The CCITT considering (a) the operational provisions for the telex service and the gentex network indicated in Recommendations F.60 and F.20; (b) the overall subscriber-to-subscriber performance objectives; (c) the technical provisions in Recommendations R.57 and R.58 concerning standard limits of transmission quality; (d) the need to standardize the signalling functions in international/intercontinental transit exchanges; (e) the telex signalling specified in Recommendations U.1 (types A and B), U.11 (type C) and U.12 (type D); (f) the level differences existing among the type A, B, C and D signalling functions.