TCP IP Illustrated

When we discuss tcp well see that it provides a

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: bsequent reads. The application is not notified that multiple reads are being fulfilled from a single UDP datagram. The TLI API does not discard the data. Instead a flag is returned indicating that more data is available, and subsequent reads by the application return the rest of the datagram. When we discuss TCP we'll see that it provides a continuous stream of bytes to the application, without any message boundaries. TCP passes the data to the application in whatever size reads the application asks for-there is never any data loss across this interface. 11.11 ICMP Source Quench Error Using UDP we are also able to generate the ICMP "source quench" error. This is an error that may be generated by a system (router or host) when it receives datagrams at a rate that is too fast to be processed. Note the qualifier "may." A system is not required to send a source quench, even if it runs out of buffers and throws datagrams away. Figure 11.18 shows the format of the ICMP source quench error. We have a perfect scenario with our test network for generating this error. We can send datagrams from bsdi to the router sun across the Ethernet that must be routed across the dialup SLIP link. Since the SLIP link is about 1000 times slower than the Ethernet, we should easily be able to overrun its buffer space. The following command sends 100 1024-byte datagrams from the host bsdi through the router sun to solaris. We send the datagrams to the standard discard service, where they'll be ignored: bsdi % sock -u -i -w1024 -n100 solaris discard Figure 11.18 ICMP source quench error. Figure 11.19 shows the tcpdump output corresponding to this command. 1 0.0 bsdi .1403 > solaris.discard: udp 1024 26 lines that we don't show file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/udp_user.htm (20 of 29) [12/09/2001 14.46.58] Chapter 11. UDP: User Datagram Protocol 27 28 29 30 173 174 0.10 0.11 0.11 0.11 (0.00) (0.01) (0.00) (0.00) bsdi.1403...
View Full Document

Ask a homework question - tutors are online