opnet slides
TRANSCRIPT
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Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
Session 1332
Network Analysis, Planning, and Troubleshooting
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Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 2
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Wireless LAN (WLAN) overviewWLAN model support Capabilities Node models Attributes StatisticsWLAN nodes architecture
Lab 1: Hidden node scenarioLab 2: Infrastructure Extended Service Set (ESS)Lab 3: PCF access mode Mobile IPLab 4: Roaming
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Wireless LAN overviewWLAN model support Capabilities Node models Attributes StatisticsWLAN nodes architecture
Lab 1: Hidden node scenarioLab 2: Infrastructure ESSLab 3: PCF access mode Mobile IP Lab 4: Roaming
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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
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Based on IEEE 802.11 and IEEE 802.11b standardsModeled 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
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Sense the medium
If the medium is busy, defer
When the medium becomes idle again,
transmit after a random backoff
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Requires centralized coordination Introduces contention free period
(CFP)Use for “near” real-time servicesForces a “fair” access to the medium
during the CFP
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Basic building block: Basic Service Set (BSS)
Independent BSS
Infrastructure BSS
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Infrastructure Extended Service Set (ESS)BSS 1 BSS 2 BSS 3
Internet
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Wireless LAN overviewWLAN model support Capabilities Node models Attributes StatisticsWLAN nodes architecture
Lab 1: Hidden node scenarioLab 2: Infrastructure ESSLab 3: PCF access mode Mobile IP Lab 4: Roaming
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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
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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
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Wireless LAN Workstation
Wireless LAN Server
Router with WLAN interface (Access Point*)
Wireless LAN Station (Non-IP based)
Bridge with WLAN Port (Access Point)
* Unless the interface belongs to a WLAN backbone
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Node Attributes
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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
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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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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
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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.
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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 noiseWill not change the status of the receiver to "busy" from the point of
view of the MAC layer Sensitivity indicatorVendor specific
PCF Parameters Configure PCF operation mode
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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
CFP CFP
CFP Interval = 10 msec.
Beacon Interval = 20 msec.
CFP Beacon Multiple = 2
0 2010 30 40 50 msec.
CFP Offset = 1
= TBTT
CFP CFP
CFP Interval = 10 msec.
Beacon Interval = 20 msec.
CFP Beacon Multiple = 2
0 2010 30 40 50 msec.
CFP Offset = 1
= TBTT= TBTT
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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
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.
BSS A Ch1 BSS B Ch6 BSS C Ch11
BSS D Ch2 BSS E Ch7
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Needed when the connection is weakened/lost with APTwo 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 usedWLAN Beacon Efficiency Mode (default: Enabled)WLAN AP Connectivity Check Interval (default: 10 seconds)
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Global Statistics Node Statistics
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Wireless LAN overviewWLAN model support Capabilities Node models Attributes StatisticsWLAN nodes architecture
Lab 1: Hidden node scenarioLab 2: Infrastructure ESSLab 3: PCF access mode Mobile IP Lab 4: Roaming
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Objective Show the impact of the RTS/CTS mechanism as a measure to prevent
the hidden node problem
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Wireless LAN overviewWLAN model support Capabilities Node models Attributes StatisticsWLAN nodes architecture
Lab 1: Hidden node scenarioLab 2: Infrastructure ESSLab 3: PCF access mode Mobile IP Lab 4: Roaming
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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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Wireless LAN overviewWLAN model support Capabilities Node models Attributes StatisticsWLAN nodes architecture
Lab 1: Hidden node scenarioLab 2: Infrastructure ESSLab 3: PCF access mode Mobile IP Lab 4: Roaming
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Objective Use PCF mechanism to improve the performance of real-time
applications over WLAN
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Wireless LAN overviewWLAN model support Capabilities Node models Attributes StatisticsWLAN nodes architecture
Lab 1: Hidden node scenarioLab 2: Infrastructure ESS Lab 3: PCF access mode Mobile IPLab 4: Roaming
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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 endpointsMobile IP router based networks (legacy end nodes) Registration/Deregistration over UDP Foreign agent care of address
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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
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Mobile node at the home network No tunneling is required
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Mobile node at a foreign network Data from server is tunneled by home agent to foreign agent
IP Tunnel
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Home Agent Interface NameName of a physical or loopback interface to enable the home agent
service IP address has to be pre-assigned to the interface
Agent TypeHome Agent
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Foreign Agent Interface NameName of a physical or loopback interface to enable the foreign agent
serviceUsually a roaming capable (e.g. radio) interface
Agent Type Foreign Agent
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Mobile Router Interface NameName of a physical or loopback interface to enable the Mobile Router
serviceNeed 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 TypeMobile Router
Home Agent IP Address IP address of the HA interface
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Mobile Node Interface NameName 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
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Wireless LAN overviewWLAN model support Capabilities Node models Attributes StatisticsWLAN nodes architecture
Lab 1: Hidden node scenarioLab 2: Infrastructure ESSLab 3: PCF access mode Mobile IPLab 4: Roaming Mobile IP
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Objective Configure Mobile IP network utilizing WLAN roaming capabilities Adjust Mobile IP handoff parameters to achieve less communication
interrupts
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RTS/CTS option can help alleviate the hidden node problem Additional APs provides more capacity and support scalabilityUse PCF option to provide QoSUse roaming feature to model mobile scenariosOPNET 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.
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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”
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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
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Session 1529: Understanding WLAN Model Internals and InterfacesSession 1318: Planning and Analyzing UMTS NetworksSession 1807: Introduction to Next Generation Wireless
Technologies