The IEEE 802.15.4 Standard and the ZigBee Specifications Course T-110.5111 (Computer Networks II – Advanced Topics) Lecture about Wireless Personal Area Networks

Mario Di Francesco Department of Computer Science and Engineering, Aalto University Department of Computer Science and Engineering, University of Texas at Arlington

October 15, 2012

Architecture and objectives

Upper layers

Network layer IEEE 802.2 LLC Other LLC SSCS

Data link layer

IEEE 802.15.4 MAC IEEE 802.15.4 868/915 MHz PHY

IEEE 802.15.4 2400 MHz PHY

Physical layer

Architecture

Objectives

two physical (PHY) layer

low-rate

MAC layer

low-power

ZigBee for the upper layers

low-complexity

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

2/58 October 15, 2012 T-110.5111 WPAN Lecture

Components Full Function Device (FFD)

Reduced Function Device (RFD)

Implements the entire standard

Implements a reduced portion of the standard

Coordinator manages (part of) the network PAN coordinator manages the whole PAN (unique in the network)

cannot be a (PAN) coordinator only communicates with FFDs

(Regular) Device communicates with FFDs and/or RFDs

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

3/58 October 15, 2012 T-110.5111 WPAN Lecture

Topology Star

Peer-to-peer FFD RFD

C

PAN Coordinator

C C

all messages flow through the center (hub) of the star

neighboring nodes can communicate directly only available to FFDs

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

4/58 October 15, 2012 T-110.5111 WPAN Lecture

Radio and modulation (1 of 2) Two distinct physical layers PHY 868/915 MHz PHY 2400 MHz

Shared features direct sequence spread spectrum (DSSS) ISM (Industrial, Scientific and Medical) bands

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

5/58 October 15, 2012 T-110.5111 WPAN Lecture

Radio and modulation (2 of 2) PHY 2400 MHz

PHY 868/915 MHz Channel 0

Channels 1-10

2 MHz

5 MHz

Channels 11-26

f (MHz) 868.0 868.6

902.0

928.0

f (MHz) 2400.0

868 MHz (Europe) 1 channel (20 kbps)

2483.5

16 channels 250 kbps bandwidth

915 MHz (USA) 8 channel (40 kbps)

orthogonal encoding (1 sym = 4 bits)

differential encoding (1 sym = 1 bit)

O-QPSK modulation

BPSK encoding IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

6/58 October 15, 2012 T-110.5111 WPAN Lecture

Format of the PHY frame

PHY Protocol Data Unit (PPDU)

Synchronization Header

PHY Header

Preamble

Start-of-frame delimiter

Frame length

PHY Service Data Unit (PSDU)

4 bytes

1 byte

1 byte

≤ 127 bytes

Header

Payload

synchronization preamble

is the same as the MSDU

delimiter of the PHY frame

maximum size of 127 bytes

frame length IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

7/58 October 15, 2012 T-110.5111 WPAN Lecture

Available primitives Transceiver modes RX_ON active in receive mode TX_ON active in transmit mode TRX_OFF inactive (idle mode)

Link Quality Indication (LQI) “quality” of received frames SNR, ED, or both

Clear Channel Assessment (CCA) Different modes

Channel Selection Energy Detection (ED)

1. energy above threshold 2. carrier sense only 3. combination of 1 and 2 IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

8/58 October 15, 2012 T-110.5111 WPAN Lecture

Addressing modes PAN address PANs can be co-located 16 bits chosen by the PAN coordinator

Device address 64-bit IEEE Extended Unique Identifier (EUI-64) 24-bit Organizationally Unique Identifier (OUI) 40 bits assigned by the manufacturer

16-bit short address assigned by the PAN coordinator during association

Overhead reduction flag in the frame control field IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

9/58 October 15, 2012 T-110.5111 WPAN Lecture

Format of the MAC frame

MAC Protocol Data Unit (MPDU)

MAC Header

MAC Service Data Unit (MSDU)

MAC Footer

Frame control

Sequence number

Addressing fields

Payload

Frame check sequence

2 bytes

1 byte

≤ 20 bytes

Variable

2 bytes

Header frame control sequence number

Frame payload Footer frame check sequence (FCS) ITU-T CRC-16

addressing fields IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

10/58 October 15, 2012 T-110.5111 WPAN Lecture

Frame types Beacon frame synchronization and management of the PAN list of devices with pending messages superframe parameters

