copyright © 2004 opnet technologies, inc. confidential, not for distribution to third parties....
TRANSCRIPT
OPNETWORK 2004 SessionCopyright © 2004 OPNET Technologies, Inc.
Confidential, not for distribution to third parties.
Planning and Analyzing Wireless LANs Network Analysis, Planning, and Troubleshooting
Session 1332
*
Session Abstract
*
Agenda
WLAN model support
Break
Lab 3: PCF access mode
Lab 4: Mixed 11b/11g WLAN Performance
*
Agenda
WLAN model support
Break
Lab 3: PCF access mode
Lab 4: Mixed 11b/11g WLAN Performance
*
Why Wireless LAN?
Ease of installation
Can go where wires cannot
Reduced cost-of-ownership
Uses license-free radio spectrum
*
Wireless LAN Support in OPNET
Based on IEEE standards
802.11: 1 and 2 Mbps
802.11b: 5.5 and 11 Mbps
802.11a and 802.11g: 6, 9, 12, 18, 24, 36, 48, and 54 Mbps
Supported physical layers
Direct-Sequence Spread-Spectrum (DSSS)
Extended Rate PHY-OFDM (ERP-OFDM)
PCF MAC operation: Poll based
*
Distributed Coordinated Function (DCF)
If the medium is busy, defer
When the medium becomes idle again, transmit after a random backoff
*
Point Coordination Function (PCF) Operation
Requires centralized coordination
*
Reliable data transmission via RTS-CTS exchange (threshold based)
Request To Send – Clear To Send
Fragmentation (threshold based)
Protection for mixed 11b/11g wireless LANs
CTS-to-self or regular RTS/CTS exchange
Roaming (can be turned on/off)
*
Agenda
WLAN model support
Break
Lab 3: PCF access mode
Lab 4: Mixed 11b/11g WLAN Performance
*
WLAN Models: Typical Use Cases
Study wireless LANs as an alternate/supplemental local area network technology
Analyze network performance by varying network load (e.g., number of nodes, application traffic) for independent and infrastructure BSS network configurations
Evaluate optional protocol-specific features like fragmentation and reassembly or RTS/CTS frame exchange against various network conditions
*
1332 Planning and Analyzing Wireless LANs
WLAN Models: Typical Use Cases (cont.)
Investigate the impact of mobility on applications running on mobile nodes and the efficiency of the wireless LANs being visited
Find out what to expect when upgrading your 11b WLAN to an 11g WLAN
Study the effects of different operational channel assignment choices on overall performance in networks with large number of wireless LANs
(R&D) Modify the logic of standard WLAN algorithms to conduct experiments with new ideas and prospective improvements
*
Agenda
WLAN model support
Break
Lab 3: PCF access mode
Lab 4: Mixed 11b/11g WLAN Performance
*
Supported Network Configurations
*
Supported Network Configurations (Cont.)
*
Node Models
Wireless LAN Station (Non-IP based)
Bridge with WLAN Port (Access Point)
* Unless the interface belongs to a WLAN backbone
*
Statistics
*
Statistics (cont.)
*
Attributes
*
Model Attribute Definitions
Identifies the BSS to which a WLAN MAC belongs
Also needed for roaming enabled nodes for initial association
If set to “Auto Assigned,” the entire OPNET subnet will be considered as a single BSS
If configured for one WLAN node, then it needs to be configured for all WLAN nodes in the network
Access Point Functionality
Used to configure BSS and ESS topologies
Required to be Enabled
*
Configuring PHY and Data Rate
First select the physical layer technology
Then select the data rate for data transmissions among the available data rates
*
Configuring Operation Channel
*
Example
5 BSSs: from “BSS A” to BSS “E” where A < B < C < D < E
Ch 1
Ch 2
Ch 3
Ch 4
Ch 5
Ch 6
Ch 7
Ch 8
Ch 9
Ch 10
Ch 11
2,401 MHz
2,451 MHz
2,473 MHz
Reserved Frequency Band for WLAN Channels in U.S. at 2.4 GHz (11/11b/11g)
BSS A Ch 1
BSS B Ch 6
BSS C Ch 11
BSS D Ch 2
BSS E Ch 7
Ch 36
Ch 40
Ch 44
Ch 48
5,170 MHz
5,210 MHz
5,230 MHz
Reserved Frequency Band for WLAN Channels in U.S. at 5 GHz (11a)
BSS A Ch 36
BSS B Ch 40
BSS C Ch 44
BSS D Ch 48
*
Transmitting and Receiving
Packet Reception Power Threshold
Vendor specific
Packets whose reception power is less than threshold will not be sensed by the MAC
Such packets may still cause interference noise at the receiver
* Two key attributes that determine the sensing and communication distance between WLAN nodes
*
Model Attribute Definitions (cont.)
