TCP/IP Features

TCP/IP includes many important features that you'll learn about in this book. In particular, pay close attention to the way the TCP/IP protocol suite addresses the following problems:

• Logical addressing

• Routing

• Name service

• Error control and flow control

• Application support

These issues are at the heart of TCP/IP. The following sections introduce these important features. You'll learn more about these features later in this book.

Logical Addressing

A network adapter has a unique and permanent physical address. The physical address is a number that was given to the card at the factory. On a local area network, low-lying hardware-conscious protocols deliver data across the physical network using the adapter's physical address. There are many network types, and each has a different way of delivering data. On a basic ethernet network, for example, a computer sends messages directly onto the transmission medium. The network adapter of each computer listens to every transmission on the local network to determine whether a message is addressed to its own physical address.

By the Way

As you'll learn in Hour 9, "Network Hardware," today's ethernet networks are a bit more complicated than the idealized scenario of a computer sending messages directly onto the transmission line. Ethernet networks sometimes contain hardware devices such as switches and hubs to manage the signal.

On large networks, of course, every network adapter can't listen to every message. (Imagine your computer listening to every piece of data sent over the Internet.) As the transmission medium becomes more populated with computers, a physical addressing scheme cannot function efficiently. Network administrators often segment networks using devices such as routers to reduce network traffic. On routed networks, administrators need a way to subdivide the network into smaller subnetworks (called subnets) and impose a hierarchical design so that a message can travel efficiently to its destination. TCP/IP provides this subnetting capability through logical addressing. A logical address is an address configured through the network software. In TCP/IP, a computer's logical address is called an IP address. As you'll learn in Hour 4, "The Internet Layer," and Hour 5, "Subnetting," an IP address can include

• A network ID number identifying a network

• A subnet ID number identifying a subnet on the network

• A host ID number identifying the computer on the subnet

The IP addressing system also lets the network administrator impose a sensible numbering scheme on the network so that the progression of addresses reflects the internal organization of the network.