
126 CHAPTER SIX
Reader layer
The Reader layer defines the allowable content and format of messages sent between
the reader and host. This layer comprises the Open System Interconnection (OSI) Pre-
sentation and Application layers. The protocol specifically allows this layer to make use
of multiple MTBs, although a particular instance will use only one MTB at a time. Also,
regardless of the MTB, the reader can hold a conversation with only one host at a time.
Messaging layer
This layer lives on top of the Transport layer and is responsible for managing connec-
tions and security and for packaging the host commands and reader responses and noti-
fications so they can pass back and forth on the Transport layer. Any encryption,
authentication, or session management occurs in this layer. This layer describes how a
conversation between the reader and host starts and stops and defines the shape of the
frame, or the envelope in which messages pass back and forth. This layer is logically
identical to the OSI Session layer.
Transport layer
This is the lowest layer, and it describes either the services provided by an OS or the
hardware needed to support networking. It corresponds roughly to the OSI Physical,
Data Link, and Network layers. The Transport layer is the physical connection and the
networking connection between the reader and host—for instance, TCP over Ethernet
using Cat 5 cables, an RS485 network ...