Sets the packet size threshold for which the request-to-send (RTS)/clear-to-send (CTS) mechanism will be used
Solution to hidden terminal problem
Prevent large packets to be dropped
Overhead due to the RTS/CTS frame exchange
Short and Long Retry Limits
Specifies maximum number of transmission attempts for a data frame
Two independent counters
Long retry count incremented only if a data transmission fails despite a successful RTS/CTS exchange
High retry limits may perform better in noisy networks
Low retry limits can be suitable for network with high mobility
*
Lab #1: Hidden Node
Objective
Show the impact of the RTS/CTS mechanism as a measure to prevent the hidden node problem
*
Break
*
Lab #2: Infrastructure BSS
Become familiar with WLAN model attributes needed to configure BSSs
Use the model to select an appropriate WLAN topology according to the application traffic
*
Model Attribute Definitions (cont.)
Large Packet Processing
Action taken in the case: higher layer packet size maximum allowed data size
Based on this, a packet will be dropped or fragmented
Outside the scope of the standard
Max Receive Lifetime (seconds)
Maximum time for a packet to wait to be reassembled at receiver’s reassembly buffer
Buffer Size (bits)
*
PCF Configuration
PCF Parameters
PCF Functionality
Beacon Interval
CFP Interval
CFP Beacon Multiple
Max Failed Polls
Specifies the maximum number of consecutive polls by the AP without a valid response from MAC that is being polled
*
Lab #3: PCF Access Mode
Objective
Use PCF mechanism to improve the performance of real-time applications over WLAN
*
Model Attribute Definitions (cont.)
Alternative to RTS/CTS frame exchange
Roaming Capability
Enables the MAC to perform scanning procedures to associate with another AP when the communication is lost with the current one
Requires configuration of regular WLAN operational channels
Cannot be turned on for APs
*
Global Attributes
Faster simulation execution
Requires setting the altitude of the nodes
WLAN Transmission Candidacy
Provides an option to block any communication and interference between the WLAN nodes of different subnets for faster simulations
*
Global Attributes (cont.)
WLAN Beacon Efficiency Mode
An option to turn off APs’ periodic beacon messages for faster simulation execution
PCF enabled APs continue transmitting beacons
Does not prevent roaming of stations and AP evaluation
A distance based approximation approach is used for AP evaluation
WLAN AP Connectivity Check Interval
Used only by roaming capable stations when beacon efficiency is on
Specifies how frequently the distance with the current AP will be evaluated
*
Modeling Node Mobility
Trajectories
Modifying node position programmatically, e.g., “Random Waypoint”
*
Random Waypoint Mobility
Location of each waypoint is randomly chosen within specified rectangle
Speed between waypoints, and pause time at a waypoint follow specified random distributions
Configure using Random Waypoint “utility” object
Specify rectangular region via coordinates, or graphically using the “wireless domains” object
Define random waypoint profiles by specifying speed, start time, stop time, and pause time
GUI support for assigning profiles to a set of mobile nodes
“Random_Mobility” example project
*
Objective
Compare the total achievable WLAN throughputs measured in a mixed 11b/11g WLAN and in an all-11g WLAN to study the performance degradation in 11g WLANs that support legacy nodes
*
Additional Resources
Click on “Help” menu and select “Product Documentation”
“Model Descriptions Model Usage Guides Wireless LAN (802.11)”
IEEE standards
IEEE 802.11-1999
Wireless LAN FAQs
http://www.opnet.com/support
Click on “FAQs” link under “Technical Resources”
Search the FAQ database using the keywords “Wireless LAN” or “WLAN”
*
Related Wireless Sessions
Session 1529: Understanding WLAN Model Internals, Interfaces, and Performance
Session 1530: Modeling Custom Wireless Effects
Session 1815: Introduction to Wireless LAN Protocols
*
Take-Away Points
DES models provides extensive support for modeling wireless LAN networks, e.g.,:
Analyzing network performance, with and without mobility
Studying the effects of transient conditions and protocol overhead
Deployment of explicit traffic sources (e.g., TCP/IP-based applications or raw traffic generators) over WLAN technology
Simulate large wireless LAN network topologies
Reduce simulation execution time by using simulation efficiency modes (global attributes)
Study the interaction between legacy and new wireless LAN technologies
Find the most optimal configuration (e.g., when using PCF) to achieve optimum performance for all wireless applications
CFP
CFP
Planning and Analyzing Wireless LANs Network Analysis, Planning, and Troubleshooting
Session 1332
*
Session Abstract
*
Agenda
WLAN model support
Break
Lab 3: PCF access mode
Lab 4: Mixed 11b/11g WLAN Performance
*
Agenda
WLAN model support
Break
Lab 3: PCF access mode
Lab 4: Mixed 11b/11g WLAN Performance
*
Why Wireless LAN?
