2. OPNET Modeler Day 2

3. © copyright 2001 OPNET Technologies, Inc. 2 Course Outline Events and Event List Concepts Process Modeling Process Modeling Lab Collecting Scalar Statistics Radio Modeling

4. Events and Event List Concepts

5. © copyright 2001 OPNET Technologies, Inc. 4 Agenda Event-driven Simulation Event List and the Simulation Time Clock Simulation Kernel Interrupts Processes and Interrupts Event List Example

6. © copyright 2001 OPNET Technologies, Inc. 5 Event-Driven Simulation Events are specific activities that occur at a certain time OPNET simulations are event-driven Simulation time advances when an event occurs A different method might be to sample at regular intervals –Disadvantages: Accuracy of results is limited by the sampling resolution Simulation is inefficient if nothing happens for long periods

7. © copyright 2001 OPNET Technologies, Inc. 6 TimeEvent Type Module 0.0 Initializesrc.gen 0.0Initialize src.rte 4.3Timer expiressrc.gen 4.3Packet arrivessrc.rte Head Event List Concepts Single global event list Shared simulation time clock Events scheduled in time order Event removed from event list when it completes

8. © copyright 2001 OPNET Technologies, Inc. 7 The Simulation Kernel Simulation Kernel (SK) manages the event list SK delivers each event, in sequence, to the appropriate module SK receives requests from processes and inserts new events in the event list

9. © copyright 2001 OPNET Technologies, Inc. 8 Event Generation and Cancellation Events can be generated in several ways –BEGSIM/ENDSIM interrupts –Self interrupts –Packet arrivals (STRM interrupts) –Writing to a statwire (STAT interrupts) Events can be cancelled before they occur

10. © copyright 2001 OPNET Technologies, Inc. 9 Interrupts First event in the event list becomes an interrupt Delivered by the Simulation Kernel to the designated module Data associated with the event can be obtained by the module Processors and queues can have BEGSIM interrupts

11. © copyright 2001 OPNET Technologies, Inc. 10 How Does the Event List Work? New event reaches head of event list, which causes Simulation Kernel to deliver an interrupt to the appropriate module Simulation Kernel regains control from module Process within the module gains control and processes interrupt Simulation Kernel deletes event from event list, allowing new event to reach head of list

12. © copyright 2001 OPNET Technologies, Inc. 11 Event List Implementation The Simulation Kernel uses an efficient proprietary algorithm to maintain the event list Event times are expressed as double-precision, floating-point numbers and are used to keep the event list sorted 0.01234 56789 11111 11 0.01234 56789 11111 22 0.01234 56789 11111 33 0.01234 56789 11111 44 0.01234 56789 11111 55 0.01234 56789 11111 66 0.01234 56789 11111 77 Suppose that this interrupt triggers an event to occur at 0.01234 56789 11111 75. The Simulation Kernel minimizes the time required to place this event at the correct place on the list.

13. © copyright 2001 OPNET Technologies, Inc. 12 Delivery of Interrupts When an interrupt is delivered to a module, control passes from the Simulation Kernel to the module If the module is a queue or processor, the interrupt is delivered to the process running within the module Other modules have default behaviors

14. © copyright 2001 OPNET Technologies, Inc. 13 Event List Concepts Reviewed Events must exist in the event list at the start of a simulation –A processor or queue module has the begsim interrupt attribute enabled An event list typically has a few events – each event may schedule other events The event list is always growing and shrinking An event is pending until executed A pending event can be cancelled

15. © copyright 2001 OPNET Technologies, Inc. 14 Forced States Forced (green) and unforced (red) states differ significantly in execution timing In a forced state, the process: –Invokes the enter executives –Invokes the exit executives –Evaluates all condition statements –If exactly one condition statement evaluates to true, the transition is traversed to the next state OPNET convention: code in enter execs only Transition to next state Forced (green) states Enter execs invoked No blocking or waiting Exit execs invoked Enter execs invoked Exit execs invoked No blocking or waiting

16. © copyright 2001 OPNET Technologies, Inc. 15 Unforced States In an unforced state, the process: –Invokes the enter executives –Places a marker at the middle of the state –Releases control to the Simulation Kernel and becomes idle –Resumes at the marker and processes the exit execs when next invoked Start of invocation End of invocation Unforced (red) states Transition to next state Blocking, waiting for invocation Exit execs processed when invocation occurs Enter execs invoked Next invocation starts here Blocking, wait for next invocation

17. © copyright 2001 OPNET Technologies, Inc. 16 Transitions Between States After completing the exit executives, the process evaluates the conditions for all transitions from the state One and only one condition statement must evaluate to true The single true transition is taken to the next state A transition with condition = “default” is true if and only if no other conditions are true A transition with no condition set is termed unconditional and is always true