Acknowledgment frame MAC payload MAC command command identifier (1 byte) command payload IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

11/58 October 15, 2012 T-110.5111 WPAN Lecture

Channel access methods

MAC

Beacon enabled

Non-beacon enabled

Superframe Structure

Contention based

Contention based

Contention free

Unslotted CSMA-CA

Slotted CSMA-CA

Reserved time slot

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

12/58 October 15, 2012 T-110.5111 WPAN Lecture

Superframe structure Active Beacon

Beacon

GTS

0

1

2

3

4

5

CAP

6

7

8

9

10

11

12

GTS

13

14

Inactive

15

CFP

SD = aBaseSuperFrameDuration*2SO sym BI = aBaseSuperFrameDuration*2BO sym

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

13/58 October 15, 2012 T-110.5111 WPAN Lecture

Active period Contention Access Period (CAP) always present in the superframe immediately follows the beacon slotted CSMA-CA protocol

Contention Free Period (CFP) optional contiguous slots at the end of the superframe without CSMA-CA All transactions end within the CAP (CFP)

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

14/58 October 15, 2012 T-110.5111 WPAN Lecture

Superframe parameters Beacon interval BI = aBaseSuperFrameDuration· 2BO sym interval between subsequent beacons 0 ≤ BO ≤ 14, if BO = 15 no beacons

Superframe duration SD = aBaseSuperFrameDuration· 2SO sym duration of the active part 0 ≤ SO ≤ BO ≤ 14, if SO = 15 only active period (no duty-cycle) aBaseSuperFrameDuration = 960 sym ≈ 32 µs (2.4 GHz PHY) IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

15/58 October 15, 2012 T-110.5111 WPAN Lecture

Synchronization Tracking mode the device gets the first beacon then activates the transceiver before the subsequent one

Non tracking mode the device only gets a single beacon it has to reactivate the transceiver for at most aBaseSuperframeDuration· (2BO + 1) sym

Orphaned device does not detect beacons for aMaxLostBeacons (4) superframes IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

16/58 October 15, 2012 T-110.5111 WPAN Lecture

GTS management Features of GTSs unidirectional at most 7, all in the CFP each spanning one or more contiguous slots

GTS allocation managed by the PAN coordinator the device requests a GTS to the PAN coordinator the PAN coordinator decides whether to assign it or not

advertised in the GTS parameters of the superframe not always possible no GTS available cannot reduce the size of the CAP further IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

17/58 October 15, 2012 T-110.5111 WPAN Lecture

Frame spacing Frames need to be separated by an Inter Frame Space (IFS)

Long frame

Another frame LIFS

Short frame

Another frame SIFS

if pframe ≤ aMaxSIFSFrameSize (18) bytes then SIFS (Short IFS) ≥ aMinSIFSPeriod (12) sym if pframe > aMaxSIFSFrameSize bytes then LIFS (Long IFS) ≥ aMinLIFSPeriod (40) sym IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

18/58 October 15, 2012 T-110.5111 WPAN Lecture

The CSMA-CA algorithm Common features wait before transmitting without RTS/CTS

Two variants slotted (beacon enabled mode CAP) unslotted (non-beacon enabled mode)

Features backoff period slot of 20 sym (6= superframe slot) slotted variant aligns rx/tx to backoff periods

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

19/58 October 15, 2012 T-110.5111 WPAN Lecture

Initialization CSMA-CA

Parameters

NB number of backoffs (i.e., backoff attempts)

NB=0

CW contention window BE backoff exponent

CW=2

macMinBE = 3 (default) Battery Life Extension?

Yes

BE=min(2, macMinBE)

Battery Life Extension

No

power saving mode

BE=macMinBE

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

20/58 October 15, 2012 T-110.5111 WPAN Lecture

Main loop Delay for a random backoff period ∈ [0, 2BE-1]

Slotted mode

waiting and CCAs are aligned to backoff periods

Perform CCA on backoff period boundary

two CCAs before tx

Yes Channel idle?

backoff timer stopped at the end of the CAP and reactivated at the beginning of the subsequent one

No

No

CW=2, NB=NB+1 BE=min(BE+1, aMaxBE)

CW=CW-1

NB > macMaxCSMA Backoffs?

