1 / 40

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)

keaton-petty
Télécharger la présentation

Session Abstract

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related