18. © copyright 2001 OPNET Technologies, Inc. 17 How a Process Handles an Interrupt Flow diagram showing how a process handles an interrupt: (except the initial interrupt) Implement exit execs Set marker; block and wait for interrupt Receive interrupt Evaluate condition statements Red state? Yes No Follow transition to next state Implement enter execs Find marker

19. © copyright 2001 OPNET Technologies, Inc. 18 Process Model Example Model with three forced states and one unforced state: 3. Transition occurs.6. Transition occurs. 2. Exit execs invoked immediately. Transition condition (pk_count == 0) evaluates to true. 5. Exit execs invoked immediately. 8. Marker is placed and process stops here. 7. Enter execs invoked.4. Enter execs invoked. 1. Initial interrupt delivered and the enter execs invoked.

20. © copyright 2001 OPNET Technologies, Inc. 19 The Simulation Kernel and Processes Control passes between the Simulation Kernel (SK) and multiple processes ( pr1, pr2, etc.), as described below: Description In controlIdle Read first event on event list. Deliver to appropriate process ( pr1 ). SKAll processes Invoke enter and exit execs of initial state ( forced1 ). Evaluate pr1 SK; other processes condition statements and transition to next state ( forced2 ). Invoke enter and exit execs of forced2. Transition to next state ( unforced ). Invoke enter execs of next state ( unforced ). Release control to SK. Become idle. Remove first event from event list. Advance next event toSKAll processes head of list. Deliver interrupt to pr2. Invoke enter and exit execs of initial state (this process model is not shown). pr2 SK ; other processes Evaluate condition statements and transition to next state

21. © copyright 2001 OPNET Technologies, Inc. 20 Event List Example Consider this model: Network model Node model Node model: src Node model: dest1 Network model

22. © copyright 2001 OPNET Technologies, Inc. 21 Event List Example (cont.) The network model has three nodes ( src, dest1, dest2 ) relying on two node models (both dest nodes use the same node model) In the src node model, packets are generated at gen and sent by queue to either transmitter (tx0 / tx1) Packets then flow across a link to a destination node ( dest1, dest2 ) where they are received ( rx ) and thrown out ( sink ) Three modules ( gen, queue, and sink ) have process models associated with them

23. © copyright 2001 OPNET Technologies, Inc. 22 The BEGSIM Interrupt BEGSIM is an interrupt that occurs at simulation time 0.0, before any other type of interrupt A BEGSIM interrupt usually initializes a module and schedules future events Any processor or queue can have its begsim intrpt attribute enabled, resulting in an event being placed on the event list for time 0

24. © copyright 2001 OPNET Technologies, Inc. 23 Event List Example (cont.) The begsim intrpt attribute for modules src.gen and src.queue is enabled; this places two events in the event list TimeEvent TypeModule 0.0BEGSIMsrc.gen 0.0BEGSIM src.queue Node model

25. © copyright 2001 OPNET Technologies, Inc. 24 Processing the First Interrupt Consider the process model specified by the src.gen module Node model: src Process model: gen

26. © copyright 2001 OPNET Technologies, Inc. 25 Starting the Simulation Simulation Kernel reads the event at the head of the event list, and delivers control to the process in the src.gen module Process begins execution at the initial state, marked with the black arrow Process executes the Init state’s enter execs TimeEvent TypeModule 0.0BEGSIMsrc.gen 0.0BEGSIM src.queue

27. © copyright 2001 OPNET Technologies, Inc. 26 Processing the First Interrupt in Process gen (cont.) Process model Process model: gen

28. © copyright 2001 OPNET Technologies, Inc. 27 Because Init is a forced (green) state, process immediately invokes and completes the exit execs. Process evaluates all condition statements. This state has only one departing transition which evaluates to true. Process transitions to Wait state. Processing the First Interrupt in Process gen (cont.)

29. © copyright 2001 OPNET Technologies, Inc. 28 Process model Process invokes and completes the enter execs of Wait. Processing the First Interrupt in Process gen (cont.)

30. © copyright 2001 OPNET Technologies, Inc. 29 Line 9 of the enter execs schedules a self interrupt using a KP. This adds an event to the event list. Process places a marker at the middle of Wait. Process becomes idle. TimeEvent TypeModule 0.0BEGSIMsrc.gen 0.0BEGSIM src.queue 4.3SELFsrc.gen Marker Processing the First Interrupt in Process gen (cont.)

