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IEEE 802.11 Architecture

IEEE 802.11 Architecture

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IEEE 802.11 Architecture

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  1. IEEE 802.11 Architecture

  2. Module contents • IEEE 802.11 Terminology • IEEE 802.11 MAC Frames • Operational Processes • Configuration parameters

  3. PC-Card Hardware Radio Hardware 802.11 frame format WMAC controller with Station Firmware (WNIC-STA) 802.3 frame format Platform Computer Driver Software (STADr) Ethernet V2.0 / 802.3 frame format Protocol Stack IEEE 802 .11 TerminologySTA (Station) Station (STA) Architecture: • Device that contains IEEE 802.11 conformant MAC and PHY interface to the wireless medium, but does not provide access to a distribution system • Most often end-stations available in terminals (work-stations, laptops etc.) • Implemented in ORiNOCO IEEE 802.11 PC-Card • Ethernet-like driver interface • supports virtually all protocol stacks • Frame translation according to IEEE Std 802.1H • IEEE 802.3 frames: translated to 802.11 • Maximum Data limited to 1500 octets • Transparent bridging to Ethernet

  4. PC-Card Hardware Radio Hardware 802.11 frame format WMAC controller with Access Point Firmware (WNIC-AP) 802.3 frame format Bridge Software Driver Software (APDr) Ethernet V2.0 / 802.3 frame format Kernel Software (APK) Bridge Hardware Ethernet Interface IEEE 802 .11 TerminologyAP (Access Point) Access-Point (AP) Architecture: • Device that contains IEEE 802.11 conformant MAC and PHY interface to the wireless medium, providing access to a distribution system for associated stations • Most often infra-structure products that connect to wired backbones • Implemented in ORiNOCO IEEE 802.11 PC-Card inserted in AP-500, AP-1000, AP-2000 • STAs select an AP and “associate with it • APs : • Support roaming • Provide time synchronization (beaconing) • Provide Power Management support

  5. BSS IEEE 802 .11 TerminologyBasic Service Set (BSS) Basic Service Set (BSS): • A set of stations controlled by a single “Coordination Function” (=the logical function that determines when a station can transmit or receive) • Similar to a “cell” in Cellular network terminology • A BSS can have an Access-Point (both in standalone networks and in building-wide configurations), or can run without and Access-Point (in standalone networks only) • Station-to-Station traffic is relayed by the Access Point

  6. IBSS IEEE 802 .11 TerminologyIndependent Basic Service Set (IBSS) Independent Basic Service Set (IBSS): • A Basic Service Set (BSS) which forms a self-contained network in which no access to a Distribution System is available • A BSS without an Access-Point • Station-to-station traffic flows directly without any relay action • All stations in the cell will be able to receive frames transmitted by another station in the cell (filtering of traffic for subsequent processing is based on MAC address of the receiver)

  7. BSS IEEE 802 .11 TerminologyExtended Service Set (ESS) - Integrated DS Extended Service Set (ESS): • A set of one or more Basic Service Sets interconnected by a Distribution System (DS) • Traffic always flows via Access-Point Distribution System (DS): • A system to interconnect a set of Basic Service Sets • Integrated; A single Access-Point in a standalone network • Wired; Using cable to interconnect the Access-Points • Wireless; Using wireless to interconnect the Access-Points

  8. BSS Distribution System BSS IEEE 802 .11 TerminologyExtended Service Set (ESS) - Wired DS Extended Service Set (ESS): • A set of one or more Basic Service Sets interconnected by a Distribution System (DS) • Traffic always flows via Access-Point Distribution System (DS): • A system to interconnect a set of Basic Service Sets • Integrated; A single Access-Point in a standalone network • Wired; Using cable to interconnect the Access-Points • Wireless; Using wireless to interconnect the Access-Points

  9. IEEE 802 .11 TerminologyExtended Service Set (ESS) - Wireless DS Extended Service Set (ESS): • A set of one or more Basic Service Sets interconnected by a Distribution System (DS) • Traffic always flows via Access-Point Distribution System (DS): • A system to interconnect a set of Basic Service Sets • Integrated; A single Access-Point in a standalone network • Wired; Using cable to interconnect the Access-Points • Wireless; Using wireless to interconnect the Access-Points BSS Distribution System BSS

