Transcript Intro to MD Training

Modeler Day 3
Modeler
Day 3
1
© copyright 2003 OPNET Technologies, Inc.
Modeler Day 3
Course Content
DAY 3:
DAY 4:
• Configuring Standard Applications {LABs}
• Traffic Modeling Techniques {LABs}
• Modeling Large Networks
• Process Modeling Methodology
• Accelerating Wireless Simulations{LABs}
• Custom Wireless Effect {LABs}
• Importing Topology and Traffic
• Debugging Simulation Models{LABs}
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Modeler Day 3
Configuring
Standard
Applications
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© copyright 2003 OPNET Technologies, Inc.
Modeler Day 3
Agenda
• Application basics
•
•
•
•
Network traffic (users, devices, networks, etc.)
Modeling traffic in OPNET
Application modeling techniques
OPNET application architecture
• Configuring applications workflow
•
•
•
•
•
Configure applications
Define profiles
Configure server/peer
Deploy profiles
Lab 1: OPNK2003 cyber café
• Configuring analytical traffic on client-client applications
• Concepts and attributes
• Lab 2: VoIP configuration
• Easy configuration of application traffic
• Concepts and attributes
• Lab 3: application demands
• Troubleshooting
• Lab 4: troubleshooting (bonus)
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Modeler Day 3
Take-Away Points
• Standard applications available
• Application configuration
• Defining user profile
• Client & server setup for standard applications
• Application demands
• Application modeling techniques
• Application troubleshooting
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© copyright 2003 OPNET Technologies, Inc.
Modeler Day 3
Agenda
• Application basics
•
•
•
•
Network traffic (users, devices, networks, etc.)
Modeling traffic in OPNET
Application modeling techniques
OPNET application architecture
• Configuring applications workflow
•
•
•
•
•
Configure applications
Define profiles
Configure server/peer
Deploy profiles
Lab 1: OPNK2003 cyber café
• Configuring analytical traffic on client-client applications
• Concepts and attributes
• Lab 2: VoIP configuration
• Easy configuration of application traffic
• Concepts and attributes
• Lab 3: application demands
• Troubleshooting
• Lab 4: troubleshooting (bonus)
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Modeler Day 3
How Do We Define Network Traffic?
• Source (user, group of users)
• Destination (user, server)
• Traffic patterns
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Modeler Day 3
Applications
REQUEST
• Client-server applications
RESPONSE
• Examples: HTTP, FTP
REQUEST
RESPONSE
• Peer-peer applications
REQUEST
RESPONSE
• Examples: voice, video
• Multi-tier applications
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REQUEST
2
REQUEST
3
4
RESPONSE
RESPONSE
• Examples: web-based applications, e-commerce, home-grown
applications
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Modeler Day 3
Application Modeling Techniques
• Explicit
• Simulate all packets in detail
• Very high fidelity results
• Potentially longer run times
• Analytical
• Simulate majority of traffic using mathematical representation
• Faster simulation run times
• Hybrid
• Combination of both explicit and analytical modeling techniques
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Modeler Day 3
OPNET Application Architecture
Profiles
Describe user behaviour
Applications
Define application configuration
Tasks
Describe basic unit of user activity
Custom
application
Phases
Define communication patterns within each task
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Modeler Day 3
Profile and Applications: Example
Profiles
Apps
Engineer
HTTP
FTP
Marketing Department
Video
HTTP
Sales Engineer
Voice
Database
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Modeler Day 3
Configuring Application Models:
Workflow
Configure applications
Define profiles
Configure servers/peers
Deploy profiles
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© copyright 2003 OPNET Technologies, Inc.
Modeler Day 3
Agenda
• Application basics
•
•
•
•
Network traffic (users, devices, networks, etc.)
Modeling traffic in OPNET
Application modeling techniques
OPNET application architecture
• Configuring applications workflow
•
•
•
•
•
Configure applications
Define profiles
Configure server/peer
Deploy profiles
Lab 1: OPNK2003 cyber café
• Configuring analytical traffic on client-client applications
• Concepts and attributes
• Lab 2: VoIP configuration
• Easy configuration of application traffic
• Concepts and attributes
• Lab 3: AppDemands
• Troubleshooting
• Lab 4: troubleshooting (bonus)
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Modeler Day 3
Configuring Applications
Configure applications
Define profiles
Configure servers/peers
Deploy profiles
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Modeler Day 3
Configure Applications
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Modeler Day 3
Applications: Built-in Common Applications
Standard
applications
Name
Description
Custom Application
Generic/customizable application
Database
Data entry/query application
E-mail
E-mail application
FTP
File transfer protocol application
HTTP
Web-browsing application
Print
Print job
Remote Login
Telnet application application
Video Conferencing
Client-to-client video application
Voice
Client-to-client voice application
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Modeler Day 3
Applications
• Session of specific request/response patterns
• Commonly used applications: email, http, ftp…
• Common settings to all applications
• Type of service
• Symbolic server name
• RSVP parameters
• Specific settings to each application
• HTTP page configurations
• FTP file sizes
• Database query ratio
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Modeler Day 3
Application Definition Utility
• Contains all application definitions
“FTP (Light)”
Application Definition
• Reusability
• Across clients
• Across scenarios
• Easier deployment
• Easier change
I’m running
I
“FTP (Light)”
I’m running
I
“FTP (Light)”
I’m running
“FTP I(Light)”
I’m running
I
“FTP (Light)”
I’m running
I
“FTP (Light)”
I’m running
“FTP I(Light)”
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Modeler Day 3
Symbolic Server Name
Application has a
symbolic server name,
e.g. “FTP (Light)”
Mapping between
symbolic server
name and actual
server name
Actual server name is
specified in server, e.g.
