T.I. has officially begun his 11-month stint in an Arkansas prison -- law enforcement sources tell TMZ the rapper checked in "sometime this afternoon."

If you recall, T.I. was sentenced to 11 months behind bars after his drug possession arrest on the Sunset Strip back in September -- an arrest that caused law enforcement officials to revoke his probation stemming from a federal gun conviction back in 2009.

A spokesperson for the prison tells us T.I. will go through the normal process -- which means he'll be processed, pose for a prison photo, and will be given a bunk assignment.

As for the shower issue -- we're told T.I.'s prison has a community shower situation.

We're told T.I. will have access to a television room for general viewing.

T.I. will be issued a standard prison uniform -- khaki trousers, khaki button down shirt and black shoes.

Inmates at the prison can make phone calls -- but they're limited to 300 minutes per month.