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Session Abstract

Session Abstract. Agenda. Wireless LAN (WLAN) overview WLAN model support Capabilities Node models Attributes Statistics WLAN nodes architecture Lab 1: Hidden node scenario Lab 2: Infrastructure Extended Service Set (ESS) Lab 3: PCF access mode Mobile IP Lab 4: Roaming. Agenda.

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Session Abstract

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Presentation Transcript

  1. Session Abstract

  2. Agenda • Wireless LAN (WLAN) overview • WLAN model support • Capabilities • Node models • Attributes • Statistics • WLAN nodes architecture • Lab 1: Hidden node scenario • Lab 2: Infrastructure Extended Service Set (ESS) • Lab 3: PCF access mode • Mobile IP • Lab 4: Roaming

  3. Agenda • Wireless LAN overview • WLAN model support • Capabilities • Node models • Attributes • Statistics • WLAN nodes architecture • Lab 1: Hidden node scenario • Lab 2: Infrastructure ESS • Lab 3: PCF access mode • Mobile IP • Lab 4: Roaming

  4. Why Wireless LAN? • Mobility • Users do not have to be plugged in • Real-time data from anywhere in the organization • 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 802.11 and IEEE 802.11b standards • Modeled data rates • 1.0 Mbps • 2.0 Mbps • 5.5 Mbps • 11.0 Mbps • Supported physical layers • Direct-sequence spread-spectrum (DSSS) • Frequency Hopping spread-spectrum (FHSS) • Infrared light (IR) • 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 Topologies • Basic building block: Basic Service Set (BSS) • Independent BSS • Infrastructure BSS

  9. Wireless LAN Topologies (cont.) • Infrastructure Extended Service Set (ESS) BSS 1 BSS 2 BSS 3 Internet

  10. Agenda • Wireless LAN overview • WLAN model support • Capabilities • Node models • Attributes • Statistics • WLAN nodes architecture • Lab 1: Hidden node scenario • Lab 2: Infrastructure ESS • Lab 3: PCF access mode • Mobile IP • Lab 4: Roaming

  11. WLAN OPNET Model: Typical Use Cases • Study wireless LANs as an alternate/supplemental local area network technology • Analyze network performance by varying the network demand (e.g., number of nodes, application traffic) • Evaluate optional protocol-specific features like fragmentation and reassembly or RTS/CTS frame exchange against various network conditions • Set up independent and infrastructure BSS networks and evaluate their performance under different traffic and configurations

  12. WLAN OPNET Model: Typical Use Cases (contd.) • Tune PCF parameters to achieve maximum performance for different applications • Study the impact of mobility on applications running at mobile node and efficiency of the wireless LANs being visited • Modify the logic of standard WLAN algorithms to conduct experiments with new ideas and prospective improvements

  13. 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

  14. Attributes Node Attributes

  15. Model Attribute Definitions • RTS Threshold (bytes) • Set the packet size threshold for which the ready to send (RTS)/clear to send (CTS) WLAN mechanism will be used • Solution to hidden terminal problem • Prevent large packets to be dropped • Overhead due to the RTS/CTS frame exchange • Short Retry Limit • Maximum transmission attempts for data frames with a size shorter than or equal to RTS Threshold • High values for retry limit will produce a more reliable transmissions but will create overhead • Long Retry Limit • Maximum transmission attempts for data frames with a size greater than RTS Threshold • Set a lower value than Short Retry Limit will help to decrease the amount of buffer required

  16. 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

  17. Model Attribute Definitions (cont.) • BSS Identifier • Identifies the BSS to which a WLAN MAC belongs to • 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

  18. Model Attribute Definitions (cont.) • Data Rate (bps) • Support for 1.0 Mbps, 2.0 Mbps, 5.5 Mbps, and 11.0 Mbps • Networks with higher data rate are more sensitive to external interference • Different data rates are supported in the same BSS • Physical Characteristics • Set the physical layer used by the model: Frequency Hopping, Direct Sequence or Infrared. Internal attributes like interframe spacing values and MAC header are dependent on the physical layer.

  19. Model Attribute Definitions (cont.) • Packet Reception Power Threshold • Defines the received power threshold value in Watts at the radio receiver for arriving WLAN packets • Packets with a power less than threshold will be considered as noise • Will not change the status of the receiver to "busy" from the point of view of the MAC layer • Sensitivity indicator • Vendor specific • PCF Parameters • Configure PCF operation mode

  20. Model Attribute Definitions (cont.) • 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 acknowledgement from MAC that is being polled

  21. BSS A  Ch1 BSS B  Ch6 BSS C  Ch11 Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 Ch 9 Ch 10 Ch 11 BSS D  Ch2 BSS E  Ch7 2.401 MHz 2.451 MHz 2.473 MHz Reserved Frequency Band for WLAN Channels in U.S. Auto-allocation of WLAN channels to BSSs (New in 10.0) • Channel Settings • Bandwidth and frequency settings • Default value “Auto Assigned” • A WLAN channel will be assigned to each BSS automatically • Manual assignments are supported: pre-defined “channels” or any value • Must be consistent across the BSS • Example • 5 BSSs: from “BSS A” to BSS “E” where A < B < C < D < E