31. © copyright 2001 OPNET Technologies, Inc. 30 Processing the Second Interrupt at module src.queue Simulation Kernel removes the first event and advances the next event to the head of the event list. The simulation time remains 0.0. Simulation Kernel delivers a BEGSIM interrupt to src.queue. Process in src.queue module gains control. It executes until it reaches an unforced (red) state, places a marker, and then becomes idle. (This model is not shown.) TimeEvent TypeModule 0.0BEGSIMsrc.queue 4.3SELF src.gen First event is removed

32. © copyright 2001 OPNET Technologies, Inc. 31 Processing the Next Interrupt at module src.gen Simulation Kernel removes the previous event and advances the next event to the head of the event list. The simulation time becomes 4.3 seconds. Simulation Kernel delivers the SELF interrupt to the gen process. The process resumes at the marker in the middle of Wait. Process invokes and completes the exit execs of Wait. TimeEvent TypeModule 4.3SELFsrc.gen

33. © copyright 2001 OPNET Technologies, Inc. 32 Continuing the Process at gen Process evaluates all condition statements when leaving Wait. This state has one outgoing conditional transition that evaluates to true.

34. © copyright 2001 OPNET Technologies, Inc. 33 Continuing the Process at gen (cont.) Process transitions to Send. Process invokes the enter execs of Send and calls op_pk_send( ) to send a packet. This results in an event of type STRM being placed on the event list. TimeEvent TypeModule 4.3SELFsrc.gen 4.3STRMsrc.queue

35. © copyright 2001 OPNET Technologies, Inc. 34 Continuing the Process at gen (cont.) Process immediately invokes and completes the exit execs, because Send is a forced (green) state. Process evaluates all possible transitions. One evaluates to true. Process transitions to Wait Process invokes enter execs of Wait, schedules another SELF interrupt in the event list and becomes idle. Simulation Kernel takes control and processes the next event in the list.

36. © copyright 2001 OPNET Technologies, Inc. 35 Simulation Termination Simulations terminate in one of four ways: –The event list is emptied –Simulation attribute duration expires –A process calls for termination, using the KP op_sim_end() –A fatal error occurs

37. © copyright 2001 OPNET Technologies, Inc. 36 How Does Time Advance? Simulation time advances only when an event with a later time is processed from the event list No simulation time occurs during the execution of a process No time elapses during transitions between states A process model must always have an unforced (red) state so time can advance –Avoid endless looping between forced (green) states

38. © copyright 2001 OPNET Technologies, Inc. 37 Events and Event List Concepts: Summary Forced and unforced states execute differently Any processor or queue can have the attribute begsim intrpt enabled, scheduling an event for time 0.0 Control passes dynamically between the Simulation Kernel and individual processes

39. Process Modeling

40. © copyright 2001 OPNET Technologies, Inc. 39 Agenda Process models Process Editor –State transitions –Executive blocks Kernel Procedures Examine acb_fifo Lab: Modify a process model

41. © copyright 2001 OPNET Technologies, Inc. 40 Process Models Process models represent algorithms –Communications protocols and algorithms –Shared-resource managers –Queuing disciplines –Specialized traffic generators –Statistic-collection mechanisms –Control Processes Process Editor provides the features for creating process models

42. © copyright 2001 OPNET Technologies, Inc. 41 1. Create state 2. Create transition 3. Set initial state 4. Edit state variable 5. Edit temporary variable 6. Edit header block 7. Edit function block 8. Edit diagnostic block 9. Edit termination block 10. Compile process model 1 2 3 4 5 6 7 8 9 10 Process Editor Toolbar Buttons:

43. © copyright 2001 OPNET Technologies, Inc. 42 State Transitions Transitions connect states –Conditional –Unconditional –Transition executive Exactly one condition must evaluate to true If the condition statement (x == y) is true, the transition executive (Reset_Timers) is invoked Transition executiveCondition statement

44. © copyright 2001 OPNET Technologies, Inc. 43 State Executive Blocks Each state has two executive blocks –Enter executives are invoked upon entering a state –Exit executives are invoked before exiting a state

45. © copyright 2001 OPNET Technologies, Inc. 44 Introduction to Kernel Procedures Pre-written functions for difficult, tedious, or common operations KPs free users from addressing memory management, data structure, handling event processing, etc. KPs focus on communication modeling All KPs begin with prefix op_

46. © copyright 2001 OPNET Technologies, Inc. 45 Common Kernel Procedures Packet Package: op_pk_create () op_pk_create_fmt () op_pk_copy () op_pk_get () op_pk_total_size_get () op_pk_nfd_set () op_pk_nfd_get () op_pk_send () op_pk_send_delayed () op_pk_destroy () Subq Package: op_subq_pk_insert () op_subq_pk_remove () Interrupt Package: op_intrpt_schedule_self () op_intrpt_type () op_intrpt_strm () op_intrpt_code () Simulation and Event Packages: op_ev_cancel () op_sim_time () ID, Topo and Internal Model Access Packages: op_id_self () op_topo_parent () op_topo_child () op_ima_obj_attr_get () Distribution Package: op_dist_load () op_dist_outcome () Naming convention for Kernel Procedures - op_ _

