Extended Channel Interpretations (ECI)  Introduction:

Barcodes and other data carriers can convey general-purpose text (as opposed to serial-numbers, etc.), and this leads to both the opportunities and the difficulties in supporting international character sets. 
The mapping of graphical characters to binary form varies between countries and even between computer operating systems.
A protocol is required to convey the identity of the coded character set (i.e., the graphical characters) that was intended when the bar code was printed. 

To make practicable use of compression and encryption schemes in high capacity data carriers, a protocol is required so that the receiving system is aware that the decoded data needs some specified expansion and/or decryption processing before its content can be used. 

Many high-capacity data carriers provide structured append modes where the concatenated data can exceed the storage capacity of practicable reading equipment. Thus a standard protocol is required so that symbols scanned out-of-order can be identified and sequenced correctly at the receiving system. 

Recognising the need to provide guidance to data carrier designers and systems implementers, AIM Inc. defines in this document two Reference Models for data interchange in bar coding systems: 

The Basic Channel Model (BCM) describes the functional components that co-operate to convey a message via a traditional bar coding system, and also the data flows between these components.

The Extended Channel Model (ECM) adds a processing layer to the front and back ends of the Basic Channel, to enable ECI-capable data carriers to convey both the message and information about that message (i.e., what coded character set was used; whether the message is encrypted). 

AIM Inc. has defined a new protocol for utilising the new facilities provided by the Extended Channel Model. 
The ECI protocol is based on the GLIs defined in the original AIM PDF417 specification and was extended to be data carrier independent during the development of the MaxiCode and Data Matrix standards. 
It is now supported by many data carriers.

The technical standard defines the Extended Channel Interpretation (ECI) protocol, and specifies methods for using ECI escape sequences within this protocol to convey Extended Channel information.