Presented by: Anh Dang Balaji Krishnamoorthy Manoj Iyer

  2. Motivation • Heterogeneous, distributed networks • Protocol converters allow communication among incompatible network protocols • The authors of this paper describe a new synthesis technique used in protocol converter design and modeling

  3. Service and Protocol Concepts Communication services (to users) is organized as a stack of layers. Each layer offers services to the next higher layer • High-level abstraction: providing a number of communication services to users (service level) • Low-level abstraction: number of cooperating protocol entities (PEs) exchange protocol messages called protocol data units (PDUs) (protocol level)

  4. Converter Design Approaches • Top-down:service-level conversion • Easy to implement, tends to be “passive” • Bottom-up:protocol-level conversion • Very powerful, very complex • Hybrid: combination of Top-down and Bottom-up

  5. Converter Properties • Safety • Free from deadlock or livelock, and is complete • Liveness • Performs the required functionality • Timeliness • Satisfies the timing of both protocols

  6. Converter Design Criteria • Modeling formalism • CFSM, Petri Nets, etc. • Design approach • Service level, protocol level, or hybrid • Design methodology • Analytic: trial-and-error iterations • Synthetic: systematic, safe generation

  7. Design Criteria (con’t) • Information transfer issues • Direct: no buffers, messages transmitted immediately to each protocol • Indirect: messages stored in non-FIFO buffer, re-ordered, and transmitted • Synchronization issues • Mapping of messages (traces) to ensure compatibility

  8. Design Criteria (con’t) • Timeliness • Internal timing and protocol requirements • Data loss and recovery • Dynamicity • Self-induced, active communication • Concurrency • Complexity

  9. Timed Petri Net Model • Standard Petri net with predicated and timed transitions • New notations • Input/Output actions marked with +/- • Parallel composition: PN1 || PN2 • Trace “schuffling”: t1 t2 • Complement of a trace: ~t

  10. Some more for petri net

  11. Synthesis Technique • Greatest common service definition • Trace generation and collection • Trace synchronization • Synthesis of Petri Net model

  12. Greatest Common Service • Start with both service descriptions • I/O operations are service primitives • Map equivalent primitives into a service interface converter (SIC) • Remove primitives not mapped in SIC

  13. Example: GCSD ?

  14. Trace Generation • Interested in traces of each separate network which contribute to the GCSD • Can be found with following analysis: • Let TN be set of traces at {lower,upper}_N • Find N’, a pruning with contributions to S’N • Find us_N, composition of lower services and communication channel • TN = N’ || us_N

  15. TABP ={ACCEPT –DATA(bit) (+ACK(~bit) –DATA(bit))* +ACK(bit),+DATA(bit) (-ACK(~bit) +DATA(bit))* DELIVER -ACK(bit),+DATA(bit) DELIVER (-ACK(~bit) +DATA(bit))* -ACK(bit),+DATA(bit) (+DATA(bit))* DELIVER -ACK(bit),+DATA(bit) DELIVER (+DATA(bit))* -ACK(bit)} TPE ={SEND +poll (-data SEND) (-data SEND)* -end,+poll SEND (-data SEND) (-data SEND)* -end,(+poll)*,-poll (+data RECEIVE) (+data RECEIVE)* +end,(-poll)*} Example: Trace Generation

  16. Trace Synchronization • For trace sets TN and TM found above: • Prune the protocol components TRN, TRM • Take complements to get TCN • Schuffle the complements (TCN TCM) • 14 rules for ordering data, confirmation, ack, and nack messages safely • (N+m,N-c)  (M-m) = (N+m,M-m,N-c)

  17. TCABP = {lower_ABP} ~TCABP ={-DATA(bit) (+ACK(~bit) -DATA(bit))* +ACK(bit),+DATA(bit) (-ACK(~bit) +DATA(bit))* -ACK(bit),-DATA(bit) (-DATA(bit))* +ACK(bit)} TCPE = {lower_ABP} ~TCABP ={-poll (+data SEND) (+data SEND)* +end,(-poll)*,+poll (-data SEND) (-data SEND)* -end, (+poll)*} Example: Trace Synchronization TC = TCABPTCPE

  18. Result (after PN synthesis)

  19. Example: Alternating Bit (pick one)

  20. Example: Poll-End (pick one)

  21. Summary • Hybrid approach • Starts with service specification, but performs all synthesis on protocols • Timed Petri net model • Can incorporate timing in specification • Models concurrency and comes with well-known analysis algorithms • Resulting converter is safe and functional

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