(a) Customary practice. Under Federal law (Rule 28(b), Rules of Civil Procedure for the District Courts of the United States) and under the laws of some of the States, a commission to take depositions can be issued to a foreign official or to a private person in a foreign country. However, this method Is rarely used; commissions are generally issued to U.S. consular officers. In those countries where American consular officers are not permitted to take testimony (see 192.55(c)) and where depositions must be taken before a foreign authority, letters rogatory are usually issued to a foreign court.