TCP IP Illustrated

As an example we ping the host gemini from the host

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Unformatted text preview: example, we ping the host gemini from the host sun: sun % ping gemini PING gemini: 56 data 64 bytes from gemini 64 bytes from gemini 64 bytes from gemini 64 bytes from gemini 64 bytes from gemini 64 bytes from gemini bytes (140.252.1.11): (140.252.1.11): (140.252.1.11): (140.252.1.11): (140.252.1.11): (140.252.1.11): icmp_seq=0. icmp_seq=l. icmp_seq=2. icmp_seq=3. icmp_seq=4. icmp seq=5. time=373. time=360. time=340. time-320. time=330. time=310. ms ms ms ms ms ms file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/pingprog.htm (6 of 13) [12/09/2001 14.46.45] Chapter 7. Ping Program 64 bytes from gemini (140.252.1.11): icmp seq=6. time==290. ms 64 bytes from gemini (140.252.1.11): icmp_seq-7. time=300. ms 64 bytes from gemini (140.252.1.11): icmp_seq=8. time=280. ms 64 bytes from gemini (140.252.1.11): icmp_seq=9. time=290. ms 64 bytes from gemini (140.252.1.11): icmp_seq=10. time=300. ms 64 bytes from gemini (140.252.1.11): icmp_seq=ll. time=280. ms --gemini PING Statistics-12 packets transmitted, 12 packets received, 0% packet loss round-trip (ms) min/avg/max = 280/314/373 Note that the first RTT is not a multiple of 10 ms, but every other line is. If we run this numerous times, we see this property every time. (This is not caused by the resolution of the clock on the host sun, because we know that its clock provides millisecond resolution from the tests we run in Appendix B.) Also note that the first RTT is larger than the next, and they keep decreasing, and then they range between 280 and 300 ms. If we let it run for a minute or two, the RTTs stay in this range, never going below 260 ms. If we calculate the expected RTT at 9600 bits/sec (Exercise 7.2) we get 180 ms, so our observed values are about 1.5 times the expected value. If we run ping for 60 seconds and look at the average RTT it calculates, we find that with V.42 and V.42bis our average is 277 ms. (This is better than the average printed for our preceding example, because we ran it longer to amortize the longer RTTs at the beginning.) If we turn o...
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