Naming

In an informal way, we've already looked at a lot of the different names used for identification in the Internet. You should already have seen most of these terms.

• Domain Names are alphanumeric strings used by users to identify Internet hosts. www.FreeSoft.org is a domain name. Domain names are converted into IP addresses by DNS.

• IP Addresses are 32-bit numbers used to identify Internet hosts by the IP Protocol. Sometimes IP addresses must be written in a human-readable format; dotted quad notation is used, with each of the four bytes written as a decimal number, separated by periods. 205.216.34.7 is a dotted quad IP address.

• Service Names are short strings that identify particular services on an Internet host. They must be converted to port numbers before use, which is commonly done using a services table, /etc/services on UN*X machines. Examples of service names are telnet, smtp, and http.

• Port Numbers identify particular services on an Internet host to the TCP and UDP Protocols. They are 16-bit numbers, usually written in decimal, and known by convention. For example, port 25 is used for SMTP mail transfers, and port 80 for HTTP Web transfers.

• Universal Resource Locators (URLs) are used by the World Wide Web to locate and identify Web documents and other resources. URLs typically contain service names, domain names and sometimes port numbers. URLs also include a string, usually a filesystem path, to distinguish between different documents available through a single server.