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Unformatted text preview: e acknowledgment for the retransmitted data finally arrives. This is because we don't
know to which transmission the ACK corresponds. (Perhaps the first transmission was delayed and not
thrown away, or perhaps the ACK of the first transmission was delayed.)
Also, since the data was retransmitted, and the exponential backoff has been applied to the RTO, we reuse
this backed off RTO for the next transmission. Don't calculate a new RTO until an acknowledgment is
received for a segment that was not retransmitted. 21.4 An RTT Example
We'll use the following example throughout this chapter to examine various implementation details of TCP's
timeout and retransmission, slow start, and congestion avoidance. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_time.htm (5 of 29) [12/09/2001 14.47.26] Chapter 21. TCP Timeout and Retransmission Using our sock program, 32768 bytes of data are sent from our host slip to the discard service on the host
vangogh.cs.berkeley.edu using the command:
slip % sock -D -i -n32 vangogh.cs.berkeley.edu discard
From the figure on the inside front cover, slip is connected from the 140.252.1 Ethernet by two SLIP links,
and from there across the Internet to the destination. With two 9600 bits/sec SLIP links, we expect some
This command performs 32 1024-byte writes, and since the MTU between slip and bsdi is 296, this
becomes 128 segments, each with 256 bytes of user data. The total time for the transfer is about 45 seconds
and we see one timeout and three retransmissions.
While this transfer was running we ran tcpdump on the host slip and captured all the segments sent and
received. Additionally we specified the -D option to turn on socket debugging (Section A.6). We were then
able to run a modified version of the trpt(8) program to print numerous variables in the connection control
block relating to the round-trip timing, slow start, and congestion avoidance.
Given the volume of trace outp...
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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