WashingtonDC_Server
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Modeler Day 3
Application Definition Object
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Modeler Day 3
Example: File Transfer Protocol
• Upload or download of files:
• Using file size distribution
• Using Inter-request time distribution
FTP (Application)
PUT
GET
PUT
InterRequest
Time
InterRequest
Time
PUT
time
InterRequest
Time
Specific FTP
settings
Common
settings
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Modeler Day 3
Example: Hypertext Transfer Protocol (HTTP)
• Download of a web page:
• Using distribution for number of objects in page and sizes
• Using page interarrival time distribution
HTTP (Application)
Web page
download
Page Inter arrival
Time
Web page
download
Web page
download
time
Page Inter arrival
Time
Specific HTTP
settings
Common
settings
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Modeler Day 3
Hypertext Transfer Protocol (cont.)
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Profiles
Configure applications
Define profiles
Configure servers/peers
Deploy profiles
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Modeler Day 3
Define Profiles
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Modeler Day 3
Profiles
• Profile = Reusable collection of applications
• Describes activity patterns of:
• an individual user
• a group of users
Engineer
Engineer
Engineer
CFO
Marketing department
CEO
Help desk
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Modeler Day 3
Profile Configuration Object
• Contains all profile definitions
• Reusability
• Across clients
• Across scenarios
• Easier deployment
• Easier change
Engineer
Profile
Definition
I’m an
I
engineer
I’m an
I
engineer
I’m an
I
engineer
I’m an
I
engineer
I’m an
I
engineer
I’m an
I
engineer
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Modeler Day 3
Profile Properties
Repeatability
Profile Name
Operation Mode
Applications
Duration
Start Time
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Modeler Day 3
Profile Name, Start Time, and Duration
• Example:
• “Engineer” profile
• Starting at 9:00am
• Lasting 8 hours
Duration
Engineer
9:00am
12:00pm
5:00pm
Start Time
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Modeler Day 3
Profile Repeatability
• Serial mode
Engineer
Engineer
Inter-repetition time
Engineer
Inter-repetition time
Engineer
Inter-repetition time
• Concurrent mode
Engineer
Engineer
Inter-repetition time
Engineer
Inter-repetition time
Engineer
Inter-repetition time
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Modeler Day 3
Applications in Profile
I have the definitions of the
following applications:
• Database Access (Light)
• Email (Light)
• Web Browsing (Light)
• FTP
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Application Scheduling
• Multiple applications per profile
“Engineer” profile
Database
Web Browsing
Web Browsing
Web Browsing
Email
FTP
9:00am
FTP
FTP
FTP
12:00pm
FTP
17:00pm
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Modeler Day 3
Operation Mode
• Simultaneous
Database
Web Browsing
Email
FTP
9:00am
12:00pm
17:00pm
• Serial (ordered/random)
Database
9:00am
Web Browsing
Email
12:00pm
FTP
17:00pm
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Modeler Day 3
Applications in Profile
Repeatability
Name
Start Time Offset
Duration
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Modeler Day 3
Name, Start Time Offset, and Duration
• Example:
• “FTP” application
• Starting 2 hours after profile “Engineer” starts
• Lasting 4 hours
Engineer (Profile)
FTP (Application)
PUT
Start time offset
9:00am
PUT
GET
PUT
Duration
11:00am
3:00pm
5:00pm
Note: an application will not last longer than the profile
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Modeler Day 3
Application Repeatability
• Serial mode
FTP
FTP
Inter-repetition time
FTP
Inter-repetition time
FTP
Inter-repetition time
• Concurrent mode
FTP
FTP
Inter-repetition time
FTP
Inter-repetition time
FTP
Inter-repetition time
Note: an application will not repeat and last longer than the profile
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Modeler Day 3
Configure Servers/Peers
Configure applications
Define profiles
Configure servers/peers
Deploy profiles
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Modeler Day 3
Configure Server/Peers (cont.)
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Modeler Day 3
Server Supported Service Setup
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Modeler Day 3
Server CPU Setup
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Modeler Day 3
Server Address
• Uniquely identifies server
• Server address to be mapped to the symbolic server name
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Modeler Day 3
Deploy Profiles
Configure applications
Define profiles
Configure servers/peers
Deploy profiles
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Modeler Day 3
Deploy Profiles (cont.)
