Zig BeeIEEE 802 15 4 Overview 1 New

Zig. Bee/IEEE 802. 15. 4 Overview 1

New trend of wireless technology n n Most Wireless industry focus on increasing high data throughput A set of applications requiring simple wireless connectivity, relaxed throughput, very low power, short distance and inexpensive q q q Industrial Agricultural Vehicular Residential Medical 2

What is Zig. Bee Alliance? n n An organization with a mission to define reliable, cost effective, low-power, wirelessly networked, monitoring and control products based on an open global standard Alliance provides interoperability, certification testing, and branding 3

IEEE 802. 15 working group 4

Comparison between WPAN 5

Zig. Bee/IEEE 802. 15. 4 market feature n n n Low power consumption Low cost Low offered message throughput Supports large network orders (<= 65 k nodes) Low to no Qo. S guarantees Flexible protocol design suitable for many applications 6

Zig. Bee network applications monitors sensors automation control monitors diagnostics sensors INDUSTRIAL & COMMERCIAL CONSUMER ELECTRONIC S TV VCR DVD/CD Remote control Zig. Bee PERSONAL HEALTH CARE consoles portables educational LOW DATA-RATE RADIO DEVICES TOYS & GAMES HOME AUTOMATION PC & PERIPHERAL S mouse keyboard joystick security HVAC lighting closures 7

Wireless technologies Range Meters 10, 000 GSM GPRS EDGE 3 G 2000 2003 -4 2005 1, 000 802. 11 b Zig. Bee 100 Bluetooth 2. 0 Bluetooth 10 100 1, 000 Hiper LAN/2 Wi. Media Bluetooth 1. 5 10 802. 11 a/g 10, 000 Bandwidth kbps 100, 000 8

Zig. Bee/802. 15. 4 architecture n Zig. Bee Alliance q q q n 45+ companies: semiconductor mfrs, IP providers, OEMs, etc. Defining upper layers of protocol stack: from network to application, including application profiles First profiles published mid 2003 IEEE 802. 15. 4 Working Group q Defining lower layers of protocol stack: MAC and PHY 9

How is Zig. Bee related to IEEE 802. 15. 4? n n n Zig. Bee takes full advantage of a powerful physical radio specified by IEEE 802. 15. 4 Zig. Bee adds logical network, security and application software Zig. Bee continues to work closely with the IEEE to ensure an integrated and complete solution for the market 10

IEEE 802. 15. 4 overview 11

General characteristics n n n n n Data rates of 250 kbps , 20 kbps and 40 kpbs. Star or Peer-to-Peer operation. Support for low latency devices. CSMA-CA channel access. Dynamic device addressing. Fully handshaked protocol for transfer reliability. Low power consumption. 16 channels in the 2. 4 GHz ISM band, 10 channels in the 915 MHz ISM band one channel in the European 868 MHz band. Extremely low duty-cycle (<0. 1%) 12

IEEE 802. 15. 4 basics n 802. 15. 4 is a simple packet data protocol for lightweight wireless networks q q Channel Access is via Carrier Sense Multiple Access with collision avoidance and optional time slotting Message acknowledgement and an optional beacon structure Multi-level security Works well for n q Long battery life, selectable latency for controllers, sensors, remote monitoring and portable electronics Configured for maximum battery life, has the potential to last as long as the shelf life of most batteries 13

IEEE 802. 15. 4 device types n There are two different device types : q q n The FFD can operate in three modes serving q q q n A full function device (FFD) A reduced function device (RFD) Device Coordinator PAN coordinator The RFD can only operate in a mode serving: q Device 14

FFD vs RFD n Full function device (FFD) q q q n Any topology Network coordinator capable Talks to any other device Reduced function device (RFD) q q Limited to star topology Cannot become a network coordinator Talks only to a network coordinator Very simplementation 15

Star topology Network coordinator Master/slave Full Function Device (FFD) Reduced Function Device (RFD) Communications Flow 16

Peer to peer topology Point to point Tree Full Function Device (FFD) Communications Flow 17

Device addressing n Two or more devices with a POS communicating on the same physical channel constitute a WPAN which includes at least one FFD (PAN coordinator) n Each independent PAN will select a unique PAN identifier n All devices operating on a network shall have unique 64 -bit extended address. This address can be used for direct communication in the PAN n The address can use a 16 -bit short address, which is allocated by the PAN coordinator when the device associates 18