  10. BSS Distribution System BSS IEEE 802 .11 TerminologySSID (Network name) Service Set Identifier (SSID): • “Network name” • One network (ESS or IBSS) has one SSID • 32 octets long string • Needed to separate one network from the other • Used during initial establishment of communication between STA and AP to allow STA to select the correct AP • Can be viewed as Security Provision in combination with so-called “Closed Option” (not providing the correct SSID means no access to the network) BSSID = xx-xx-xx-xx-xx-xx SSID = ABCD BSSID = yy-yy-yy-yy-yy-yy

  11. BSS Distribution System BSS IEEE 802 .11 TerminologyBSSID (Cell Identifier) Basic Service Set Identifier (BSSID) • “cell identifier” • One BSS has one BSSID • 6 octets long (MAC address format) • In ESS is the same as the MAC address of the radio in the AP • In IBSS the value of BSSID will be randomly generated, and with local-bit on • Used as filter for multi-cast traffic and for traffic from other networks (in IBSS networks) • Used during hand-over (roaming) to other AP, in identifying the “old” AP BSSID = xx-xx-xx-xx-xx-xx BSSID = yy-yy-yy-yy-yy-yy SSID = ABCD

  12. Bytes: 2 2 6 6 6 2 6 0-2312 4 Frame Frame Duration Sequence Addr 1 Addr 2 Addr 3 Addr 4 CRC Body Control ID Control 802.11 MAC Header Bits: 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Pwr More Type SubType Retry WEP Rsvd Version DS DS Frag Mgt Data Frame Control Field IEEE 802.11 MAC Frames Frame Formats MAC Header format differs per Type: • Control Frames (several fields are omitted) • Management Frames • Data Frames

  13. Bits: 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Pwr More Type SubType Retry WEP Rsvd Version DS DS Frag Mgt Data Frame Control Field To DS From DS Address 1 Address 2 Address 3 Address 4 0 0 DA SA BSSID N/A 0 1 DA BSSID SA N/A 1 0 BSSID SA DA N/A 1 1 RA TA DA SA IEEE 802.11 MAC Frames Address Field Description Addr. 1 = All stations filter on this address. Addr. 2 = Transmitter Address (TA), Identifies transmitter to address the ACK frame to. Addr. 3 = Dependent on To and From DS bits. Addr. 4 = Needed to identify the original source of WDS (Wireless Distribution System)frames

  14. Bits: 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Pwr More Type SubType Retry WEP Rsvd Version DS DS Frag Mgt Data Frame Control Field IEEE 802.11 MAC Frames Type field descriptions Type and subtype identify the function of the frame: • Type=00 Management Frame Beacon (Re)Association Probe (De)Authentication Power Management • Type=01 Control Frame RTS/CTS ACK • Type=10 Data Frame

  15. Beacon Timestamp, Beacon Interval, Capabilities, SSID, Supported Rates, parameters, Traffic Indication Map Probe SSID, Capabilities, Supported Rates Probe Response Timestamp, Beacon Interval, Capabilities, SSID, Supported Rates, parameters same for Beacon except for TIM Dis-association Reason code Authentication Algorithm, Sequence, Status, Challenge Text Association Request Capability, Listen Interval, SSID, Supported Rates Association Response Capability, Status Code, Station ID, Supported Rates Re-association Request Capability, Listen Interval, SSID, Supported Rates, Current AP Address Re-association Response Capability, Status Code, Station ID, Supported Rates De-authentication Reason IEEE 802.11 MAC Frames Management Frames

  16. Operational processesAssociation • Process within an ESS where an STA establishes a relationship with an AP • Before a STA can access an ESS, “Association” has to be completed • STA will scan the available channels in the 2.4 GHz band to select AP (with matching SSID) that has the best communications quality • Active Scan (sending a “Probe request” on specific channels and assess response) • Passive Scan (assessing communications quality from beacon message) • AP maintains list of associate stations in MAC FW • Record station capability (data-rate) • To allow inter-BSS relay • Station’s MAC address is also maintained in bridge learn table in the Access Point associated with the port it is located on

