Chapter 15 Wireless LANs and PANs

Transcription

1 Chapter 15 Wireless LANs and PANs Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 1

2 Outline Introduction Wireless Local Area Networks (WLANs) Enhancement for IEEE WLANs Wireless Metropolitan Area Networks (WMANs) using WiMAX and Mesh Networks Mesh Networks Wireless Personal Area Networks (WPANs) ZigBee Summary Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 2

3 Scope of Various WLAN and WPAN Standards Power consumption Complexity n* a HiperLAN WMN * WiMAX g* b WLAN WMAN I Bluetooth WPAN Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved * Standard in progress Data rate 3

4 Wireless Local Area Networks (WLANs) IEEE group published a standard for WLANs named as IEEE (now known as IEEE n) Higher bit rates at 2.4GHz ISM band resulted in high-speed standard called the IEEE b (popularly known as Wi-Fi) Can be used to have an ad hoc network using peer-to-peer mode, Or, as a client/server wireless configuration (Infrastructure) Ad hoc Client/server Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 4

5 IEEE It is the standard for wireless LANs. It specifies MAC procedures and operate in 2.4 GHz range with data rate of 1Mbps or optionally 2Mbps. User demand for higher bit rates and international availability of 2.4 GHz band has resulted in development of a high speed standard in the same carrier frequency range. This standard called b, specifies a PHY layer providing a basic data rate of 11 Mbps and a fall-back rate of 5.5 Mbps. 5

6 IEEE In the ad hoc network mode, as there is no central controller, the wireless access cards use the CSMA/CA protocol to resolve shared access of the channel. In the client/server configuration, many PCs and laptops, physically close to each other (20 to 500 meters), can be linked to a central hub [AP] A larger area can be covered by installing several APs The access points track movement of users and make decisions on whether to allow users to communicate WLAN cards could be operated in continuous aware mode (radio always on) and power saving polling mode (radio in sleep state to extend battery life) 6

7 Distributed Wireless Network Station Wired network Access point Access point Distributed system Station Access point Station Station Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 7

8 IEEE and variants IEEE a With a throughput up to 54Mbps IEEE a operates on 5GHz It has less interference as compared to IEEE b/g since 2.4GHz band is heavily used Uses orthogonal frequency-division multiplexing (OFDM) with 52 subcarriers spanning over a 20MHz spectrum IEEE b (WiFi) Operates on 2.4GHz band with throughput of up to11mbps Direct-sequence spread spectrum DSSS on PHY layer IEEE g Operates on 2.4G using either DSSS or OFDM Can achieve higher throughput of up to 54Mbps IEEE n Multiple-input multiple-output (MIMO) technology Bandwidth can be 40MHz in 2.4GHz and 5GHz Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 8

9 Enhancement for IEEE WLANs The keys behind all the above networks are the wireless cards and wireless LAN access points In an ad hoc network mode, there is no central controller, the wireless access cards use CSMA/CA protocol to resolve shared access MAC layer access uses one of following methods: distributed coordination function (DCF), point coordination function (PCF), and hybrid coordination function (HCF) DCF is carrier sense multiple access with collision avoidance (CSMA/CA) and senses the medium before sending frame 9

10 Enhancement for IEEE WLANs IEEE e working group has developed enhanced DCF (EDCF) so that the differentiated service could be provided MSs with shorter AIFS have a higher priority to access channel than stations with longer AIFS Two EDCF priority schemes: interframe space (IFS) priority scheme and contention window (CW) priority scheme IFS priority scheme works better when the number of competing stations is large and can improve up to 50% for the real-time packets 10

11 Issues in MAC Protocol Challenges security related and support of multicast and location management Many mobile applications require support for group communication Location-based services include providing listings of local restaurants or movie theaters, emergency services, and vehicle tracking Scalability is a major concern to WLANs In client server model, many PC s or laptops physically close to each other (20-500m) can be linked to a central hub (access point) which acts as a bridge between the wireless and wired network A large area can be covered by installing several access points in the building 11

