CHAPTER 29
WITNESSES
Witness from prison
205. A prisoner who is in a prison may be subpoenaed as a witness only if the court before which the prisoner is to appear as a witness authorizes that the prisoner be subpoenaed as a witness, and the court may give such authority only if it is satisfied that the evidence in question is reasonably necessary and material and that the public safety or order will not be endangered by the calling of the witness.
Other forms of cooperation
Cooperation under procedures of national law
Procedure for witness testimony - national proceedings
Temporary transfer of persons in custody for purposes of identification or for obtaining testimony or other forms of assistance - national proceedings
Assistance of States in the attendance and testimony of witnesses and production of documents
EDIT.