Opnet Slides

Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties.

Session 1332

Network Analysis, Planning, and Troubleshooting

Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 2


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


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


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


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


Sense the medium

If the medium is busy, defer

When the medium becomes idle again,

transmit after a random backoff


Requires centralized coordination Introduces contention free period

(CFP)Use for “near” real-time servicesForces a “fair” access to the medium

during the CFP


Basic building block: Basic Service Set (BSS)

Independent BSS

Infrastructure BSS


Infrastructure Extended Service Set (ESS)BSS 1 BSS 2 BSS 3

Internet





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


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


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


Node Attributes


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


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


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


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.


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


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


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


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)


Global Statistics Node Statistics






Objective Show the impact of the RTS/CTS mechanism as a measure to prevent

the hidden node problem





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






Objective Use PCF mechanism to improve the performance of real-time

applications over WLAN



Lab 1: Hidden node scenarioLab 2: Infrastructure ESS Lab 3: PCF access mode Mobile IPLab 4: Roaming


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


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


Mobile node at the home network No tunneling is required


Mobile node at a foreign network Data from server is tunneled by home agent to foreign agent

IP Tunnel



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


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


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


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



Lab 1: Hidden node scenarioLab 2: Infrastructure ESSLab 3: PCF access mode Mobile IPLab 4: Roaming Mobile IP


Objective Configure Mobile IP network utilizing WLAN roaming capabilities Adjust Mobile IP handoff parameters to achieve less communication

interrupts


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.


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”

http://www.opnet.com/support


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


Session 1529: Understanding WLAN Model Internals and InterfacesSession 1318: Planning and Analyzing UMTS NetworksSession 1807: Introduction to Next Generation Wireless

Technologies

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