TCP IP Illustrated

The echo of the second 2 bytes is received in segment

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Unformatted text preview: Nagle algorithm when typing characters that generate multiple bytes of data. file:///D|/Documents%20and%20Settings/bigini/Docum...i/homenet2run/tcpip/tcp-ip-illustrated/tcp_int.htm (8 of 14) [12/09/2001 14.47.18] Chapter 19. TCP Interactive Data Flow Figure 19.6 shows the time line for this exchange. At the bottom of this figure we show the 6 bytes going from the client to the server with their sequence numbers, and the 8 bytes of echo being returned. When the first byte of input is read by the rlogin client and written to TCP, it is sent by itself as segment 1. This is the first of the 3 bytes generated by the Fl key. Its echo is returned in segment 2, and only then are the next 2 bytes sent (segment 3). The echo of the second 2 bytes is received in segment 4 and acknowledged in segment 5. The reason the echo of the first byte occupies 2 bytes (segment 2) is because the ASCII escape character is echoed as 2 bytes: a caret and a left bracket. The next 2 bytes of input, a left bracket and an M, are echoed as themselves. The same exchange occurs when the next special function key is typed (segments 6-10). As we expect, the time difference between segments 5 and 10 (slip sending the acknowledgment of the echo) is a multiple of 200 ms, since both ACKs are delayed. file:///D|/Documents%20and%20Settings/bigini/Docum...i/homenet2run/tcpip/tcp-ip-illustrated/tcp_int.htm (9 of 14) [12/09/2001 14.47.18] Chapter 19. TCP Interactive Data Flow Figure 19.6 Time line for Figure 19.5 (watching the Nagle algorithm). We now repeat this same example using a version of rlogin that has been modified to turn off the Nagle algorithm. Figure 19.7 shows the tcpdump output. (Again, we have deleted the type-of-service information and the window advertisements.) 1 2 3 4 5 6 7 8 9 10 11 12 13 0.0 0.002163 (0.0022) 0.004218 (0.0021) 0.280621 (0.2764) 0.281738 (0.0011) 2.477561 (2.1958) 2.478735 (0.0012) 3.217023 (0.7383) 3.219165 (0.0021) 3.221688 (0.0025) 3.460626 (0.2389) 3.489414 (0.0288) 3.640356 (0.1509) type Fl key slip.1023 > vangogh.login: 2 slip.1023 &g...
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