GTP Standardization
GTP was originally standardized within ETSI (GSM standard 09.60). With the creation of the UMTS standards this was moved over to the 3GPP which, as of 2005 maintains it as 3GPP standard 29.060. GTP' uses the same message format, but its special uses are covered in standard 32.295 along with the standardized formats for the charging data it transfers.
Later versions of TS 29.060 deprecate GTPv1/v0 interworking such that there is no fallback in the event that the GSN does not support the higher version.
GTPv2 (for evolved packet services) went into draft in early 2008 and was released in December of that year. GTPv2 offers fallback to GTPv1 via the earlier "Version Not Supported" mechanism but explicitly offers no support for fallback to GTPv0.
Read more about this topic: GPRS Tunnelling Protocol