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IEEE 802.15.4 Overview

IEEE 802.15.4 Overview. 2007/11/28 Chia-Hung Tsai. IEEE 802.15 working group. Comparison between WPAN. ZigBee/IEEE 802.15.4 market feature. Low power consumption Low cost Low offered message throughput Supports large network orders (<= 65k nodes) Low to no QoS guarantees

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IEEE 802.15.4 Overview

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  1. IEEE 802.15.4 Overview 2007/11/28 Chia-Hung Tsai

  2. IEEE 802.15 working group

  3. Comparison between WPAN

  4. ZigBee/IEEE 802.15.4 market feature • Low power consumption • Low cost • Low offered message throughput • Supports large network orders (<= 65k nodes) • Low to no QoS guarantees • Flexible protocol design suitable for many applications ，

  5. ZigBee/802.15.4 architecture • ZigBee Alliance • Defining upper layers of protocol stack: from network to application, including application profiles • First profiles published mid 2003 • IEEE 802.15.4 Working Group • Defining lower layers of protocol stack: MAC and PHY

  6. IEEE 802.15.4 device types • There are two different device types : • A full function device (FFD) • A reduced function device (RFD) • The FFD can operate in three modes by serving as • Device • Coordinator • PAN coordinator • The RFD can only serve as: • Device

  7. Star topology Network Network coordinator coordinator Master/slave Full Function Device (FFD) Reduced Function Device (RFD) Communications Flow

  8. Tree topology Tree Full Function Device (FFD) Communications Flow

  9. Device addressing • Two or more devices communicating on the same physical channel constitute a WPAN. • A WPAN includes at least one FFD (PAN coordinator) • Each independent PAN will select a unique PAN identifier • All devices operating on a network shall have a unique 64-bit extended address. This address can be used for direct communication in the PAN • A device can also have a 16-bit short address, which is allocated by the PAN coordinator when the device associates with its coordinator.

  10. Superframe • A superframe is divided into two parts • Inactive: all station sleep • Active: • Active period will be divided into 16 slots • 16 slots can further divided into two parts • Contention access period • Contention free period

  11. Superframe • Beacons are used for • starting superframes • synchronizing with other devices • announcing the existence of a PAN • informing pending data in coordinators • In a beacon enabled network, • Devices use the slotted CAMA/CA mechanism to contend for the usage of channels • FFDs which require fixed rates of transmissions can ask for guarantee time slots (GTS) from the coordinator

  12. Superframe • The structure of superframes is controlled by two parameters: beacon order (BO) and superframe order (SO) • BO decides the length of a superframe • SO decides the length of the active potion in a superframe • For a beacon-enabled network, the setting of BO and SO should satisfy the relationship 0≦SO≦BO≦14 • For channels 11 to 26, the length of a superframe can range from 15.36 msec to 215.7 sec (= 3.5 min).

  13. Superframe • Each device will be active for 2-(BO-SO) portion of the time, and sleep for 1-2-(BO-SO) portion of the time • In IEEE 802.15.4, devices’ duty cycle follow the specification

  14. Starting and Maintaining PANs • Scanning Through Channels • Energy scan • Active scan • Devices are instructed to begin a channel scan through MLME-SCAN.request primitive • The scan results shall be returned via the MLME-SCAN.confirm primitive • During the scan, device shall suspend beacon transmission

  15. Starting a PAN • A PAN shall be started by an FFD only after an active channel scan and a suitable PAN ID has been selected • An FFD uses the MLME-START.request primitive to begin operating a PAN • The MAC sublayer shall set the logical channel in phyCurrentChannel and the PAN identified in macPANId • Then this FFD can begin operating as a PAN coordinator

  16. Beacon Generation • An FFD shall use the MLME-START.request primitive to begin transmitting beacon • BeaconOrder • SuperframeOrder • The FFD may either begin beacon transmission as • The PAN coordinator of a new PAN • A device on previously established PAN

  17. Association procedures (1/2) • A device becomes a member of a PAN by associating with its coordinator • Procedures

  18. Association procedures (2/2) • In IEEE 802.15.4, association results are announced in an indirect fashion • A coordinator responds to association requests by appending devices’ long addresses in beacon frames • Devices need to send a data request to the coordinator to acquire the association result • After associating to a coordinator, a device will be assigned a 16-bit short address.

  19. Association • A device shall only attempt to associate after having completed either an active channel scan or passive channel scan • The results of channel scan would have then been used to choose a suitable PAN • A coordinator shall only allow association if macAssociationPermit is set to TRUE

  20. Association • The device shall set the necessary values for association • phyCurrentChannel shall be set to an appropriate channel • macPANId shall be set to the identifier of the PAN with which to associate • macCoordShortAddress or macCoordExtendedAddress, depending on which is knowing from the beacon frame of the coordinator

  21. Association • An unassociated device shall initiate the association procedure by sending an associate request command to the coordinator of an existing PAN • The coordinator that successfully receives this request will reply an acknowledgment frame • The ACK frame to an request command does not mean that this device has associated. • The coordinator needs time to determine whether the resource available on the PAN are sufficient

  22. Association • If sufficient resources are available, the coordinator shall • allocate a short address to the device and • generate an association response command containing the new address and a status indicating a success association • If sufficient resources are not available, the coordinator shall • generate an association response command containing the status indicating a failure association • The association response command frame shall be added to the list of pending transaction stored on the coordinator

  23. Association • After receiving the ACK, the device shall wait for at most aResponseWaitTime symbols for the decision • The device attempt to track the beacon for the association response command • If the device does not extract the response after timeout, the association attempt shall be deemed a failure • The device shall terminate any tracking of the beacon

  24. Association • On receiving the association response command, the device shall send an ACK frame • If successfully associated, the device shall store the short address and extended address of coordinator • If unsuccessfully associated, the device shall set macPANId to the default value (0xffff)

  25. Lab report • Analyze the WUART application • Trace code • Sniffer - TestUtility.bin • Hand in a lab report • Due day 12/11 • Describe the procedure of building a 802.15.4 network in WUART application • Include the log analysis about sniffer

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