Digital local, transit, combined and international exchanges in integrated digital networks and mixed analogue-digital networks : supplements: recommendations Q.500-Q.554 / International Telecommunication Union
Interworking of signalling systems : recommendations Q.601-Q.699 / International Telecommunication Union
Specifications of signalling system No. 7 : recommendations Q.721 - Q.766 / International Telecommunication Union
Specifications of signalling system No. 7 : recommendations Q.771 - Q.795 / International Telecommunication Union