ZigBee and 802.15.4

Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. IEEE 802.15.4 Standard Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. IEEE 802.15.4 Basics 802.15.4 is a simple packet data protocol for lightweight wireless networks 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 Three bands, 27 channels specified 2.4 GHz: 16 channels, 250 kbps 868.3 MHz : 1 channel, 20 kbps 902-928 MHz: 10 channels, 40 kbps Works well for 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 Copyright 2002 The ZigBee Alliance, Inc.

Introduction to the IEEE 802.15.4 Standard IEEE 802.15.4 standard released May 2003 Semiconductor manufacturers Sampling Transceiver ICs and platform hardware/software to Alpha Customers now Users of the technology Defining application profiles for the first products, an effort organized by the ZigBee Alliance Copyright 2002 The ZigBee Alliance, Inc.

ZigBee Application Framework IEEE 802.15.4 standard Includes layers up to and including Link Layer Control LLC is standardized in 802.1 Supports multiple network topologies including Star, Cluster Tree and Mesh Features of the MAC: Association/dissociation, ACK, frame delivery, channel access mechanism, frame validation, guaranteed time slot management, beacon management, channel scan Low complexity: 26 primitives versus 131 primitives for 802.15.1 (Bluetooth) IEEE 802.15.4 MAC IEEE 802.15.4 LLC IEEE 802.2 LLC, Type I IEEE 802.15.4 2400 MHz PHY 868/915 MHz PHY Data Link Controller (DLC) Networking App Layer (NWK) ZigBee Application Framework Channel scan for beacon is included, but it is left to the network layer to implement dynamic channel selection Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. IEEE 802.15.4 MAC Overview Employs 64-bit IEEE & 16-bit short addresses Ultimate network size can reach 264 nodes (more than we’ll probably need…) Using local addressing, simple networks of more than 65,000 (2^16) nodes can be configured, with reduced address overhead Three devices specified Network Coordinator Full Function Device (FFD) Reduced Function Device (RFD) Simple frame structure Reliable delivery of data Association/disassociation AES-128 security CSMA-CA channel access Optional superframe structure with beacons GTS mechanism Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. IEEE 802.15.4 Device Types Three device types Network Coordinator Maintains overall network knowledge; most sophisticated of the three types; most memory and computing power Full Function Device Carries full 802.15.4 functionality and all features specified by the standard Additional memory, computing power make it ideal for a network router function Could also be used in network edge devices (where the network touches the real world) Reduced Function Device Carriers limited (as specified by the standard) functionality to control cost and complexity General usage will be in network edge devices All of these devices can be no more complicated than the transceiver, a simple 8-bit MCU and a pair of AAA batteries! Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Data Frame format One of two most basic and important structures in 15.4 Provides up to 104 byte data payload capacity Data sequence numbering to ensure that all packets are tracked Robust frame structure improves reception in difficult conditions Frame Check Sequence (FCS) ensures that packets received are without error Frame control: + type of frame (4 types), format of address field, controls Ack, I.e. specifies how the frame looks and what it contains. The ACK and MAC command are lower level used for peer-to-peer Sequence number: and Frame check sequency: verifies the integrity of the MAC frame. A transmission is considered successful if the ack frame contains the same sequence number as the previous frame. FCS is a 16-bit cyclic redundancy check (CRC) Address field size: can contain both source and destination info Copyright 2002 The ZigBee Alliance, Inc.

Acknowledgement Frame Format The other most important structure for 15.4 Provides active feedback from receiver to sender that packet was received without error Short packet that takes advantage of standards-specified “quiet time” immediately after data packet transmission Frame control: + type of frame (4 types), format of address field, controls Ack, I.e. specifies how the frame looks and what it contains. The ACK and MAC command are lower level used for peer-to-peer Sequence number: and Frame check sequency: verifies the integrity of the MAC frame. A transmission is considered successful if the ack frame contains the same sequence number as the previous frame. FCS is a 16-bit cyclic redundancy check (CRC) Address field size: can contain both source and destination info Copyright 2002 The ZigBee Alliance, Inc.

