Geostationary satellite And Global Communication 

A satellite which is at rest with respect to the Earth is known as geo-stationary satellite.
Geostationary satellite rotates in the direction of rotation of Earth (West to East) about its own axis and completes one revolution in 24 hours.
It is kept at a height of 36,000 km above the Earth's surface in equatorial plane.
Under these conditions, the satellite appears stationary from Earth surface.
  Hence known as geo-stationary satellite.

Global Communication
A geostationary satellite can establish can establish a communication link over some part (40%)
of the Earth  but a single satellite can not cover the total part (100%) of the Earth.
This is due to curvature of Earth.
So, at least three satellites kept in stationary orbit are required to give communication link to cover total part of Earth as shown in fig.
Each geo-stationary satellite is 120 degree apart from each other.

So Guys, Here we can define Global communication -
Using three Geostationary satellite placed at the vertices of an equilateral triangle in equatorial plane,
the entire Globe (Earth) can be linked covered by the communication network an this is know as Global Communication.

Each satellite covers  one third of the globe (Earth).

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