  17. Operational processesAuthentication • Process within an ESS to control access to the network • Stations need to identify themselves to other Access-Points prior to data traffic or association • Open System Authentication • Uses null authentication algorithm • Default • Shared Key Authentication • Uses WEP privacy algorithm • Optional

  18. Operational processesStarting an ESS • The infrastructure network is identified by its SSID (network name) • All APs have to be configured to use this SSID • ORiNOCO wireless stations will be configured to set their desired SSID to the value of SSID configured in the APs • On power up stations will issue Probe Requests and will locate the AP that they will associate with: • “best” Access-Point with matching SSID • “best” Access-Point if the “desired SSID” has been set to “ANY” or a blank (empty) string (known as the “broadcast SSID”

  19. Operational processesStarting an IBSS • Station configured for IBSS operation will: • Scan the band (using Probe requests) using the SSID it was configured with • Received Probe Responses that match the SSID contain indication about sender of the Probe Response: • If sender is an AP, the station will associate to the AP • If sender is another STA in IBSS mode, the station will join this IBSS, and will obtain the BSSID of the starter to be able to filter traffic (for network separation) • When no Probe Responses are received with matching Network Name, Station will start the IBSS network: • Set an BSSID (randomly generated, in MAC address format with local bit on) • Start sending Beacons • All Stations in an IBSS network will participate in sending beacons. • All stations start a random timer prior to the point in time when next Beacon is to be sent. • First station whose random timer expires will send the next beacon

  20. Free access when medium is free longer than DIFS DIFS Contention Window Busy Medium PIFS DIFS SIFS Backoff-Window Next Frame Slot time Select Slot and Decrement Backoff as long as medium is idle. Defer Access Operational processesTraffic Flow On transmit: • STA that wants to send makes an “Clear-Medium” check to see if the medium is available • After Busy Medium condition has cleared, STA will await for DIFS and contends for the medium • When winning the contention, STA will transmit the frame. • The Address 1 field of the frame contains: • The BSSID (when STA operates in an ESS) • The MAC address of the recipient or a Multi-cast address (when STA operates in an IBSS)

  21. DIFS Bytes: Src 2 2 6 6 6 2 6 0-2312 4 Data Frame Frame Duration Sequence Addr 1 Addr 2 Addr 3 Addr 4 CRC SIFS Body Control ID Control Dest Ack 802.11 MAC Header To DS From DS Address 1 Address 2 Address 3 Address 4 DIFS Contention Window 0 0 DA SA BSSID N/A 0 1 DA BSSID SA N/A Other Next MPDU 1 0 BSSID SA DA N/A Backoff after Defer Defer Access 1 1 RA TA DA SA Operational processesTraffic Flow On receive: • RF receivers on the same channel will process first part of frame (Frame header) and examine Address1 • When the STA is in ESS operation and the Addr1 is uni-cast it is matched to its own MAC address, and accepted when the same • When the STA is IBSS operation and the Addr1 is a uni-cast and matching its own MAC address, Addr3 (the BSSID) is compared to the BSSID obtained during IBSS set-up (has to to be the same) • When Addr1 is multi-cast, the receiver will accept the frame, when Addr3 (the BSSID) matches the one obtained during association to the AP or during IBSS creation • Uni-cast frames are replied to with ACK after observing the SIFS period

  22. ORiNOCO PC-Card Association table Intra-BSS Relay ACK Packet for STA-2 ACK Packet for STA-2 Operational processesTraffic flow - bridging and relaying • On STA Association: • STA is recorded in Association Table within PC card FW • STA’s MAC address is recorded in the Bridge Learn table of the AP-500, AP-1000, AP-2000 correlated to the port is was detected on: • 1 = Ethernet • 2 = PC card (Slot-A on dual slot AP) • 3 = PC card in Slot-B • 4-15 = WDS ports (on AP-2000) • Intra-BSS traffic handled by FW in PC Card, without consulting Bridge Learn table except for: • AP-2000 (always checks bridge table for port #) • AP-500/AP-1000 with so-called “Access Control” enabled, to prevent non-authenticated STAs accessing other stations in the BSS AP-500, AP-1000, AP-2000 Bridge learn table MAC addr. Port #. 2 xxx yyy 2 STA-1 STA-2 STA-1 xxx STA-2 yyy