47. © copyright 2001 OPNET Technologies, Inc. 46 Kernel Procedures Help From the Help menu, select Online Documentation and refer to the Simulation Kernel manual Press + to view Essential Kernel Procedures Press + + to view All Kernel Procedures Each KP is described in several paragraphs. Review at least the Abstract, Syntax, and Return Value fields. KP Name Syntax Return Value Example The manual is divided into sections by KP family (such as Anim, Dist, Sim, Stat) and sorted by KP name within each section. Details Purpose Errors Reference Abstract

48. © copyright 2001 OPNET Technologies, Inc. 47 State transition diagrams C programming language Library of OPNET Kernel Procedures (KPs) State variables (private to each process) Temporary variables Proto-C™

49. © copyright 2001 OPNET Technologies, Inc. 48 Example Process Model: acb_fifo Queue process model Characteristics –Has a service rate, in bits/sec –FIFO queue Active Concentrating Bit-oriented First In First Out queue –Active: Has a processor –Concentrating: Will take from many input streams and output to only one stream –Bit-oriented: Delay is based on number of bits processed

50. © copyright 2001 OPNET Technologies, Inc. 49 acb_fifo: State Overview Purpose of each state –init initializes state variables –arrival queues packets –svc_start calculates when the packet can be sent –svc_compl sends the packet –idle is the wait state

51. © copyright 2001 OPNET Technologies, Inc. 50 acb_fifo: Idle state Packet arrival –Packet is queued in arrival –To svc_start if not busy –Back to idle if busy Service completion –Sends queued packet in svc_compl To svc_start if queue nonempty Back to idle if queue busy

52. © copyright 2001 OPNET Technologies, Inc. 51 acb_fifo: arrival State Gets the incoming packet Tries to queue packet Destroys packet if queue is full

53. © copyright 2001 OPNET Technologies, Inc. 52 acb_fifo: svc_start State Begins servicing the packet Schedules an interrupt for service completion

54. © copyright 2001 OPNET Technologies, Inc. 53 acb_fifo: svc_compl State Sends the serviced packet Receiving module will get control immediately

55. © copyright 2001 OPNET Technologies, Inc. 54 Lab: Expand the network Lab Book: Lab #13 –The bank’s network has expanded to 4 source nodes, 12 switch nodes, and 3 destination nodes –Design a switch node with 4 inputs and 2 outputs –This switch takes an input from any input port and sends it to a random output port

56. © copyright 2001 OPNET Technologies, Inc. 55 Process Modeling: Summary Process models –Finite state machines –Proto-C –acb_fifo Kernel Procedures

57. Process Modeling Lab

58. © copyright 2001 OPNET Technologies, Inc. 57 Lab Description This lab uses the project bank_net, to model changes in the transaction rate and measure the effects of those changes Create modified sink process model to compute ETE delay –Get the packet –Obtain the creation time –Write out its ETE delay as a global statistic –Destroy the packet Incorporate new sink process model into existing node model Create ETE delay statistic probe Run simulation Filter the “View Results” graphs to answer questions

59. © copyright 2001 OPNET Technologies, Inc. 58 Lab Description Lab Book: Lab #14 What is the average end-to-end delay (ETE delay) for all transactions when the generation rate is 0.4 seconds/transaction (or 2.5 transactions/second)? For this generation rate, what percentage of the packets incurred an ETE delay of less than 1 second?

60. Collecting Scalar Statistics

61. © copyright 2001 OPNET Technologies, Inc. 60 Agenda Conceptual goals: –Creation of an attribute of a process model –Collect scalar statistics Tool goals: –View scalar analysis results

62. © copyright 2001 OPNET Technologies, Inc. 61 Creating an Attribute for the Process Model 2 44 1 3

63. © copyright 2001 OPNET Technologies, Inc. 62 Scalar Statistics A scalar statistic is a single value representing a statistic computed over an interval, typically the entire simulation. A scalar statistic: –Allows for parametric studies. –Must be plotted versus another scalar. –Shows the effect that making a change has on certain output parameters. –Is usually a summary of some aspect of a network’s behavior.

64. © copyright 2001 OPNET Technologies, Inc. 63 Vectors, Scalars, Probes, and Output Files Probes collect data at a designated node, link or module. There are two types of output: –vector –scalar A vector statistic is a single output plotted versus simulation time. (Example: throughput as it evolves over time).

