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Typical Access Point Architectures

Typical Access Point Architectures . John Klein Symbol Technologies, Inc. Jklein@sj.symbol.com. Bob Beach Symbol Technologies, Inc. Beach@sj.symbol.com. Outline of presentation. Part 1 – WLAN Architecture and Functional Decomposition Typical WLAN Topology

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Typical Access Point Architectures

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  1. Typical Access Point Architectures John Klein Symbol Technologies, Inc. Jklein@sj.symbol.com Bob Beach Symbol Technologies, Inc. Beach@sj.symbol.com Beach & Klein, Symbol Technologies, Inc.

  2. Outline of presentation • Part 1 – WLAN Architecture and Functional Decomposition • Typical WLAN Topology • Typical Access Point Hardware Architecture • Typical Access Point Software Architecture • Access Point Functional Decomposition • Access Point Core Details • Access Point Core Functional Decomposition • Part 2 – Distribution • Distribution of Access Point Functions • Questions and Discussion Beach & Klein, Symbol Technologies, Inc.

  3. Part 1 WLAN Architecture and Functional Decomposition Beach & Klein, Symbol Technologies, Inc.

  4. Typical WLAN Topology Distribution Switches 802.1Q trunk links Access Switches Beach & Klein, Symbol Technologies, Inc.

  5. Typical Access Point Hardware Architecture (Dual Radio) RF Circuit D/A 802.11 Baseband / MAC 802.3 MAC / PHY A/D RF Circuit D/A 802.11 Baseband / MAC A/D Flash Control CPU Beach & Klein, Symbol Technologies, Inc.

  6. Typical Access Point Software Architecture (1) RTOS / System Services Session Manager Authorization, 802.11i, WPA Key Mgmt Control Manager TFTP / FTP 802.1x WEB / HTTP Association, Roaming, Session TMO 802.11k SNMP / MIB 802.11d CLI Upper Level 802.11f FW Mgmt VLANs 802.1Q Flash / Config QoS 802.11e 802.1p TCP / IP / UDP Stack BOOTP / DHCP Client Telnet Client PPP RS 232 Driver AP Core Lower Level + PHY Radio Driver(s) Ethernet PHY Radio PHY RS-232 Port Beach & Klein, Symbol Technologies, Inc.

  7. Access Point Functional Decomposition (1) • PHY: Ethernet PHY, Radio PHY, represent interfaces to the respective hardware for data path and control of the HW interface. • RS 232 Driver interfaces to the RS 232 port out of the fast path AP Core • PPP provides a PPP or sometimes a PPPoE interface from the RS-232 port to the CLI in the Control Manager. • Access Point Core is discussed in detail later in this presentation. Beach & Klein, Symbol Technologies, Inc.

  8. Access Point Functional Decomposition (2) • TCP/ IP / UDP Stack: Standard TCP stack for handling IP and UDP traffic. Minor changes for some routing functions are possible. • BOOTP / DHCP Client handles DHCP and BOOTP Services from servers. Vendor specific options for FW download, ACL, Filters, and Configuration download. • Telnet Client interfaces the CLI from the Command Manager to the Ethernet interface Beach & Klein, Symbol Technologies, Inc.

  9. Access Point Functional Decomposition (3) • Session Manager: Handles high level session information for each STA. Keeps status and state. • Authorization via 802.1x or other means • Handles security key management for each client and BC/MC keys per VLAN / SSID • Association and roaming processing (in / out) • 802.11d and 802.11f functionality • STA timeout and disassociation due to inactivity • Future placeholder for 802.11k setup information • Client / SSID VLAN information and setup for STA • QoS information and setup for STA Beach & Klein, Symbol Technologies, Inc.

  10. Access Point Functional Decomposition (4) • Control Manager: Handles external command and control interfaces for the AP. • TFTP / FTP are used for downloading FW, configuration files, ACLs, as well as offloading configurations and debug dumps • WEB / HTTP, SNMP / MIB, and CLI are used to get and set AP configuration parameters and collect runtime information and statistics • FW Mgmt manages burning of new FW into the AP • Flash / Config handles configuration data on the secondary storage device Beach & Klein, Symbol Technologies, Inc.

  11. TCP Interface Access Point Core Upper Level MAC Beacons, Start Rates, Other Mgmt ACL, Filters, LT Rate Scaling, Beacon Prep 802.3 Pkts STA Data Pkt Scheduler Session Control Format Packet (.11 / .3) 802.1p 802.11e 802.11 Pkts Encrypt / MIC PSP Buffering Packet Ack Request Decrypt / MIC Transmit Queues Transmit Queues Lower Level MAC Other Mgmt Pkts Packet Classification and Address Recognition Data Packets Reassembly Ack from STA Probe Requests Packet CRC PSP Poll Packet RF Transmit Scheduler Acks and Probes Retries Probe Resp Ack Multi ESS/BSS Instant Rates Fragmentation PSP Data Beacons Other Mgmt Queue Manager Buffer Pool Ingress Queues Channel Access PCF, DCF, HCF, SIFS Receive Queues Receive PHY Transmit PHY Beach & Klein, Symbol Technologies, Inc.