MAC Command Frame format Mechanism for remote control/configuration of client nodes Allows a centralized network manager to configure individual clients no matter how large the network Frame control: + type of frame (4 types), format of address field, controls Ack, I.e. specifies how the frame looks and what it contains. The ACK and MAC command are lower level used for peer-to-peer Sequence number: and Frame check sequency: verifies the integrity of the MAC frame. A transmission is considered successful if the ack frame contains the same sequence number as the previous frame. FCS is a 16-bit cyclic redundancy check (CRC) Address field size: can contain both source and destination info Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Beacon Frame format Frame control: + type of frame (4 types), format of address field, controls Ack, I.e. specifies how the frame looks and what it contains. The ACK and MAC command are lower level used for peer-to-peer Sequence number: and Frame check sequency: verifies the integrity of the MAC frame. A transmission is considered successful if the ack frame contains the same sequence number as the previous frame. FCS is a 16-bit cyclic redundancy check (CRC) Address field size: can contain both source and destination info Beacons add a new level of functionality to a network Client devices can wake up only when a beacon is to be broadcast, listen for their address, and if not heard, return to sleep Beacons are important for mesh and cluster tree networks to keep all of the nodes synchronized without requiring nodes to consume precious battery energy listening for long periods of time Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. MAC Options Two channel access mechanisms Non-beacon network Standard ALOHA CSMA-CA communications Positive acknowledgement for successfully received packets Beacon-enabled network Superframe structure For dedicated bandwidth and low latency Set up by network coordinator to transmit beacons at predetermined intervals 15ms to 252sec (15.38ms*2n where 0  n  14) 16 equal-width time slots between beacons Channel access in each time slot is contention free Three security levels specified None Access control lists Symmetric key employing AES-128 Carrier sense multiple access with collision avoidance CSMA-CA Copyright 2002 The ZigBee Alliance, Inc.

Non-Beacon vs Beacon Modes Non-Beacon Mode A simple, traditional multiple access system used in simple peer and near-peer networks Think of it like a two-way radio network, where each client is autonomous and can initiate a conversation at will, but could interfere with others unintentionally However, the recipient may not hear the call or the channel might already be in use Beacon Mode A very powerful mechanism for controlling power consumption in extended networks like cluster tree or mesh Allows all clients in a local piece of the network the ability to know when to communicate with each other Here, the two-way radio network has a central dispatcher who manages the channel and arranges the calls As you’ll see, the primary value will be in system power consumption Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc.

Example of Non-Beacon Network Commercial or home security Client units (intrusion sensors, motion detectors, glass break detectors, standing water sensors, loud sound detectors, etc) Sleep 99.999% of the time Wake up on a regular yet random basis to announce their continued presence in the network (“12 o’clock and all’s well”) When an event occurs, the sensor wakes up instantly and transmits the alert (“Somebody’s on the front porch”) The ZigBee Coordinator, mains powered, has its receiver on all the time and so can wait to hear from each of these stations Since ZigBee Coordinator has “infinite” source of power it can allow clients to sleep for unlimited periods of time to allow them to save power Copyright 2002 The ZigBee Alliance, Inc.

Example of Beacon Network Now make the ZigBee Coordinator battery-operated also All units in system are now battery-operated Client registration to the network Client unit when first powered up listens for the ZigBee Coordinator’s network beacon (interval between 0.015 and 252 seconds) Register with the coordinator and look for any messages directed to it Return to sleep, awaking on a schedule specified by the ZigBee Coordinator Once client communications are completed, ZigBee coordinator also returns to sleep This timing requirement potentially impacts the cost of the timing circuit in each end device Longer intervals of sleep mean that the timer must be more accurate or Turn on earlier to make sure that the beacon is heard, increasing receiver power consumption, or Improve the quality of the timing oscillator circuit (increase cost) or Control the maximum period of time between beacons to not exceed 252 seconds, keeping oscillator circuit costs low Application examples: environmental sensors in the forest Copyright 2002 The ZigBee Alliance, Inc.

