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Unformatted text preview: ut, we can't show it all. Instead we'll look at pieces as we proceed through the
chapter. Figure 21.2 shows the transfer of data and acknowledgments for the first 5 seconds. We have
modified this output slightly from our previous display of tcpdump output. Although we only measure the
times that the packet is sent or received on the host running tcpdump, in this figure we want to show that
the packets are crossing in the network (which they are, since this LAN connection is not like a shared
Ethernet), and show when the receiving host is probably generating the ACKs. (We have also removed all
the window advertisements from this figure, slip always advertised a window of 4096, and vangogh
always advertised a window of 8192.) file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_time.htm (6 of 29) [12/09/2001 14.47.26] Chapter 21. TCP Timeout and Retransmission Figure 21.2 Packet exchange and RTT measurement.
Also note in this figure that we have numbered the segments 1-13 and 15, in the order in which they were
sent or received on the host slip. This correlates with the tcpdump output that was collected on this host. Round-Trip Time Measurements
Three curly braces have been placed on the left side of the time line indicating which segments were timed
for RTT calculations. Not all data segments are timed. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_time.htm (7 of 29) [12/09/2001 14.47.26] Chapter 21. TCP Timeout and Retransmission Most Berkeley-derived implementations of TCP measure only one RTT value per connection at any time. If
the timer for a given connection is already in use when a data segment is transmitted, that segment is not
The timing is done by incrementing a counter every time the 500-ms TCP timer routine is invoked. This
means that a segment whose acknowledgment arrives 550 rns after the segment was sent could end up with
either a 1 tick RTT (implying 500 ms) or a 2 tick RTT (implying 1000 ms).
In addition to this tick counter for ea...
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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.
- Spring '12