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University of Texas at Arlington @ CSE UTA An Ubiquitous Architectural Framework and Protocol for Object Tracking using RFID Tags Pradip De, Kalyan Basu and Sajal K. Das Center for Research in Wireless Mobility and Networking CReWMaN Department of Computer Science and Engineering The University of Texas at Arlington Arlington, TX 76019
PRESENTATION OUTLINE WHAT IS RFID ? APPLICATION AREAS MULTI-TAG READING COLLISION ARCHITECTURE AND TRACKING PROTOCOL DELAY ANALYSIS REFERENCES
What is RFID? • RFID as a technology.. • RFID TAGS (Transponders) • Tags consist of an Integrated Circuit (IC) and an Antenna • Tags can be as small as a grain of rice ! • Read Only or Read/Write or a combination of both • Active or Passive • Various Frequency ranges of operation • RFID Readers(Transceivers) • A Microcontroller based Interrogating Devices • Equipped with standard interfaces to interact with backend computing host systems
RFID Applications.. • RFID provides a quick, flexible and reliable electronic means to detect, track and control a variety of items • A Plethora of Application areas – • Pharmaceutical - embedded RFID tags in prescription bottles • Amusement Parks - Location Stations • Libraries and Video Stores – Theft Detection and Misplacement • Security – Hands Free Access to secured areas • Toll Payment at Roads and Bridges • Logistics and Supply Chain Management are the major areas where this technology is deployed
Checked Baggage passes under scanner RF tags incorporated into retail tickets
Multiple Tag Reading - Collision • What happens when multiple tags are in the reader’s range? • All tags will become excited at the same time • Reader cannot detect individual tags from each other • A Collision Avoidance Algorithm necessary • A Query Tree Protocol has been proposed by the MIT-AutoID Center • Basic Idea is to sequentialize the reading of multiple tags • Achieves an O(n) bound for reading ‘n’ tags • 2.881n – 1 <= E[Ts] <= 2.887n - 1 Ching Law, Kai Lee and Kai-Yeing Siu, Efficient Memoryless Protocol for Tag Identification. MIT AutoId Center, October 2000
Architecture • Objective of the Architecture • Basically a Distributed Tracking Architecture for Objects that are transacted between organizations • To harness RFID technology to provide automatic visibility and control over transacted items • Minimize delay and error incurred due to the involvement of human attendance
Architecture Components • A Few Terminologies defined… • Electronic Product Code • 96 bits • Hierarchical • A Data Routing Server • Data Capture, Data Monitor and Data Transmission • Physical Markup Language (PML) • Common Language for describing physical objects • Based on the syntax of XML • Every property of the object captured
Architecture Components • A Few Terminologies defined… • PML Server • Repository for all types of information regarding the objects • Homes both static and dynamic information • Global Mobility Server • Used to translate mobility queries into decisions • The execution is done with the help of the other components • Object Naming Service (ONS) • Similar in structure to the Internet DNS • Maps the EPC to the IP Address of its Home PML Server
Site2 Home Server Intranet Interior Area 2 Site-2 Gateway Server Org-B RFID Readers Gateway Server Data Routing Server-2 Org-A Internet Intranet Main Site Data Routing Server Inter Organization Network RFID Readers Interior Area Intranet Site-1 Site1 Home Server Data Routing Server-1 Interior Area 1 Tracking ArchitectureA High Level View
GW-PML GW-PML PML-s PML-s PML-1 SAV-m SAV-1 PML-1 SAV-m SAV-1 The Abstract Architecture Schematic Global Mobility Server Global Mobility Cache ONS Internet . . . . Org-1 Org-k ... ... Subnet-1 Subnet-s Subnet-1 Subnet-s ... ...
Application layer Mobility Management Model • TheMobility Management Protocol is fundamentally a discrete time mobility tracking mechanism • A simple use-case is to track Transfer of Shipment from source GW-PML (sG) to destination GW-PML (dG) • Mobile node (MN) is the highest level moving object • MN identifies the whole object encapsulation hierarchy e.g., Truck -> Pallets -> Cases -> Items • Mobility Tracking managed at two levels • Inter-GW-PML • Intra-GW-PML
Application layer Mobility Management Model • Initial Handshake between source GW-PML and destination GW-PML before transfer starts • During its transit, the MN’s current point of attachment is its care-of address (CoA) • Transfer ends when MN’s CoA is same as destination GW-PML • In course of this transit the MN might attach to several intermediate foreign GW-PMLs (fG) in between which would be updated accordingly • Care-of Address assignment is basically association of tag with current foreign GW-PML • This address can be made hierarchical to identify the foreign attachment point with the desired granularity
Inter-GW-PML Mobility Foreign GW-PML Home GW-PML Destination GW-PML Source GW-PML MN INVITE ACK UPDATE SRC-DEST / DURATION ESTIMATE ACK DETECT/ ASSOCIATE CoA UPDATE CoA ACK CoA/ SEND SRC-DEST ADDRESS REGISTER REGISTER-ACK INVITE-RELAY ACK-RELAY
Intra GW-PML Level Mobility • Within the domain of one single GW-PML • Micro-mobility scenario with more frequent movements and updates • Two types of movement • System Deliberated - Initiated by the GW-PML • System Non Deliberated – Involuntary !