  23. Bytes: Channel 11 2 2 6 6 6 2 6 0-2312 4 Frame Frame Duration Sequence Channel 1 Addr 1 Addr 2 Addr 3 Addr 4 CRC Body Control ID Control 802.11 MAC Header To DS From DS Address 1 Address 2 Address 3 Address 4 0 0 DA SA BSSID N/A 0 1 DA BSSID SA N/A Channel 6 1 0 BSSID SA DA N/A 1 1 RA TA DA SA Operational processesTraffic flow - WDS operation • At this time implemented in the AP-2000 • Up to 6 WDS links can be maintained by a single ORiNOCO PC Card within the AP • Each link is associated with a separate port within the bridge learn table • Linkage is established by identifying the MAC address of the PC Card at the other end of the link (at both ends) • Frames on the WDS link use all 4 addresses in the MAC header • Received frames transferred on the WDS link are filtered on first address • Addr3 and Addr4 are used as address pair in 802.3 frame and passed to bridge

  24. AP-500, AP-1000 ORiNOCO PC-Card Bridge learn table xxx 2 Association table yyy 2 STA-1 STA-2 Intra-BSS Relay Associate ACK Associate Packet for STA-2 ACK Packet for STA-2 Operational processesTraffic flow - Intra-BSS BSS-A STA-1 xxx STA-2 yyy

  25. AP-500, AP-1000 or AP-2000 AP-500, AP-1000 or AP-2000 ORiNOCO PC-Card ORiNOCO PC-Card Association table Association table Bridge learn table Bridge learn table ACK Packet for STA-2 ACK Packet for STA-2 Operational processesTraffic flow - Inter-BSS with wired DS Backbone yyy 2 xxx 1 yyy 1 STA-2 xxx 2 STA-1 BSS-B STA-2 yyy STA-1 xxx BSS-A

  26. Bridge learn table Bridge learn table Packet for STA-2 ACK Packet for STA-2 Packet for STA-2 ACK ACK Operational processesTraffic flow - Inter-BSS with wireless DS AP-2000 ORiNOCO PC-Card AP-2000 yyy 2 Association table xxx 4 ORiNOCO PC-Card STA-2 yyy 4 Association table WDS Relay xxx 2 Wireless Backbone STA-1 WDS Relay BSS-B STA-2 yyy STA-1 xxx BSS-A

  27. Operational processesCoalescence of IBSS networks • Different IBSS networks with same SSID might exist, if cell members are out of each other’s radio-range, when they start up. • Two networks are shown with different BSSIDs: BSSID-a and BSSID-b • Both networks are configured with the same SSID (SSID-a) BSSID-a SSID-x SSID-x BSSID-b

  28. Operational processesCoalescence of IBSS networks • When a station moves it might get into radio-range of a neighboring cell (from BSSID-a to BSSID-b) • It will receive the Beacons from the neighboring cell, and examines these for the SSID. • It will find that these Beacons contain the same SSID • Based on time-stamp information in all Beacon messages received (from BSSID-a and BSSID-b) the station might decide to join the other network BSSID-a SSID-x SSID-x BSSID-b

  29. Operational processesCoalescence of IBSS networks • To join the network it will obtain the BSSID from the frame header of the Beacon message • Once joined it will participate in sending beacons according to the coordination of the new cell, and using the new BSSID • Other stations close to the last one that joined the new cell, will be able to receive the beacons now as well BSSID-a SSID-x SSID-x BSSID-b

  30. Operational processesCoalescence of IBSS networks • The process repeats itself and another station might add itself to the network • This can continue until all stations might have joined the cell BSSID-a SSID-x SSID-x BSSID-b

  31. Operational processesCoalescence of IBSS networks • The two cells have grown to one; this is known as “Coalescence”. • When a station in this large cell will not hear Beacons anymore (if no Beacons have been received for 10 seconds), the station assumes that it is alone and restarts as IBSS station • Scans all channels • May find another AP or Station that sends Probe Responses with matching SSID, and connects • Or starts new IBSS (with new BSSID) BSSID-a SSID-x SSID-x BSSID-b

