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NCC Simulation Model: Phase II:

Simulating the Operations of the Network Control Center

(PROGRESS REPORT: DECEMBER 15, 1992)

By: Norman M. Benjamin

Dr. Arthur S. Paul

Dr. Tepper L. Gill

(NASA-CR-191616) NCC SIMULATION

MOOEL: SIMULATING THE OPERATIONS OF

THE NETWORK CONTROL CENTER_ PHASE 2

Progress Report (Howard Univ.)

23 p

N93-16716

Unclas

63/32 0136203
DRAFT DRAFT DRAFT

NCC Simulation Model: Phase II:

Simulating the Operations of the Network Control Center

By Norman M. Benjamin

3bmdatlng the Ol_n_J_ons of the I_It_4_ Conool _ 15,1992 P_GE I

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Table of Contents

1. INTRODUCTION .................................................................................................. 3

2. NCC OVERVIEW .................................................................................................. 3

3. MEASURES AND METRICS .............................................................................. 5

4. SCOPE OF MODEL ............................................................................................... 5

5. SYSTEM ABSTRACTION AND MODEL DESCRIPTION .................................. 6

5.1. SYSTEM ABSTRACTION ................................................................................. 6

5.2. MODEL DESCRIPTION ..................................................................................... 7

5.2.1. SERVER PROCESS ......................................................................................... 8

5.2.2. GENERATOR PROCESS ................................................................................. 8

5.2.3. LINK FACILITY .............................................................................................. 8

5.2.4. INTERRUPT FACILITY .................................................................................. 9

5.3. MODEL WORK CHARACTERIZATION ........................................................... 9

5.3.1. INTERNAL PROCESSES ............................ _................................................... 9

5.3.2. INTERNAL MESSAGE PATHS ...................................................................... 10

5.3.2.1. CCS MESSAGE PATHS ............................................................................... 10

5.3.2.2. SPS MESSAGE PATHS ................................................................................ 12

5.3.2.3. ITS MESSAGE PATHS ................................................................................. 13

6. SIMULATION PROGRAM .................................................................................... 13

6.1. NETWORK DOMAIN DESCRIPTION ............................................................... 13

6.2. NODE DOMAIN DESCRIPTION ....................................................................... 14

6.2.1. EXTERNAL SUBNET NODE MODELS ........................................................ 15

6.2.2. INTERNAL SUBNET NODE MODELS .......................................................... 16

6.2.2.1. PROCESS DOMAIN DESCRIPTION ........................................................... 18

7. MODEL VERIFICATION AND VALIDATION .................................................... 18

7.1. MODEL PERFORMANCE CHARACTERISTICS .............................................. 18

7.2. PAPER MODEL .................................................................................................. 18

8. OUTPUT ANALYSIS ............................................................................................ 18

9. APPENDIX A: MODEL REPORTS ...................................................................... 18

10. REFERENCES ..................................................................................................... 18

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1. INTRODUCTION

The simulation of the NCC is in the second phase of development. This phase seeks to further develop the

work performed in phase one. Phase one concentrated on the computer systems and interconnecting

network. The focus of phase two will be the implementation of the network message dialogues and the

resources (i.e schedulable elements of the SN) controlled by the NCC. These resources are requested,

initiated, monitored and analyzed via network messages. In the NCC network messages are presented in

the form of packets that are routed across the network. These packets are generated, encoded, decoded

and processed by the network host processors that generate and service the message traffic on the network

that connects these hosts. As a result, the message traffic is used to characterize the work done by the

NCC and the connected network.

Phase one of the model development represented the NCC as a network of bi-directional single server

queues and message generating sources. The generators represented the external segment processors.

The server based queues represented the host processors. The NCC model consists of the internal and

external processors which generate message traffic on the network that links these hosts. The external

processors represented are the POCC, NASCOM, WSGT, FDF, SDPF and JSC. These connect to the

internal processors which are the CCS, SPS and ITS. To fully realize the objective of phase two it is

necessary to identify and model the processes in each internal processor. These processes live in the

operating system of the internal host computers and handle tasks such as high speed message exchanging,

ISN and NFE interface, event monitoring, network monitoring, and message logging. Inter process

communication is achieved through the operating system facilities. The overall performance of the host

is determined by its ability to service messages generated by both internal and external processors.