CW=0?

Yes Failure

No

In both cases

Yes

default max backoffs is 4

Success

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

21/58 October 15, 2012 T-110.5111 WPAN Lecture

Channel access example Slotted CSMA-CA

B

C 12

13

14

B

0

1

2

Superframe Slot

Packet arrival

A

15

CCA Backoff

Backoff

aUnitBackoffPeriod Data

Backoff

Backoff

Data

Backoff timer paused

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

22/58 October 15, 2012 T-110.5111 WPAN Lecture

Communication reliability CRC (FCS) check CRC-16 computed over header and payload checked against the FCS

Acks and retransmissions at most aMaxFrameRetries = 3 ack waiting time is macAckWaitDuration (54 sym)

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

23/58 October 15, 2012 T-110.5111 WPAN Lecture

Acks and retransmissions Ack timing Frame

Ack tack aUnitBackoffPeriod

Frame

Ack

tack

tack = aTurnAroundTime (unslotted) aTurnAroundTime ≤ tack ≤ aTurnAroundTime + aUnitBackoffPeriod (slotted) tack < SIFS < LIFS, at most aMaxFrameRetries = 3 IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

24/58 October 15, 2012 T-110.5111 WPAN Lecture

Sending data Non-beacon enabled

Beacon enabled (CAP) Coordinator

Device

Coordinator

Device

Beacon Data

Acknowledgement

Data

Acknowledgement

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

25/58 October 15, 2012 T-110.5111 WPAN Lecture

Receiving data (indirect transfer) Beacon enabled (CAP) Coordinator

Non-beacon enabled

Device

Coordinator

Device

Data request

Beacon

Acknowledgement Data

Data request

Acknowledgement

Acknowledgement Data Acknowledgement

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

26/58 October 15, 2012 T-110.5111 WPAN Lecture

Peer-to-peer communications We have previously considered star topology FFD or RFD devices

Peer-to-peer topology only between FFDs according to the tx case already seen in the non-beacon enabled mode synchronization not defined by the standard

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

27/58 October 15, 2012 T-110.5111 WPAN Lecture

Security Unsecured mode no security delegated to the upper layers

ACL mode based on Access Control Lists

Secured mode access control anti-replay protection confidentiality and integrity of messages

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

28/58 October 15, 2012 T-110.5111 WPAN Lecture

Scanning modes ED channel scan (only FFDs) ED of the PHY layer

Active channel scan (only FFDs) sends a beacon request command waits for a reply

Passive channel scan waits for a beacon

Orphan channel scan resynchronization of orphaned nodes IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

29/58 October 15, 2012 T-110.5111 WPAN Lecture

PAN creation FFD intending to be a PAN coordinator starts an active channel scan selects a (possibly unused) channel selects a PAN identifier starts transmitting beacons (in the beacon-enabled mode)

PAN identifier conflict detection and resolution are supported by the MAC layer

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

30/58 October 15, 2012 T-110.5111 WPAN Lecture

Association Coordinator

Device

Message exchange the first ack does not imply that the request has been accepted

Association request Acknowledgement

it depends on available resources

Data request

replies obtained as an indirect transmission

Acknowledgement

maximum waiting time aResponseWaitTime (30720 sym)

Association response Acknowledgement

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

31/58 October 15, 2012 T-110.5111 WPAN Lecture

Dissociation

Coordinator

Spontaneous

Device

decided by the device ack not really needed

Dissociation notification Acknowledgement

Spontaneous

Forced Data request

decided by the coordinator

Acknowledgement Disassociation notification

Coordinator driven

indirect transfer ack not really needed

Acknowledgement

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

32/58 October 15, 2012 T-110.5111 WPAN Lecture

References E. Callaway et al., Home Networking with IEEE 802.15.4: A Developing Standard for Low-Rate Wireless Personal Area Networks, IEEE Communications Magazine, August 2002 IEEE 802.15.4, Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (LR-WPANs), May 2003 Paolo Baronti, Prashant Pillai, Vince W.C. Chook, Stefano Chessa, Alberto Gotta, Y. Fun Hu, Wireless sensor networks: A survey on the state of the art and the 802.15.4 and ZigBee standards, Computer Communications, Volume 30, Issue 7, 26 May 2007, Pages 1655–1695

