TCP IP Illustrated

Time390 ms 64 bytes from 128321302 icmpseq14 time110

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Unformatted text preview: ime=390. ms 64 bytes from ( icmp_seq=14. time=110. ms 64 bytes from ( icmp_seq=15. time=170. ms 64 bytes from ( icmp_seq=16. time=100. ms ^? type interrupt key to stop ----vangogh.CS.Berkeley.EDU PING Statistics---17 packets transmitted, 8 packets received, 52% packet loss round-trip (ms) min/avg/max = 100/501/1780 Either the echo requests or the echo replies for sequence numbers 1, 2, 3, 4, 6, 10, II, 12, and 13 were lost somewhere. Note also the large variance in the round-trip times. (This high packet loss rate of 52% is an anomaly. This is not normal for the Internet, even on a weekday afternoon.) It is also possible across WANs to see packets duplicated (the same sequence number printed two or more times), and to see packets reordered (sequence number N +1 printed before sequence number N). Hardwired SLIP Links Let's look at the round-trip times encountered over SLIP links, since they often run at slow asynchronous speeds, such as 9600 bits/sec or less. Recall our serial line throughput calculations in Section 2.10. For this example we'll set the speed of the hardwired SLIP link between hosts bsdi and slip to 1200 bits/sec. We can estimate the round-trip time as follows. First, notice from the example Ping output shown earlier that by default it sends 56 bytes of data in the ICMP message. With a 20-byte IP header and an 8-byte ICMP header this gives a total IP datagram size of 84 bytes. (We can verify this by running tcpdump -e and seeing the Ethernet frame sizes.) Also, from Section 2.4 we know that at least two additional bytes are added: the END byte at the beginning and end of the datagram. It's also possible for additional bytes to be added by the SLIP framing, but that depends on the value of each byte in the datagram. At 1200 bits/sec with 8 bits per byte, I start bit, and I stop bit, the rate is 120 bytes per second, or 8.33 ms per byte. Our estimate is then (86 x 8.33 x 2), or 1433 ms. (The multiplier of 2 is because we are calculating the round-trip time.)...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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