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Session Abstract

Session Abstract. 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)

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Session Abstract

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  1. Session Abstract

  2. 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

  3. 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

  4. 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

  5. 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

  6. Distributed Coordinated Function (DCF) Sense the medium If the medium is busy, defer When the medium becomes idle again, transmit after a random backoff

  7. 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

  8. 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)

  9. 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

  10. 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

  11. 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

  12. 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

  13. BSS 1 BSS 2 BSS 3 Infrastructure BSS Ad Hoc Network Internet Extended Service Set Supported Network Configurations

  14. Wireless Backbone Supported Network Configurations (Cont.)

  15. 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

  16. Statistics Global Statistics Node Statistics

  17. Statistics (cont.)

  18. Attributes

  19. 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

  20. Configuring PHY and Data Rate • First select the physical layer technology • Then select the data rate for data transmissions among the available data rates

  21. Configuring Operation Channel • Channel assignments must be consistent within BSS

  22. BSS A  Ch 1 BSS B  Ch 6 BSS C  Ch 11 Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 Ch 9 Ch 10 Ch 11 BSS D  Ch 2 BSS E  Ch 7 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 36 BSS D  Ch 48 BSS B  Ch 40 BSS C  Ch 44 Ch 36 Ch 40 Ch 44 Ch 48 5,170 MHz 5,230 MHz 5,190 MHz 5,210 MHz Reserved Frequency Band for WLAN Channels in U.S. at 5 GHz (11a) Auto-Allocation of WLAN channels to BSSs • Example • 5 BSSs: from “BSS A” to BSS “E” where A < B < C < D < E

  23. 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

  24. 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

  25. Lab #1: Hidden Node • Objective • Show the impact of the RTS/CTS mechanism as a measure to prevent the hidden node problem

  26. Break

  27. 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

  28. 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

  29. 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

  30. Lab #3: PCF Access Mode • Objective • Use PCF mechanism to improve the performance of real-time applications over WLAN

  31. 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

  32. 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

  33. 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

  34. Modeling Node Mobility • Three methods to enable node mobility • Trajectories • Specifying a “motion vector” via attributes • Modifying node position programmatically, e.g., “Random Waypoint”

  35. 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

  36. 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

  37. 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”

  38. 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

  39. 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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