2.1 Introduction
This chapter provides an overview of the
protocols in the TCP/IP suite that are used in the examples
throughout the book. Our goal is to provide enough detail from a
network programming perspective to understand how to use the
protocols and provide references to more detailed descriptions of
their actual design, implementation, and history.
This chapter focuses on the transport layer:
TCP, UDP, and Stream Control Transmission Protocol (SCTP). Most
client/server applications use either TCP or UDP. SCTP is a newer
protocol, originally designed for transport of telephony signaling
across the Internet. These transport protocols use the
network-layer protocol IP, either IPv4 or IPv6. While it is
possible to use IPv4 or IPv6 directly, bypassing the transport
layer, this technique, often called raw
sockets, is used much less frequently. Therefore, we have a
more detailed description of IPv4 and IPv6, along with ICMPv4 and
ICMPv6, in Appendix A.
UDP is a simple, unreliable datagram protocol,
while TCP is a sophisticated, reliable byte-stream protocol. SCTP
is similar to TCP as a reliable transport protocol, but it also
provides message boundaries, transport-level support for
multihoming, and a way to minimize head-of-line blocking. We need
to understand the services provided by these transport protocols to
the application, so that we know what is handled by the protocol
and what we must handle in the application.
There are features of TCP that, when understood,
make it easier for us to write robust clients and servers. Also,
when we understand these features, it becomes easier to debug our
clients and servers using commonly provided tools such as
netstat. We cover various topics in this chapter that fall
into this category: TCP's three-way handshake, TCP's connection
termination sequence, and TCP's TIME_WAIT state; SCTP's four-way
handshake and SCTP's connection termination; plus SCTP, TCP, and
UDP buffering by the socket layer, and so on.
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