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

33/58 October 15, 2012 T-110.5111 WPAN Lecture

The ZigBee consortium

Wireless Control That Simply Works

Objectives

Reference scenarios

interoperability between platforms of different vendors low-energy

industrial and commercial consumer electronics and PC peripherals personal healthcare and home automation

low-cost high node density IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

34/58 October 15, 2012 T-110.5111 WPAN Lecture

The protocol stack (1 of 2) Application (APL) Layer Application Framework

…

Endpoint 1 APSDE-SAP

Endpoint 0 APSDE-SAP

IEEE 802.15.4 defined ZigBeeTM Alliance defined

Layer interface

Reflector Management

-

NLDE-SAP

Network (NWK) Layer NWK Security Management

NWK Message Broker

Routing Management

Network Management

MLDE-SAP

MLME-SAP

Medium Access Control (MAC) Layer

End manufacturer defined Layer function

APS Message Broker

NLME-SAP

Security Service Provider

ASL APS Security Management

APSME-SAP

Application Support Sublayer (APS)

ZDO Management Plane

Endpoint 240 APSDE-SAP

Application Object 1

ZDO Public Interfaces

Application Object 240

ZigBee Device Object (ZDO)

PLME-SAP

PD-SAP

Physical (PHY) Layer 2.4 GHz Radio

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

868/915 MHz di

35/58 October 15, 2012 T-110.5111 WPAN Lecture

The protocol stack (2 of 2) The layers Application layer (APL) service discovery binding between devices and services communication modes

Network layer (NWK) network topology addressing and routing

physical and MAC layers defined by the IEEE 802.15.4 standard

Other elements ZDO Management Plane Security Service Provider IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

36/58 October 15, 2012 T-110.5111 WPAN Lecture

ZigBee device model Type Application Device Type ZigBee Logical Device Type IEEE 802.15.4 Device Type

Description Represents the type of device from the user perspective Represents the type of device from the network perspective Represents the type of ZigBee hardware (radio) platform

Elements Motion detection sensor, light switch, etc. Network coordinator, router, end device Full Function Device, Reduced Function Device

ZigBee products are a combination of Application, Logical e Physical Device Types how to combine the different Device Types is defined by the vendor or by a profile IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

37/58 October 15, 2012 T-110.5111 WPAN Lecture

The application layer (APL) Sublayers Application Framework (AF) contains the higher layer application components (application objects) defined by the vendor

Application Support Layer (APS) links the application layer to the network layer

ZigBee Device Object (ZDO) is a special application object with management purposes

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

38/58 October 15, 2012 T-110.5111 WPAN Lecture

General concepts (1 of 2) Profile an agreement over messages, formats and actions adopted by the applications running on different devices to create a given distributed application

Component a physical object and the corresponding application profile

ZigBee device a (set of) component(s) sharing a ZigBee transceiver each device has a unique 64-bit IEEE address and a 16-bit network address IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

39/58 October 15, 2012 T-110.5111 WPAN Lecture

General concepts (2 of 2) Attribute an entity representing a physical quantity or state

Endpoint a specific (sub)component within a ZigBee device each device supports up to 240 endpoints with distinct addresses

Cluster container of attributes or a message has a unique 8-bit address within a certain profile

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

40/58 October 15, 2012 T-110.5111 WPAN Lecture

Sample addressing at the application layer

ZigBee Radio

Home Control Profile

ZigBee Device

light control (on/off) dimmer motion detection

Legend Endpoint

ZigBee Radio Link

Cluster

ZigBee Device

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

41/58 October 15, 2012 T-110.5111 WPAN Lecture

Application Framework (1 of 2) Features contains application objects provides two data services key value pair service (KVP) messsage service (MSG)

Observations exploits services made available by the APS control and management of application objects are handled by the ZigBee Device Object (ZDO)

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

42/58 October 15, 2012 T-110.5111 WPAN Lecture

Application Framework (2 of 2) Key Value Pair (KVP) service allows to manipulate attributes defined within the application objects takes an approach based on state variables with transitions get, get response commands set, event (and eventual response) commands uses data structures in compressed XML format

