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Unformatted text preview: ong with the first segment of data in Exercise
18.9.) This generates the ICMP error in line 4 and we see that the router bsdi generates
the newer ICMP error containing the MTU of the outgoing interface.
It appears that before this error makes it back to solaris, the FIN is sent (line 5). Since
slip never received the 512 bytes of data discarded by the router bsdi, it is not
expecting this sequence number (513), so it responds in line 6 with the expected
sequence number (1).
At this time the ICMP error has made it back to solaris and it retransmits the 512
bytes of data in two 256-byte segments (lines 7 and 9). Both are sent with the DF bit set, file:///D|/Documents%20and%20Settings/bigini/Docum...i/homenet2run/tcpip/tcp-ip-illustrated/tcp_fut.htm (4 of 20) [12/09/2001 14.47.33] Chapter 24. TCP Futures and Performance since there could be another router beyond bsdi with a smaller MTU.
A longer transfer was run (taking about 15 minutes) and after moving from the 512-byte
initial segment to 256-byte segments, solaris never tried the higher segment size
Big Packets or Small Packets?
Conventional wisdom says that bigger packets are better [Mogul 1993, Sec. 15.2.8]
because sending fewer big packets "costs less" than sending more smaller packets. (This
assumes the packets are not large enough to cause fragmentation, since that introduces
another set of problems.) The reduced cost is that associated with the network (packet
header overhead), routers (routing decisions), and hosts (protocol processing and device
interrupts). Not everyone agrees with this [Bellovin 1993].
Consider the following example. We send 8192 bytes through four routers, each
connected with a Tl telephone line (1,544,000 bits/sec). First we use two 4096-byte
packets, as shown in Figure 24.3. Figure 24.3 Sending two 4096-byte packets through four routers.
The basic problem is that routers are store-and-forward devices. They normally receive
the entire input packet, validate the IP header including the IP checksum,...
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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