g., whether the reader contacts the host or the host contacts the
reader), initialization messages required to establish synchronization, and means for provisioning
of con?¬?guration information.
The speci?¬?cation also de?¬?nes two message channels: a control channel (carries requests
issued by the host to the reader, and responses from the reader back to the host) and a
noti?¬?cation channel (carries messages issued asynchronously from the reader to the host).
The protocol speci?¬?cation can conceptually be divided into subsystems, the read subsystem
(which consists of Sources [read tags], ReadTriggers [initiate read operations], and
TagSelectors [de?¬?nes and maintains a list of ?¬?lter patterns], and acquires data from one or
more tags from a single source called a read cycle), event subsystem (provides event
smoothing, for example, when a tag ?¬?rst enters or leaves the RF ?¬?eld), the output subsystem
(which determines what data to communicate with the host), and the communication
subsystem (which consists of a speci?¬?c MTB). The speci?¬?cation contains a list of commands
(or functions) along with parameters (data ?¬?eld) and objects (variables). Also de?¬?ned are
a number of MTBs.
2.7 Low-Level Reader Protocol
The Low-Level Reader Protocol (LLRP) (EPCglobal, 2007e) de?¬?nes a protocol to provide
control of RFID air protocol operation timing and access to air protocol command parameters,
and is the second generation of the Reader Protocol de?¬?ned earlier.
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