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Modeler Day 3
Client Profile Setup
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Modeler Day 3
Destination Preferences
• No destination preference => Randomly select among destinations supporting service
• Selection weight set on destinations
My weight is 10
Choose me!
Server2 is 5X more
likely to be chosen
Client
Server1
?
My weight is 50
Choose me!
Server2
 Explicitly configure destination(s) => Randomly select among destinations specified on client
 Weight set on client
I have to choose between:
- Server1: weight 20
- Server2: weight 10
Client
?
Server1 is 2X more
likely to be chosen
Server1
Server2
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Modeler Day 3
Configuring Destination Preferences
Application refers to a
symbolic server name,
e.g. web_browsing_server
Mapping between
symbolic server
name and actual
server name
Actual server name is
specified in server, e.g.
WashingtonDC_Server
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Modeler Day 3
Configuring Destination Preferences
(cont.)
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Modeler Day 3
Application Statistics
• Local and global statistics
• Client/Server statistics or
calling/called party statistics
• Specific to each application
• Local statistic results will be
grouped per profile/application
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Modeler Day 3
Lab 1: OPNK2003 Cyber Cafe
• Objective
• Apply workflow to configure application traffic
• Application configuration
• User behavior profiles
• Configure servers to support applications
• Deploy user profiles
Configure applications
Define profiles
Configure servers/peers
Deploy profiles
• Refer to lab handout “Lab1: HTTP Application Configuration Lab” on page 1
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© copyright 2003 OPNET Technologies, Inc.
Modeler Day 3
Agenda
• Application basics
•
•
•
•
Network traffic (users, devices, networks, etc.)
Modeling traffic in OPNET
Application modeling techniques
OPNET application architecture
• Configuring applications workflow
•
•
•
•
•
Configure applications
Define profiles
Configure server/peer
Deploy profiles
Lab 1: OPNK2003 cyber café
• Configuring analytical traffic on client-client applications
• Concepts and attributes
• Lab 2: VoIP configuration
• Easy configuration of application traffic
• Concepts and attributes
• Lab 3: AppDemands
• Troubleshooting
• Lab 4: troubleshooting
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Modeler Day 3
Configuring Analytical Traffic on Voice and
Video Applications
• Voice and video: intensive discrete-event applications
• Streaming applications
• Each small packet is modeled
• Long simulation run
• Not scalable
• Solution to improve simulation performances
• Analytical traffic
• Interpret all traffic as a background traffic flow
• Loss of accuracy
• Hybrid traffic
• Model part of the discrete traffic in an analytical flow
• Keep accurate response time and jitter
• Still model specific internals of voice application
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Modeler Day 3
Hybrid Traffic Concept
Discrete event traffic
Analytical traffic
Hybrid traffic
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Modeler Day 3
VoIP “Traffic Mix” Attribute
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Modeler Day 3
Video Conferencing “Traffic Mix” Attribute
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Modeler Day 3
Methodology
• Configure most of your VoIP or video nodes with background
traffic
• Configure the node of interest to use discrete traffic
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Modeler Day 3
Lab2: Configuring VoIP
• Objective
• Apply hybrid traffic to generate VoIP traffic and get end-to-end delay
• Refer to lab handout “Lab2: VoIP Application Configuration Lab” on page 26
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© copyright 2003 OPNET Technologies, Inc.
Modeler Day 3
Agenda
• Application basics
•
•
•
•
Network traffic (users, devices, networks, etc.)
Modeling traffic in OPNET
Application modeling techniques
OPNET application architecture
• Configuring applications workflow
•
•
•
•
•
Configure applications
Define profiles
Configure server/peer
Deploy profiles
Lab 1: OPNK2003 cyber café
• Configuring analytical traffic on client-client applications
• Concepts and attributes
• Lab 2: VoIP configuration
• Easy configuration of application traffic
• Concepts and attributes
• Lab 3: AppDemands
• Troubleshooting
• Lab 4: troubleshooting (bonus)
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Modeler Day 3
Application Demand Definition
• Abstract of a client-server or client-client application
• Connects two end-nodes
• Request/response oriented configuration
• Available in “applications” object palette
• Advantages
•
•
•
•
Configuration friendly
Custom-made traffic
Possibility to use discrete, hybrid, or analytical traffic
Visual representation of the application flows
• Limitations
• No specific internals of a standard application
• Only for simple traffic patterns
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Modeler Day 3
Application Demand Concepts
Requests
Client
or
server
Client
or
server
Responses
Rate
(requests/hour)
Start
Time
End
Time
Time
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Modeler Day 3
Application Demand Deployment
• Click and connect
• No need for configuration objects
• Right-click on demand to configure
• Demands can be copied and
pasted for duplication
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Modeler Day 3
Application Demand Attributes
• Generic traffic configuration
• Duration
• Request parameters
• Response parameters
• Hybrid traffic
• Transport protocol
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Modeler Day 3
Application Demand Deployment Wizard
• Faster deployment to create application demands
• Full mesh
• From one node to many nodes
• From many nodes to one node
• Note:
• If 2 or more nodes are selected before starting wizard, configuration applies to selected nodes only
• If no node is selected before starting wizard, configuration applies to all nodes in network
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Modeler Day 3
Application Demand Statistics
• Statistics per demand collected
on end-nodes
• Traffic sent/received
• Response time
• No global statistics
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Modeler Day 3
Lab3: Deploying Application Demands
• Objective
• Generate traffic quickly using Application Demands
• Please refer to lab handout “Application Demand Configuration Lab”
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Modeler Day 3
Agenda
• Application basics
•
•
•
•
Network traffic (users, devices, networks, etc.)