Growing the Network In a beacon-environment, growing the network means keeping the overall network synchronized According to pre-existing network rules, the joining network’s PAN Coordinator is probably demoted to Router, and passes along information about its network (as required) to the PAN coordinator Beacon information passed from ZigBee Coordinator to now-Router, router knows now when to awake to hear network beacon Joining Network Existing network’s Coordinator Demoted to router New link established Copyright 2002 The ZigBee Alliance, Inc.

Frequencies and Data Rates The two PHY bands (UHF/Microwave) have different physical, protocol-based and geopolitical characteristics Worldwide coverage available at 2.4GHz at 250kbps 900MHz for Americas and some of the Pacific 868MHz for European-specific markets Copyright 2002 The ZigBee Alliance, Inc.

ISM Band Interference and Coexistence Potential for interference exists in every ISM band, not just 2.4GHz IEEE 802.11 and 802.15.2 committees are addressing coexistence issues ZigBee/802.15.4 Protocol is very robust Clear channel checking before transmission Backoff and retry if no acknowledgement received Duty cycle of a ZigBee-compliant device is usually extremely low It’s the “cockroach that survives the nuclear war” Waits for an opening in otherwise busy RF spectrum Waits for acknowledgements to verify packet reception at other end Copyright 2002 The ZigBee Alliance, Inc.

PHY Performance 802.15.4 has excellent performance in low SNR environments Copyright 2002 The ZigBee Alliance, Inc.

IEEE1451.5 Sensor Group Wireless Criteria A survey was conducted mid-2002 on the characteristics of a wireless sensor network most important to its users In order of importance, these characteristics are 1. Data Reliability 2. Battery Life 3. Cost 4. Transmission Range 5. Data Rate 6. Data Latency 7. Physical Size 8. Data Security How would you modify these requirements, if at all? Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. 802.15.4 and the IEEE 802.15.4 Composed of many of the individuals and companies that make up the ZigBee Alliance Developed the basic PHY and MAC standard with the requirement that 15.4 be simple and manageable and that high-level functionality (networking, security key management, applications) be considered The ZigBee Alliance is A consortium of end users and solution providers, primarily responsible for the development of the 802.15.4 standard Developing applications and network capability utilizing the 802.15.4 packet delivery mechanism Addresses application and interoperability needs of a substantial part of the market Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Mission Statement ZigBee Alliance members are defining global standards for reliable, cost-effective, low power wireless applications. The ZigBee Alliance is a rapidly growing, non-profit industry consortium of leading semiconductor manufacturers, technology providers, OEMs and end users worldwide. Copyright 2002 The ZigBee Alliance, Inc.

What is the ZigBee Alliance? Organization defining global standards for reliable, cost-effective, low power wireless applications A rapidly growing, worldwide, non-profit industry consortium of Leading semiconductor manufacturers Technology providers OEMs End-users Sensors are one of the reasons for ZigBee! Copyright 2002 The ZigBee Alliance, Inc.

What is ZigBee technology? Cost-effective, standards-based wireless networking solution Developed for and targets applications that need Low to moderate data rates and low duty cycles Low average power consumption / long battery life Security and reliability Flexible and dynamic network topologies Star, cluster tree and mesh networks Interoperable application frameworks controlled by an industry alliance to ensure interoperability/compatibility Copyright 2002 The ZigBee Alliance, Inc.

The ZigBee Alliance Solution Targeted at Industrial and Commercial control/monitoring systems Wireless sensor systems Home and Building automation and controls Medical monitoring Consumer electronics PC peripherals Industry standard through application profiles Primary drivers Simplicity Long battery life Networking capabilities Reliability Low cost Alliance member companies provide interoperability and certification testing Copyright 2002 The ZigBee Alliance, Inc.