IEEE 802. 15. 4 physical layer 19

IEEE 802. 15. 4 PHY overview n PHY functionalities: q q q Activation and deactivation of the radio transceiver Energy detection within the current channel Link quality indication for received packets Clear channel assessment for CSMA-CA Channel frequency selection Data transmission and reception 20

IEEE 802. 15. 4 PHY overview n Operating frequency bands 868 MHz/ 915 MHz PHY Channel 0 868. 3 MHz 2. 4 GHz PHY 2. 4 GHz Channels 1 -10 902 MHz Channels 11 -26 2 MHz 928 MHz 5 MHz 2. 4835 GHz 21

Frequency bands and data rates n The standard specifies two PHYs : q 868 MHz/915 MHz direct sequence spread spectrum (DSSS) PHY (11 channels) n n q 1 channel (20 Kb/s) in European 868 MHz band 10 channels (40 Kb/s) in 915 (902 -928)MHz ISM band 2450 MHz direct sequence spread spectrum (DSSS) PHY (16 channels) n 16 channels (250 Kb/s) in 2. 4 GHz band 22

PHY frame structure n PHY packet fields q q Preamble (32 bits) – synchronization Start of packet delimiter (8 bits) – shall be formatted as “ 11100101” PHY header (8 bits) –PSDU length PSDU (0 to 127 bytes) – data field Sync Header Start of Preamble Packet Delimiter 4 Octets 1 Octets PHY Header Frame Reserve Length (1 bit) (7 bit) 1 Octets PHY Payload PHY Service Data Unit (PSDU) 0 -127 Bytes 23

IEEE 802. 15. 4 MAC 24

Superframe n A superframe is divided into two parts q q Inactive: all devices sleep Active: n n Active period will be divided into 16 slots can further divided into two parts § § Contention access period Contention free period 25

Superframe n Beacons are used for q q n starting superframes synchronizing with associated devices announcing the existence of a PAN informing pending data in coordinators In a beacon enabled network, q q 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 26

Superframe n The structure of superframes is controlled by two parameters: beacon order (BO) and superframe order (SO) q q n n 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. q which means very low duty cycle 27

Superframe n n 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 BO-SO 0 1 2 3 4 5 6 7 8 9 ≧ 10 Duty cycle (%) 100 50 25 12 6. 25 3. 125 1. 56 0. 78 0. 39 0. 195 < 0. 1 28

Data transfer model (device to coordinator) n Data transferred from device to coordinator q q In a beacon-enable network, device finds the beacon to synchronize to the superframe structure. Then using slotted CSMA/CA to transmit its data. In a non beacon-enable network, device simply transmits data using unslotted CSMA/CA Communication to a coordinator In a beacon-enabled network Communication to a coordinator In a non beacon-enabled network 29

Data transfer model (coordinator to device) n Data transferred from coordinator to device q In a beacon-enable network, the coordinator indicates in the beacon that the data is pending. Device periodically listens to the beacon and transmits a MAC command request using slotted CSMA/CA if necessary. Communication from a coordinator In a beacon-enabled network 30

Data transfer model (coordinator to device) n Data transferred from coordinator to device q In a non-beacon-enable network, a device transmits a MAC command request using unslotted CSMA/CA. If the coordinator has its pending data, the coordinator transmits data frame using unslotted CSMA/CA. Otherwise, coordinator transmits a data frame with zero length payload. Communication from a coordinator in a non beacon-enabled network 31

Channel access mechanism n Two type channel access mechanism: q q In non-beacon-enabled networks unslotted CSMA/CA channel access mechanism In beacon-enabled networks slotted CSMA/CA channel access mechanism 32

CSMA/CA algorithm n In slotted CSMA/CA q The backoff period boundaries of every device in the PAN shall be aligned with the superframe slot boundaries of the PAN coordinator n q i. e. the start of first backoff period of each device is aligned with the start of the beacon transmission The MAC sublayer shall ensure that the PHY layer commences all of its transmissions on the boundary of a backoff period 33

CSMA/CA algorithm n Each device shall maintain three variables for each transmission attempt q q q NB: number of time the CSMA/CA algorithm was required to backoff while attempting the current transmission CW: contention window length, the number of backoff periods that needs to be clear of channel activity before transmission can commence (initial to 2 and reset to 2 if sensed channel to be busy) BE: the backoff exponent which is related to how many backoff periods a device shall wait before attempting to assess a channel 34

