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aFor rates less than 1544 kbps, it is possible to use any n x 64 kbps information rate without overhead, but the only INTELSAT-recommended rates are 64, 192, and 384 kbps. The use of the optional Reed-Solomon outer coding is not defined for any information rate less than 1.544 Mbps, which does not use overhead.

b The optional Reed - Solomon outer coding can be used with the information rates shown with an "X."

cThe carriers in this column are small IDR carriers that can be used with the circuit multiplication concept described in Appendix B of the reference publication. [For a definition of the IBS overhead framing, see IESS-309 (IBS).]

dX = Recommended rate corresponding to the type of overhead.

eThese are standard ITU-T hierarchical bit rates. Other n x 64 kbps information rates above 1.544 Mbps are also possible and must have an ESC overhead of at least 96 kbps (the overhead framing will be defined on a case-by-case basis by INTELSAT). Source: Table 1, INTELSAT IESS-308, Rev. 7 (Ref. 1).

For certain information rates—namely, 1.544, 2.048, 6.312, 8.448, 32.064, 34.368, and 44.736 Mbps—an overhead structure has also been defined to provide engineering service circuits (ESCs) and maintenance alarms. This overhead increases the data rate of these carrier sizes by 96 kbps. The overhead adds its own frame alignment signal and thus passes the information data stream transparently. For the provision of ESC and alarms on IDR (intermediate data rate) carrier sizes larger than 1.544 Mbps, and overhead of 96 kbps must be used. For other information rates larger than 1.544 Mbps that are not listed above, INTELSAT will determine the overhead framing structure on a case-by-case basis.

The occupied satellite bandwidth unit for IDR carriers is approximately equal to 0.6 times the transmission rate.* To provide a guardband between

*The transmission rate (R) is defined as the bit rate entering the QPSK modulator at the earth station (i.e., after the addition of any overhead or FEC) and is equal to twice the symbol rate at the output of the QPSK modulator.

TABLE 7.2 IDR Performancea

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