2. Modeling Process CSCE 668Set 14: Simulations 2 May be several algorithms (processes) runs on each processor to simulate the desired communication system. For example, a processor run two algorithms (processes) at the same time ◦ one process (algorithm) that uses the broadcast service ◦ another process (algorithm) that implements the asynchronous broadcast system on top of the asynchronous point-to-point message-passing system proposed facility

3. Modeling Process (Cont.) Ordering of process, forming a “Stack of protocols” ◦ Environment communicates with the top layer ◦ Each process uses communication primitives to interact with the layer beneath it ◦ The bottom layer communicates with the Communication System CSCE 668Set 14: Simulations3 Algorithm composition

4. Simulation for Modeling Process CSCE 668Set 14: Simulations 4 layer 1layer 2layer 3 environment communication system modeled as a problem spec (interface & allowable sequences) modeled as a problem spec (interface & allowable sequences) modeled as state machines communicate via appropriate primitives: shared events Layered model

5. Simulation for Modeling Process (Cont.) CSCE 668Set 14: Simulations 5 layer 1layer 2layer 3 environment communication system Send Propagation of events

6. Modeling Process Specifications (1) A system consists of ◦ A collection of n processors (or nodes), p 0 through p n-1 ◦ A communication system C linking the nodes ◦ Environment E Notes ◦ Environment E and Communication system C are given as problem specifications ◦ Node is a hardware notion ◦ Running on each node are one or more processes  Processes are organized into a single stack of layers  The same number of layers on each node CSCE 668Set 14: Simulations6

7. Modeling Process Specifications (2) Each process is state machine (modeled as an automaton) ◦ Has a set of states, including a subset of initial states ◦ Has hour kinds of events  Inputs coming in from the layer above (or the environment, if this is the top layer)  Outputs going out to the layer above  Inputs coming in from the layer below (or the communication system, if this is the bottom layer)  Outputs going out to the layer below ◦ Events of type 1 and 2 form the top interface of the process ◦ Events of type 3 and 4 form the bottom interface of the process CSCE 668Set 14: Simulations7

8. CSCE 668Set 14: Simulations 8 layer i - 1 layer i layer i + 1 Propagation of events Top interface of layer i Bottom interface of layer i 12 34

9. Modeling Process Specifications (3) Events ◦ Concepts  An event is said to be enabled in a state of a process if there is a transition from that state labeled with that event  Inputs from the environment and from the communication system are called node inputs A configuration of the system specifies a state for every process on every node ◦ A configuration does not include the state of the communication system ◦ An initial configuration contains all initial states

10. Modeling Process Specifications (4) An execution of the system is a sequence C 0 e 1 C 1 e 2 C 2 … of alternating configurations C i and events e i ◦ If it is finite, ending with a configuration ◦ Satisfies the following conditions  Configuration C 0 is an initial configuration