Ease of installation
Can go where wires cannot
Reduced cost-of-ownership
Uses license-free radio spectrum
*
Wireless LAN Support in OPNET
Based on IEEE standards
802.11: 1 and 2 Mbps
802.11b: 5.5 and 11 Mbps
802.11a and 802.11g: 6, 9, 12, 18, 24, 36, 48, and 54 Mbps
Supported physical layers
Direct-Sequence Spread-Spectrum (DSSS)
Extended Rate PHY-OFDM (ERP-OFDM)
PCF MAC operation: Poll based
*
Distributed Coordinated Function (DCF)
If the medium is busy, defer
When the medium becomes idle again, transmit after a random backoff
*
Point Coordination Function (PCF) Operation
Requires centralized coordination
*
Reliable data transmission via RTS-CTS exchange (threshold based)
Request To Send – Clear To Send
Fragmentation (threshold based)
Protection for mixed 11b/11g wireless LANs
CTS-to-self or regular RTS/CTS exchange
Roaming (can be turned on/off)
*
Agenda
WLAN model support
Break
Lab 3: PCF access mode
Lab 4: Mixed 11b/11g WLAN Performance
*
WLAN Models: Typical Use Cases
Study wireless LANs as an alternate/supplemental local area network technology
Analyze network performance by varying network load (e.g., number of nodes, application traffic) for independent and infrastructure BSS network configurations
Evaluate optional protocol-specific features like fragmentation and reassembly or RTS/CTS frame exchange against various network conditions
*
1332 Planning and Analyzing Wireless LANs
WLAN Models: Typical Use Cases (cont.)
Investigate the impact of mobility on applications running on mobile nodes and the efficiency of the wireless LANs being visited
Find out what to expect when upgrading your 11b WLAN to an 11g WLAN
Study the effects of different operational channel assignment choices on overall performance in networks with large number of wireless LANs
(R&D) Modify the logic of standard WLAN algorithms to conduct experiments with new ideas and prospective improvements
*
Agenda
WLAN model support
Break
Lab 3: PCF access mode
Lab 4: Mixed 11b/11g WLAN Performance
*
Supported Network Configurations
*
Supported Network Configurations (Cont.)
*
Node Models
Wireless LAN Station (Non-IP based)
Bridge with WLAN Port (Access Point)
* Unless the interface belongs to a WLAN backbone
*
Statistics
*
Statistics (cont.)
*
Attributes
*
Model Attribute Definitions
Identifies the BSS to which a WLAN MAC belongs
Also needed for roaming enabled nodes for initial association
If set to “Auto Assigned,” the entire OPNET subnet will be considered as a single BSS
If configured for one WLAN node, then it needs to be configured for all WLAN nodes in the network
Access Point Functionality
Used to configure BSS and ESS topologies
Required to be Enabled
*
Configuring PHY and Data Rate
First select the physical layer technology
Then select the data rate for data transmissions among the available data rates
*
Configuring Operation Channel
*
Example
5 BSSs: from “BSS A” to BSS “E” where A < B < C < D < E
Ch 1
Ch 2
Ch 3
Ch 4
Ch 5
Ch 6
Ch 7
Ch 8
Ch 9
Ch 10
Ch 11
2,401 MHz
2,451 MHz
2,473 MHz
Reserved Frequency Band for WLAN Channels in U.S. at 2.4 GHz (11/11b/11g)
BSS A Ch 1
BSS B Ch 6
BSS C Ch 11
BSS D Ch 2
BSS E Ch 7
Ch 36
Ch 40
Ch 44
Ch 48
5,170 MHz
5,210 MHz
5,230 MHz
Reserved Frequency Band for WLAN Channels in U.S. at 5 GHz (11a)
BSS A Ch 36
BSS B Ch 40
BSS C Ch 44
BSS D Ch 48
*
Transmitting and Receiving
Packet Reception Power Threshold
Vendor specific
Packets whose reception power is less than threshold will not be sensed by the MAC
Such packets may still cause interference noise at the receiver
* Two key attributes that determine the sensing and communication distance between WLAN nodes
*
Model Attribute Definitions (cont.)