2. NCC OVERVIEW

::qallb

"_"The NCC is located at the Goddard Spaceflight Center and provides scheduling and control services to

the NASA SN. The SN provide tracking and data acquisition services to a large community of low-earthorbiting spacecrafls. Spacecraft data is down linked through TDRS to the WSGT. The data is then

quality checked at the NASA NGT which is co-located with WSGT. The data is then forwarded over

NASCOM's telecommunications links to the NCC at Goddard and relayed to the project users. User

spacecraft telemetry data do not pass through the NCC.

The NCCDS is specifically responsible for scheduling, control, fault isolation and accountability to ensure

that users receives their data as scheduled. The NCCDS is provided with support services from the FDF

and the SDPF. The FDF provides tracking data analysis together with orbit determination for spacecraft

vector generation. The SDPF receives and processes scientific data for users.

S#mdating 11_ t)pcratlom of the Network Control _ 15,1992 PAGE 3

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The NCCDS is derided into three major subsystems. The service planning segment (SPS), which

schedules TDRSS services; the communication and control segment (CCS), which controls and monitors

the quality of active services; and the intelligent terminal segment (ITS) with the intersegment network

CISN)which provides the interface between the console operators and the SPS and CCS. The specific

functions of providing the management and resources for scheduling, controlling, and monitoring the

performance of NASA's SN are summarized as follows:

*Scheduling of Network Resources

Forecast Scheduling and conflict resolution

Real-time scheduling and conflict resolution

*Network Performance Monitoring

Ground equipment status messages from WSGT

Data quality messages from NGT

*Acquisition Data Management (Secure and Un-secure)

Non-secure- Routing of data from FDF to WSGT

Secure: Generation of pointing data using the Acquisition Data facility software and

subsequently transmitting vectors to WSGT.

°NCC Database Management

Maintain a library of all current databases.

Restores data as required.

Troubleshooting of database anomalies

Maintain all database documentation

•Network Fault Isolation

Real-time fault isolation which is accomplished by teams of Performance Analysts and

TDRSS Network Controllers.

Post-event analysis performed by teams of TDRSS Network Analysis who evaluate

electronically logged messages in the NCC data systems.

.Network Accountability and Reporting

Operation of a Service Accounting System (SAS) that counts the data messages received

from user services and uses the data to compute time and resource usage for billing purposes.

This data is also used by the SN Network Anomaly Committee to evaluate and resolve all

documented network anomalies.

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3. MEASURING THE PERFORMANCE OF THE NCC

3.1. FRAMEWORK

Havingdecidedtousea queuing-typemodeltorepresenttheNCC, we areconstrainedbyqueuingtheory

to limited set of performance measures. These measures are basically:

Mean waiting time

Mean service time

Mean delay (waiting time plus service time)

Mean queuelength

These are fairly stable statistics that should not vary greatly from one run to the next, if, of course, the

run-times are sufficiently long to attain stability in the process.

Other measuressuchas:

Maximum waiting time

Maximum service time

Maximum delay (waiting time plus service time)

Maximum queue length

can be observed, but they are likely to vary substantially from one run to the next, even if the nan-times are

long and the system attains stability.

Still other measures such as:

Probability that the waiting time exceeds some threshold value P(W > Tw)

Probability that the service time exceeds some threshold value P(W > Ts)

Probability that the delay exceeds some threshold value P(W > Td)

Probability that the queue length exceeds some threshold value P(Q > cO

can be computed, but the problem would be to establish threshold values that have some physical or

operational significance.

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We have suggested one measure of performance that is not typical that is "the minimum capacity of the

server required for zero wait or no queuing'. This measure will help to establish the required capacity for

the processors being modeled.

At the current stage of development, all of these measures can be observed for the NCC as a system, and

the CCS, the SPS, and the ITS as subsystems.

We are proposing that the next logical step in developing this model should be to separate the manual

processing from the automated processing. This should have a tremendous impact on the fidelity of the

model. It will allow us to take a more analytical look at different processes with the goal of optimizing the

allocation of tasks and processes to manual and automated servers. It will allow us to conduct "What If'

analyses. It will provide insights into design options for the SNC, and it can be the basis for a subsequent

elaboration of the model to include cost as a measure of performance.

