hw9_solution.txt Page 1 1. Realtime video communication has several unique characteristics: 1) Dropped frames (pictures) are usually not retransmitted; 2) The data rate is constant; 3) The data frames are ordered. Discuss: a) Why TCP is not appropriate to support realtime video? b) If UDP is used, how to reorder the data frames? A. a) First, TCP retransmits dropped packets, which is not needed in realtime video streaming. Second, TCP responds to congestion by decreasing the transmission rate, which is negative to video streaming that requires constant rate. b) UDP does not provide sequence numbers, therefore, it is not able to handle packet mis-order. A simple way is to design a protocol that gives sequence numbers and performs reordering and let it run on top of UDP. 2. Suppose station A simultaneously maintains three TCP connections to station B, C and D. Discuss if station A can use the same TCP port for the three connections? If yes, how does station A distinguish packets from different remote stations? If no, briefly explain why.
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