  22. Roaming (New in 10.0) • Needed when the connection is weakened/lost with AP • Two approaches for scanning for a new AP • Based on signal strength (monitors AP’s periodic beacons) • Realistic • Based on distance • Efficient • Configure the simulation attribute to determine the approach to be used • WLAN Beacon Efficiency Mode (default: Enabled) • WLAN AP Connectivity Check Interval (default: 10 seconds)

  23. Statistics Global Statistics Node Statistics

  24. Statistics (cont.)

  25. Agenda • Wireless LAN overview • WLAN model support • Capabilities • Node models • Attributes • Statistics • WLAN nodes architecture • Lab 1: Hidden node scenario • Lab 2: Infrastructure ESS • Lab 3: PCF access mode • Mobile IP • Lab 4: Roaming

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

  27. Agenda • Wireless LAN overview • WLAN model support • Capabilities • Node models • Attributes • Statistics • WLAN nodes architecture • Lab 1: Hidden node scenario • Lab 2: Infrastructure ESS • Lab 3: PCF access mode • Mobile IP • Lab 4: Roaming

  28. 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

  29. Break

  30. Agenda • Wireless LAN overview • WLAN model support • Capabilities • Node models • Attributes • Statistics • WLAN nodes architecture • Lab 1: Hidden node scenario • Lab 2: Infrastructure ESS • Lab 3: PCF access mode • Mobile IP • Lab 4: Roaming

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

  32. Agenda • Wireless LAN overview • WLAN model support • Capabilities • Node models • Attributes • Statistics • WLAN nodes architecture • Lab 1: Hidden node scenario • Lab 2: Infrastructure ESS • Lab 3: PCF access mode • Mobile IP • Lab 4: Roaming

  33. Mobile IP • A new model in 10.0 • Implementation based on the following RFCs: • RFC 3220: IP Mobility Support for IPv4 • RFC 2003: IP Encapsulation Within IP • RFC 1256: ICMP Router Discovery Messages • Supported features • Dynamic tunneling endpoints • Mobile IP router based networks (legacy end nodes) • Registration/Deregistration over UDP • Foreign agent care of address

  34. Mobile IP (cont.) • Why use Mobile IP? • Uninterrupted service for mobile users • Transparent to transport layer and applications • IP level roaming between different IP subnets/providers • Operational implementations • Cisco Mobile IP routers • Various Linux implementation (for Laptops and PDAs) • Future enhancements • Co-located care of address • Route optimization • IPv6 support

  35. Mobile IP Example • Mobile node at the home network • No tunneling is required

  36. Mobile IP Example (cont.) • Mobile node at a foreign network • Data from server is tunneled by home agent to foreign agent IP Tunnel

  37. Mobile IP Attributes: Router

  38. Mobile IP Attributes: Router (cont.) • Home Agent • Interface Name • Name of a physical or loopback interface to enable the home agent service • IP address has to be pre-assigned to the interface • Agent Type • Home Agent

  39. Mobile IP Attributes: Router (cont.) • Foreign Agent • Interface Name • Name of a physical or loopback interface to enable the foreign agent service • Usually a roaming capable (e.g. radio) interface • Agent Type • Foreign Agent

  40. Mobile IP Attributes: Router (cont.) • Mobile Router • Interface Name • Name of a physical or loopback interface to enable the Mobile Router service • Need to be a loopback interface if more than one roaming interfaces • The interface must have an IP address that falls into the same IP subnet as the HA • Agent Type • Mobile Router • Home Agent IP Address • IP address of the HA interface

  41. Mobile IP Attributes: Host • Mobile Node • Interface Name • Name of a physical or loopback interface to enable the Mobile Node service • The interface must have an IP address that falls into the same IP subnet as the HA • Home Agent IP Address • IP address of the HA interface

  42. Agenda • Wireless LAN overview • WLAN model support • Capabilities • Node models • Attributes • Statistics • WLAN nodes architecture • Lab 1: Hidden node scenario • Lab 2: Infrastructure ESS • Lab 3: PCF access mode • Mobile IP • Lab 4: RoamingMobile IP

  43. Lab #5: Roaming Mobile IP • Objective • Configure Mobile IP network utilizing WLAN roaming capabilities • Adjust Mobile IP handoff parameters to achieve less communication interrupts

  44. Takeaway Points • RTS/CTS option can help alleviate the hidden node problem • Additional APs provides more capacity and support scalability • Use PCF option to provide QoS • Use roaming feature to model mobile scenarios • OPNET provides extensive modeling support for modeling wireless LAN networks: • Discrete Event Simulation for modeling protocol algorithms, optional standard features, transient effects, protocol overhead traffic, deployment of explicit traffic sources (TCP/IP-based applications or raw traffic generators) over WLAN technology, etc.

  45. Additional Resources • Wireless LAN Model Usage Guide • Click on “Help” menu and select “Product Documentation” • “Model Descriptions  Model Usage Guides Wireless LAN (802.11)” • 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”

  46. References • IEEE 802.11 standard • RFC 3220 IP Mobility Support for IPv4 • Gast, Matthew S., 802.11 Wireless Networks: The Definitive Guide, O’Reilly & Associates, April 2002

  47. Related Wireless Sessions • Session 1529: Understanding WLAN Model Internals and Interfaces • Session 1318: Planning and Analyzing UMTS Networks • Session 1807: Introduction to Next Generation Wireless Technologies

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