3.2. SELECTED INDICATORS OF THE NCC'S OPERATIONAL

EFFECTIVENESS

The NCC has established specific quantifiable requirements that it must achieve in providing services to

SN users. These requirements have been analyzed as a basis for selecting the following indicators of the

operational effectiveness of the NCC:

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3.2.1. Utilization of NCC's Communications Capacity

• Average communications capacity utilized by incomine messages (single user)

• Percentage of times that incoming messages (single user) exceeds 56 kilobits per second

• Maximum communications capacity utilized by incoming messages (single user)

• Average communications capacity utilized by incomin_ messages multiple user

• Percentage of times that incoming messages (multiple user) exceeds 112 kilobits per second

• Maximum communications capacity utilized by incoming messages multiple user

• Average queue time at the CCS from incoming messages

• Minimum communication speed to ensure zero queue time at the CCS from incoming messages

• Maximum queue time at the CCS from incomine messages

• Average communications capacity utilized by _ messages (single user)

• Percentage of times that _ messages (single user) exceeds 56 kilobits per second

• Maximum communications capacity utilized by _ messages (single user)

• Average communications capacity utilized by _ messages multiple user

• Percentage of times that _ messages (multiple user) exceeds 112 kilobits per second

• Maximum communications capacity utilized by _ messages multiple user

• Average queue time at the CCS from _ messages

• Minimum communication speed to ensure zero queue time at the CCS from _ messages

• Maximum queue time at the CCS from _ messages

3.2.2. Operational Effectiveness Measures

The followingaresuggestedasindicatorsoftheoperationaleffectiveness oftheNCC:

$1_ul_ulng :i_ Opera:Ion* of the N¢tw_k Con:tel _ 15.1992 PAGE 7

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• Average delay [processing time plus queuing time] at the NCC

• Average delay at the CCS

• Average delay at the ITS

• Average delay at the SPS

• Average processing time for the NCC

• Average processing time for the CCS

• Average processing time for the ITS

• Average processing time for the SPS

• Average queue time within the NCC

• Average queue time at the CCS

• Average queue time at the ITS

• Average queue time at the SPS

• Maximum queue time within the NCC

• Maximum queue at the CCS

• Maximum queue at the ITS

• Maximum queue at the SPS

• Average Utilization-NCC

• Average utilization-CCS

• Average utilization-ITS

• Average utilization-SPS

• Minimum capacity of the NCC to ensure zero queue

• Minimum capacity of the CSS to ensure zero queue

• Minimum capacity of the ITS to ensure zero queue

• Minimum capacity of the SPS to ensure zero queue

3.2.3. Acknowledgements and Response Time

• Percentage of times the NCC fails to send response to originator of specific schedule request

within one (1) minute of receipt of request.

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OPERATIONAL SCENARIOS

What is the effect on the NCC upon losing a particular SN service (SA or MA antenna(s))?

[Actual loss of the service will no be modeled, however, an estimation of the arrival distribution

of the SDRs and SARs due to the loss will need to be identified]

o What is the effect on the NCC of adding new users?

[An increase in the number (and arrival rate) of all message types will need to be determined using

the NPAS mission and extrapolation

o What will be the effect on NCC's performance of changing from WSGT/NGT to STGT

[The FIMS and NSS messages will be removed and the number of bursts of SHOs sent will be

reduced but the size (number of SHOs) of the bursts be larger]

o What will be the effect on NCC's performance of adding another TDRS?

[Same as adding new users///]

o What will be the effect on NCC's performance from installing faster computers at the CCS, ITS,

and SPS?

[Change the service rates for the respective processors, and observe changes in the NCC's

performance]

o What will be the effect on NCC's performance from incorporating improved scheduling

algorithms (more flexible gereric request parameters, better conflict resolution, more

automatiom)?

o What will be the effect on the NCC's performance from incorporating improved priority

schemes?

o In the current configuration, at what point will the NCC become saturated?

4. SCOPE OF MODEL

In this version of the simulation model of the NCC the objects that represent the NCC internal processors

are being enhanced. The processors are the CCS, SPS, and ITS. These objects will now include

representations of the major processes that run on these computers. Each processor, (CCS, ITS or SPS),

will contain a single server that will act as the centural processing unit (CPLD. The CPU will be

responsible for servicing the processes of these hosts on a priority basis. The CCS processes modeled are

the interfaces to both the ISN and NFE, the high-speed-message-exchange, the network monitor, and the

event monitor. On the SPS, the active and forecast schedulers, and the acquisiton processes are

represented. The display request process is the only process of the ITS that is modeled.

