TCP IP Illustrated

If the order of receipt were 1 3 4 2 two duplicate

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Unformatted text preview: ion occurs on the Internet, although it rarely leads to congestion. Chapter 21 21.1 The next timeout is for 48 seconds: 0+4x12. The factor of 4 is the next multiplier in file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/append_d.htm (14 of 20) [12/09/2001 14.48.04] Appendix D: Solutions to Selected Exercises the exponential backoff. 21.2 It appears SVR4 still uses the factor ID instead of 4D in the calculation of RTO. 21.3 The stop-and-wait protocol used by TFTP is limited to 512 bytes of data per round trip. 32768/512 x 1.5 is 96 seconds. 21.4 Show four segments, numbered 1,2,3, and 4. Assume the order of receipt is 1, 3, 2, and 4. The ACKs generated by the receiver will be ACK 1 (a normal ACK), ACK 1 (a duplicate ACK when segment 3 is received out of order), ACK 3 when segment 2 is received (acknowledging both segments 2 and 3), and then ACK 4. Here one duplicate ACK is generated. If the order of receipt were 1, 3, 4, 2, two duplicate ACKs would be generated. 21.5 No, because the slope is still up and to the right, not downward. 21.6 See Figure E.1. 21.7 In Figure 21.2 the segments contain 256 bytes of data, which takes approximately 250 ms to transfer across the 9600 bits/sec CSLIP link between slip and bsdi. Assuming the data segments are not queued somewhere between bsdi and vangogh, they arrive at vangogh about 250 ms apart. Since this exceeds the 200-ms delayed ACK timer, each segment is acknowledged when the next delayed ACK timer expires. Chapter 22 22.1 The ACKs are probably all delayed on the host bsdi, because there is no reason to send them immediately. That's why the relative times have 0.170 and 0.370 as the fractional part. It also appears that the 200-ms timer on bsdi is running about 18 ms behind the same timer on sun. 22.2 The FIN flag, just like the SYN flag, occupies 1 byte in the sequence number space. "The advertised window appears to be 1 byte smaller because TCP allows room for the 1 byte of sequence number space...
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