Modeling traffic in OPNET
Application modeling techniques
OPNET application architecture
• Configuring applications workflow
•
•
•
•
•
Configure applications
Define profiles
Configure server/peer
Deploy profiles
Lab 1: OPNK2003 cyber café
• Configuring analytical traffic on client-client applications
• Concepts and attributes
• Lab 2: VoIP configuration
• Easy configuration of application traffic
• Concepts and attributes
• Lab 3: AppDemands
• Troubleshooting
• Lab 4: troubleshooting (bonus)
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Modeler Day 3
Troubleshooting Guidelines
• «I don't see any traffic» or «I don't see expected traffic»
•
•
•
Check simulation logs
Look at the “Common problems” section of this presentation
Use constant distributions to make profile scheduling deterministic
•
Collect application Traffic Sent/Received stats in “All Values” mode
• Shows exact size and time data was sent
Make sure this is not a network issue
• Connect an application demand between your client and server
• See if you get application demand response time statistics
•
•
•
•
Scale down the network
• Isolate the problem
Use “User Defined Reports” in “Scenarios” menu
• Globally visualize attribute settings
Use “Network Difference Report” in “Scenarios” menu
• Compare to a similar working scenario
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Modeler Day 3
Troubleshooting: Simulation Logs
• Simulation = first place to look at
• Available in “DES” menu
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Modeler Day 3
Troubleshooting: Simulation Logs (cont.)
 Profile won't repeat if profile
duration is equal to simulation
duration.
Simulation
“Engineer” profile
“Engineer”
profile
 In serial mode, an application will
not start if previous application
duration is equal to profile
duration.
Simulation
“Engineer” profile
“FTP”
application
“HTTP” application
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Modeler Day 3
Troubleshooting: Simulation Logs (cont.)
• Profile set on a client doesn't exist
Sorry, I don’t
know what an
engineer is.
I’m an
engineer
?
“Engineer” profile
 Service set on server doesn't exist
Sorry, I don’t
know what “FTP
(Light)” is.
?
I’m running
“FTP
(Light)”
“FTP (Light)” application
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Modeler Day 3
Troubleshooting: Simulation Logs (cont.)
 Service set on server doesn't exist
Sorry, I don’t
know what “FTP
(Light)” is.
?
Profile
“engineer” uses
“FTP (Light)”
• All required application parameters are not
configured
“FTP (Light)”
is a FTP
application
Sorry, I need more
information to use
“FTP (Light)”:
• File size
• Inter-request time
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Modeler Day 3
Common Problems
 ‘Profile start time + application start time offset’
protocols and spanning tree algorithm etc’
I want to send this
FTP packet

<
‘Convergence time of routing
Wait, I don’t have a
route to the server yet
‘Profile start time + application start time offset’ > ‘Simulation end time’
 Common when using exponential distribution with start time and/or start time offset
Simulation
Profile start time
Simulation
“Engineer” profile
Profile start time
Application start time offset
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Modeler Day 3
Common Problems (cont.)
 If application duration is longer than profile duration, application will
be terminated when profile is over.
Simulation
“Engineer” profile
“FTP”
application
 The symbol map “Unlimited” for profile and application “Repeatability” has
a default interarrival time of 300 secs by default.
“Engineer”
profile
“Engineer”
profile
300 secs
“Engineer”
profile
300 secs
“Engineer”
profile
Etc…
300 secs
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Modeler Day 3
Common Problems (cont.)
