Cabletron Systems 3Com manual Data Rate Requirement

Page 21

Theory of Operation 21

Direct-Sequence Spread Direct Sequence Spread Spectrum (DSSS) uses a high-speed, non-information Spectrum bearing signal to spread the transmitted information over a segment of the

radio frequency band or spectrum. The AirConnect access point uses DSSS for radio communication.

Direct-sequence systems communicate by continuously transmitting a redundant pattern of bits called a chipping sequence. Each bit of transmitted data is mapped into chips by the access point to find the chipping sequence corresponding to the output signal.

Wireless clients receiving a direct-sequence transmission use the same chipping sequence to recreate the original data transmitted by the access point. Intercepting and decoding a direct-sequence transmission requires a predefined algorithm to associate the chipping sequence used by the transmitting access point to the receiving wireless client. This algorithm is established when the access point and wireless client are configured. The bit redundancy within the chipping sequence enables the receiving wireless client to recreate the original data pattern, even if bits in the chipping sequence are corrupted by interference.

Wireless Client APs recognize wireless clients as they associate with the AP. The AP keeps a list of Association Process the wireless clients it services. Wireless clients associate with an AP based on the

following conditions:

■Signal strength between the AP and wireless client

■Wireless clients currently associated with the AP

■Wireless client Supported Rate (see table below).

■Positive match between the wireless client and encryption keys (optional)

■Positive wireless client authorization by the Access Control List (optional)

Data Rate

Requirement

 

 

11 Mbps

Optional

5.5 Mbps

Optional

2 Mbps

Required

1 Mbps

Required

 

 

Wireless clients perform preemptive roaming by intermittently scanning for APs and associating with the best available AP. Before roaming and associating with APs, wireless clients perform scans to collect AP statistics and determine the direct-sequence channel used by the AP.

Scanning is a periodic process where the wireless client sends out messages on all frequencies defined by the country code. The statistics enable a wireless client to reassociate by synchronizing its frequency to the AP. The wireless client continues communicating with that AP until it needs to switch cells or roam.

Wireless clients perform scans at start-up. In a scan, a wireless client uses a sequential set of channels as the scan range. For each channel in range, the wireless client tests for Clear Channel Assessment (CCA). When a transmission-free channel becomes available, the wireless client broadcasts a probe with the wireless LAN service area and the broadcast HSA_ID. An AP-directed probe response generates a wireless client Acknowledgment (ACK)