Why do we need ZigBee technology? ONLY standards-based technology that Addresses the unique needs of most remote monitoring and control and sensory network applications Enables the broad-based deployment of wireless networks with low cost, low power solutions Provides the ability to run for years on inexpensive primary batteries for a typical monitoring application Copyright 2002 The ZigBee Alliance, Inc.

What kind of battery life can a user expect? ZigBee protocol was designed from the ground up to support very long life battery applications Users can expect Near-shelf life in a typical monitoring application Battery life is ultimately a function of battery capacity and application usage Many industrial applications are in harsh thermal environments Batteries may include alkalines or Li-primaries Other forms of power generation might include solar, mechanical, piezoelectric Copyright 2002 The ZigBee Alliance, Inc.

The ZigBee Alliance Solution Targeted at home and building automation and controls, consumer electronics, toys etc. Industry standard (IEEE 802.15.4 radios) Primary drivers are simplicity, long battery life, networking capabilities, reliability, and cost Copyright 2002 The ZigBee Alliance, Inc.

The Wireless Market ZigBee 802.11b 802.11a/HL2 & 802.11g Bluetooth 2 TEXT GRAPHICS INTERNET HI-FI AUDIO STREAMING VIDEO DIGITAL VIDEO MULTI-CHANNEL VIDEO LAN 802.11b 802.11a/HL2 & 802.11g SHORT < RANGE > LONG Bluetooth 2 ZigBee PAN Bluetooth1 LOW < DATA RATE > HIGH Copyright 2002 The ZigBee Alliance, Inc.

LIGHT COMMERCIAL CONTROL Applications BUILDING AUTOMATION CONSUMER ELECTRONICS security HVAC AMR lighting control access control TV VCR DVD/CD remote patient monitoring fitness monitoring PERSONAL HEALTH CARE PC & PERIPHERALS ZigBee Wireless Control that Simply Works mouse keyboard joystick Future applications include Toys and Games, like consoles controllers, portable game pads (like gameboys), educational toys like leap frog stuff, and fun toys like RC (remote control) toys, etc. INDUSTRIAL CONTROL RESIDENTIAL/ LIGHT COMMERCIAL CONTROL asset mgt process control environmental energy mgt security HVAC lighting control access control lawn & garden irrigation Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Promoter Companies Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Promoters Participants And more each month… Copyright 2002 The ZigBee Alliance, Inc.

Development of the Standard ZigBee Alliance 50+ companies Defining upper layers of protocol stack: from network to application, including application profiles IEEE 802.15.4 Working Group Defining lower layers : MAC and PHY SILICON ZIGBEE STACK APPLICATION Customer IEEE 802.15.4 ZigBee Alliance Copyright 2002 The ZigBee Alliance, Inc.

ZigBee Topology Models Mesh Star ZigBee coordinator Cluster Tree ZigBee Routers ZigBee End Devices Copyright 2002 The ZigBee Alliance, Inc.

Competitive or Complementary? ZigBee and Bluetooth Competitive or Complementary? Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. ZigBee and Bluetooth Optimized for different applications ZigBee Smaller packets over large network Mostly Static networks with many, infrequently used devices Home automation, toys remote controls Energy saver!!! Bluetooth Larger packets over small network Ad-hoc networks File transfer; streaming Screen graphics, pictures, hands-free audio, Mobile phones, headsets, PDAs, etc. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. ZigBee and Bluetooth Address Different Needs Bluetooth is a cable replacement for items like Phones, Laptop Computers, Headsets Bluetooth expects regular charging Target is to use <10% of host power Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. ZigBee and Bluetooth Address Different Needs ZigBee is better for devices where the battery is ‘rarely’ replaced Targets are : Tiny fraction of host power New opportunities where wireless not yet used Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. ZigBee and Bluetooth Air interface ZigBee DSSS- 11 chips/ symbol 62.5 K symbols/s 4 Bits/ symbol Peak Information Rate ~128 Kbit/second Bluetooth FHSS 1 M Symbol / second Peak Information Rate ~720 Kbit / second Copyright 2002 The ZigBee Alliance, Inc.

