2. Answer these questions: a) Explain why fast fading is a problem for mobile communications. b) How does IP deal with packets that do not fit into the maximum frame size supported by the Network Access Layer ? Explain in no more than . page. c) Explain how radio signals with frequencies between 2 MHz and 30 MHz can reach receivers at a very long distance (thousands of km). (in no more than . page.) d) Why do most ground-based satellite antennas have a parabolic shape ? Can you give an example of a satellite radio link that uses a dipole antenna for the ground station? Explain that choice. a. For mobile communication, the mobile station or user is likely to be moving, and as a result the path lengths of all the signals being received are changing. also many objects around may also be moving. Automobiles and even people will cause reflections that will have a significant effect on the received signal. Accordingly multipath fading has a major bearing on mobile communications. Fast fading as one of the multipath fading is a problem for mobile communication is because it occurs over a relatively short distance. b. fragmentate it to smaller size, add header then send it. IP allows fragmentation dividing the datagram into pieces, each small enough to pass over the single link that is being fragmented for, using the MTU parameter configured for that interface. This fragmentation process takes place at the IP layer and marks packets it fragments as such, so that the IP layer of the destination host knows it should reassemble the packets into the original datagram !c.!Signal!with!frequencies between 2 MHz and 30 MHz travels along sky wave. With the sky wave propagation, a signal from an earth based antenna is reflected from the ionized layer back down to the earth, a sky wave signal can travel through a number of hops, bouncing back and forth between ionosphere and earth’s surface thus can propagate thousands of kilometers from the transmitter. d.!Satellite!transmit!at!very!high!frequency,!the!optimal!frequency!range!for!satellite!transmission! is!1! to!10GHz.!Parabolic!antenna!achieves!higher!antenna!gain!when!frequency! increases(see! table!5.2).!Then!apply! to!path! loss!model,!with! such!high!frequency,! dipole antenna will have very small transmission range, while Parabolic!antenna!can!achieve!large!transmission!range.!Cross! dipole! or! turnstile! antenna! is! used! for! receiving! satellite! image! from! the!137MHz!band.!This! is!an!example! for!dipole!antenna.!We!can!see! the! frequency! is!low.!The!choice!lies!in!which!frequency!band!are!they!communication!with.!For!normal!satellite!communication,!I!will!choose!parabolic!antenna.!