Sets the packet size threshold for which the request-to-send (RTS)/clear-to-send (CTS) mechanism will be used
Solution to hidden terminal problem
Prevent large packets to be dropped
Overhead due to the RTS/CTS frame exchange
Short and Long Retry Limits
Specifies maximum number of transmission attempts for a data frame
Two independent counters
Long retry count incremented only if a data transmission fails despite a successful RTS/CTS exchange
High retry limits may perform better in noisy networks
Low retry limits can be suitable for network with high mobility
*
Lab #1: Hidden Node
Objective
Show the impact of the RTS/CTS mechanism as a measure to prevent the hidden node problem
*
Break
*
Lab #2: Infrastructure BSS
Become familiar with WLAN model attributes needed to configure BSSs
Use the model to select an appropriate WLAN topology according to the application traffic
*
Model Attribute Definitions (cont.)
Large Packet Processing
Action taken in the case: higher layer packet size maximum allowed data size
Based on this, a packet will be dropped or fragmented
Outside the scope of the standard
Max Receive Lifetime (seconds)
Maximum time for a packet to wait to be reassembled at receiver’s reassembly buffer
Buffer Size (bits)
*
PCF Configuration
PCF Parameters
PCF Functionality
Beacon Interval
CFP Interval
CFP Beacon Multiple
Max Failed Polls
Specifies the maximum number of consecutive polls by the AP without a valid response from MAC that is being polled
*
Lab #3: PCF Access Mode
Objective
Use PCF mechanism to improve the performance of real-time applications over WLAN
*
Model Attribute Definitions (cont.)
Alternative to RTS/CTS frame exchange
Roaming Capability
Enables the MAC to perform scanning procedures to associate with another AP when the communication is lost with the current one
Requires configuration of regular WLAN operational channels
Cannot be turned on for APs
*
Global Attributes
Faster simulation execution
Requires setting the altitude of the nodes
WLAN Transmission Candidacy
Provides an option to block any communication and interference between the WLAN nodes of different subnets for faster simulations
*
Global Attributes (cont.)
WLAN Beacon Efficiency Mode
An option to turn off APs’ periodic beacon messages for faster simulation execution
PCF enabled APs continue transmitting beacons
Does not prevent roaming of stations and AP evaluation
A distance based approximation approach is used for AP evaluation
WLAN AP Connectivity Check Interval
Used only by roaming capable stations when beacon efficiency is on
Specifies how frequently the distance with the current AP will be evaluated
*
Modeling Node Mobility
Trajectories
Modifying node position programmatically, e.g., “Random Waypoint”
*
Random Waypoint Mobility
Location of each waypoint is randomly chosen within specified rectangle
Speed between waypoints, and pause time at a waypoint follow specified random distributions
Configure using Random Waypoint “utility” object
Specify rectangular region via coordinates, or graphically using the “wireless domains” object
Define random waypoint profiles by specifying speed, start time, stop time, and pause time
GUI support for assigning profiles to a set of mobile nodes
“Random_Mobility” example project
*
Objective
Compare the total achievable WLAN throughputs measured in a mixed 11b/11g WLAN and in an all-11g WLAN to study the performance degradation in 11g WLANs that support legacy nodes
*
Additional Resources
Click on “Help” menu and select “Product Documentation”
“Model Descriptions Model Usage Guides Wireless LAN (802.11)”
IEEE standards
IEEE 802.11-1999
Wireless LAN FAQs
http://www.opnet.com/support
Click on “FAQs” link under “Technical Resources”
Search the FAQ database using the keywords “Wireless LAN” or “WLAN”
*
Related Wireless Sessions
Session 1529: Understanding WLAN Model Internals, Interfaces, and Performance
Session 1530: Modeling Custom Wireless Effects
Session 1815: Introduction to Wireless LAN Protocols
*
Take-Away Points
DES models provides extensive support for modeling wireless LAN networks, e.g.,:
Analyzing network performance, with and without mobility
Studying the effects of transient conditions and protocol overhead
Deployment of explicit traffic sources (e.g., TCP/IP-based applications or raw traffic generators) over WLAN technology
Simulate large wireless LAN network topologies
Reduce simulation execution time by using simulation efficiency modes (global attributes)
Study the interaction between legacy and new wireless LAN technologies
Find the most optimal configuration (e.g., when using PCF) to achieve optimum performance for all wireless applications
CFP
CFP