Transcript OPNETWORK 2004 Session

Session 1332
Planning and Analyzing
Wireless LANs
Network Analysis, Planning, and
Troubleshooting
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
1332 Planning and Analyzing Wireless LANs
Session Abstract
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Agenda
 Wireless LAN (WLAN) overview
 OPNET WLAN models use cases
 WLAN model support
 Network configurations
 Node models
 Statistics
 Node attributes
 Global attributes
 Mobility modeling
 Lab 1: Hidden node scenario
 Break
 Lab 2: Infrastructure Extended Service Set (ESS)
 Lab 3: PCF access mode
 Lab 4: Mixed 11b/11g WLAN Performance
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Agenda
 Wireless LAN overview
 OPNET WLAN models use cases
 WLAN model support
 Network configurations
 Node models
 Statistics
 Node attributes
 Global attributes
 Mobility modeling
 Lab 1: Hidden node scenario
 Break
 Lab 2: Infrastructure Extended Service Set (ESS)
 Lab 3: PCF access mode
 Lab 4: Mixed 11b/11g WLAN Performance
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Why Wireless LAN?
 Availability
 Open specifications
 Mobility
 Users do not have to be plugged in
 Ease of installation
 No need for cabling through/around walls
 Can go where wires cannot
 Reduced cost-of-ownership
 Easier to move, add, and change
 Uses license-free radio spectrum
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Wireless LAN Support in OPNET
 Based on IEEE standards
 Modeled data rates
 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)
 Frequency Hopping Spread-Spectrum (FHSS)
 Infrared light (IR)
 Orthogonal Frequency Division Multiplexing (OFDM)
 Extended Rate PHY-OFDM (ERP-OFDM)
 DCF MAC operation: Contention based (CSMA/CA)
 PCF MAC operation: Poll based
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Distributed Coordinated Function (DCF)
Sense the medium
If the medium is busy,
defer
When the medium
becomes idle again,
transmit after a
random backoff
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1332 Planning and Analyzing Wireless LANs
Point Coordination Function (PCF) Operation
 Requires centralized coordination
 Introduces contention free period
(CFP)
 Use for “near” real-time services
 Forces a “fair” access to the
medium during the CFP
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Wireless LAN Support in OPNET (cont.)
 Reliable data transmission via RTS-CTS exchange (threshold
based)
 Request To Send – Clear To Send
 Fragmentation (threshold based)
 Exponential back-off – reduced collision probability
 Protection for mixed 11b/11g wireless LANs
 CTS-to-self or regular RTS/CTS exchange
 Roaming (can be turned on/off)
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Agenda
 Wireless LAN overview
 OPNET WLAN models use cases
 WLAN model support
 Network configurations
 Node models
 Statistics
 Node attributes
 Global attributes
 Mobility modeling
 Lab 1: Hidden node scenario
 Break
 Lab 2: Infrastructure Extended Service Set (ESS)
 Lab 3: PCF access mode
 Lab 4: Mixed 11b/11g WLAN Performance
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
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
 Tune PCF parameters to achieve maximum performance for
different applications
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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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
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Agenda
 Wireless LAN overview
 OPNET WLAN models use cases
 WLAN model support
 Network configurations
 Node models
 Statistics
 Node attributes
 Global attributes
 Mobility modeling
 Lab 1: Hidden node scenario
 Break
 Lab 2: Infrastructure Extended Service Set (ESS)
 Lab 3: PCF access mode
 Lab 4: Mixed 11b/11g WLAN Performance
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Supported Network Configurations
BSS 1
BSS 2
BSS 3
Ad Hoc Network
Internet
Infrastructure BSS
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Extended Service Set
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1332 Planning and Analyzing Wireless LANs
Supported Network Configurations (Cont.)
Wireless Backbone
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1332 Planning and Analyzing Wireless LANs
Node Models
Wireless LAN Station (Non-IP based)
Wireless LAN Workstation
Wireless LAN Server
Bridge with WLAN Port (Access Point)
Router with WLAN interface (Access Point*)
* Unless the interface belongs to a WLAN backbone
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1332 Planning and Analyzing Wireless LANs
Statistics
Global Statistics
Node Statistics
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1332 Planning and Analyzing Wireless LANs
Statistics (cont.)