 Voice and video conferencing can be configured between two
clients/LANs only.
wrong
Voice/Video
 Applications other than voice and video conferencing can be
configured between a client/LAN and a server/LAN only.
wrong
FTP, email,
database, http,
remote login, print
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Modeler Day 3
Advanced Troubleshooting
• Run OPNET debugger (ODB)
• Diagnostic traces
• Per application type: “ltrace gna_<application_type_name>”
Examples: “ltrace gna_email”, “ltrace gna_ftp”, “ltrace gna_http”
• For all applications: “ltrace gna”
• Simple example
• Start simulation under ODB
• ODB> ltrace gna
• ODB> cont
• This is an advanced technique. For more details, see session 1502: Debugging Simulation Models — Introduction
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Modeler Day 3
Lab4: Troubleshooting
• Objective
• Learn how to troubleshoot an application setup
• Please refer to lab handout “Application Troubleshooting Lab”
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Modeler Day 3
Configuring Custom Application:
Workflow
Break down the application
Configure tasks
Configure custom app
Define Profiles
Configure tiers
Deploy profiles
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Modeler Day 3
Breakdown of the Application
•
Identify the tiers
For example, an online e-commerce application might involve
•
Client
•
Web server
•
Authentication server
•
Database server
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Modeler Day 3
Summary
• Standard applications available
• Profile configuration
• Application configuration
• Client & server setup for standard applications
• Application demands
• Application modeling techniques
• Troubleshooting
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Modeler Day 3
Traffic Modeling
Techniques
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Modeler Day 3
Outline
• Motivation for traffic modeling
• Traffic representation
• Traffic generation: sources and import methods
• Traffic modeling: comparison of various OPNET approaches
• Lab #1
• Compare accuracy and speed of explicit traffic simulation
with background traffic
• Lab #2
• End-to-end delays using hybrid simulation
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Modeler Day 3
Motivation
• It is critical to provide good inputs (garbage in → garbage out)
• network topology
• traffic
• It is equally critical to choose a traffic modeling technique
• simulation speed vs. accuracy
• This session focuses on modeling traffic
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Modeler Day 3
Outline
• Motivation for traffic modeling
• Traffic representation
• Traffic generation: sources and import methods
• Traffic modeling: comparison of various OPNET approaches
• Lab #1
• Compare accuracy and speed of explicit traffic simulation
with background traffic
• Lab #2
• End-to-end delays using hybrid simulation
• Lab #3
• Flow Analysis
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Modeler Day 3
Real-world Traffic Representation
• Types of traffic
• WAN, LAN, application traffic
• Traffic representation in OPNET
Traffic Type
OPNET Representation
Packet by Packet
Explicit Traffic
Aggregated Traffic
Traffic Flows, Device/Link Loads
(Background Traffic)
• Choice of representation depends on modeling purpose
• Packet by packet
• End-to-end delays, protocol details, segmentation effects
• Aggregated traffic
• Capacity planning, steady-state routing analysis
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Modeler Day 3
Parameters in Traffic Representation
• Traffic Parameters
File Size
Interarrival
time
• Packet inter-arrival time or arrival rate
• seconds, packets/second
• Packet size
• bits, bytes etc.
• bits/sec = bits/pkt * pkts/sec
• Variability settings
• Probability Distribution Function (PDF)
• standard (exponential, bernoulli etc)
• custom
• build your own with PDF editor
• scripted
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Modeler Day 3
Outline
• Motivation for traffic modeling
• Traffic representation
• Traffic generation: sources and import methods
• Traffic modeling: comparison of various OPNET approaches
• Lab #1
• Compare accuracy and speed of explicit traffic simulation
with background traffic
• Lab #2
• End-to-end delays using hybrid simulation
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Modeler Day 3
Sources of Explicit Traffic
• Explicit traffic injected at
• Application Layer
• email, HTTP, FTP etc
• ACE, app_demands
• Network Layer
• RPG (self-similar traffic generator)
• Lower layers
• Native protocol sources
• Ethernet, ATM, Frame Relay etc
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Modeler Day 3
Sources of Aggregated Traffic
• Traffic flows injected at
• Application Layer
• app_demands
• Network Layer
app_demand
• IP traffic flows
• Lower Layers
• ATM traffic flows
IP Traffic Flow
• Element loads
• CPU utilization
• Link loads
• Do not require source models
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Modeler Day 3
Traffic Data Import
Traffic
Data
Network monitoring
software samples traffic
periodically using probes
Export to text
files or OPNET
recognizable
formats
Import into OPNET
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Importing Explicit Traffic – Packet Trace
• Packet traces
captured using
network analyzer
• Sniffer analyzer
• tcpdump
• windump
• Application
Characterization
Editor (ACE)
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Modeler Day 3
Importing Server Data
• Import from
• HP OpenView
Performance Agent
• BMC Patrol
• Concord SysEDGE
• NetIQ AppManager
• Generic XML
• Server
Characterization
Editor (SCE)
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Modeler Day 3
Importing Aggregated Traffic – Flow
Data
• Flow-specific data
• Demand objects
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Modeler Day 3
Importing Aggregated Traffic – Link Loads
• Link load information from
• Concord NetworkHealth
• MRTG
• Spreadsheet (text info)
• Can be converted into traffic
flows
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Modeler Day 3
Outline
• Motivation for traffic modeling
• Traffic representation
• Traffic generation: sources and import methods
• Traffic modeling: comparison of various OPNET approaches
• Lab #1
• Compare accuracy and speed of explicit traffic simulation
with background traffic
• Lab #2
• End-to-end delays using hybrid simulation
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Simulation Techniques