NCC network dialogues are also implemented, network dialogues are any specific set of messages that are

necessary to complete a task. Dialogues take place between external segment processors and one or morc

of the NCCDS. An example of a dialogue is the schedule dissemination. During schedule dissemination

to POCCs the active scheduler or the forecast scheduler process will initiate the dialogue with a 9401, or

a 9402, or a 9403. The POCC will respond with an 0360 acknowledgement. The following message

dialogues between the NCC and the external segments have been implemented.

$isvulatin8 th, Opo-ations of rh_ Netvsork Control _ 15, I9¢/'2 PAGg'9

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Message Dialogues:

Ground Control Message Requests

Schedule Dessemination

Performance Data Dessemination

Return Channel Time Delay Measurement

Schedule Services

Acquisition failure Notification

The arrival statistics of all messages will be determined by the output of the study performed by Stanford -

• The dialogues will be initated by setting up statistical distributions to trigger the first message in

the dialogue sequence. The means and variances of these distributions will be determined by Eric

Richmond.

5. SYSTEM ABSTRACTION AND MODEL DESCRIPTION

5.1. System Abstraction

The system abstraction and model description that was done in the Phase I model was modified to

eliminate the representation of the NFE. The NFE will be synthesized into the interface between the

external segments and the NCC. This change will not affect the implementation accuracy of the model

since the actions of the NFE is not considered in the problem analysis. These model abstraction changes

will reduce the global view of the network to two distinct set of objects. The objects axe classified as the

external segment objects and the internal segment objects. A significant reduction in the runtime

performance of the model is also expected.

NCC

Externalsegments to NCC_

Figure 1: Model Abstraction: Network View.

The inter-relationships between the segments of the system as seen from a performance point of view is

directly related to the message traffic generated by each object. This approach to abstraction will allow

the objects to be represented as processes and generators and the message traffic will characterize the

work done in the model. -,

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The external segment is mainly concerned with the generation of messages that are sent by the external

processors to the NCC. A message generator objects will be use to generate messages to drive the

simulation model based on data collected from NCC log tapes. The model will be required to handle the

generation of messages for an eight hour shift. To ensure that the rate at which messages are generated

closely matches the actual message traffic pattern in the real system, stochastic distributions will be

attached to each message during each shift. The arrival rates of each message type/class will be

computed from the sample data collected. The arrival rates will be used as input into the model as

parameters of the stochastic distn'bution function used to determine the times at which messages will be

generated.

The internal segment objects represent the NCC. The model of the NCC is made-up of three fixed

communication nodes that represent the CCS, ITS, and SPS, see Figure 2. Each of these fixed

communication nodes has incorporated into it, a unique node object. This was necessary because of the

functional difference between the CCS, ITS and SPS. The internal segment objects are externally linked

to the external segment objects via the CCS by two message streams. The SPS and ITS are linked to the

CCS by the ISN which is a fiber based ethemet LAN. In this phase of the modeling effort, the ISN is

represented by a virtual ethernet backbone model. This virtual backbone is a media access protocol

developed in the form of an OPNET process model. The virtual backbone does not require a physical bus

implementation. It however, has all the attributes of a bus except the collisions associated with this type

of CSMA/CD protocol. All processors has the ability to initate and process message dialogues.

5.2. Model Description

The model is represented by two sets of objects connected by two ruff-directional streams. The objects are

representations of the external segment and the internal segment. The streams act as an interface

between the external segments and the NCC. The external segment object will house the all the sources

and sinks that are external to the NCC. The external segments represented are the FDF, NASCOM,

NGT, POCCs, SDPF, and WSGT. The NCC houses the CCS, ITS, and SPS. The CCS, ITS, and SPS

contain servers that are used to process incoming messages and generators for message creation. The

external segment objects contain one or more message generators and a sink. Each generator will be

linked to an object called the segment queue that is used as an interface between the CCS and the external

segments. The link between the generator and the segment queue is a uni-directional stream. Unidirectional streams also link the segment queue to the sink process of the external segment object. All

process timing is controlled by the generation of interrupts.