65. © copyright 2001 OPNET Technologies, Inc. 64 Scalar Statistics A scalar statistic is a single value representing a statistic computed over an interval, typically the entire simulation (example: average end-to-end delay for all received packets in a simulation). Scalar statistics: –Must be plotted versus another scalar statistic –Allows for parametric studies –Requires many simulation runs because each run produces only one data point

66. © copyright 2001 OPNET Technologies, Inc. 65 Collecting Scalar Statistics Use any of three methods to collect a scalar statistic: –A statistic probe created in the Probe Editor (as below) –An attribute probe –The KP op_stat_scalar_write (scstat_name, value) 21 3

67. © copyright 2001 OPNET Technologies, Inc. 66 Using the Simulation Sequence Editor In order to collect scalar statistics, a scalar file must be specified. This output file will record the scalar simulation statistics. There is only one data point per simulation run. The simulation program appends data to an existing file, allowing for multi- simulation parametric studies.

68. © copyright 2001 OPNET Technologies, Inc. 67 Using the Simulation Sequence Editor By promoting an object’s attribute to the simulation level, multiple values for that attribute can be set. By left-clicking on a blank under “Attribute” the user can add a currently promoted attribute. After adding the attribute to the table, the user can select multiple values for that statistic, and simulations will run with each value. 1234

69. © copyright 2001 OPNET Technologies, Inc. 68 Plotting a Scalar Panel 12543

70. © copyright 2001 OPNET Technologies, Inc. 69 Understanding the Problem and Questions Modify the Bank_net project to include a custom generator that has an attribute transaction_rate, the transaction rate in transactions per second. Answer the following questions: –Are your results the same with this customized generator as with the ideal generator? Hint: run the simulation with the same probe file as before. Verify that results are the same. –What is the maximum generation rate such that the average ETE delay for all transactions is less than 5 seconds? Hint: run multiple simulations with different transaction rates, collecting scalar data.

71. © copyright 2001 OPNET Technologies, Inc. 70 Creating a Custom Generator — Procedure 1.Determine functionality of the process model. 2.Determine necessary states. 3.Create transitions between states. Write condition statements and create macros for them. 4.Determine state variables. 5.Use C code and KPs to implement each state’s enter and exit executives. 6.Declare variables. 7.Compile the process model.

72. © copyright 2001 OPNET Technologies, Inc. 71 Functionality of the Process Model The process model must: –Include a custom attribute, transaction_rate. –Generate packets as specified in the original problem: Packet interarrivals are exponentially distributed. Packet size varies according to a normal distribution with a mean size of 3200 bits and a standard deviation of 20 bits. –Write any necessary statistics.

73. © copyright 2001 OPNET Technologies, Inc. 72 Useful KPs for This Model dist_ptr = op_dist_load (dist_name, dist_arg0, dist_arg1) loads a distribution to generate stochastic values. rand_num = op_dist_outcome (dist_ptr) generates a random value from the specified distribution. op_intrpt_schedule_self (time, code) schedules a self interrupt for the invoking process. pkptr = op_pk_create (bulk_size) creates a packet. pkptr = op_pk_create_fmt (“ _trans_pkt”) creates a packet of specific format. op_pk_bulk_size_set (pkptr, bulk_size) sets the bulk size of a packet.

74. © copyright 2001 OPNET Technologies, Inc. 73 Useful KPs for This Model op_pk_send (pkptr, outstrm_index) forwards a packet through an output packet stream and schedules its arrival at a destination module. current_time = op_sim_time () obtains the current simulation time. object_id = op_id_self () obtains the value of the surrounding processor or queue. op_ima_obj_attr_get (objid, attr_name, value_ptr) obtains the value of an attribute for the specified object.

75. © copyright 2001 OPNET Technologies, Inc. 74 Lab Approach and Hints Remember the questions we are trying to answer: –Are your results the same with this customized generator as with the ideal generator? –What is the maximum generation rate such that the average ETE delay for all transactions is less than 5 seconds? 1. Create a new generator process model. a. Create an attribute of the process named transaction_rate. b. Place states and transitions. c. Define code in executive blocks. d. Compile the process model. NOTE: if you do not want to create this model, it is available as model "mdlr_lab12_gen". Examine it to see how it was implemented. 2. Modify the node model to include the new generator process (use a processor instead of an ideal generator). 3. Modify probe file to capture the scalar statistic ETE delay by adding a global statistic probe. 4. Run multiple simulations and view output in the Analysis Tool. To ensure convergence, you may want to run with a duration longer than 1000 sec (however, the simulations will take longer to complete).

76. © copyright 2001 OPNET Technologies, Inc. 75 Lab Results

77. © copyright 2001 OPNET Technologies, Inc. 76 If you finish early, try the Advanced Lab Modify the sink process to collect the total number of bits that it receives (use op_pk_total_size_get ()). At the end of the simulation, write out the the statistic: –"Global Bit Throughput" = total bits received / total simulation time Add an additional receiver to the PHIL node model that also sends packets to the sink module. Add an additional New York node that sends bank transactions to PHIL. Plot the scalar panel ETE Delay vs. Global Bit Throughput for a variety of transaction rates.