12 Roofnet and HyperLAN Roofnet is an experimental multi-hop IEEE b consists of about 50 nodes in apartments of Cambridge Few nodes act as gateways to wired Internet Requires no pre-configuration and users can connect on the fly HiperLAN stands for high-performance LAN Employs 5.15GHz and 17.1GHz frequency bands and has a data rate of 23.5Mbps with a coverage of 50m and mobility < 10 m/s Supports 25 audio connections at 32 kbps with a maximum latency of 10 ms, 1 video connection of 2Mbps with 100ms latency, and data rate of 13.4 Mbps 12

13 Features of Hiper LAN/2 HiperLAN type 2 has been specifically developed to have a wired infrastructure Type 1 has a distributed MAC with QoS provisions, whereas type 2 has a centralized scheduled MAC Type 1 is based on Gaussian minimum shift keying (GMSK), whereas type 2 is based on OFDM HiperLAN/2 automatically performs handoff to the nearest AP which is basically a radio BS that covers an area of about 30 to 150 meters 13

14 Features of Hiper LAN/2 The goals of HiperLAN are: QoS (to build multiservice networks) Strong security Handoff when moving between local area and wide areas Increased throughput Ease of use, deployment, and maintenance Affordability Scalability The connection oriented approach makes support for QoS easy It supports automatic frequency allocation, eliminating the need for manual frequency planning as in cellular networks 14

15 HyperLAN/2 Features Fixed network AP AP AP AP MS MS A simple HyperLAN/2 system 15

16 HyperLAN/2 Features MS may at any time request the AP and enter a low-power state for a sleep period Control is centralized at AP Channel spacing is 20MHz allowing high bit rates per channel Selective repeat ARQ is an error control mechanism used Radio link control (RLC) protocol provides following services: Association control with feature negotiation Encryption algorithms and convergence layers, authentication, key negotiation, and convergence layer negotiation Radio resource control to support handoff capability, to perform radio measurements in assisting the APs in selecting an appropriate radio channel, and to run the power-saving algorithm Connection control for the establishment and release of user connections 16

17 HomeRF Two kind of networks: HomeRF (for home), Hiper LAN (for business workspace). 43 million US homes now contain more than one PC. A home network typically consists of one high speed internet access port providing data to multiple networked nodes. Home networking allows all computers in a home to simultaneously utilize the same high speed ISP (Internet Service Provider) account. Home networking allows two options: wired solution and wireless solution. 17

18 HomeRF (cont d) Wired Solutions such as Ethernet, phone line offers a fast reliable secure connections, but the cost of wiring and installation is high. Wireless networks such as PC-Centric Data offer more mobility to the users of the network. 18

19 Architecture of HomeRF System Satellite dish Phone connection Cell phone Baby monitor Main PC Clock Wireless headset Palmtop Fridge data pad Television Handheld communicator Laptop 2 nd PC Cable modem Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 19

20 Advantages of Wireless HomeRF Mobility Flexibility: Simultaneous internet access while sharing a single internet connection with other PCs. Simple: Installation time is small. Economical: Less than $100 for each networked PC. Secure Based on industry Standards: Enables interoperability between many different manufacturers. 20

21 HomeRF Technology In HomeRF all the devices can share the same connections for voice and data Provides the foundation for a broad range of interoperable consumer devices A specification for wireless communications in the home called Shared Wireless Access Protocol (SWAP) has been developed 21

22 Home RF Network A network consists of Resource providers, which are gateways to different resources like cordless phones, printers, fileservers and TV. The goal of Home RF is to integrate all of them in to a single Network suitable for all applications and also remove all wires and utilize RF links in the network. This will support the mobility of devices. With Home RF, cordless phone can connect to PSTN ordinarily, but can also connect through a PC for enhanced services. 22

