Difference: commission & letters rogatory

Commission	Letters Rogatory
An instrument issued by a court of justice, or other competent tribunal to authorize a person to take depositions, or do any other act by authority of such court or tribunal.	An instrument sent in the name and by authority of a judge or court to another, requesting the latter to cause to be examined, upon interrogatories filed in a cause pending before the former, a witness who is within the jurisdiction of the judge or court to whom such letters are addressed.
Issued to a non-judicial foreign officer who will directly take the testimony.	Issued to the appropriate judicial officer of the foreign country; such officer will then direct somebody in said foreign country to take down the testimony
Applicable rules of procedure are those of the requesting court; the rules of procedure in issuing a commission are entirely under its control.	The methods of procedure must, from the nature of the case, be altogether under the control of the foreign tribunal which is appealed to for assistance in the administration of justice.
Resorted to if permission of the foreign country is given.	Resorted to if the execution of the commission is refused in the foreign country.
Leave of court is not necessary.	Leave of court is necessary.