GWPML PML-SRC SAV-DEST PML-DEST SAV-SRC RELOCATE TAG DETACH ACK TAG DEPARTED IMMINENT TAG ALERT TAG ATTACH TAG ARRIVAL ACK System Deliberated - Intra GW-PML Level
GW-PML PML-SRC SAV-DEST PML-DEST SAV-SRC TAG ATTACH NEW TAG ARRIVAL CONFIRM DEPARTURE QUERY TAG TAG DEPARTED ACCEPT TAG ARRIVAL OK System Non Deliberated - Intra GW-MMS Level
Object Tracking Protocol Messages • Start – This a Request Message to the receiver asking for the required amount of buffer for the mobility data that would be subsequently sent. • Start_Ack – Acknowledge the previous request, notifying the sender of the amount of buffer provided. • Tag_Data – The data message containing the tag mobility information. • Message_Ack – This acknowledges the correct receipt of the previous tag data. • Relocate– Message asserting departure of tag • Tag_Departed– Message confirming tag departure • Probe– Probe a node to check its state • Alive– Reply to a probe
Object Tracking Protocol Messages • Registration_Request– request message sent by a node at startup, to its parent in the mobility architecture hierarchy to initiate the process of identifying itself and establish a communication channel. • Registration_Grant – Grant of a registration request for a communication channel. • Grant_Ack– Finish the handshake by acknowledging the grant. • Subscription_Solicitation– A solicitation broadcast message sent by a node on startup, to its children, to announce its presence and seek their registration
INIT Recvd Start from SAV/ Send Start_Ack Recv Tag Info/ Update PM2T, Assert Flag System Initialized Recvd Relocate from GW-PML/ Send to SAV START RECV Message End from SAV && Flag = 0/ Send Message_Ack Tag Departed from EDM Message End from SAV && Flag = 1/ Send Message_Ack to SAV, Send Start to GW-PML Recvd Message_Ack from GW-PML RELOCATE Alive SAV Activity Period Timeout/ Send Probe REQ SENT PROBE SENT Recvd Start_Ack from GW-PML/ Send Tag Info to GW-PML Architecture Detail – Finite State Machine Finite State Machine of PML Server
INIT Recvd Start from PML/ Send Start_Ack Recv Tag Info/ Update IGWMT, Assert Flag System Initialized RELOCATE Relocate START RECV Tag Departed Message End from PML && Flag = 0/ Send Message_Ack Message End from PML && Flag = 1/Send Message_Ack to PML, Send Start to Home GW-PML Recvd Start from Remote GW-PML/Send Start_Ack Recv Message_Ack from Home GW-PML Alive Tag Rcvd/Update HGWMT, Send Message_Ack REQ SENT PML Activity Period Timeout/ Send Probe WAIT FOR TAG PROBE SENT Recvd Start_Ack from Home GW-PML/ Send Tag Info to Home GW-PML Architecture Detail – Finite State Machine Finite State Machine of GW-PML
System Initialization • Savant initialization • Send Registration Solicitation Message to well-known PML server and setup communication channel with it • PML Server Initialization • Send Registration Solicitation Message to well-known GW-PML • Broadcast Subscription SolicitationMessages to the attached Savants • Setup communication channels with both GW-PML and Savants • GW-PML Initialization • Broadcast Subscription SolicitationMessages to the attached PML Servers • Setup communication channels with the attached PML Servers
System Initialization PML Server SAV SAV Set GW-PML PML Server Registration Request Registration Request Broadcast Subscription Sol Registration Grant Registration Grant Reg Request Grant Acknowledge Grant Acknowledge Reg Grant Communication channel established Grant Acknowledge Communication channel established At SAV Startup At PML Server Startup At startup, the GW-PML follows the same steps as the PML server performs with the Savant set
Mobility Information Storage And Management • Mobility information updated in real-time by the management system • Update of location information is event-based • Mobility information stored hierarchically at the GW-PML and PML Server levels. • A system configurable time-point T (in the past) till when history information captured in real-time mobility databases • Beyond T, history information resides in archives separate from the mobility databases • Granularity of information in the stored archives may be less
Mobility Information Storage And Management • The ONS stores the address of the Home GW-PMLs • Each GW-PML stores the location history of the objects owned by it at the GW-PML level in a table called Home-GWMobility History Table (HGWMT) • The tag list in HGWMT is fairly constant • A cache called the Global Mobility Cache (GMC) associated with the Global Mobility Server (GMS), caches recently accessed objects and their location history from the corresponding GW-PMLs
Mobility Information Storage And Management • Each GW-PML also stores a second mobility management table called the Internal GW Mobility Management Table (IGWMT) • IGWMT captures the location history among the PML Servers under its purview • The tag list is variable depending on the number of objects in the domain in the allotted time frame • The IGWMT is hierarchical and extends down to the PML Server level • The PML Server level table is called the PMLMobility Management Table (PM2T) • The access down these tables is through hashed indices
GW-PML TAG PML . . . . . . PML TAG SAV . . INFORMATION DATABASE . . IGWMT PM2T Access of Internal Mobility Databases The Internal Tables are hashed according to the Tag keys
GW-PML GW-PML PML-s PML-s SAV-1 SAV-m SAV-m PML-1 SAV-1 PML-1 Location Storage Information – Overall View Home Address Table Global Mobility Service Global Mobility Cache . . . . HGWMT-1 IGWMT-1 Org-1 HGWMT-k IGWMT-k Org-k ... ... Subnet-1 PM2T-1 Subnet-s PM2T-1 PM2T-s PM2T-s Subnet-s Subnet-1 ... ...
