Question

Q3) The goal of this question is to explore the impact of bit error rate (BER) on the packet error for multihop wireless networks. Assume a packet of size 512 bytes is transmitted across intermediate nodes until reaching its destination. Assume a communication channel has bit error rate (BER) = 10^-5.

What is the probability of packet receiving incorrectly over 50 links?

Answer 1

In the reference example implementation, the packet sending times are clocked to the integer multiples of RTT (see Figure 2-6). For example, Packets #2 and 3 are sent together at the time = 1 × RTT; packets #4, 5, 6, and 7 are sent together at the time = 2 × RTT; and so on. Obviously, this does not reflect the reality, as illustrated in Figure 2-1. Your task is to implement a new version of the TCP Tahoe simulator, so that segments are sent one-by-one, independently of each other rather than all “traveling” in the same array. When designing your new version, there are several issues to consider. Your iterations are not aligned to RTT as in the reference implementation, but you need to make many more iterations. How many? You calculate this as follows. We are assuming that the sender always has a segment to send (sending a large file); so, it will send if EffectiveWindow allows. Given the speed of the first link (10 Mbps) and the segment size (MSS = 1KB), you can calculate the upper limit to the number of segments that can be sent within one RTT. This yields your number of iterations per one RTT; the total number of iterations should be run for at least 100 × RTT for a meaningful comparison with the reference example. When your modified TCPSimulator.java invok