White paper:
Simple Lightweight RFID Reader Protocol (SLRRP)
Abstract This white paper provides an overview of the state of RFID reader network communications and outlines the enterprise networking environment in which the next generation RFID reader infrastructure will operate.
It then provides an
overview of the “network side” reader protocol currently being developed in the proposed IETF Simple Lightweight RFID Reader Protocol (SLRRP) Working Group. Lastly, the proposed SLRRP standard is compared to reader protocols developed under other standards bodies which do not adequately address the network complexities and reader control issues required by the next generation of RFID deployments.
February 2005
The information contained in this document represents the current view of Reva Systems on the issues discussed as of the date of publication. Because Reva Systems must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Reva Systems, and Reva Systems or its respective suppliers cannot guarantee the accuracy of any information presented after the date of publication. This white paper is for informational purposes only. All trademarks and registered trademarks are the property of their respective holders. © 2005 Reva Systems. All rights reserved.
Reva Systems, 100 Apollo Drive, Chelmsford, MA 01824 http://www.revasystems.com
Rev 003
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Introduction Radio Frequency Identification (RFID) is a technique whereby a device, known as an RFID 'reader', can remotely sense the presence of, and access embedded memory on, a transponder, known as a 'tag'. Particular attention has been recently focused on new-generation RFID technology employing low-cost, uniquely serialized, passive tags operating in the worldwide unlicensed UHF spectrum. Early adopters of this technology from a wide variety of industries (including retail, military, healthcare and manufacturing) are very enthusiastic about the potential of RFID to create operational efficiencies, enhance safety factors, deter counterfeiting, reduce cost and enable new processes.
Emerging Network-Centric RFID Readers were originally operated as peripherals, typically connected to a host computer via a serial port, to support a dedicated application. Such a configuration is referred to as application-centric. This approach can provide adequate functionality for deployments involving modest numbers of readers performing a specific, targeted business function. To accommodate production implementations on a larger scale, a new generation of readers is being developed. These networked devices support TCP/IP stacks connected via wired (Ethernet) or wireless (802.11) LAN technology. A network of readers serves up required RFID data to a variety of RFID-enabled client applications running on enterprise computing resources. We refer to this configuration of readers as network-centric. In some ways, this evolution resembles the transition that occurred in the very early days of computer networking. At that time, each new "application" of connected computing required an entirely new network to be setup and configured. As the need for more and more such networks grew, the cost and complexity of this approach became overwhelming. Organizations were compelled to evolve their approach to networking, eventually deploying a single, shared "infrastructure," to which computers and/or devices created connections as their applications required. In much the same fashion, a network-centric RFID infrastructure will support the acquisition and presentation of tag data for a variety of application needs, enterprise-wide; in essence, the RFID equipment will become a “tag acquisition network,” and this network will become an integral part of any robust enterprise computing environment. We envision a typical RFID deployment comprising a network of RFID readers controlled by one or more Reader Network Controller (RNC) elements. RNCs provide the control and data path interface to a reader network and may be software/middleware on a server, embedded software in a router/switch, or a standalone device. The RNCs are connected to hosts/servers running client applications or integration middleware that consume the acquired tag data. (See Figure 1.)
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Figure 1: RFID Infrastructure Network Tags
Client
IP Network Client
RNC
Readers
RNC Client
RNC
Client
RNC
RF
IP Network
Tags
Readers Tags
Need for Standards The requirement for air protocol standards governing the interaction between readers and tags (e.g. EPCglobal UHF Gen2, ISO 18000) that enable readers and tags from different manufacturers to co-exist and interoperate has been clear for some time. Significant progress has been made in reaching agreements on these standards. These standards will allow users to buy the most cost-effective tags available, with the knowledge that they and their trading partners will be able to read the tags globally, no matter which brand of reader they install. Standard protocols for the over-the-air transmissions enable this and have been promulgated by ISO, EPCglobal and others. Enterprises that deploy readers want the ability to choose the best reader for each function or location (dock door, conveyor belt, shelf, etc.). In addition to supporting the required air protocols, it would be beneficial to the user if the readers had the same “network side” protocols. This would permit users to substitute readers based on cost and performance, and would enable reader vendors to introduce new models of readers quickly and efficiently, saving the costs of proprietary protocol development. Furthermore, application and middleware vendors currently have individual requirements for accessing RFID data which translate into a growing burden on RFID equipment manufacturers to support not only their own, but their partners’ proprietary interfaces as well. A standard network side protocol would benefit vendors who produce RFID data-consuming applications and integration frameworks by speeding time-to-market and easing the effort to implement solutions. Proposals for network-side protocol standards have begun to emerge from the various world standards bodies (ISO, IETF) as well as the EPCglobal consortium.
