13. Recommendation G.772 DIGITAL PROTECTED MONITORING POINTS Note - The detailed requirements contained in this Recommendation are applicable to the 2048kbit/s hierarchy. The application of the principles defined in this Recommendation to the 1544kbit/s hierarchy is for fur- ther study. 1. Definition A protected monitoring point provides a digital interface at which it is possible to monitor the transmitted signal and to make measurements with suitable test equipments [1]. 2. Location The possible locations for protected monitoring points can be: a) at the output ports of an equipment, b) in the signal path between equipments. Some examples are shown in Figure 1. 3. Electrical characteristics of the protected monitoring point Note - The reference for all parameters associated with protected moni- toring points shall be the relevant output interface as defined in RecommendationG.703. (See Figures 1 and 2.) 3.1 Impedance The load impedance presented by the test equipment at the protected monitoring point is the nominal impedance for the corresponding trans- mission path interface as defined in RecommendationG.703. 3.2 Attenuation The attenuation between the transmission path interface and the protected monitoring point, when the impedance presented by the test and measur- ing equipment connected to the protected monitoring point is equal to the nominal impedance for the relevant interface as defined in RecommendationG.703, shall be A + 1dB for all frequencies in the range 2.5% to 150% of the nominal bit rate at the interface. Different values may be necessary at different nominal bit rates. The value of A is under study. The digital signal level presented at the transmission path interface of the protected monitoring point shall be as defined in RecommendationG.703 but modified by the characteristics of the interconnecting cable. The attenuation of the cable shall be assumed to follow a _f loss and the loss X at a frequency equal to both the nominal bit rate is given below: 0 < X < 3 dB for 64 kbit/s 0 < X < 6 dB for 2 and 8 Mbit/s 0 < X < 12 dB for 34 and 140 Mbit/s Note - For a protected monitoring point device at an equipment output port, as described in Figure1a, the value of X is 0dB. 3.3 Protection of the PMP device 3.3.1 The protection of the protected monitoring point device against electrostatic discharges shall accord with the requirements of CCITT RecommendationK.y [3] and IEC Publication801.2 [4]. 3.3.2 No damage shall result from the application of any load impedance, including short and open circuits, to the protected monitoring point. 3.3.3 The protection against the inadvertent application of voltages to the protected monitoring point is under study. 4. Electrical characteristics of the transmission path interface Note - The reference for all parameters associated with the transmission path interface shall be the relevant output interface as defined in RecommendationG.703. 4.1 Impedance The transmission path interface shall have the nominal impedance as defined in RecommendationG.703 for the relevant bit rate output inter- face. 4.2 Return loss With the transmission path interface terminated with its nominal imped- ance, the return loss shall comply with the requirements defined in RecommendationG.703 for the relevant bit rate output interface. This shall apply with any value of load impedance, including short and open circuits, applied to the protected monitoring point. 4.3 Attenuation The attenuation in the transmission path, when the transmission path interface is terminated in its nominal impedance, shall be less than YdB (see Figure2) for all frequencies in the range 2.5% to 150% of the nomi- nal bit rate, when the protected monitoring point is terminated in any load impedance, including short and open circuit. The value of Y is for further study, 1dB has already been proposed. 4.4 Impact of the protected monitoring point on the maximum cable length The introduction of a protected monitoring point as described in Figure1b with an attenuation of YdB will effectively reduce the maxi- mum attenuation allowed for in RecommendationG.703 by YdB. 4.5 Protection of the transmitted signal Under study. The degree of protection shall be specified in terms of an X% variation in the pulse mask of the signal on the transmission path when the protected monitoring point is terminated in any impedance including short and open circuit. FIGURE 2 Definition of A, X and Y REFERENCES 1. CCITT Recommendation "Maintenance terminology and definitions", Vol.IV, RecommendationM.60. 2. CCITT Recommendation "Physical/electrical characteristics of hierar- chical digital interfaces", Vol.III, RecommendationG.703. 3. CCITT Recommendation "Resistability of subscribers terminals to overvoltages and overcurrents", Vol.IX, RecommendationK.y. 4. IEC Publication, "Prescriptions relatives aux décharges électrosta- tiques", Publication801-2. 14. Supplement No. 32 Transfer of alarm information on 60-channel transmultiplexing equipment (Melbourne, 1988; referred to in Recommendation G.793) The text of this Supplement has not been included in the final report, but will be printed in the Blue Book at the appropriate place. 15. Supplement No. 33 Example of fibre design guidelines (diagrams used in Japan and the United Kingdom, referred to in Recommendations G.652 and G.634) The text of this Supplement has not been included in the final report, but will be printed in the Blue Book at the appropriate place. 16. Supplement No. 34 Temperature in underground containers for the installation of repeaters (referred to in Recommendation G.950) The text of this Supplement has not been included in the final report, but will be printed in the Blue Book at the appropriate place.