Using the spectral allocation of Fig. $2-46$ and the information given in the text, how many Mbps does a cable system allocate to upstream and how many to downstream?With six satellite necklaces, the entire earth is covered, as suggested by

Fig. $2-52($a$).$ Here we see a caller

at the North Pole contacting a satellite directly overhead. Each satellite has four

neighbors with which it can communicate, two in the same necklace $($shown$)$ and

two in adjacent necklaces $($not shown$).$ The satellites relay the call across this grid

until it is finally sent down to the callee at the South Pole.

An alternative design to Iridium is Globalstar. It is based on $48$ LEO satel$-$

lites but uses a different switching scheme than the one used by Iridium. Whereas

Iridium relays calls from satellite to satellite, which requires complex switchingFigure $2-52.($a$)$ Relaying in space. $($b$)$ Relaying on the ground.