TCP IP Illustrated

TCP IP Illustrated

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Unformatted text preview: ledged, and echoed averaged around 16 ms. To generate data faster than this we would have to be typing more than 60 characters per second. This means we rarely encounter this algorithm when sending data between two hosts on a LAN. Things change, however, when the round-trip tune (RTT) increases, typically across a WAN. Let's look at an Rlogin connection between our host slip and the host vangogh.cs.berkeley.edu. To get out of our network (see inside front cover), two SLIP links must be traversed, and then the Internet is used. We expect much longer round-trip times. Figure 19.4 shows the time line of some data flow while characters were being typed quickly on the client (similar to a fast typist). (We have removed the file:///D|/Documents%20and%20Settings/bigini/Docum...i/homenet2run/tcpip/tcp-ip-illustrated/tcp_int.htm (5 of 14) [12/09/2001 14.47.18] Chapter 19. TCP Interactive Data Flow type-of-service information, but have left in the window size advertisements.) Figure 19.4 Dataflow using rlogin between slip and vangogh.cs.berkeley.edu. The first thing we notice, comparing Figure 19.4 with Figure 19.3, is the lack of delayed ACKs from slip to vangogh. This is because there is always data ready to send before the delayed ACK timer expires. Next, notice the various amounts of data being sent from the left to the right: 1, 1, 2, 1, 2, 2, 3, 1, and 3 bytes. This is because the client is collecting the data to send, but doesn't file:///D|/Documents%20and%20Settings/bigini/Docum...i/homenet2run/tcpip/tcp-ip-illustrated/tcp_int.htm (6 of 14) [12/09/2001 14.47.18] Chapter 19. TCP Interactive Data Flow send it until the previously sent data has been acknowledged. By using the Nagle algorithm only nine segments were used to send 16 bytes, instead of 16 segments. Segments 14 and 15 appear to contradict the Nagle algorithm, but we need to look at the sequence numbers to see what's really happening. Segment 14 is in response to the ACK received in segment 12, since the acknowledged sequence number is 54...
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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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