"According to ITU-R Recommendation SNG.770-1@ Satellite News Gathering (SNG) is defined as ""Temporary and occasional transmission with short notice of television or sound for broadcasting purposes@ using highly portable or transportable up-link earth stations ..."". EN 301 210 [2] describes the frame structure@ channel coding and modulation system for Digital Satellite News gathering (DSNG). For SNG technical and/or programme co-ordination@ and interruptible feed-back@ ITU-R Recommendation SNG.771-1 recommends ""that SNG earth stations should be equipped to provide two-way satellite communication circuits which must be available prior to@ during and after@ the transmission of the vision and associated sound or sound programme signal. These circuits will provide communications between the SNG operator@ the satellite operator and the broadcaster; that two or more duplex circuits should be provided@ whenever possible within the same transponder as the programme vision and associated sound or sound programme signal"". The same Recommendation considers ""that throughout the world@ where news events take place@ uniform technical and operational standards for communication should be established to ensure prompt activation of the SNG service"". The availability of co-ordination (communication) circuits by satellite may be particularly useful in areas where access to the public switched or cellular telephone networks is difficult or impossible. For these purposes@ the same antennas of the DSNG stations may often be used@ and the same frequency resources (or at least the same satellite transponder) as the main DSNG signal may be exploited. Other frequency resources may also be chosen according to the operational conditions and requirements. To achieve a two-way (i.e. full-duplex) communication channel@ two independent carriers have to be transmitted@ one from the DSNG terminal@ the other from a fixed station. Depending on the service requirements@ various scenarios are possible@ some of which require reduced communication capacity@ others are more demanding (in terms of the number of required connections and up-link facilities). Figure 1 shows two examples of implementation of the co-ordination channels between the DSNG terminal@ the broadcaster@ the DSNG operator (when required) and the satellite operator: Scenario A (two up-links for co-ordination carriers): the DSNG terminal and a central station (e.g. the broadcaster's fixed station) up-link a single co-ordination carrier each@ containing U multiplexed circuits. In this scenario@ the terrestrial infrastructure (e.g. PSTN) is used to forward the co-ordination circuits from the central station to the DSNG operator and the satellite operator and the co-ordination equipment at the DSNG terminal has to transmit and receive a single co-ordination carrier. Scenario B (four up-links for co-ordination carriers): the DSNG terminal up-links a single co-ordination carrier@ containing three multiplexed channels (U=3)@ while the broadcaster@ the DSNG operator and the satellite operator up-link a total of three co-ordination carriers@ each with a single circuit. In this scenario@ the co-ordination equipment at the DSNG terminal has to transmit a single co-ordination carrier@ and to receive three carriers at the same time."