5.2.1. Server Process

The server processes performs all the required message processing within any processor. This object

receives messages from any number of sources. The message are held for a simulated duration that is

equal to the service time specified for that message. The message is then forwarded to its destination

module. The forwarding algorithm uses the message ,_/pe_class as an index to determine where to send

the message.

51smdatlng thG Op_ratlona ofthG Net_,_ Contro/ _ 15,1992 PAaI_ I 1

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The possible message sources are streams and sub-queues that may be part of the server object. The server

polls the sources, bases on a predetermined priority, to access messages waiting to be processed. When a

message is found it is given its simulated service time then removed from the source to a destination

specified by the message path field in the message.

5.2.2. Generator Process

The generator processes are process objects that are responsible for the generation of messages within the

system. The generoator uses a message traffic definition record of the following format:

type_class:

path

mean

variance

destination

distribution_type

The message type&lass

Message path through the processors within the NCC

Message traffic mean

Message traffic variance

Message trallic destination

Message generation distribution type

The generator uses the mean and variance to generate messages of that specific type/class based on the

outcomes of the distribution. The destination is the final destination of the message. The path is the route

through the sub-processes of the CCS, ITS, and SPS that the message will take.

5.2.3. Link Facility

Connectivity between the objects is accomplished through point-to-point links and a virtual bus. The bus

exist between the CCS, SPS, and ITS. The bus represent the ISN. All other objects are connected by unidirectional point-to-point links.

5.2.4. Interrupt Facility

The heartbeat of the model is based on four events. The first occurs when the time to generate a new

message arrives. The inter-arrival times of these events are characterized by the parameters of the

distribution function assigned tO that message type. All message generators contain distribution functions

that generate interrupts which initiate the creation of a message. The second type of events are the class

of stream interrupts that are generated when a message arrives at an object. This type of event is

automatically generated whenever a message sent from one object to another arrives at its destination.

The third event is a service completion interrupt. This event is a server generated interrupt and it signals

the completion of simulated service to a message. All post message servicing activities are initiated by

this event. The final event is the dialogue response event. Messages that are a part of a dialogue sequence

will either be destroyed or trigger another message. The receiving processor will determine if the message

received needs a response or is triggering message. If either case is true the creation of the response

message will be scheduled with the generator.

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5.3. Model Work Characterization

A measure of the work done by the system is obtained by summing the simulated processing time for each

message by each processor. NCC host processor perform pre-determined operations on messages by

allocating each message processing time on its server. These operations are associated with logging,

monitoring, routing, and scheduling. The simulation of these operations is accomplished by holding the

message in a queue representing the process for some specified time. The work done by any processor

can be computed as a function of the total time spent servicing messages. Each host processor is also

eqnippedwithan

5.3.1. Internal Processes

The processes identified in the CCS are the NFE and ISN interfaces, the high speed message exchange,

the logger, the network monitor and the event monitor. All messages entering the CCS travel to the high

speed message exchange and is simultaneously logged by the logger. The forwarding algorithm uses the

path field of the message to determine the path the message takes through the processor. The ISN

provides the interface between the CCS and the ITS and the SPS.

The SPS consists of four distinct processes. These are the acquisition process, the SAR muter, the active

schedule process and the forecast schedule process. Messages entering the SPS are routed to the

acquisition process or the SAR router. From the SAR router the messages are passed to other SPS

processes.

Messages to the ITS are destroyed. Those leaving the ITS are sent to the ISN were they are routed to their

respective destinations.

5.3.2. Internal Message Paths

Messages generated by the external processors first enter the CCS internal processor. Messages entering

the internal processors follow specific paths to their final destination. Messages generated by the internal

processors passes through the CCS as they travel to the intended external processor. Combination of the

possible routes of the messages through each internal processsor led to the identification of distinct paths.

$trcadattn E th_ Operations of the N, twork Contro/ _ 15,1992 P^_'_ 13

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5.3.2.1. CCS MESSAGE PATHS

Messages entering the CCS are created by the the external segment processors, the ITS and SPS or the

network and event monitors within the CCS. All messages entering the CCS go to the logger and the

high speed message exchange. Messages to the logger are sent to a sink. Those to the high speed

message exchange are muted to either the ISN, the network monitor or the event monitor. Messages to

the ISN proceed to the SPS or the ITS for processing. Messages sent to the network monitor initiates

dynamic display messages before they are destroyed. These dynamic displays are routed to the ISN to be

displayed on the ITS. Messages sent to the event monitor are the GCMR's. These initiates GCM

messages before being destroyed.

