The original release of the EIA/TIA-95-B standard defined the protocol messages and formats to be used in the CDMA system. This release is know as Revision 0 of the IS-95 standard. Since the release of Revision 0, a newer standard has been released for cellular CDMA that is called the Revision A standard of IS-95.
The IS-95-A standard is backward compatible with the original Revision standard. However, it introduces a number of new messages, service options and new addressing modes. IS-95-A now supports more powerful protocol methods that expand the paging, handoff and system parameter message capabilities of the CDMA system.
In addition, a new phone addressing method has been added that is based on the International Mobile Station Identity (IMSI) rather than MIN or ESN. IMSI’s are currently used by the GSM system and the adoption of this addressing mode will give CDMA a smoother integration path into international systems.
The IS-95A cellular protocol has been further upgraded to include 14400 bps traffic channels. This is called the TSB-74 protocol standard.