23 Comparison of WLAN Standards Technology Operational spectrum IEEE b (WiFi) Wireless LAN HomeRF 2.4 GHz 2.4 GHz 5.GHz HiperLAN Physical layer DSSS FHSS with FSK OFDM with QAM Channel access CSMA/CA CSMA CA and TDMA Nominal data rate Central resource control/tdma/tdd 2 Mbps 10 Mbps 32 54Mbps Coverage 100 m >50m m Power level issues <350mA current drain <300mA peak current Interference Present Present Minimal Uses low power states like sleep Price/complexity Medium (<$100) Medium High (>$100) Security Low High High 23

24 Wireless Metropolitan Area Networks (WMANs) IEEE based WiMAX Offers less expensive opportunity Supports point-to-multipoint broadband wireless access Very high bit rates in the range of 3.5 MHz Support a variety of backhaul requirements, including both ATM and packet-based protocols Convergence sublayers are used to map the transport-layer specific traffic to a MAC and offers features such as payload header suppression, packing, and fragmentation Supports percent link availability MAC supports automatic repeat request (ARQ) 24

25 Protocol Stack Packet convergence Sublayer (PCS) ATM Packet SSCS (security sublayer )

26 Convergence Sublayer (CS) Brief Functions Mapping external network data into MAC SDU Classifying external network SDU Associating to MAC connection ID Payload header suppression (PHS) Common Part Sublayer (CPS) Core MAC functionality System access Bandwidth allocation Connection establishment Connection maintenance Handover and Power amanagement Security Sublayer PHY Authentication (RSA X.509/EAP) Security key exchange (3DES) Encryption (AES) Multiple sections

27 Service Specific Convergence Sublayer (SSCS) The CS performs the following functions: accepting higher-layer PDUs from the higher layer performing classification of higher-layer PDUs processing (if required) the higher-layer PDUs based on the classification delivering CS PDUs to the appropriate MAC SAP receiving CS PDUs from the peer entity Currently, two CS specifications are provided Asyncronous Transfer Mode (ATM) CS Packet CS Such as IP, PPP, Ethernet, etc., Other CSs may be specified in the future.

28 Packet Convergence Sublayer (PCS) Packet convergence sublayer (PCS) The packet CS resides on top of the Common Part Sublayer (CPS) The PCS performs the following functions, utilizing the services of the MAC sublayer: a) Classification of the higher-layer protocol PDU into the appropriate connection b) Suppression of payload header information (optional) c) Delivery of the resulting CS PDU to the MAC SAP associated with the service flow for transport to the peer MAC SAP d) Receipt of the CS PDU from the peer MAC SAP e) Rebuilding of any suppressed payload header information (optional)

29 Wireless Metropolitan Area Networks (WMANs) Data to the subscriber stations are multiplexed in TDM fashion. The uplink (UL) is shared between SSs in TDMA fashion SS has a standard 48-bit MAC address MAC PDU consists of a fixed-length MAC header, a variablelength payload, and an optional cyclic redundancy check (CRC) MAC supports various higher-layer protocols such as ATM or IP HT=0 (1) EC(1) Type (6) Rsv(1) CI(1) EKS (2) Rsv(1) LEN Msb(3) LEN lsb (8) CID msb (8) CID lsb (8) HCS (8) 29

30 IEEE MAC MAC supports both TDD and FDD 10 66GHz: line-of-sight (LOS) needed Burst design allows coexistence of both TDD and FDD forms 2 11GHz: three air interfaces are defined Three 2 11GHz Air Interface of the IEEE a Draft 3 Specifications Air Interface WMAN SC2 WMAN OFDM WMAN OFDMA Specification A single-carrier modulation is used License-exempt bands necessarily use this TDMA access interface. OFDM is present with a 256-point transform Each receiver is assigned a set of multiple carriers to enable multiple access. OFDM is present with a point transform 30

31 IEEE MAC Physical Layer Channel bandwidths are 20, 25MHz (typical U.S. allocation) or 28MHz (typical European allocation) Frame size can be 0.5, 1, or 2 ms Negotiated burst profile is used to provide synchronization with the Down Link P MAC PDU which has started in previous TC PDU First MAC PDU, this TC PDU Second MAC PDU, this TC PDU TC sublayer PDU 31

