A typical geostationary satellite might have twenty-four 36 MHz Ku-band transponders, linear polarized. It may or may not also have C-band transponders which can be either 36 MHz or 72 MHz.
In Ku-band, if you have a SCPC link composed of two high-end SCPC modems (Comtech EF Data, Newtec, etc), two very powerful SSPAs and two 12 to 14 meter size dishes you can do OC-3 bandwidth, or 155 Mbps full duplex. This will require a full 36 MHz transponder dedicated to your link, so it's a configuration only seen rarely. You would essentially be leasing 1/24th of the satellite's total transponder capacity. This only works with very large earth stations due to the path loss involved and the link budget required to use 32APSK modulation. If you cannot do 32APSK due to weak Tx power or smaller dish size, it may work at 16APSK/16QAM but at lower data rates.
It is rare to see an entire 36 MHz transponder dedicated to an SCPC link between two giant earth stations, so more typically it will be divided up into slices between guard bands, used by dozens of different customers' point to point or TDMA networks. Because these serve smaller remote VSATs, modulation will typically be 8PSK or worse, so the overall data throughput of a full 36MHz transponder serving multiple small VSAT networks in a particular area will be much worse than 155Mbps full duplex.
tl;dr: one $200 million 6000 kilogram satellite has much less data capacity than a two strand fiber optic cable using a few wavelengths of DWDM. 24 x 155 Mbps is much less throughput than two strands multiplied by 10Gbps full duplex per wavelength x 40 wavelengths.
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