Delay Analysis… • Delay incurred in sending ‘n’ EPC tags from a reader to the Home GW-PML • Assumptions made – • The connection from the Reader onwards to the Network is assumed to follow standard Internet Protocols • The Reader uses the Query Tree Protocol to read the tags • The tags arrive in batches at the readers • The inter-arrival time of the tag batches at the Readers follow a negative exponential distribution • The size of the packets (which is proportional to the number of tags in a batch) arriving at the Savant and PML Server also follow a negative exponential distribution. • The processing time of a packet is proportional to the size of the packet – thus negative exponential distribution Ching Law, Kai Lee and Kai-Yeing Siu, Efficient Memoryless Protocol for Tag Identification. MIT AutoId Center, October 2000
Delay Analysis… • The total delay equation is given by – Ttotal = E[TReader] + q * E[TSavant-PML] + (1 - q - p) * (E[TSavant-PML] + E[TPML-GW-PML]) + p* (E[TSavant-PML] + E[TPML-GW-PML + E[TGW-PML-HomeGW-PML) • p = prob that tag from different GW-PML • q = prob that tag from same PML server • E[TReader] = O(n) ≈ 2.88 * n • E[TSavant-PML] = Txdelay + E[TPML] / (1 - ρP) • Txdelay is the transmission delay of the packet containing the tag information • ρP is the average occupancy of the PML Server • E[TPML] is the average holding time at the PML Server
Delay Analysis… • E[TPML-GW-PML] = Txdelay + E[TGW-PML] / (1 - ρG) • E[TGW-PML] is the average holding time at the GW-PML • ρGis the average occupancy at the GW-PML • Txdelay is the transmission delay of the packet containing the tag information • E[TGW-PML-HomeGW-PML] = Txdelay + E[THomeGW-PML] / (1 - ρH) • E[THomeGW-PML] is the average holding time at the remote Home GW-PML • Txdelay is the transmit delay to the Home GW-PML which we assume as the average Internet Delay
Delay Analysis Results • The average Internet delay for a packet varies between 10 and 100 msec • 4 packets sent to complete one update • We consider only the packet containing the tag information • 96 bits for each of the EPC and Reader ID and a 32 bit timestamp value • Assuming a 1 Mbps data rate we get transmit delays ranging from 24 to 113 msec for transferring 100 to 500 tags. • average read rate of tags found to be around 800 – 1000 tags/sec PML SAV START START_ACK TAG_INFO MESSAGE_ACK Andrew Corlett, D. I. Pullin and Stephen Sargood, Statistics of one-way Internet Packet Delays. 53rd IETF, Minneapolis, March 18, 2002 http://www.matrics.com/products/readers.shtml
Future Work… • Extend the protocol to incorporate much needed security issues • Enhancement of the architecture to suit scenarios where surveillance and tracking is critical and intelligently predict intrusion or unwanted activities in such environments • Inclusion of several application services above this architecture • Inter-operate this tracking technology with other mobility management systems (e.g.,cellular network) to obtain continuous time mobility
References • The Association for Automatic Identification and Data Capture Technologies. http://www.aimglobal.org/technologies/rfid/ • RFID Journal. http://www.rfidjournal.com/ • Kai-Yeing Siu, Ching Law and Kayi Lee, Efficient Memoryless Protocol for Tag Identification. MIT Auto-Id Center, October, 2000 • MIT Auto-ID Center Publications at http://www.autoidcenter.org/ • R. Bridgelall. Enabling mobile commerce through pervasive communications with ubiquitous RF tags; WCNC, 2003 • V. Stanford. Pervasive computing goes the last hundred feet with RFID systems; Pervasive Computing, IEEE, Volume: 2, Issue: 2, April-June 2003 Pages: 9-14 • The Savant - Version 0.1 (Alpha), Technical Manual. Oat Systems and MIT Auto-Id Center, February, 2002 • David L. Brock, The Physical Markup Language - A Universal Language for Physical Objects. MIT Auto-Id Center, February, 2001 • Mark Harrison et al, PML Server Developments, White Paper. MIT Auto-Id Center, June, 2003