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Unformatted text preview: gets fragmented into four pieces. Assume
that fragments 1 and 2 make it to the destination, with fragments 3 and 4 being lost. The
application then times out and retransmits the UDP datagram 10 seconds later and this datagram
is fragmented identically to the first transmission (i.e., same offsets and lengths). Assume that
this time fragments 1 and 2 are lost but fragments 3 and 4 make it to the destination. Also
assume that the reassembly timer on the receiving host is 60 seconds, so when fragments 3 and
4 of the retransmission make it to the destination, fragments 1 and 2 from the first transmission
have not been discarded. Can the receiver reassemble the IP datagram from the four fragments
it now has?
11.6 How do you know that the fragments in Figure 11.15 really correspond to lines 5 and 6 in
11.7 After the host gemini had been up for 33 days, the netstat program showed that 129
IP datagrams out of 48 mi1110n had been dropped because of a bad header checksum, and 20
TCP segments out of 30 mi1110n had been dropped because of a bad TCP checksum. Not a
single UDP datagram was dropped, however, because of a UDP checksum error, out of the
approximately 18 mi1110n UDP datagrams. Give two reasons why. (Hint: See Figure 11.4.)
11.8 In our discussion of fragmentation we never said what happens to IP options in the IP
header-are they copied as part of the IP header in each fragment, or left in the first fragment
only? We've described the following IP options: record route (Section 7.3), time-stamp (Section
7.4), strict and loose source routing (Section 8.5). How would you expect fragmentation to
handle these options? Check your answer with RFC 791.
11.9 In Figure 1.8 we said that incoming UDP datagrams are demultiplexed based on the
destination UDP port number. Is that correct? file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/udp_user.htm (29 of 29) [12/09/2001 14.46.58] Chapter 12. Broadcasting and Multicasting Broadcasting and Multicasting
We mentioned in Chapter 1 that there...
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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