Message (MSG) service allows the application profile to use its own frame format has more flexibility than the KVP apprach

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

43/58 October 15, 2012 T-110.5111 WPAN Lecture

The application support layer (APS) Objective interfacing the application layer (AP) with the network layer

Features generation of messages at the application layer (APDUs) binding between devices and services transport of APDUs between different devices

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

44/58 October 15, 2012 T-110.5111 WPAN Lecture

Message transmission Message format Octets: 1

Frame control

0/1

0/1

0/2

0/1

Destination endpoint

Cluster Identifier

Profile Identifier

Source endpoint

Variable

Frame payload

Addressing fields APS header

APS payload

Transmission modes direct or indirect transmissions unicast or broadcast transmissions acknowlegments and (optional) retransmissions

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

45/58 October 15, 2012 T-110.5111 WPAN Lecture

Binding Definition creation of a unidirectional link between devices and endpoints every devices keeps a binding table with entries in the format

(as , es , cs ) = {(ad1 , ed1 ), (ad2 , ed2 ), . . . , (adn , edn )} where as address of the source device in the link es endpoint of the source device in the link cs cluster identifier used in the link adi the i-th destination device address in the link edi the i-th destination endpoint address in the link IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

46/58 October 15, 2012 T-110.5111 WPAN Lecture

Features of the NWK layer Objectives ensures the proper functioning of the MAC layer provides an interface to the application level

Major features services for creating a PAN (ZigBee Coordinator) services for device association (ZigBee Router and End Devices) logical address assignment and routing (ZigBee Router)

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

47/58 October 15, 2012 T-110.5111 WPAN Lecture

Network management Network creation, device association and dissociation high-level primitives of the IEEE 802.15.4 standard

Additional functions message filtering broadcast transmissions

Message format Octets: 2

Frame Control

2

2

1

1

Variable

Destination Address

Source Address

Radiusa

Sequence Numberb

Frame Payload

Routing Fields NWK Header aCCB

NWK Payload

Comment #125 IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

48/58 October 15, 2012 T-110.5111 WPAN Lecture

ZigBee devices ZigBee Coordinator manages the entire network PAN coordinator in IEEE 802.15.4 (FFD)

ZigBee Router manages device association routes the messages to devices coordinator in IEEE 802.15.4 (FFD)

ZigBee End Device regular device in the network RFD or FFD in IEEE 802.15.4 IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

49/58 October 15, 2012 T-110.5111 WPAN Lecture

Network topologies Tree network non beacon-enabled mode of IEEE 802.15.4 beacon-enabled mode of IEEE 802.15.4 active periods of different superframes should not interfere Beacon Interval

Beacon

CAP

Inactive Period Superframe Duration

Mesh network corresponds to the peer-to-peer network of IEEE 802.15.4 devices cannot use IEEE 802.15.4 beacons IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

50/58 October 15, 2012 T-110.5111 WPAN Lecture

Distributed address assignment (1 of 2) Used in tree networks (nwkUseTreeAddrAlloc = TRUE)

Parameters Cm max number of children (per parent) nwkMaxChildren Lm maximum depth of the tree nwkMaxDepth Rm max number of routers (per parent) nwkMaxRouters The address block assigned by each parent at level d to their own (child) routers is

Cskip (d ) =

   1 + Cm · (Lm − d − 1)

Lm −d −1 1 + C − R − C · R m m m m   1 − Rm IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

if Rm = 1 otherwise

51/58 October 15, 2012 T-110.5111 WPAN Lecture

Distributed address assignment (2 of 2) Parent node accepts children if Cskip (d ) > 0 uses Cskip (d ) as offset for router childrens the n-th address An is given by An = Aparent + Cskip (d ) · Rm + n with 1 ≤ n ≤ (Cm − Rm ) and Aparent the parent address

Observations addresses are sequentially assigned a block of addresses cannot be shared between multiple devices one parent can run out of addresses while another parent has unused addresses IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

52/58 October 15, 2012 T-110.5111 WPAN Lecture

Address assigned by upper layers Used in the general case (nwkUseTreeAddrAlloc = FALSE)