Messages generated by the ITS are sent to the CCS via the ISN. The ISN broadcasts these messages to the

network monitor where they initiate the generation of other messages before being destroyed. The newly

generated messages are sent to the high speed message exchange where they are routed to the respective

external generators.

Messages generated by the SPS are also sent to the CCS via the ISN. The ISN broadcasts these messages

to the high speed message exchange where they are routed to the respective external processors.

Seven distinct paths were identified for the CCS processor. These paths and messages traversing them are

described below:

ISN

f

NFE

i r

Communication

H_h ExchangeS_a 1

Eveni

Monitor Network Monitor 1

J

CC___ -.

$1mulmlngtlsGOpar_IonaofOreNctv,,oc'k Conoxd _ I5,1992 P^G_'14

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PATH l NI_ -> high speed message exchange -> ISN

PATH2 NI_ -> high speed message exchange -> network monitor -> ISN

ISN

f

NFE

CommunlcationJ

| Message

Lcommunicatlon ,_ge

[ Event Monior 11 Netw°rk Monitor

CCS

PATH 3 SPS -> ISN -> high speedmessage exchange -> Nl_

PATH 4 ITS -> ISN -> network monitor -> high speed message exchange -> NFE

PATH 5-

PATH 6

NFE -> high speed message exchange -> ISN

NFE -> high speed message exchange -> event monitor

PATH 7 Event monitor -> high speed message exchange -> NFE

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5.3.2.2. SPS MESSAGE PATHS

SPS PATH

MessagesthroughtheSPS canbegeneratedby a SPS processorcanbe receivedviatheISN fromthe

CCS. Messages received from the ISN travelled through the CCS according to path 1. As a result the

path of all messages entering the SPS is defined as path 1. These messages are routed to the acquisition

process or the SAP, router.

The acquisitionprocessroutesthemessagesitreceivesbacktotheISN tobebroadcasttotheCCS. The

SAR routerroutesthemessagesitreceivestoeithertheactivescheduleprocessortheforecastschedule

process.The messagestothesetwo processesfromtheSAR routerinitiates thegenerationofother

messages.ThesegeneratedmessagesaresenttotheSAR routerwheretheytraveltotheISN tobcrouted

to their various destinations.

Messages leaving the SPS processor enter the CCS via the ISN. These messages travel through the CCS in

the path defined as path 3. As a result the path of all messages leaving the SPS is also defined as path 3.

This path is independent of the possible routes travelled by messages through the SPS.

There are three possible routes for messages entering the SPS. Descriptions of these routes and messages

are given below:

Route 1)ISN -> Acquisition Process

Messages for this route are: 0309, 0310, 0315, 0351, 0353, 0361, 0362, and 0365. The names of these

messages were given for the CCS paths.

Route2) ISN -> SAR Router-> ActiveScheduleProcess

Messages for this route are: 8651, 9910 and 9911. The names of these messages were given for the CCS

paths.

Route 3) ISN -> SAR Router -> Forecast Schedule Process

Message for this route is 9910.

Three routes also exists for messages leaving the SPS. Description of these routes are given below:
5.3.2.3.ITS MESSAGEPATHS

All messages to the ITS are destroyed at the sink. Display requests generated at the ITS are sent to the

ISN where they are routed to their various destinations. The architecture for messages travelling through

the ITS is shown in figure.

6. SIMULATION PROGRAM

The simulation program is an OPNET implemention of the abstracted model, that uses discrete event

simulation in a network of queues to represent the NCC and its external segments. The model is made up

of fixed communication nodes connected by a virtual bus and point-to-point finks. The virtual bus is a

network bus implementation that does not allow collisions. This design decision was necessary to reduce

the model runtime. Each node acts as a message generating and message processing servers. The

external nodes are made up of generator and sink processes. The internal nodes are single servers that

service multiple subqueues within each node. These internal processors are represented by a combination

of OPNETqueues and processor models. The networks that connect the processors are represented by

OPNETpacket streams that are initiated and terminated by point-to-point transmitters and point-to-point

receivers respectively. A complete set of model reports are provided in Appendix A.

