Although WAN connections are typically made through serial interfaces, not all serial links are connected to a WAN. Explain: The two most common types of circuit-switched WAN technologies are the public switched telephone network (PSTN) and the integrated services digital network (ISDN).
An astronaut is tethered by a strong cable to a spacecraft. The astronaut and her spacesuit have a total mass of 100kg , while the mass of the cable is negligible. The mass of the spacecraft is 9.50Ý104kg . The spacecraft is far from any large astronomical bodies, so we can ignore the gravitational forces on it and the astronaut.