Layer above the network picks the block of addresses to assign next address to assign nwkNextAddress number of available addresses nwkAvailableAddresses step used when assigning addresses nwkAddressIncrement

Algorithm a router accepts associations if nwkAvailableAddresses > 0 the device is assigned the address nwkNextAddress the router decrements nwkAvailableAddresses and adds nwkAddressIncrement to nwkNextAddress IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

53/58 October 15, 2012 T-110.5111 WPAN Lecture

Hierarchical routing Finding the descendants D is a descendant of A (at level d) if A < D < A + Cskip (d − 1)

Forwarding towards descendants if D is an End Device1 the next hop is N = D if D is a Router the next hop is





D − (A + 1 ) N =A+1+ · Cskip (d ) Cskip (d ) 1

I.e., D > A + Rm · Cskip (d ) IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

54/58 October 15, 2012 T-110.5111 WPAN Lecture

Table-driven routing Features uses a simplified version of the Ad Hoc On Demand Distance Vector Routing (AODV) protocol every device with enough memory resources keeps a routing table

Hybrid solution hierarchical and table-driven routing can be used together if the destination is in the routing table then the corresponding entry is used if the destination is not known and the routing table has room for a new entry then the device starts route discovery otherwise messages are routed along the tree IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

55/58 October 15, 2012 T-110.5111 WPAN Lecture

Routing metric (1 of 2) Definitions P path of length L, i.e., (D1 , D2 , . . . , DL )

(Di , Di +1 ) link (sub-path of length 2) C (Di , Di +1 ) cost of the link (Di , Di +1 )

Cost of a link cost of a link l

[0, 1, . . . , 7] 3 C {l } =

   7



  min 7, round



1 pl4



where pl is the probability of delivering a message over link l IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

56/58 October 15, 2012 T-110.5111 WPAN Lecture

Routing metric (2 of 2) Path cost path cost C {P } =

L−1 X i =1

C {(Di , Di +1 )}

Observations pl can be estimated through the LQI of IEEE 802.15.4 use of the metric route discovery route maintenance

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

57/58 October 15, 2012 T-110.5111 WPAN Lecture

References ZigBee Alliance, ZigBee Specification, Version 1.0, December 2004 Don Sturek, ZigBee V1.0 Architecture Overview, ZigBee Open House Presentations, Oslo, June 2005 Ian Marsden, Network Layer Technical Overview, ZigBee Open House Presentations, Oslo, June 2005 Paolo Baronti, Prashant Pillai, Vince W.C. Chook, Stefano Chessa, Alberto Gotta, Y. Fun Hu, Wireless sensor networks: A survey on the state of the art and the 802.15.4 and ZigBee standards, Computer Communications, Volume 30, Issue 7, 26 May 2007, Pages 1655–1695

IEEE 802.15.4 and ZigBee M. Di Francesco Aalto University

58/58 October 15, 2012 T-110.5111 WPAN Lecture

Computer Networks II Advanced Features (T-110.5111) Bluetooth Mario Di Francesco, PhD Postdoctoral Researcher – DCS Research Group Based on slides previously done by Matti Siekkinen and reused with permission For classroom use only, no unauthorized distribution

Bluetooth  Originally as cable replacement technology  Follows the main objectives of WPAN technologies – low-cost, low-power, short range

 Main features – devices find and connect to each other via inquiry and paging processes – pairing for authenticated use of services – master and slave devices  together form a piconet

– different application profiles (and stacks)  e.g. hands-free, streaming audio and video

– secure data transfer Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Piconets and scatternets  A master and up to 7 active slaves form a piconet – up to 255 parked nodes in addition

 Two piconets can be connected to form a scatternet

Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Bluetooth “flavors”  Version 2 + EDR – a.k.a. Classic – Enhanced Data Rate (EDR) adds 2 and 3 Mbps rates – basic rate is still 1 Mbps

 Version 3 + HS – adds alternate MAC + PHY (Wi-Fi) to provide higher speed data channels

 Version 4 – adds Bluetooth low energy – targets embedded low-power devices  runs up to two years on coin cell battery Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Protocol stack

Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Layers  Radio layer – channel access and modulation

 Link control (or baseband) – framing and management of time slots

 Link manager – establishment of logical channels between devices

 Logical link control and adaptation protocol (L2CAP) – framing of variable-length messages and reliability