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Contents Version AirConnect 11 Mbps Wireless LAN Access Point User GuideBayfront Plaza Santa 3Com CorporationClara, California 95052-8145Contents Installing Access Point Hardware Monitoring Wireless Clients Access Point Installation Configuring the AP Access Point Specifications Technical Support Page Introduction Overview of Digital Wireless NetworkingAirConnect Network TopologiesOverview of Digital Wireless Networking AirConnect Network Topologies Wireless clients AirConnect AccessPoint To the Ethernet LANAirConnect Access Point Wireless clients and APs PowerBASE-TRadio Basics Results in the original digital dataRadio Basics 802.1d Spanning Tree Support Wireless LAN Service AreaSite Surveys Filtering and Access Control Network Control Protocol NCP as described PPP Connection Data Rate Requirement Overview of Digital Wireless Networking Theory of Operation Simple Network Management Protocol Snmp Programmable Snmp Trap Support Using SnmpManagement protocol MIB Increased MIB SupportMethod Description Using the User InterfacePrecautions Installing Access Point HardwarePackage Contents RequirementsStandard power supply 115/230VAC, 50/60Hz, 24V/14 Power OptionsRemote power distribution system, Part Number AP-PS-11 US line cord Part NumberMounting the AP BelowWall Mount To mount an AP on a wall Ceiling Mount To mount an AP on a ceiling Mounting the AP Using PowerBASE-TPowerBASE-T can be used to power the AP LED Indicators Off Blinking Power No power Power on During boot sequenceCondition, and other activity 3Com Support Center TroubleshootingVerify AP Operation Electrical Management System EMS operating outletNetwork connection verification Verify Network Wiring TopologyPage System Properties Monitoring StatisticsInterface Statistics Forwarding CountsEthernet Statistics Radio FrequencyStatistics Statistics window, select Main Menu→Misc Statistics MiscellaneousPress Esc or Previous F4 to exit Type Name DefinitionClearing Statistics Known APsSelect Clear All Statistics Gaining access to the User Interface UI Gaining Access to the User Interface UI Using a Web BrowserHelp File Access Setup Network Web Server Help File AccessSelect Virtual Directory Accessing the Web Browser UISelect Close/Exit Select System ConfigurationSelect Save F1 to save the configuration Select Special Functions Select Reset APType the case sensitive AP name Under Configuration, select Security Select System PasswordSelect Easy Setup--Easy Setup Select Easy Setup--Easy Setup Click Add/Delete GatewaysParameter Description Adding Allowed Wireless Clients Adding or Deleting a Range of Allowed Wireless ClientsAdding or Deleting Disallowed Wireless Clients Considerations For the Short RF Preamble setting, click DisabledEnabling or Disabling Encryption Select Configuration--SecurityEnable or disable interfaces on the AP Interface Description Default ConditionFrequency No. of Channels Country Enter the Multicast Mask data and voice values Snmp Trap Description Default Value Select Enabled or Disable All for All Snmp TrapsConfiguring the Originating Modem Configuring the Answering Modem Filtering to Forward PacketsFiltering to Discard Packets Click Delete Filter Removing Filtered Packet Types Networking ProtocolsDisabling Type Filtering Under Configuration, select FirmwareSpecial Function Description Active. Clear the wireless client association table forMonitoring Wireless Clients Wireless ClientsSelect Regular at the Wireless Clients prompt Indicates a 3Com voice-enabled device Ascii Interface Latest version. Refer to Manually Updating AP Firmware onVersions Enable serial port Configure the AP for the followingArrow/Function Key Control Character Prompt Description To exit from submenus, press EscPress Tab to select System Password Select Telnet LoginsTo enable and configure the serial port connection on the AP Configuring The Serial PortConfiguring the Dial-Up System Setting DescriptionHanging Up Select Modem HangupWindow InstallationConfiguring the AP That can associate with this AP. The default is Disabled Wsaid PPP Direct Establishing a ConnectionPPP with Modems Originating AP Set the Connect Mode to AnswerAnswering AP From the answering APs UIFor automatic dial-out, reset the AP Press up/down arrows to toggle between range and individual Range of Wireless ClientsRemoving Allowed Wireless Clients Enable/Disable the ACLRemoving All Allowed Wireless Clients Adding Disallowed Wireless Clients Load ACL from Wireless Client ListRemoving Disallowed Wireless Clients Address FilteringSetting Logging Clearing WirelessClients from the AP OptionsManually Updating AP FirmwarePrevious version of AP firmware Remainder of this procedure uses Windows 98 as an example Select Alter Filenames/HELP URL/TFTP and press EnterType the firmware file name in the Download Filename field Open the Special Functions window Select Transfer from the emulation program menu barSelect Send File Select Alter Filenames/HELP URL/TFTP Server and press Enter Download is complete when the UI displaysAuthentication Using MD5Performing Pings Extended RoamingWireless client and the access point EncryptionHex-digit sequence Restoring Configurations Press the Tab key to highlight .Short RF Preamble EnabledSelect Restore Factory Configuration Physical Characteristics Access Point SpecificationsRadio Characteristics Frequency No. of Channels Country Output CharacteristicsNetwork Characteristics Technical Support ServicesOnline Technical World Wide Web SiteNorth America Latin AmericaTo obtain an RMA number, call or fax Page Ascii IndexSnmp agent 3Com AirConnect Access Point 3Com Corporation Limited WarrantyObtaining Warranty Radio Frequency Interference Requirements Canada Regulatory Compliance Information3Com End User Software License Agreement Important Read Before Using This Product
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