Protocol Stack Comparison ZigBee and Bluetooth Silicon RF Baseband Link Controller Voice Link Manager Host Control Interface L2CAP Telephony Control Protocol Intercom Headset Cordless Group Call RFCOMM (Serial Port) OBEX Bluetooth Stack Applications vCard vCal vNote vMessage Networking Dial-up Fax Service Discovery User Interface Silicon PHY Layer MAC Layer Data Link Layer Network Layer ZigBee Stack Application Application Interface Zigbee Bluetooth Protocol Stack Comparison Copyright 2002 The ZigBee Alliance, Inc.

ZigBee protocol is optimized for timing critical applications ZigBee and Bluetooth Timing Considerations ZigBee: Network join time = 30ms typically Sleeping slave changing to active = 15ms typically Active slave channel access time = 15ms typically Bluetooth: Network join time = >3s Sleeping slave changing to active = 3s typically Active slave channel access time = 2ms typically ZigBee protocol is optimized for timing critical applications Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. ZigBee and Bluetooth Bluetooth ZigBee AIR INTERFACE FHSS DSSS PROTOCOL STACK 250 kb 28 kb BATTERY rechargeable non-rechargeable DEVICES/NETWORK 8 255 LINK RATE 1 Mbps 250 kbps RANGE ~10 meters (w/o pa) ~30 meters Comparison Overview Copyright 2002 The ZigBee Alliance, Inc.

An Application Example Battery Life & Latency in a Light Switch Wireless Light switch – Easy for Builders to Install A Bluetooth Implementation would either : keep a counter running so that it could predict which hop frequency the light would have reached or use the inquiry procedure to find the light each time the switch was operated. Copyright 2002 The ZigBee Alliance, Inc.

Light switch using Bluetooth Option 1: use counter to predict hop frequency reached by light The two devices must stay within 60 us (~1/10 of a hop) With 30ppm crystals, devices need to communicate once a second to track each other's clocks. Assume this could be improved by a factor of 100 then devices would need to communicate once every 100 seconds to maintain synchronization. => 900 communications / day with no information transfer + perhaps 4 communications on demand 99.5% Battery Power wasted Copyright 2002 The ZigBee Alliance, Inc.

Light switch using Bluetooth Option 2: Inquiry procedure to locate light each time switch is operated Bluetooth 1.1 = up to 10 seconds typical Bluetooth 1.2 = several seconds even if optimized Unacceptable latency Copyright 2002 The ZigBee Alliance, Inc.