 Application profiles span almost the whole stack

Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Radio layer  License-free ISM band at 2.402 – 2.480 GHz – 79 channels 1 MHz wide

 Channel access – Adaptive Frequency-Hopping (AFH) spread spectrum  up to 1600 hops/s  all nodes of piconet hop synchronously – master dictates timing and decides the pseudorandom hop sequence

 dynamically exclude channels with interference – channel map update

 Three modulations – 1-bit symbol per μs for 1Mbps rate – 2/3-bit symbol per μs (EDR) for 2/3 Mbps rates (respectively)

Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Other layers  Link control and timeslot management – time division multiplexing with 625μs slots – master transmission at each even slots and slaves at each odd slot

 Link manager and link establishment – secure simple pairing – Synchronous Connection Oriented (SCO) link  master and slave set up a periodic schedule  real time data (e.g., phone calls)

– Asynchronous ConnectionLess (ACL) link  master polls, slave responds  packet data, best effort

 L2CAP – gets packets and outputs frames for the link manager – (de)multiplexes data for upper layers Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Frame structure Basic data rate

specifies the slave

Enhanced data rate

specifies the master

Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

higher rate modulation only here

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Establishment of a new connection  Inquiry – discovers units in range  their device addresses and clocks

 Paging – establishes an actual connection M

INQUIRY

ID

S

INQUIRY SCAN

BACKOFF

PAGE

ID

FHS

INQUIRY RESPONSE

Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

PAGE SCAN

ID

MASTER RESPONSE

ID

FHS

CONNECTION

ID

SLAVE RESPONSE

POLL

NULL

CONN

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Inquiry  Inquiry Scan – performed by device that wants to be discovered – periodically listens for inquiry packets on a special inquiry hopping sequence of 32 frequencies

 Inquiry – sends an inquiry packet with a specific inquiry access code – the code indicates who should respond  either generic or dedicated to certain type of devices

 Inquiry Response – sends a response packet containing the responding device address after receiving inquiry message during the inquiry scan – sends to corresponding inquiry hopping response sequence  for each inquiry hop there is a corresponding inquiry response hop Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Paging  Page – Master sends a page message to slave’s address – Send to special page hopping sequence of 32 frequencies – Master uses the clock information from slave to be paged  Estimate where in the hop sequence slave is listening in page scan mode  Send to the frequencies just before and after

 Page Scan – Slave enters page scan state when it wishes to receive page packets – Slave listens to packets addressed to its DAC

 Page Response – Upon receiving page message, slave enters page response state – Send back a page response containing its DAC – Use frequencies from corresponding page response sequence  For each page hop there is a corresponding page response hop

Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Pairing  Used to establish a link key – e.g. to prevent eavesdropping an man-in-the-middle attacks – PIN code pairing (legacy pairing) – Secure Simple Pairing

 Authentication based on shared secret  Encryption of data based on shared secret – based on SAFER+ block cipher

5478

5478

Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Bluetooth Low Energy Introduction  History – – – –

Nokia initiated project Bluetooth Low End Extension (2004) WiBree (2006) part of Bluetooth v4.0 (2009)

 Characteristics – – – –

very low-power consumption cheap for small amounts of data two implementations  single mode for low-power devices (e.g., sensors)  dual mode for less constrained devices (including Bluetooth Classic) Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Bluetooth Low Energy Technical aspects  Radio characteristics – same frequency band as Classic but only 40 channels 2 MHz wide – AFH similar to Classic and raw data rate of 1 Mbps

 Simpler stack and protocols – only L2CAP, link layer, and PHY – reduced number of states  Standby, Advertising, Scanning, Initiating, and Connection

– low-power achieved through a low duty-cycle mechanism  periodic wake-ups for connection events and then sleep

 Market availability – besides devkits, recently appeared in off-the-shelf smartphones  iPhone 4S and 5, iPad 3rd gen, Samsung Galaxy S3 Computer networks II – Advanced topics T-110.5111 – Bluetooth (15.10.2012)

Mario Di Francesco http://www.uta.edu/faculty/mariodf

Computer Networks II – Advanced Features (T-110.5111)

Mario Di Francesco, PhD [email protected] http://www.uta.edu/faculty/mariodf