Slotted CSMA/CA 35

Unslotted CSMA/CA 36

GTS concepts n n A guaranteed time slot (GTS) allows a device to operate on the channel within a portion of the superframe A GTS shall only be allocated by the PAN coordinator The PAN coordinator can allocated up to seven GTSs at the same time The PAN coordinator decides whether to allocate GTS based on: q q Requirements of the GTS request The current available capacity in the superframe 37

GTS concepts n A GTS can be deallocated q q n n n At any time at the discretion of the PAN coordinator or By the device that originally requested the GTS A device that has been allocated a GTS may also operate in the CAP A data frame transmitted in an allocated GTS shall use only short addressing The PAN coordinator shall be able to store the info of devices that necessary for GTS, including starting slot, length, direction and associated device address 38

GTS concepts n n n Before GTS starts, the GTS direction shall be specified as either transmit or receive Each device may request one transmit GTS and/or one receive GTS A device shall only attempt to allocate and use a GTS if it is currently tracking the beacon If a device loses synchronization with the PAN coordinator, all its GTS allocations shall be lost The use of GTSs be an RFD is optional 39

Association procedures n n A device becomes a member of a PAN by associating with its coordinator Procedures 40

Association procedures n n 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. 41

Zig. Bee Network Layer Protocols 42

Zig. Bee network layer overview n n Zig. Bee network layer provides reliable and secure transmissions among devices Three kinds of networks are supported: star, tree, and mesh networks 43

Zig. Bee network layer overview n Three kinds of devices in the network layer q q q n n Zig. Bee coordinator: response for initializing, maintaining, and controlling the network Zig. Bee router: form the network backbone Zig. Bee end device In a tree network, the coordinator and routers can announce beacons. In a mesh network, regular beacons are not allowed. q Devices in a mesh network can only communicate with each other by peer-to-peer transmissions 44

Address assignment in a Zig. Bee network n n In Zig. Bee, network addresses are assigned to devices by a distributed address assignment scheme Zig. Bee coordinator determines three network parameters q q q n the maximum number of children (Cm) of a Zig. Bee router the maximum number of child routers (Rm) of a parent node the depth of the network (Lm) A parent device utilizes Cm, Rm, and Lm to compute a parameter called Cskip q which is used to compute the size of its children’s address pools 45

Cskip=31 For node C 0 1 node A n If a parent node at depth d has an address Aparent, q q the nth child router is assigned to address Aparent+(n -1)×Cskip(d)+1 nth child end device is assigned to address Aparent+Rm×Cskip(d)+n Total: 127 32 63 94 125, 126 32 C 46

Zig. Bee routing protocols n In a tree network q n Utilize the address assignment to obtain the routing paths In a mesh network q Two options n n n Reactive routing: if having routing capacity Use tree routing: if do not have routing capacity Note: q Zig. Bee coordinators and routers are said to have routing capacity if they have routing table capacities and route discovery table capacities 47

Zig. Bee routing in a tree network n Routing procedures q q When a device receives a packet, it first checks if it is the destination or one of its child end devices is the destination If so, n q Otherwise, n n this device will accept the packet or forward this packet to the designated child this device will relay packet along the tree The relationships between ancestors and descendants can be easily inferred by network addresses 48

Zig. Bee routing in a mesh network n The route discovery in a Zig. Bee network is similar to the AODV routing protocol q q n Links with lower cost will be chosen into the routing path. The cost of a link is defined based on the packet delivery probability on that link Route discovery procedure q q The source broadcasts a route request packet Intermediate nodes will rebroadcast route request if n n q q They have routing discovery table capacities The cost is lower Otherwise, nodes will relay the request along the tree The destination will choose the routing path with the lowest cost and then send a route reply 49

Zig. Bee routing in a mesh network 50

Summary of Zig. Bee network layer n Pros and cons of different kinds of Zig. Bee network topologies Pros Cons Star 1. Easy to synchronize 2. Support low power operation 3. Low latency 1. Small scale Tree 1. Low routing cost 1. Route reconstruction is costly 2. Can form superframes to support sleep 2. Latency may be quite long mode 3. Allow multihop communication Mesh 1. Robust multihop communication 2. Network is more flexible 3. Lower latency 1. Cannot form superframes (and thus cannot support sleep mode) 2. Route discovery is costly 3. Needs storage for routing table 51