“Network-Side” Standards Development ISO developed the first standards for communicating with RFID readers. In Specifications 15961 and 15962, ISO defines sophisticated tag data access mechanisms for the ISO 18000 family of air protocols. While these were the first standards to be developed, they have not achieved widespread commercial acceptance. This is primarily because they were conceived before the advancing requirements of network-centric RFID emerged and therefore focus on a single family of air protocols and the limited control capabilities that those protocols
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provide. More recently, EPCglobal has undertaken the development of a standardized interface between readers and applications. This interface is known as the “Reader Protocol” or RP. The first version of this protocol is commonly referred to as RP1.0. The initial thrust of RP is to capture, with a common interface, the general functionality commonly found in the current generation of RFID readers in the marketplace. Since the new air protocols are significantly advanced, it is doubtful that many reader manufacturers will implement RP1.0 because it cannot leverage the improvements that new readers will be capable of delivering. By design, RP is an application-centric protocol; it was developed as a high-level protocol, with HTTP and XML interfaces. These interfaces support services designed to off-load processing functions from the applications, thus providing applicationcentric operation. RP’s scope can be summarized as reading and writing tag ids and killing tags. The RP1.0 specification does not seek to provide the access or control capabilities that network-centric operations will require. SLRRP is a reader protocol that has been designed for use in enterprise IP networks. The primary goals are to convey configuration, control parameters, pass status, and transfer tag information to and from multi-protocol RFID readers. SLRRP is meant to be lightweight, enabling low cost reader implementations while providing a networkcentric interface that addresses scalability and flexibility in the following dimensions: • Air protocols: SLRRP provides an extensible mechanism to support existing and new air protocols developed in any standards body. • Reader density: SLRRP uses efficient encoding which provides a high performance solution to tackle the protocol processing overhead at the RNC and thus respond to the real-time requirements for reactive control of RF/airprotocols, as the reader density increases. • Diversity of Reader control capabilities: SLRRP provides a very granular interface for control of RF and air-protocol parameters to accommodate the spectrum of reader control requirements. At one end, there are readers which when provided hints of the target tag/RF environment can autonomously control the air-protocol/RF parameters. At the other end, there are readers that require real-time hand-holding in terms of air-protocol/RF parameters. And, there is a continuum in between. • Diversity of application requirements: There are a number of applications that access the RFID infrastructure. “Access” may mean gaining visibility into the tag data and/or performing other tag access operations like lock/unlock/write/kill. Multiple application requirements translate into a set of access operations that a reader or a set of readers perform on tags as and when they are observed. SLRRP provides a versatile interface to create and manage tag access rules at the readers. • Diversity of tag capabilities: Tags from different tag manufacturers may have a different set of capabilities. This is important, especially for tags built to the Class 1 Gen 2 air-interface standard which has a number of features that are optional. Tag manufacturers will have proprietary extensions based on these optional features. The capabilities of these tags can be ascertained based on TID1 look-ups, and SLRRP provides a flexible interface to allow for this. 1
TID is equivalent to the tag’s make or model number.
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How Do the Standards Compare? The table on the last page highlights the key areas of difference between the three main options for a standardized reader protocol: SLRRP, RP, and ISO 15961/2. Only those elements that are substantially different between the protocols are highlighted in the table. Areas of commonality have been left out, in the interests of brevity. The primary differences between the protocols are in three areas: air protocol support, parameter control, and access capabilities. SLRRP is intended to be air protocol-agnostic and designed to support all common air protocols (including: EPCglobal Gen 1 and Gen 2, and ISO). SLRRP provides granular control of the airprotocol and RF parameters. EPC RP has no interface to control the air-protocol and RF parameters. SLRRP provides a very flexible interface to create and manage tag access rules at the reader. EPC RP has no support for creating and managing tag access rules at the reader. Moreover, EPC RP is designed to support only read, write and kill operations.
Conclusion The RFID market is evolving rapidly. Prototype and pilot projects are demonstrating the potential of RFID-based systems, and larger scale deployments of these systems are being undertaken, involving a large and increasing number of readers. In largescale deployments, the RF bandwidth and the reader processing power become valuable resources; managing them efficiently introduces complex new challenges in the RFID infrastructure. The SLRRP reader protocol provides a flexible, lightweight control and data path interface to efficiently manage readers and collect the tag information harvested by those readers. We believe SLRRP plays a key role in meeting the challenges posed by large-scale, network-centric RFID deployments.
Next Steps At this time, the Standard Lightweight RFID Reader Protocol effort is in the exploratory phase within the IETF process. A mailing list has been established to provide the primary discussion forum for current activities. The proposed Working Group Charter and initial Internet-Draft for SLRRP may be obtained by joining the mailing list. For more information on the mailing list and to subscribe, please visit: https://www1.ietf.org/mailman/listinfo/rfid To download the latest Internet-Draft, please access the “RFID Archives” link on this page.
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Protocol Comparison
Only significant differences between SLRRP and the other reader protocols are noted. Descriptions are as currently specified. Expectations of future support are not included. Category
IETF SLRRP
EPCglobal Reader Protocol (R1.0)
ISO 15961/ 15962
Architecture to support multiple air protocols through extensible structure
Supports identification of air protocol and specific support for control and data access
Supports only basic tag id read, write, and kill for Class 0 and Class 1 tags.
Supports ISO 18000 Family tag read and write
None specifically. Generic Read, Write & Kill support
ISO 18000 Family
Air protocol codepoints supported:
EPCglobal C0 EPCglobal C1 EPCglobal C1G2 ISO 18006-a ISO 18006-b
Tag inventory operation
Interface allows for coarse-grained and finegrained control of the inventory operation.
Only control available is Only control available is the duration of the read the duration of read cycles. cycles.
Singulation and RF control per air protocol
Yes
No
No
RF interface control (e.g., tx power, rx sensitivity)
Yes
No
No
TID Support
Yes
No
No
Tag access operation
No interface to create Interface allows for access operation rules to tag access rules at the be created and managed reader. at the reader.
No interface to create tag access rules at the reader.
Tag Filter parameter specification
Per air protocol, includes filtering on any memory content for C1G2.
Filtering on tag id
Filtering on AFI
Tag memory lock
Yes – per air protocol support
No
Yes
Tag user memory access
Yes
No
Yes
Power over Ethernet management support
Yes
No
No
Connection establishment
Reader-initiated
Host-initiated
Not defined in 15961/ 15962
Multiple Antenna Support
Yes
Yes
No
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