  12. Access Point Core Functional Decomposition (1) • Receive and Transmit queuesand Queue Manager / Free buffer pool: Nothing particularly interesting here except that there are multiple queues per ESS/BSS and per STA. • Lower Level Receive Side: handles address recognition and packet classification for inbound packets. Routes packets to the proper target destination based on classification. Reassembles inbound fragments. Received Acks and Probe requests from STAs are immediately sent to the RF Transmit scheduler. Data packets, PSP Polls, and Management packets are pushed up the stack to the Upper Level. Beach & Klein, Symbol Technologies, Inc.

  13. Access Point Core Functional Decomposition (2) • Upper Level - Various Functions: Handles incoming and outgoing bridging functions. • Keeps Long Term Rate Scaling information and calculates start rates based on time and historical performance information from the RF TX Scheduler. • Prepares Beacons that include PSP, Load and TIMS per ESS / BSS • Handles Encryption / Decryption and MIC per 802.11i • Buffers and Prioritizes outbound packets per 802.11e and 802.1p rules into Transmit Queues. • Buffers PSP packets in response to incoming PSP Poll packets received • Formats packets from 802.3 to 802.11 or 802.11 to 802.3 • Filters packets based on Type, ACLs and other filtering rules. Beach & Klein, Symbol Technologies, Inc.

  14. Access Point Core Functional Decomposition (3) • Lower Level Transmit Side: Handles all outbound per packet traffic. • Uses start rate information and makes instantaneous Transmit rate changes. Feeds back info to Long Term Rate Calculation Algorithm. • Handles instantaneous packet Acks, multiple Probe Responses per ESS / BSS • Schedules and sends out Beacons per BSS • Sends out PSP data packets to waiting PSP STAs as well as other data packets to proper ESS / BSS as they arrive from packet scheduler. • Handles packet level retries, and back offs per packet. • Fragments large packets into smaller chunks per fragmentation rules. Beach & Klein, Symbol Technologies, Inc.

  15. Access Point Core Functional Decomposition (4) • Channel Access: Handles all access to the airwaves. • Handles CCA, PCF, DCF, and HCF per 802.11 and 802.11e rules. • Handles RTS / CTS • Handles SIFS Beach & Klein, Symbol Technologies, Inc.

  16. Part 2 Distribution Beach & Klein, Symbol Technologies, Inc.

  17. Distribution of Access Point Functions (1) • PHY Level • Antenna and / or Radio + Antenna • Lower Level MAC functions have strong real time demands • Must be accomplished in micro/milliseconds • Upper Level MAC functions have strong application dependencies • User or STA application determines policy, very loose timing. • AP Control Management functions • Some functions can be placed in either category • Essentially these are implementation choices • AP and STA often mirror one another’s functions • Beacon/TIM (AP) and PSP support (STA) • Roaming: AP supplies data, SAT acts on it • RTS/CTS Beach & Klein, Symbol Technologies, Inc.

  18. Distribution of Access Point Functions (2) • Lower Level MAC • CRC • Channel Access • Timeout/retransmission • Packet Acknowledgements • Header Processing • Rate Control • RTS/CTS packets • PSP Support • Beacon/TIM Processing • Interface to PHY • Upper Level MAC • Association Management • QoS support • Roaming • Authorization • Buffer Management • Installation/configuration • Host integration • Fragmentation/reassembly • Encryption Beach & Klein, Symbol Technologies, Inc.

  19. Sessions & Mgmt Sessions & Mgmt Sessions & Mgmt L3 / TCP L3 / TCP L3 / TCP UL MAC UL MAC UL MAC LL MAC LL MAC LL MAC PHY PHY PHY LL MAC LL MAC LL MAC PHY PHY PHY RF Point RF Point RF Point L3 / TCP L3 / TCP L3 / TCP UL MAC UL MAC UL MAC LL MAC LL MAC LL MAC PHY PHY PHY UL MAC UL MAC UL MAC LL MAC LL MAC LL MAC PHY PHY PHY RF Point / Access Point RF Point / Access Point RF Point / Access Point RF Point RF Point RF Point Distribution of Access Point Functions (3) Variations on a distribution theme A Stand Alone AP (FAT) Sessions & Mgmt L3 / TCP UL MAC CAPWAP B Split Architecture I (WLAN Switch or Controller) Split Architecture II (WLAN Switch or Controller) Sessions & Mgmt L3 / TCP CAPWAP C Split Architecture III (WLAN Switch or Controller) Sessions & Mgmt CAPWAP D Beach & Klein, Symbol Technologies, Inc.

  20. Distributing Access Point Functions (4) • AP Functional Distribution can happen in one device or across several devices on the network. • Stand Alone Access Points (FAT APs) • Wireless Switch or Controller with RF Points (Thin APs) • Wireless Switch or Controller • Splits Upper Level MAC and Lower Level MAC between RF Points and Wireless Switch or Controller devices • Devices are connected via wired Ethernet infrastructure • RF Points provide PHY and Lower MAC Functions • provides RF coverage for multiple PHYs • PHY specific, POE • Wireless Switchprovides Upper MAC Functions • Plus: Security, QoS, Packet Buffering, etc. • All management and control functions • Located in secure location (computer room, closet, etc) • Less PHY specific Beach & Klein, Symbol Technologies, Inc.

  21. Questions and Answers Beach & Klein, Symbol Technologies, Inc.

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