78. Radio Modeling

79. © copyright 2001 OPNET Technologies, Inc. 78 Agenda Conceptual Goals –Introduction to radio modeling –Introduction to Transceiver Pipeline Stages –Mobile/Satellite Nodes –Custom Packets –Custom Antennas –Link Models –Custom PDFs Tool Goals –Define Trajectory –Packet Format Editor –Link Model Editor –Antenna Pattern Editor –PDF Editor

80. © copyright 2001 OPNET Technologies, Inc. 79 Radio Modeling Modeler / Radio allows models to utilize mobile nodes and mobile subnets using dynamic RF links. Node and subnet positions are updated (lazy evaluation) based on user specifications such as time step, altitude and a defined path that is anchored on absolute or relative coordinates. Radio transceivers must be used that employ a 14 stage link budget model called the Transceiver Pipeline

81. © copyright 2001 OPNET Technologies, Inc. 80 Radio Modeling Radio is a broadcast technology and depends on dynamically changing parameters. The simulation must evaluate the possible connectivity between a transmitter channel and every receiver channel for each transmission. The network level characteristics factored into these calculations are the locations of the source and destination nodes, the distance between the nodes, and the direction the radio signal travels from the source node to the destination node. If the nodes are mobile or satellite nodes, these position-related parameters may change during simulation.

82. © copyright 2001 OPNET Technologies, Inc. 81 Radio Links A radio link is not statically represented by an object, as are point-to- point and bus links. A radio link can exist between any radio transmitter–receiver channel pair and is dynamically established during simulation. The possibility of a radio link between a transmitter channel and a receiver channel depends on many physical characteristics of the components involved, as well as time-varying parameters, which are modeled in the Transceiver Pipeline Stages.

83. © copyright 2001 OPNET Technologies, Inc. 82 Radio Links In OPNET simulations, parameters such as frequency band, modulation type, transmitter power, distance, and antenna directionality are common factors that determine whether a radio link exists at a particular time or can ever exist

84. © copyright 2001 OPNET Technologies, Inc. 83 Transceiver Pipeline Models the transmission of packets across a communications channel (link) Implements the “physical layer” characteristics Divided into multiple stages, each modeling a particular aspect of the channel Determines whether or not a packet can be received at the link’s destination S1S2S3S4 TransmitterReceiver Each stage models an aspect of the link’s behavior

85. © copyright 2001 OPNET Technologies, Inc. 84 Radio Transceiver Attributes for Specifying Pipeline Stages 8 Stages (6-13) Associated with Radio Receiver 6 Stages (0-5) Associated with Radio Transmitter Receiver Group Transmission Delay Link Closure (LOS) Channel Match Tx Antenna Gain Propagation Delay Rx Antenna Gain Received Power Background Noise Interference Noise Signal-to-Noise Ratio Bit Error Rate Error Allocation Error Correction Radio TransmitterRadio Receiver

86. © copyright 2001 OPNET Technologies, Inc. 85 Radio Transmitter and Receiver Attributes Modulation - name of modulation table used to look up the bit error rate (BER) as a function of effective signal to noise ratio Channel - specifies the number and attributes of the channels in the transceiver Noise figure - represents the effect of thermal noise on radio transmission (receiver only) Ecc threshold (err/bits) - specifies the highest proportion of bit errors allowed in a packet in order for the packet to be accepted by a receiver (receiver only)... model - these attributes specify the various Transceiver Pipeline Stage models used

87. © copyright 2001 OPNET Technologies, Inc. 86 Radio Channel Attributes Data rate (bps) - rate at which data may be transmitted or received Packet formats - determines the types of packets a channel can transmit or receive Bandwidth (KHz) - specifies bandwidth of channel Min frequency (MHz) - specifies the base frequency of the channel Spreading code - used to specify a user-assigned code for the channel Power (W) - transmission power of packets transmitted through this channel (transmitter only)

88. © copyright 2001 OPNET Technologies, Inc. 87 Mobile Nodes Mobile nodes model terrestrial network elements whose positions vary with time, such as automobiles, aircraft, and ships. Mobile nodes cannot be connected to point-to-point and bus links, because they move relative to the earth. Mobile nodes may change position during a simulation, either on an assigned trajectory or by direct changes to the node’s position attributes.

89. © copyright 2001 OPNET Technologies, Inc. 88 Mobile Node Trajectories A trajectory is the path a mobile node moves along during simulation Trajectories can be created using the “Define Trajectory ” selection in the “Network” pull down menu. During simulation, the mobile node follows the trajectory by traveling in a straight line from one defined position to the next. Once the simulation time exceeds the last specified time in the trajectory file, the mobile node remains at its final position.

