1、Rec. ITU-R S.521-4 RECOMMENDATION ITU-R S .52 1-4 HYPOTHETICAL REFERENCE DIGITAL PATHS FOR SYSTEMS USING DIGITAL TRANSMISSION IN THE FIXED-SATELLITE SERVICE 1 (1978-1982-1986-1997-2000) The ITU Radiocommunication Assembly, considering a) afford guidance to designers of equipment and systems for use
2、in networks employing digital transmission techniques; b) cl d) - on-board processing with regeneration, - e) that the transmission delay variation introduced by satellite movement is of significance in some applications but the buildout of such delay variations to their worst case to provide consta
3、nt delay is outside the scope of this Recommendation: that it is desirable to establish hypothetical reference digital paths (HRDPs) for active fixed-satellite systems to that satellite-to-satellite links may be used in the fixed-satellite service (FSS); that both geostationary and non-geostationary
4、-satellite systems will be part of the FSS; that some satellite systems include: on-board processing with regeneration and switching on the satellite; f) that a FSS HRDP may form part of a hypothetical reference connection (HRX) as defined by ITU-T Recommendation G.801, Fig. 1; g) contiguous portion
5、s of a HRX; h) single HRX; j) k) that satellite links may appear in the local, national, or international portion and combinations of two or more that inter-satellite links (ISLs) among geostationary satellites and non-geostationary satellites may be part of a that a HRDP may include one or more int
6、ermediate space-to-Earth and Earth-to-space segments; that a HRDP may be independent of connections to the terrestrial network, recommends 1 connected to terrestrial networks; 2 portion may comprise one or more ISL; 3 more than one satellite, but in each case there may be only one satellite; 4 consi
7、dered as part of the terrestrial network and should not be included in the HRDP; 5 equipment necessary for connecting the diversity earth stations to the diversity switching point; that a generic HRDP shown in Fig. 1 should be used to describe satellite connections which may or may not be that a HRD
8、P for systems in the FSS should consist of one or more Earth-space-Earth links, whose space that the example HRDPs shown in Annex 1 can be used to describe satellite connections. These Figures show that links between the earth stations and their associated terrestrial digital switching centres shoul
9、d be that for site diversity earth stations, the HRDP should also include the terrestrial links and any associated 6 demultiplex equipment at the customer terminal or earth station; 7 that the HRDP includes RFDF, demodulation/modulation, error correction, buffer, processing, and multiplex/ that term
10、inal equipment or switch nodes may interface a HRDP at any bit rate. 2 Rec. ITU-R S.521-4 FIGURE 1 Generic HRDP UNI, NNI or equivalent Satellite link UNI, NNI or equivalent switch node c El station El station 4: switch node SAT: space stations in the FSS, or space station in the service interconnect
11、ed by satellite-to-satellite links NNI: network-node interface UNI: user-network interface TE: terminal equipment 052 1-01 NOTE 1 - For satellite networks where earth station processing is integrated with dynamic allocation and rearrangement of capacity across the satellite link, the equipment to pe
12、rform that processing should be regarded as part of the satellite HRDP. This processing may also include functions for: - - performance improvement, - NOTE 2 - Customer terminal equipment which would be required to support the particular service(s) being offered regardless of the transmission medium
13、 it is connected to is assumed to be outside the satellite HRDP. NOTE 3 - The HRDP considered in this Recommendation applies to public networks only. Network operators may use these HRDPs for their private networks. NOTE 4 - The HRDP in this Recommendation is not limited to point-to-point services b
14、ut may be used for multipoint and asymmetric services. NOTE 5 - The need for additional HRDP examples to encompass the range of new digital satellite systems is for further study. NOTE 6 - This Recommendation does not address allocation of performance objectives to the HRDPs. It is recognized howeve
15、r that the same HRDP may be used to represent different satellite system configurations (e.g. on-board processing, earth station processing, non-processing transponder, ISL) which may require different performance allocations. NOTE 7 - This Recommendation does not apply for end-to-end links in the B
16、SS. efficient use of satellite bandwidth, service capabilities peculiar to the satellite system. ANNEX 1 The example HRDPs shown in Figs. 2 to 6 can be used to describe satellite connections. These Figures show more than one satellite, but in each case there may be only one satellite. The terminolog
17、ies used in the Figures are shown below: - UNI: user-network interface; - NNI: network-node interface; 3 r TE Rec. ITU-R S.521-4 - SAT: satellite station (including on-board processing/switching if used); - Earth station includes RFDF, modulation/demodulation, error correction, buffer, processing, m
18、ultipleddemultiplex equipment and interfaces to terrestrial networks. Figure 2 describes a HRDP which may be in the national or international portion of a HRX, with connections to the TE: terminal equipment (including processing, multiplex equipment, interfaces to earth station). Earth Earth Local s
19、tation station switch node r terrestrial network at both ends. FIGURE 2 Satellite HRDP (with connections to the terrestrial network of both ends) Figures 3 and 4 describe HRDPs which form part of a HRX, with connection to the terrestrial network. It includes a local portion to the customer terminal.
20、 The HRDP may be in the domestic or international portion. FIGURE 3 Satellite HRDP (with connection to the terrestrial network at one end) 0521-03 4 Rec. ITU-R S.521-4 FIGURE 4 Satellite HRDP ent Switch node station *SAT includes on-board processing/switching. a) With connection to the terrestrial n
21、etwork at one end, and with on-board processing/switching satellite UNI UNI orNNI / switch node I I “I station I czF /Rrrihl station or NNI switch node b) Including control path 052 1-04 Figure 4b) describes a HRDP including a control path associated with a control earth station that is part of the
22、satellite network. Rec. 1TU-R S.521-4 Figure 5 describes a HRDP which does not connect to the terrestrial network. FIGURE 5 Satellite HRDP (no connection to the terrestrial network) 5 052145 Figure 6 describes a HRDP which includes a space-to-Earth and an Earth-to-space link to an intermediate earth station for further processing, but the HRDP does not connect to the terrestrial network. FIGURE 6 Satellite HRDP (with intermediate earth station) I 0521-06