Light switch using ZigBee With DSSS interface, only need to perform CSMA before transmitting Only 200 µs of latency Highly efficient use of battery power ZigBee offers longer battery life and lower latency than a Bluetooth equivalent. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Conclusion Bluetooth and 802.15.4 transceiver physical characteristics are very similar Protocols are substantially different and designed for different purposes 802.15.4 designed for low to very low duty cycle static and dynamic environments with many active nodes Bluetooth designed for high QoS, variety of duty cycles, moderate data rates in fairly static simple networks with limited active nodes Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. ZigBee and Bluetooth Conclusion ZigBee targets applications not addressable by Bluetooth or any other wireless standard ZigBee and Bluetooth complement for a broader solution Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability and Robustness throughout the stacks of IEEE 802.15.4 and ZigBee Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability Consistently perform a given task to the desired result despite all changes of environmental behavior Without fail A necessary ingredient of trust “When the sensor measures its environment; the controller always knows that same value” Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability The wireless medium is not a protected environment like the wired medium, but rather, it is fraught with degradations, disruptions, and pitfalls such as dispersion, multipath, interference, frequency dependent fading, sleeping nodes, hidden nodes, and security issues. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability Each of these degradations and disruptions can be mitigated by various mechanisms within the ISO layers; but not all mechanisms are compatible with all other mechanisms or may negatively impact critical performance attributes The system must be optimized for the best performance in a realistic environment Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability In addition to the previous disruptions there is the case of sending messages to devices that are not receiving, e.g. they’re in the “sleep” mode. When this happens the message needs to be buffered by another device that is able to send the message when the sleeping device wakes up. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability Interferer Router X X Multipath Sleeping Node Network Coordinator Hidden Node Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability IEEE 802.15.4 has built upon the successes of previous IEEE 802 standards by selecting those mechanisms proven to ensure good reliability without seriously degrading system and device performance. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability ISO Layers: PHY: Direct Sequence with Frequency Agility (DS/FA) MAC: ARQ, Coordinator buffering Network: Mesh Network (redundant routing) Application Support Layer: Security Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability PHY Layers: Direct sequence: allows the radio to reject multipath and interference by use of a special “chip” sequence. The more chips per symbol, the higher its ability to reject multipath and interference. Frequency Agility: ability to change frequencies to avoid interference from a known interferer or other signal source. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. IEEE 802 Direct Sequence IEEE 802. 11 11b 15.4 (900) 15.4 (2.4) Chips/Symbol 15 32 As can be seen from above, IEEE802.15.4/ZigBee has more processing gain (chips/symbol) than its predecessors Copyright 2002 The ZigBee Alliance, Inc.

Direct Sequence and Frequency Agility Desired Signal Interferer After DS correlation Over the Air 2.4 GHz PHY Channels 11-26 5 MHz 2.4 GHz 2.4835 GHz Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability MAC: ARQ (acknowledgement request) is where a successful transmission is verified by replying with an acknowledge (ACK). If the ACK is not received the transmission is sent again Coordinator buffering is where the network coordinator buffers messages for sleeping nodes until they wake again Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability Network: Mesh Networking: allows various paths of routing data to the destination device. In this way if a device in the primary route is not able to pass the data, a different valid route is formed, transparent to the user. Copyright 2002 The ZigBee Alliance, Inc.

Reliability: Mesh Networking ZigBee Coordinator (FFD) ZigBee Router (FFD) ZigBee End Device (RFD or FFD) Mesh Link Star Link Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Reliability Application Support Sub-layer(APS): Security: supports reliability by keeping other devices from corrupting communications. The APS configures the security emplaced in the MAC layer and also adds some of its own. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Robustness Let’s define robustness as the ability to tolerate significant degrading phenomena in the physical medium Multipath and interference are probably the most significant degradations to the channel model. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Robustness Frequency hopping is a method that allows the radio to periodically change channels to over time minimize the effect of a “bad” channel. While this technique is very effective in some circumstances it creates other problems such as latency, network uncertainty for sleeping nodes, loss of the product bandwidth x time, etc. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Robustness Direct Sequence with Frequency Agility (DS/FA) combines the best features of DS and FH without most of the problems caused by frequency hopping because frequency changes aren’t necessary most of the time, rather they’re appropriate only on an exception basis. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Robustness The 802.11 Working Group couldn’t agree upon which of the following PHYs was the best: FH, IR, or DS. So all three were standardized and left to the market to decide. Of the three PHYs; DS was the clear market winner. DS provided sufficient robustness with higher overall performance. Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Robustness Excess robustness does not achieve higher performance, rather it typically costs performance Copyright 2002 The ZigBee Alliance, Inc.

Copyright 2002 The ZigBee Alliance, Inc. Conclusion IEEE 802.15.4/ZigBee have addressed reliability throughout the ISO stack with proven mechanisms to minimize the uncertainty of the wireless medium Copyright 2002 The ZigBee Alliance, Inc.