• Discrete event simulation
• Model all traffic (data, signaling, management) using packets
• Account for all timers in every protocol layer
• Perform every state/event transitions of all protocol layers
• Analytical simulation
• Abstract queue performance using mathematical equations
• Model traffic as state information in various network elements
• Hybrid simulation
• Mix of modeling approaches (discrete event + analytical)
• Mixture of traffic types (explicit traffic + aggregated traffic)
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Comparison of Various Simulation Techniques
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Modeler Day 3
Examples of Analytical Methods
Used by IP CPU
Used by mac layer in
LAN models
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Analytical Simulation
• Delay estimation
• Capacity planning
• Routing analysis
• QuickPredict
• Flow Analysis
performs analytical
simulations for steadystate analysis
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Modeler Day 3
Comparison of Various Simulation Techniques
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Modeler Day 3
Example of Discrete Traffic Simulation
• TCP congestion window management
• End-to-end delays at application layer
Application
E2E Delay
Application
Presentation
Presentation
Session
Session
Transport
Congestion Window
Transport
Network
Network
Data Link Layer
Data Link Layer
Physical
Physical
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Modeler Day 3
Discrete Event Simulation
• Packet retransmission
due to varying
acknowledgment
delays
• TCP/ATM connection
setup delay for varying
congestion levels of a
network
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Comparison of Various Simulation Techniques
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Micro-Simulation – Delay Estimation
• Delay estimator (t) for explicit packets due to additional aggregated
traffic contending for a common resource (such as a link)
• Retrospective micro-sim as lazy evaluation on real packet arrival
• Sensitive to queuing schemes like PQ, CQ and WFQ
Micro-simulation
t
r1
r2
b1
b2
b3
Time
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Analytical Coupled with MicroSimulation
 When real packets are separated by a long interval
 Lazy evaluation in two stages: analytical + micro-simulation
 Currently implemented for FIFO queues only
 Gain in simulation speed compared to pure micro-simulation
Analytical-simulation Micro-simulation
t + a
r1
a
r2
b1
b2
b3
Time
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Hybrid Simulation
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Outline
• Motivation for traffic modeling
• Traffic representation
• Traffic generation: sources and import methods
• Traffic modeling: comparison of various OPNET approaches
• Lab #1
• Compare accuracy and speed of explicit traffic simulation
with background traffic
• Lab #2
• End-to-end delays using hybrid simulation
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Lab 1: Overview
•
Create a simple network with explicit traffic and run
a simulation
2. Duplicate the network and replace the explicit traffic with
corresponding background traffic
•
Run the simulation with background traffic
•
Assess/compare the accuracy and speed of the two traffic
modeling approaches
•
Refer to lab manual for instructions
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Lab 1: Network Model
Source nodes (video
servers) with different
ToS (1,2,3)
Interface with WFQ
Destination nodes
100 video users (MPEG4) - 3 available service classes
Queuing delays ?
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Modeler Day 3
Aggregated Traffic – Just a Number to
Compute a Delay
• Aggregated traffic in OPNET
• Traffic flows (routed background traffic)
• Device/link loads (static background traffic)
• Common to both type of aggregated traffic
• Internal representation: just a number for a given node/link
• Effects: only one effect – to produce a delay
• One difference between the two types of aggregated traffic
• Traffic flows (routed background traffic) needs to be propagated to each
node in the flow path  tracer packets (propagators)
2Mbp
s
2Mbp
s
2Mbps
2Mbps
2Mbp
s
2Mbps
2Mbp
s
2Mbps
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Defining Traffic Flows
• 3 basic steps
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Defining Traffic Flows (cont.)
• Each flow is broken down into intervals as specified
Interval : 300-600 seconds
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Simulating Traffic Flows
• Refresher tracer packets
I1
P1 P2 P3 P4 P5
I1
I2
I3
I4
I5
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Simulating Traffic Flows (cont.)
• Sending new information on traffic level changes
0.0
start time = 150.0
I1
I2
I3
I4
I5
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Effects on Traffic Flows
• Clipping
• Effect: to reduce traffic flows to within bottleneck capacities
• Modeled as: state information on each node, bps and pps rates inside tracer packet
diminished downstream of the bottleneck
• Segmentation:
• Effect: to reduce packet size to within MTU
• Modeled as: bps and pps rates inside the tracer adjusted to account for overhead
due to segmentation
• Load Balancing:
• Split traffic flows proportionally among available paths
• Modeled as: create copies of tracer packets with modified bps and pps rates
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Load Balancing Traffic Flows
0.375
0.75
0.5 * 0.75 = 0.375
0.375
0.375
0.25
0.25
0.25
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Outline
• Motivation for traffic modeling
• Traffic representation
• Traffic generation: sources and import methods
• Traffic modeling: comparison of various OPNET approaches
• Lab #1
• Compare accuracy and speed of explicit traffic simulation
with background traffic
• Lab #2
• End-to-end delays using hybrid simulation
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Lab 2: Hybrid Simulation - Overview
•
Video Conferencing end-to-end delays
•
WAN – with background traffic
•
Create one explicit flow – hybrid simulation
•
Observe dependence of the explicit traffic end-to-end delay on
Type of Service (ToS) used
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Lab 2: Network Model
• WAN with many background traffic flows
• One explicit video traffic flow from Seattle 
Houston (130 kbps – 360 kbps)
• End-to-End delays ?
