THE INTERNET OF THINGSAUERBACH PUBLICATIONS? ? ?Unlicensed Mobile Access Technology: Protocols, Architectures, Security, Standards and Applications ? ?Wireless Quality-of-Service: Techniques, Standards and Applications ? ?Broadband Mobile Multimedia: Techniques and Applications ? ?The Internet of Things: From RFID to the Next-Generation Pervasive Networked Systems ? ?Millimeter Wave Technology in Wireless PAN, LAN, and MAN ? ?Security in Wireless Mesh Networks ? ?Resource, Mobility and Security Management in Wireless Networks and Mobile Communications ? ?Wireless Mesh Networking: Architectures, Protocols and Standards ? ?Mobile WIMAX: Toward Broadband Wireless Metropolitan Area Networks ? ?Distributed Antenna Systems: Open Architecture for Future Wireless Communications ? ? ? ?WIRELESS NETWORKS AND MOBILE COMMUNICATIONSNew York LondonTHE INTERNET OF THINGSFrom RFID to the Next-Generation Pervasive Networked SystemsEdited by Lu Yan s Yan Zhang Laurence T. Yang s Huansheng NingAuerbach Publications Taylor 8) Includes bibliographical references and index. ISBN 978-1-4200-5281-7 (alk. paper) 1. Ubiquitous computing. 2. Radio frequency identification systems. 3. Wireless communication systems. I. Yan, Lu. II. Title. III. Series.QA76.5915.I68 2008 384.5-dc222007047411Visit the Taylor ISO 18000-6C. The EPC Gen-2 protocol is based on a masterslave-style architecture, with the interrogators acting as the masters and the tags acting as the slaves. The inter- rogators initiate all communication and actually provide the power for the tags to operate. The Gen-2 protocol is half-duplex. Three major steps are required for an interrogator to access a tag. First, the interrogator must issue a Select command to pick the tag population to which it wishes to communicate. This feature of the Select command allows the interrogator to divide up a group of tags into smaller subgroups to reduce collisions, and reducing the time required to access one or more tags. Second, the interrogator must take an inventory to determine the EPC numbers of all tags in a given population. The Query (issued only once at the begin- ning of the inventory) and QueryRep commands are the main commands used to obtain this information. When receiving a Query command, each tag selects a random number for the initial slot value and beings reducing it according to thestandardspecifications.Iftheslotvalueis0,thetagwillrespondtransmittinga16-bitrandom number uniquely identifying a tag within statistical parameters specified by the protocol. The interrogator then issues an ACK (acknowledgment) with the tags 16-bit random number, causing the tag to transmit its protocol control,18?The Internet of ThingsEPC number, and cyclic redunancy check (CRC) values to the interrogator. The CRC value is used to detect errors, possibly from interference, present in a received message. The QueryRep command is a repeated query causing all tags that have not yet responded with their 16-bit random number to decrement their slot value by 1. If the slot value is 0, the tag will reply with its 16-bit random number and the interrogator will ACK that tag and obtain the protocol control, EPC number, and CRC values. Third, after obtaining the protocol control, EPC number, and CRC values the interrogator can communicate directly with the tag to perform more complex operations, such as reading or writing memory, locking or unlocking the tag, or killing the tag.The physical link from the interrogator to the tag can function at different bit rates. Bit rates from 26.7 kbps up to 640 kbps are possible. This allows interrogators to communicate quickly with a tag under more favorable conditions, or slower to accommodate slower tags or in poor conditions. The variable data rate allowed in Gen-2 is an improvement over many Gen-1 systems, which supported only a single data rate preventing Gen-1 systems from adapting to the current environment 6. Variable data rates are useful in allowing for the worldwide operation of the Gen-2 protocol. For example, the regulations governing RF transmission require that interrogators listen to ensure the channel is clear before transmitting, reduc- ing the maximum data rate between the in