QUESTIONS FOR READERS Figure 11.9 shows some of the concepts discussed in this chapter and can be used to help you answer the following questions. 1. What are the three phases of connection-oriented communications? 2. Which fi elds are present in the TCP header but absent in UDP? Why are they not needed in UDP? 3. What is the TCP fl ow control mechanism called? 4. What does it mean when the initial sequence and acknowledgment numbers are “relative”? 5. What is the silly window syndrome? What is the Nagle algorithm? 1 byte Source Port 1 byte 1 byte 1 byte Destination Port Sequence Number Acknowledgment Number Header Length RESV Control Bits Window Size TCP Checksum wincli2 Active OPEN (Client port 2790) Urgent Pointer Options Field (variable length, maximum 40 bytes, 0 padded to 4-byte multiple) DATA (application message) H e a d e r FTP Handshake Using 1460-byte Segments bsdserver Passive OPEN OPEN OPEN SYN SEQ (ISN) e33a WIN 57344 MSS (OPT) 1460 ACK SEQ 72d2 WIN 65535 ACK e33b SYN SEQ(ISN) 72d1 WIN 65535 MSS (OPT) 1460 3-Way Handshake Complete FIGURE 11.9 The TCP header fi elds and three-way handshake example. 299 . illustrates the sockets concept in more depth, but not the use of the socket interface in a TCP/IP network. The socket interface forms the boundary between the application program written by the programmer. considers the situation for IPv4 for simplicity. This chapter will be a little different than the others. Instead of jumping right in and capturing packets and then analyzing them, the socket. identifying the client FTP process. And the FTP server’s socket address is accessed by all of the FTP clients at the same time without confusion. Now consider the server shown in Figure 12.2. Here there