6.1. Network Domain Description

The network domain is represented by the external subnet and the internal subnet. The external subnet

is made up of one fixed communication node, that contain packet generators, connected to a subnet that

represents the NCC. The NCC subnet contains fixed communication nodes that represent the CCS, ITS,

and SPS. These internal processors are connected by ISN which is represented by a virtual bus

implementation that is collision free. Packets are moved from the external subnet to the internal subnet

and back via two packet streams. The network level model is shown in Figure 6.1.

pl@. scgmtat;s _oe

Figure 6.1: NCC Model - Network Level

A view of the NCC subnet is shown in Figure 6.2.

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O

0 0

ph2_sp s ph2_its

i i

i

Flgu_e 6.2: NCC Internal Subnet

6.2. Node Domain Description

The node model domain, like the network domain contain node models that are associated with both the

internal and external segments. The node models are the representation of server, sink, generation and

communication elements. In the external segment node model attributes are used to make each segment

(node) unique. This is to facilitate creating one generic process model for all seven segments. The node

model attributes will be read by using the OPNET kernel functions. The additional attributes are:

NAME TYPE

number of messages integer

station address integer

message into file data file

The "message into file" will contain information necessary for generating messages for a given

distribution. The details of the file format will be explained in the process models discription.

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6.2.1. External Subnet Node Models

Each external segment node is a combination of a message generator and a message sink. The message

generator sends packets via a stream to the external segment queue. The function of this queue is to

collect messages from the external segment message generators and pass them on to the CCS within the

NCC. The segment queue is used only as a funnel for messages and is not an abstraction of any subsystem

being modeled. The External Segment node models are shown in Figure 6.3.

Figure 6.3: External Segment Node Models

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6.2.2. Internal Subnet Node Models

Three primary node models make up the internal processors. These are the ph2_ccs, ph2_its, and

ph2_sps. The ph2_ccs represent the CCS and is the interface to the external segments. Communication

with the external segment objects is achieved through the use a transmitter, ext_int_tx, and a receiver,

ext_int_rx. The at the heart of this object is a server process, server_router, in which all sub-processes are

represented as sub-queues. Two generators are present in this node, and are used to generate messages

for the event monitor and the network monitor. The isn is the implementation of the virtual bus used in

communication with the ITS and SPS. A sink is provided to destroy messages that exit the system.

Figure 6.4 show the CCS node model. All communications between the elements of this model is by

packet streams.

_x_tx tx_

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Figure 6.4: CCS Node Model

The SPS node model uses an architecture similar to that used by the CCS. In the SPS node model a server

element that represents the CPU of the SPS is fed packets from an implementation of the Acquisition

Process, the Active Scheduler and the forecast Scheduler. Messages arriving from the ISN are also

accepted. The messages entering the SPS are processed in accordance with the rules that govern the paths

taken by specific messages through the SPS. These rules are defined in the section labelled SPS

MESSAGE PATHS. Figure 6.5 show the elements that make up the SPS Node Model.

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The ITS messages like the SPS and CCS messages are governed by the definitions given in the section

named ITS MESSAGE PATHS. The ITS is a server based model that transmits display requests the

Network Monitor located in the CCS. accepts input messages from

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6.2.2.1. PROCESS DOMAIN DESCRIP_ON

The models on this domain are used to describe the behavior of the processor and queue models within the

node model domain. The process models used, are of two basic types, communicating processes, and

server processes. The communicating processes are logical entities that interact to accomplish some

common goal. The server processes are the entities that processes the messages in an effort to impose the

notion of work being done within the system being modeled. The logic of the process is specified in

FSM's. A FSM may be generally defined as an automaton which has states, inputs, and outputs. The

FSM models its process by responding to changes in its inputs, modifying its state, and producing new

outputs. In OPNET the primitives for building process models are states and transitions. OPNET

employs the concept of event scheduling and interrupts, in which each incident is called a simulation

event and an interrupt represents the actual execution of the scheduled event. See Appendix A for the

process models used in this model.

7. MODEL VERIFICATION AND VALIDATION

7.1. Model Performance Characteristics

7.2. Paper Model

8. OUTPUT ANALYSIS

9. APPENDIX A: MODEL REPORTS

10. REFERENCES

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