90. © copyright 2001 OPNET Technologies, Inc. 89 Defining a Trajectory Mobile nodes support an attribute called trajectory which specifies the name of an ASCII text file defining the path of the mobile node during the simulation. 2. Set the Trajectory attributes to the desired values. 1. Choose Define Trajectory from Network pull down menu 3. Click on Define Path. 5. Left-click in the work space to define intermediate positions for the mobile node. 4. Left-click at some location in the Project Editor to begin the trajectory.

91. © copyright 2001 OPNET Technologies, Inc. 90 Defining a Trajectory Continued 8. Click on complete to finish the trajectory creation process. 6. Define Trajectory Segment Information 7. Left-click in the work space to define more intermediate positions for the mobile node. 9. Type in a trajectory name. Click OK to save the trajectory.

92. © copyright 2001 OPNET Technologies, Inc. 91 Satellite Nodes Satellite nodes model network elements in orbit around the earth, such as satellites and spacecraft Like mobile nodes, satellite nodes cannot be connected by point-to-point and bus links because they change positions during a simulation Satellite nodes change position based on an assigned orbit or by direct changes to the node’s position attributes.

93. © copyright 2001 OPNET Technologies, Inc. 92 Orbits Orbits can be imported from STK and viewed using op_vuorb (shown below)

94. © copyright 2001 OPNET Technologies, Inc. 93 Lab Description This lab will model a mobile paging system. Parameters: –Telephones initiate pages addressed to a specific mobile pager –The pages are relayed through a central base station –A radio tower broadcasts the pages –If the appropriate mobile pager receives the page, an ack is transmitted back to the radio tower –The radio tower relays the ack back to the base station and a successful page statistic is recorded

95. © copyright 2001 OPNET Technologies, Inc. 94 Lab : Overview Create the acknowledgement and page packet formats Create the necessary antenna pattern, PDF, and link parameter models Use the provided node models and the newly created parameter models to build the mobile paging network Configure the radio transmitters and receivers Create trajectories for the mobile pagers Choose results, run the simulation, and view the results

96. © copyright 2001 OPNET Technologies, Inc. 95 Lab : Node Specifications Telephone Node Specification –Generates pages based on a custom PDF –Determines destination of page based on a custom PDF –Encapsulates an ack in the page –Sends the pages on the single output port to the base station

97. © copyright 2001 OPNET Technologies, Inc. 96 Lab : Node Specifications (cont.) Base Station Specification –Receives pages on one of eight input ports –Receives acks on one input port (paired with the output port) and records the Percentage of Successful Pages (i.e., the number of acks received/pages sent) Radio Tower Specification –Receives pages from the Base Station via an input port and broadcasts them to the mobiles –Receives acks from the mobiles and forwards them to the Base Station via an output port

98. © copyright 2001 OPNET Technologies, Inc. 97 Lab : Node Specifications (cont.) Mobile Specification –Receives pages and checks destination –If the mobile is the destination, decapsulates the ack and transmits it

99. © copyright 2001 OPNET Technologies, Inc. 98 Lab : Create Packet Formats Open the Packet Format Editor Create ack packet format containing 2 fields –Source Node (64 bits) –Destination Node (64 bits) Save as _ack_packet

100. © copyright 2001 OPNET Technologies, Inc. 99 Lab : Create Signal Packet Formats Open the Packet Format Editor Create page packet format containing 3 fields –Source Node (64 bits) –Destination Node (64 bits) –Encapsulated ack packet Be sure to name the encapsulated packet field “Ack Packet” as the process model in the pager that will send the acknowledgement to the base station is written to look for that name in the received packet. Save as _page_packet

101. © copyright 2001 OPNET Technologies, Inc. 100 Lab : Create Antenna Pattern Create an antenna pattern for the radio tower. –Number of phi planes = 10 –Phi planes 90 to 162 degrees = 10 db –Phi plane 72 degrees = -5 db Save as _page_ant 45123

102. © copyright 2001 OPNET Technologies, Inc. 101 Lab : Create Link Model Create a link model that supports the recently created packets and that represents a 16,384 bits/sec link. Select “File”, “New”, “Link Model”. Configure the link: –Link types supported: ptsimp and ptdup –Attributes = Values packet formats = ack_packet and page_packet data rate = 16,384 bits/sec ecc model = dpt_ecc error model = dpt_error propdel model = dpt_propdel txdel model = dpt_txdel Save as _page_link

103. © copyright 2001 OPNET Technologies, Inc. 102 Lab : Create Destination PDF Create Page Destination PDF Select “File,” “New,” “PDF Editor” –Determines which mobile pager is the destination –The mobile pagers receive pages according to the following distribution: Mobile 0: 50% Mobile 1: 15% Mobile 2: 25% Mobile 3: 10% –Use Add Impulse action button –Normalize PDF Save As: _page_dest_pdf