  32. Configuration Parameters • ORiNOCO PC-Card are used in client station and Access Point, but “behaves” differently based on the parent unit • When inserted in AP- 500, AP-1000 or AP-2000, AP firmware is downloaded into the PC-Card (Note: this is ORiNOCO/MAC FW, not “Bridge FW”) • When inserted in client station, STA firmware is active (default FW) • Requires different configuration parameter sets to support the different behavior • Configuration can be performed by: • Setting parameters at driver installation (Station) • Changing parameters in property settings via control panel on config file (Station) • Using ORiNOCO AP Manager (for AP-500, AP-1000) • Browser based configuration tool (AP-2000) • Using CLI procedures (All APs)

  33. Network Name (SSID) ASCII string to identify the network that the Access-Point is part of Frequency (channel) To indicate the frequency channel that the AP-500/1000/2000 will use for its “cell”. The channel is selected from the set that is allowed in the regulatory domain. Medium Reservation To enable/disable the RTS/CTS handshake. Threshold value 0-2346 (value=2347 disables Medium Reservation) Microwave Oven Robustness Check box to enable/disable data-rate fallback delay-mechanism to allow improved performance in presence of microwave ovens Distance between APs To specify the coverage of a “cell” in terms of the distance between the Access-Points Large Medium Small Multicast Rate To specify data-rate used for transmitting Multicast frames Configuration Parameters AP-500/1000/2000

  34. Closed System (AP) To enable rejection of association requests from stations with Network Name set to “ANY” Enable Encryption To enable/disable Encryption Encryption keys Four fields to store up to four different encryption keys Encryption key index Index identifying which of the four keys is the active one WDS MAC address of the corresponding AP in a WDS link DTIM Power Management related parameter to specify the timing of the delivery of multicast traffic to stations that have indicated to receive multicast messages while under power management. Example: DTIM=1 means multicast traffic when it arrives at the AP is passed through after every beacon DTIM=3 means multicast traffic is passed through after every 3rd beacon message Configuration Parameters AP-500/1000/2000

  35. Network Name (SSID) ASCII string to identify the network that the station wants to connect to Type of Operation To identify the kind of network that the station will be part of Network centered around APs Residential Gateway networks IBSS (peer-to-peer network) Card Power Management Check box to enable/disable Power Management Enable Encryption To enable/disable Encryption Encryption keys Four fields to store up to four different encryption keys Entries take up to 5 ASCII or 10 hexa-decimal values (when using 64 WEP) Encryption key index Index identifying which of the four keys is the active one Configuration Parameters Station parameters • Station parameters are specified per so-called “profile” • Up to 99 different profiles can be defined each having their set of parameters • Values for parameters that have a dependency on similar ones in the APs are dynamically transferred to the STA as part of the (re)-association response. Parameters that can be entered locally:

  36. (Re) association response Capability Info Status code Associat’n ID Supported Rates Vendor specific info 2 bytes 2 bytes 2 bytes 3-11 bytes 15 bytes Cell Parameters Agere Element ID Length Agere OUI Medium Density RTS/CTS Threshold interference Robustness 1 byte 1 byte 3 bytes 7 bytes 2 bytes 1 byte Configuration Parameters Dynamically assigned station parameters • Cell specific parameters are dynamically transferred to the STA as part of the (re)-association response. • Part of the Association response can be Vendor defined • Agere OUI (= Organizational Unique Identifier), identifies the frame as ORiNOCO specific • Value is x’601D’ • Agere Element ID identifies the type of information represented: • Medium Density Parameters (x’80’) • Load Balancing Information (x’81’)

  37. (Re) association response Capability Info Status code Associat’n ID Supported Rates Vendor specific info 2 bytes 2 bytes 2 bytes 3-11 bytes 15 bytes Cell Parameters Agere Element ID Length Agere OUI Medium Density RTS/CTS Threshold interference Robustness 1 byte 1 byte 3 bytes 7 bytes 2 bytes 1 byte Configuration Parameters Dynamically assigned station parameters • RTS/CTS Threshold • Interference Robustness switch • Medium Density Parameters: • Distance between APs • Energy Detect Threshold • Carrier Detect Threshold • Defer Threshold • Cell Search Threshold • Out of Range Threshold • Delta SNR

  38. Module contents • IEEE 802.11 Terminology • IEEE 802.11 MAC Frames • Operational Processes • Configuration parameters

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