32 Wireless Mesh Network Internet Backbone MR4 IGW 1 MR1 MR2 MR5 MR3 MR6 IGW 2 Mesh Clients Figure 15.9 Illustration of a Wireless Mesh Network (WMN) 32

33 Wireless Mesh Network Comprise of: Internet Gateways (IGWs) Mesh Routers (MRs) Mesh Clients (MCs) Multi-hop WMN, traffic is predominantly oriented towards IGWs from MRs Traditional routing solutions of MANETs are not adequate for WMNs TCP could result in excessive packet delays Vulnerable to variety of security attacks 33

34 Ricochet A mobile data access service that is always on, provides high speed, secure mobile access to the desktop from outside the office. It allows to link to the Internet or the corporate network without needing phone lines or cable connections. The Ricochet service is provided by Metricom. 34

35 Ricochet Mobile Communication Network Microcell radios on street lights, utility poles Network interconnection facility Gateway Wireless access point Name server Modem radio Router Computer device Gateway to Internet, Intranets, LANS, Compuserve, AOL and other on-line services Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 35

36 Ricochet The Ricochet service is a wide area wireless system using spread spectrum packet switching data. The network operates within MHz portion of RF spectrum. The Ricochet wireless Micro Cellular Data Network (MCDN), consists of shoebox sized radio receivers, called Micro cell radios. Micro cells are typically mounted to street poles. Micro cells require a small power from the street lights. Each Micro cell radio employs 162 frequency hopping channels. 36

37 The Ricochet Wireless Modem It weighs 13 ounces. Has the general dimensions of a small paperback book, plugs directly into a desktop. When a Ricochet modem is configured to operate in bridge mode, it translates signals from other Ricochet modems into signals that a wired modem can receive. V.34, 28,800 bps access Good Availability Unlimited access Flexible pricing 37

38 Services Provided by Ricochet Provides immediate, dependable and secure connections without the cost and complexities of land based phone lines. Sending s, access to documents in home networks. Many real estate agents use this to search for property listings while on road. 38

39 Comparison of WMAN Standards Technology Wireless MAN Operational spectrum Physical layer IEEE GHz, LOS required, 20/25/28MHz channels TDMA-based uplink, QPSK, 16-QAM, 64-QAM 900MHz FHSS Channel access TDD and FDD variants CSMA Minimum data rate possible 120/134.4Mbps for 25/28MHz channel 176 kbps Ricochet Coverage Typically a large city As of September, 2002 only Denver, CO Power level issues Complicated power control algorithms for different burst profiles Interference Present but limited Present Price complexity Not available Medium Security High. Defines an extra privacy sublayer for authentication Low power modem compatible with laptops and hand-held High (Patented security system) 39

40 Wireless Personal Area Network Bluetooth initially conceived to replace RS232 cables, is the only WPAN technology to be commercially available Since 2002, its presence has become visible in devices ranging from laptops to wireless mouse to cameras, to headsets, to printers and cell phones IEEE x protocols to address needs of WPANs with varied data rates Bluetooth has adopted as IEEE (medium rate) while the IEEE (high rate) and (low rate) are also available 40

41 IEEE Task Groups IEEE WPAN/Bluetooth TG1 IEEE Coexistence TG2: TG2 (the IEEE ) is developing recommended practices to facilitate coexistence of WPANs (the IEEE ) and WLANs (the IEEE ). IEEE WPAN/High Rate TG3: The TG3 for WPANs is chartered to draft a new standard for high-rate (20Mbps or greater) WPANs IEEE WPAN/Low Rate TG4: The goal is to provide a standard for ultra-low complexity, cost, and power for low-datarate (200 kbps or less) wireless connectivity among inexpensive fixed, portable, and moving devices 41

42 Bluetooth It is named after the King of Denmark that unified different factions in Christianity through the country. It is a short range RF communication. Low cost, low power, radio based wireless link eliminates the need for short cable. Bluetooth radio technology built into both the cellular telephone and the laptop would replace the cable used today to connect a laptop to cellular phone. Printers, desktops can all be wireless. It also provides a universal bridge to existing data networks. 42

