The second generation air interface for communication between an RFID reader and tag, administered by EPCglobal Inc. (www.epcglobalinc.org). It deals with the modulation scheme, packet structure, command language and methods for dealing with collision.

Ratified in 2005, Gen 2 was a major enhancement that standardized on a single data link protocol and included support for worldwide spectrum regulations. It added read/write and tag disable functions, interoperability between devices and the ability for readers to work in close proximity to each other. See RFID and EPC.

Classes
Tags were given class numbers before Gen 2 was introduced and before the term Gen 1 was coined to refer to the earlier tags and protocols. Although Gen 1 tags are expected to fade into history, there were numerous articles written that mention them. Following is an approximate summary.

         Tag   Read/
 Gen 1   Type  Write  Bits     Features

 Class 0  P    RO     64-96    Locked security tag
 Class 0+ P    R/W    64-96    R/W and WORM
 Class 1  P    R/W    64-96


 Gen 2 

 Class 0 not specified - classes 1-4 can be locked

 Class 1  P    R/W    96-496   Commonly used
 Class 2  P    R/W    96-496   Authentication
 Class 3  SP   R/W    96-496   Integrated sensing
 Class 4  A    R/W    96-496   Ad hoc networking

 P=passive;  SP=semi-passive;  A=active
 RO=read only;  R/W=rewritable
 WORM=write once read many