• Refer to lab manual for instructions
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Modeling
Large Networks
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Agenda
• Conceptual goals
• Software goals
• Importing network topologies
• Choosing aggregation levels
• Import topology
• Question and answer browser
•
•
•
•
Using LAN models
Importing traffic
Using routed background traffic
Managing projects and scenarios
•
•
•
•
Import traffic
Network browser
Traffic browser
Efficiency Modes
• Navigating Large Topologies
• Controlling Simulation Runtime
• Effectively Using Background
Traffic
•
•
•
•
•
Static Background Traffic
Event Speed Parameter
Specifying Traffic Growth
Scheduling Automated Simulations
Viewing and Editing Scheduled
Simulations Log
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Overview – Large networks
• The concept of a “large” network does not necessarily refer to the
number of nodes or the geographic extent of a network.
• A large network is any model that will generate a significant amount
of events. This translates into longer simulations and memory
limitation issues.
• We will explore methods for increasing the efficiency of your models
when the economies of scale become an issue.
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Common Pitfalls
• OPNET is powerful software that tempts users with “grand designs”.
• Common Pitfall: “I will model everything”
• Developing models without clear direction and a solid understanding
of the questions that need answering leads to inefficiency, and results
that aren’t useful.
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Questions Should Drive Model Design
• It essential to first determine which questions to answer.
• Design the model to answer those questions. Don’t try to answer
everything.
• A key factor in effective modeling is flexibility. Realize that over the
course of the modeling process that the questions may change.
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LAN Models
• Single nodes may be used to model
entire LANs.
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Why Use LAN Models?
• LAN models are a powerful
mechanism for abstracting
complex local area networks that
may contain multiple nodes with
the same configurations.
• LAN models reduce clutter in the
workspace.
• LAN models use less memory.
• LAN models generate fewer
simulation events allowing
simulations to run faster.
These models
represent the
same network.
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Additional Information About LAN Models
• LAN Models behave as if they were specific nodes modeled using
OPNET.
• The key difference is that you can collect statistics on the LAN
models but not on the specific nodes and links within the model.
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Modeling Techniques
• Design Accurate, Efficient Models
• Two Techniques
• Approximation
• Reduction
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Approximation
• Tradeoff: Precision vs. Performance
• Loss in precision means higher variance
• Overall results are still accurate
• Approximation Approach
• Apply a combination of analytically and explicitly modeled traffic
• Allows you to limit the number of variables, while retaining the proper traffic
behavior for the model
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Traffic Types
• Three different types of traffic
• Loads
• Also called “Device/Link Loads”
• Represent percentage of capacity being used
• Can be imported or manually created
• Flows
• Visualized as demand objects
• Can be imported or manually created
• Packets
• Provide detailed performance statistics
• Delay, response time, jitter
• Represent different types of application traffic
• Can be imported from optional ACE module or manually created
• All three can exist simultaneously in the network model
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Importing and Characterizing Applications
• With the Application Characterization Environment (ACE) module,
you can model any networked application by capturing the packets
associated with that application, then importing them into Modeler.
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Link Loads
• Represent utilization of individual links
• Values are represented in percentage utilization for each time period
• Utilization A->B
• Utilization B->A
• To set link loads manually:
• Right-click a link, edit attributes
• Expand “Background Utilization” attribute
• Set utilization percentages for multiple time periods
• To import data from management platforms:
• Traffic / Import Device/Link Loads
• MRTG
• InfoVista
• Concord eHealth-Network
• Text Files
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Flows
• Represent flow of network traffic between sources and destinations in
network
• Flows are represented in bits/sec and packets/sec
• Flow data can be imported from management platforms
• Cisco NetFlow (AS Aggregation or No Aggregation)
• Cflowd
• NetScout
• NetScout Ngenius
• NAI Distributed Sniffer / Sniffer Pro
• Agilent NetMetrix
• Spreadsheet / text files
• You can add new flows manually by choosing: Protocols / IP / Demands /
Configure Traffic Demands Among Selected Nodes
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Flows
• Flows are a type of traffic demand. Demands appear as dotted blue lines
from source to destination.