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1332 Planning and Analyzing Wireless LANs
Attributes
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1332 Planning and Analyzing Wireless LANs
Model Attribute Definitions
BSS Identifier
 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
 Enable or disable access-point operation in the node
 Used to configure BSS and ESS topologies
 Required to be Enabled
 For PCF operation
 To support roaming
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Configuring PHY and Data Rate
 First select the physical layer technology
 Then select the data rate for data transmissions among the
available data rates
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Configuring Operation Channel
 Channel assignments must be consistent within BSS
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1332 Planning and Analyzing Wireless LANs
Auto-Allocation of WLAN channels to BSSs
 Example
 5 BSSs: from “BSS A” to BSS “E” where A < B < C < D < E
BSS A  Ch 1
Ch 1
Ch 2
2,401 MHz
Ch 3
Ch 4
BSS B  Ch 6
Ch 5
BSS D  Ch 2
Ch 6
Ch 7
Ch 8
Ch 9
BSS C  Ch 11
Ch 10
BSS E  Ch 7
Ch 11
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 36
Ch 36
5,170 MHz
BSS B  Ch 40
BSS D  Ch 48
BSS C  Ch 44
Ch 40
Ch 44
Ch 48
5,190 MHz
5,210 MHz
5,230 MHz
Reserved Frequency Band for WLAN Channels in U.S.
at 5 GHz (11a)
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1332 Planning and Analyzing Wireless LANs
Transmitting and Receiving
 Transmit Power
 Nodes fixed transmission power in Watts
 Packet Reception Power Threshold
 Defines the receiver sensitivity in dBm
 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
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Model Attribute Definitions (cont.)
 RTS Threshold (bytes)
 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
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1332 Planning and Analyzing Wireless LANs
Lab #1: Hidden Node
 Objective
 Show the impact of the RTS/CTS mechanism as a measure to prevent
the hidden node problem
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1332 Planning and Analyzing Wireless LANs
Break
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1332 Planning and Analyzing Wireless LANs
Lab #2: Infrastructure BSS
 Objective
 Become familiar with WLAN
model attributes needed to
configure BSSs
 Use the model to select an
appropriate WLAN topology
according to the application traffic
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1332 Planning and Analyzing Wireless LANs
Model Attribute Definitions (cont.)
 Fragmentation Threshold (bytes)
 MSDU  Threshold  fragmentation
occurs
 Smaller packet size reduces packet loss but
increase overhead
 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)
 Maximum length of higher-layer data
arrival buffer
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1332 Planning and Analyzing Wireless LANs
PCF Configuration
 PCF Parameters
 PCF Functionality
 Enables / disables use of PCF
 Beacon Interval
 Specifies how often the beacons will be transmitted
 CFP Interval
 The length of each contention free period in seconds
 CFP Beacon Multiple
 Specifies the number of beacons between two CFPs
 Max Failed Polls
 Specifies the maximum
number of consecutive polls
by the AP without a valid
response from MAC that is
being polled
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1332 Planning and Analyzing Wireless LANs
Lab #3: PCF Access Mode
 Objective
 Use PCF mechanism to improve the performance of real-time
applications over WLAN
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
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1332 Planning and Analyzing Wireless LANs
Model Attribute Definitions (cont.)
 CTS-to-self Option
 802.11g specific
 Used as a protection mechanism in mixed 11b/11g networks
 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
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1332 Planning and Analyzing Wireless LANs
Global Attributes
 Closure Method (non-TMM)
 Not used during terrain modeling
 By default no closure computation
 Faster simulation execution
 Alternatively closure computation based on Earth’s line-of-sight
 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
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1332 Planning and Analyzing Wireless LANs
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
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1332 Planning and Analyzing Wireless LANs
Modeling Node Mobility
 Three methods to enable node mobility
 Trajectories
 Specifying a “motion vector” via attributes
 Modifying node position programmatically, e.g., “Random Waypoint”
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1332 Planning and Analyzing Wireless LANs
Random Waypoint Mobility
 Node moves randomly from one waypoint to another
 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
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1332 Planning and Analyzing Wireless LANs
Lab #4: Mixed 11b/11g WLAN Performance
 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
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1332 Planning and Analyzing Wireless LANs
Additional Resources
 Wireless LAN Model Usage Guide
 Click on “Help” menu and select “Product Documentation”
 “Model Descriptions  Model Usage Guides Wireless LAN
(802.11)”
 IEEE standards
 IEEE 802.11-1999
 IEEE 802.11a-1999, IEEE 802.11b-1999 and 802.11g-2003
 Wireless LAN FAQs
 Go to Support Center at OPNET’s WWW site
 http://www.opnet.com/support
 Click on “FAQs” link under “Technical Resources”
 Search the FAQ database using the keywords “Wireless LAN” or
“WLAN”
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1332 Planning and Analyzing Wireless LANs
Related Wireless Sessions
 Session 1348: Planning and Analyzing Mobile IP Networks
 Session 1345: Planning and Analyzing Mobile Ad-Hoc
Networks
 Session 1529: Understanding WLAN Model Internals,
Interfaces, and Performance
 Session 1530: Modeling Custom Wireless Effects
 Session 1815: Introduction to Wireless LAN Protocols
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1332 Planning and Analyzing Wireless LANs
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
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