43 Use of Bluetooth to connect notebook Bluetooth Cellular Link Base Station Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 43

44 Bluetooth connecting printers, PDA s, desktops, fax machines, keyboards, joysticks and virtually any other digital device Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 44

45 Bluetooth providing a universal bridge to existing data networks Fixed Line Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 45

46 Bluetooth: A mechanism to form ad hoc networks of connected devices away from fixed network infrastructures Bluetooth Personal Ad hoc Network Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 46

47 Bluetooth The ultimate goal is to make small products (PC/Laptops) have only one wire attached to power cord. In case of PDA, the power cord is also eliminated. A simple application of Bluetooth is updating the phone directory of the PC from a mobile telephone. A typical Bluetooth has a range of 10 m. 47

48 Features Fast frequency hopping to reduce interference. Adaptive output power to minimize interference. Short data packets to maximize capacity. Fast acks allowing for low coding overhead for links. Flexible packet types that support a wide application range. CVSD (Continuous Variable Slope Delta Modulation) voice coding that can withstand high bit error rates. Transmission/reception interface tailored to minimize power consumption 48

49 Architecture of Bluetooth System and Scatternet Piconet 2 S 2,3 S 2,2 S 3,1 S 3,2 M 2 S 3,3 S 2,1 S 1,2 /S 2,5 S 2,4 /S 3,4 M 3 Piconet 3 M 1 M 4 S 1,1 S 4,1 S 1,3 /S 4,4 S 1,5 Piconet 1 S 1,4 S 4,3 S 4,2 Piconet 4 Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 49

50 Bluetooth Technological Characteristics Frequency band Technology Transmission method Transmission power Range Number of devices Data speed Maximum voice channels Maximum data channels Security Power consumption Module size Price C/I co-channel C/I 1 MHz C/I 2 MHz Channel switching time 2.4 GHz (unlicensed ISM band) Spread spectrum Hybrid direct sequence and frequency hopping 1 milli-watt (0 dbm) 10 meters (40 feet) 8 per piconet, 10 piconets per coverage area Asymmetric link: kbps Symmetric link: kbps 3 per piconet 7 perpiconet Link layer w/s fast frequency hopping (1600 /sec) 30 μa sleep, 60 μa hold, 300 μa standby, 800 μa max transmit 3 square cm (0.5 square inches) Expected to fall to $5 in the next few years 11 db (0.1% BER) -8 db (0.1% BER) -40 db (0.1% BER) 220 μs 50

51 Architecture Bluetooth radio typically hops faster and uses shorter packets as compared to other systems operating in the same frequency band. Use of FEC (Forward Error Correction) limits the impact of random noise. As the interference increases, the performance decreases. 51

52 Architecture (cont d) Bluetooth devices can interact with other Bluetooth devices. One of the devices acts as a master and others as slaves. This network is called Piconet. A single channel is shared among all devices in Piconet. There can be up to seven active slaves in the Piconet. Each of the active slaves has an assigned 3 bit Active Member address. A lot of other slaves can remain synchronized to the Master through remaining inactive slaves, referred to as parked nodes. A parked device remains synchronized to the master clock and can become active and start communicating in the Piconet anytime. 52

53 Architecture (cont d) If Piconets are close to each other, they have overlapping areas The scenario where the nodes of two or more Piconets mingle is called Scatternet Before any connections in the Piconet are created all devices are in STDBY mode In this mode an unconnected unit periodically listens for message every 1.28 seconds Each times a device wakes up, it tunes on the set of 32 hop frequencies defined for that unit 53

54 Bluetooth Core Protocol Upper Layer SDP SDP Service Discovery Protocol L2CAPE LMP Audio L2CAP Logical Link Control and Adaptation Layer Protocol Baseband LMP Link Manager Protocol Low Radio Layer SDP: Provides a mean for applications to discover which services are provided by or available through a Bluetooth device L2CAP: Supports higher level protocol multiplexing, packet segmentation and reassembly and conveying of QoS information LMP: Used by Link managers for link set up and control Baseband: Enables the physical RF link between Bluetooth units forming a Piconet Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 54