• Right-click a traffic demand to edit its attributes or hide the demand
• Use View / Demand Objects to hide/show all demands
• Use Traffic / Open Flows Browser to quickly examine many flows
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Packets
• Only used for discrete event simulation (DES)
• Represent individual packets in network
• Application traffic
• LSAs
• Application Configuration node used to globally define application
traffic
• LSAs automatically sent by routers during simulation
• Capture the transient behavior of the network
•
•
•
•
Convergence
Latency
Queue depth
Protocol effects
• Verify Service Level Agreement compliance
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Converting Loads to Flows
• Import load traffic
• Gather information about traffic
characteristics in real network
• Traffic / Convert Link Utilizations to
Flows…
• Give Modeler constraints:
• List of possible endpoints of traffic
flows
• Max/min amounts of traffic per
endpoint
• Modeler performs conversion
• Caveat: This is an approximation!
• More constraints = more realistic flows
• Flow traffic can be used for failure,
routing, and QoS studies
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Summary: Traffic Modeling
• Different traffic types available for different types of studies
• Three types available for import or creation:
• Flows
• Loads
• Packets
• Flows are best choice for failure studies
• Loads are often easiest to obtain and best for viewing utilization of
current network
• Packets are only used in discrete event simulation. Packets give the
most detailed results and are the best choice for QoS studies.
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Modeler Day 3
Object Reduction
• Each and every object in a model uses memory.
• Reducing the number of objects in a simulation allows for more
efficient simulations, possibly allowing the workstation to overcome
memory limitations (reduce swapping).
• Modeler provides LANs, Clouds and devices with varying interfaces
to allow you to keep the number of objects in the network model to a
minimum without sacrificing precision.
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Object Reduction
• LANs allow you to represent any number of workstations and a
server as a single object.
• IP Clouds abstract numerous IP devices into a single cloud object.
• Each interface in a device requires memory. Creating devices that
have the minimum amount of interfaces required for a model
reduces memory needed to run simulation.
• Example-- If all the hubs in a model will only have 8 connections, it is more
efficient to use an ethernet8_hub than an ethernet64_hub. Even if this doesn’t
represent your actual hardware, it will not affect the precision of the simulation.
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Alternative Solutions
• There are other solutions that don’t involve model design.
• These alternative solutions can be characterized as “brute force”
methods.
• The advantage to alternative solutions is that it gives you more
latitude in your model designs.
• Increasing physical memory is always an effective way to increase
workstation performance.
• Increasing the swap space is another effective method to get a better
performance from a computer.
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Controlling Simulation Runtime
• Every protocol in Modeler has attributes associated with them. These
attributes represent real-world application of a protocols procedures and
techniques.
• In many cases, although representing a protocol’s actual behavior, certain
attributes may not add value to a user’s model. In fact they will generate
events that are not helpful to the results of the model and will actually
increase simulation run-time.
• Modeler accounts for this by enabling certain efficiency modes in order to
decrease the number of unimportant events and accelerate simulation runtime.
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Controlling Simulation Runtime
• When configuring a simulation,
you will be able to view and
edit a list of simulation
attributes. These attributes will
change based on the protocols
being modeled.
• Among these attributes are a
variety of efficiency modes that
are enabled.
• Right-clicking on a simulation
attribute will provide you with
a complete description of
that attribute.
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Importing Topology Information
• OPNET can import topologies from
• ACE
• ATM Text files
• HP Network Node Manager
• Device Configurations (MVI Module)
• XML files
• VNE Server
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Aliases
• An alias is a name used to reference a particular node in OPNET.
• An alias may be an IP address, MAC address or a user friendly name.
• An object may have multiple aliases.
• These aliases are used as endpoints for imported traffic.
• LAN models retain the aliases for all nodes that are contained in the
LAN.
• This makes it possible to address traffic to the appropriate LAN
model.
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Navigating Large Topologies
• OPNET provides you with various tools to facilitate the locating and
selecting of nodes in a large network:
• Select Objects Logically
• Network Browser
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Edit / Select Objects
• Choose Edit / Select
Objects to select certain
objects throughout network
based on the value of
attributes.
• Ex: Select all links with a
data rate greater than 1.544
Mbps
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Network Browser
• The Network Browser can be used to locate objects in your network.
• Choose View / Show Network Browser
• Type a search string into the “Find” box to show objects with that
string in their names.
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Modeler Day 3
Network Browser
• To view an object’s attributes, right-click the object in the workspace
or the list and select “Edit Attributes.”
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Modeler Day 3
Managing Projects and Scenarios
• Managing scenarios allows you to examine the status of scenario
results, change project/scenario names and run multiple simulations
sequentially.
Change the project
name here.
Change the scenario
name here.
Collect results on multiple scenarios by changing
the results column to <recollect>. Clicking OK
will start a simulation run for each scenario with
<recollect> set.
Change the
simulation duration.
Ok will write all of
the changes to the
project.
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Modeler Day 3
Summary
• Networks can be imported in a variety of manners.
• Modeler’s power as modeling software becomes evident with the
analysis of large networks. As the size of the model increases so does
the importance of efficient modeling.
• Avoiding common pitfalls and understanding the efficiency techniques
inherent in Modeler leads to useful results and efficient models.
• By skillfully using the combination of the three types of traffic, you
can achieve a comfortable balance of performance and precision.
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