104. © copyright 2001 OPNET Technologies, Inc. 103 Lab : Create Interarrival PDF Create Page Interarrival PDF –Determines time between pages for each telephone –Create PDF similar to the one shown below –Smooth and Normalize PDF Save as _page_pk_pdf

105. © copyright 2001 OPNET Technologies, Inc. 104 Lab : Node Descriptions In the interest of time, we (OPNET) have created all the nodes required for this lab based on the specifications outlined at the beginning of this chapter. The next several slides focus on discussing the approach and logic that went into the development of the nodes and the process models. Although the students will not have time in this course to develop these nodes themselves, we (OPNET) encourage everyone in the class to attempt to build these models at a later date as a good skill-building exercise.

106. © copyright 2001 OPNET Technologies, Inc. 105 Lab : Paging Network Model Example Open the project page_net

107. © copyright 2001 OPNET Technologies, Inc. 106 Lab : Telephone Node Model Description Added an Ideal Generator to generate page packets with the Page Interarrival PDF [Note - We used a PDF similar to the one built earlier in this lab.] Created a Source ID attribute to determine the origin of the page Created a process model that will set the fields of the page packet and encapsulate an ack packet

108. © copyright 2001 OPNET Technologies, Inc. 107 Lab : Base Station Node Model Description Added 8 receivers for incoming telephone lines Added 1 transceiver pair for communication with the radio tower Created a process model that will forward pages to the radio tower, receive acks, and record the Percentage of Successful Pages

109. © copyright 2001 OPNET Technologies, Inc. 108 Lab : Tower Node Model Description Included an antenna module that utilizes the antenna pattern created earlier in the lab Configured the radio transceivers to transmit and receive on different frequencies

110. © copyright 2001 OPNET Technologies, Inc. 109 Lab : Mobile Node Model Description Created a process model with a custom attribute Mobile ID. This process compares the Destination ID of the packet with Mobile ID and decapsulates and returns the ack if they are equal. Configured the transceivers to receive pages and transmit acks on frequencies matching the tower’s Configured the antenna module to use an isotropic antenna

111. © copyright 2001 OPNET Technologies, Inc. 110 Lab : Running the Simulation Under the “Simulation” pull-down menu, select “Choose Individual Statistics” and then under “Global Statistics” select “% of Packets Successfully Transmitted” Configure the simulation for 100 seconds Run the simulation

112. © copyright 2001 OPNET Technologies, Inc. 111 Lab : Viewing the Results Under the “Results” pull-down menu, select “View Results” and then under “Global Statistics” view “% of Packets Successfully Transmitted”.

113. © copyright 2001 OPNET Technologies, Inc. 112 Lab : Added Challenge If you have additional time, try any one or more of the following –Modify the model to include 4 additional telephones –Modify the model to include 4 additional pagers with pages evenly distributed among all 8 –Modify the model to include another base station that shares the same radio tower (Hint: Modify the ack packet format) The added challenges are not dependent on one another

114. © copyright 2001 OPNET Technologies, Inc. 113 Radio Features TMM: (Terrain Modeling Module) –The Terrain Modeling Module allows users to take into account terrain and environmental effects when modeling wireless networks. –With TMM, the user can import elevation maps that contain terrain data. –Supported map formats are DTED and DEM. –TMM also allows the user to select and compare signal loss from various propagation models. Simulation Efficiencies –DRG Dynamic Receiver Group –Parallel Processing

115. © copyright 2001 OPNET Technologies, Inc. 114 Lab: Using TMM Switch to the scenario called “TMM”

116. © copyright 2001 OPNET Technologies, Inc. 115 Lab: Viewing a Terrain Profile Using the Terrain Profile, you can view signal strength loss from a transmitter to a receiver.

117. © copyright 2001 OPNET Technologies, Inc. 116 Lab: Running a Simulation with TMM Select Configure Simulation. Check the box entitled, Use TMM.

118. © copyright 2001 OPNET Technologies, Inc. 117 Lab: Viewing Results of TMM Under the “Results” pull-down menu, select “View Results” and then under “Global Statistics” view “% of Packets Successfully Transmitted”.

119. © copyright 2001 OPNET Technologies, Inc. 118 Summary Radio models depend on dynamically changing parameters, which the simulation evaluates to determine the possible connectivity between all radio transmitters and receivers. Modeler provides the user the ability to simulate the movement of mobile nodes along trajectories and satellite nodes in orbit. The antenna, PDF, link and packet editors further expands the user’s capability to define and customize parameters that affect the behavior of the model.