55 Core Protocols 625µsec 1-slot packet 3-slot packet 5-slot packet Type User Payload (bytes) FEC Symme tric (kbps) Asymmetric (kbps) DM Yes DH No DM Yes DH No DM Yes DH No HV Yes 64.0 HV Yes HV No

56 IEEE MAC and PHY Layer Details Superframe Beacon Contention access period (CAP) Guaranteed time slot (GTS) Beacon WPAN parameters Non-QoS data frames: Short bursty data Channel access requests CAP/GTS boundary dynamically adjustable Data frames with QoS provisions: Image Files MP3 music files (multimedia files) Standard definition MPEG2, 4.5 Mb/s High-definition MPEG2, 19.2 Mb/s MPEG1, 1.5 Mb/s DVD, up to 9.8 Mb/s CD audio,!.5 Mb/s AC3 Dolby digital, 448 Kb/s MP3 streaming audio, 128 Kb/s Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 56

57 IEEE Some applications that require high data rates such as shared Internet access, distributed home entertainment, and networked gaming However, there is an even bigger market for home automation, security, and energy conservation applications IEEE defines specification for low-rate, lowpower WPANs Application areas include industrial control; agricultural, vehicular, and medical sensors; and actuators 57

58 IEEE Data Link Layer (DLL) Details Upper layers Network layer IEEE LLC, type 1 Other LLC Data link layer SSCS IEEE MAC IEEE /915 MHz PHY IEEE MHz PHY Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 58

59 General MAC frame format Bytes: MAC Layer Frame control 1 Sequence number MAC header (MHR) Variable 2 Address Info Payload MAC service data unit (MSDU) MAC protocol data unit (MPDU) Frame check sequence MAC footer (MFR) PHY Layer Synchronization header Physical header PHY service data unit (PSDU) PHY protocol data unit (PPDU) Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 59

60 PHY layer Packet Structure PHY protocol data unit (PPDU) Preamble Start of packet delimiter PHY header PHY service data unit (PSDU) 6 bytes 127 bytes PHY packet fields: Preamble (32 bits) synchronization Start of packet delimiter (8 bits) signify end of preamble PHY header (8 bits) specify length of PSDU PSDU ( 127 bytes) PHY layer payload Copyright 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved 60

61 Comparison of WPAN Systems Technology Bluetooth ( ) Bluetooth 3.0 HS Operational spectrum Physical layer details Channel access Maximum data rate 2.4GHz ISM band FHSS, 1600 hops per second Master slave polling, time division duplex (TDD) GHz ISM band Uncoded QPSK trellis coded QPSK or 16/32/64-QAM scheme CSMA CA, and guaranteed time slots (GTS) in a superframe structure 2.4GHz and 868/915MHz DSSS with BPSK or MSK (O QPSK) CSMA CA, and guaranteed time slots (GTS) in a superframe structure Up to 1Mbps 11 55Mbps 868MHz 20, 915MHz 40, 2.4GHz 250 kbps Coverage <10m <10m <20m? Power level issues 1mA 60mA <80mA Very low current drain (20 50 ma) GHz or 6 9GHz UWB radio protocol 480 Mbps ultra-low power Interference Present Present Present Minimum Price Low (<$10) Medium Very low? 61

62 ZigBee ZigBee is pertinent in various sensor applications ZigBee is designed to respond quickly, while Bluetooth takes much longer ZigBee is a control technology on wireless standard Data rate of 250 Kbps in 2.4 GHz ISM band, 20 kbps in the 868 MHz band in Europe, and 40 kbps in 915MHz band used in North America and Australia ZigBee can choose up to 16 different 5 MHz channels within 2.4 GHz band, several do not overlap with and WiFi ZigBee has active and sleep modes All devices must have a short 16-bit IEEE addressing Application layer maintains table of binding for matching two or more devices 62