Introduction to the TCP/IP application layer / DNS

Introduction to the TCP/IP application layer
11.2.1 This page will introduce some TCP/IP application layer protocols.


The session, presentation, and application layers of the OSI model are bundled into the application layer of the TCP/IP model. This means that representation, encoding, and dialog control are all handled in the TCP/IP application layer. This design ensures that the TCP/IP model provides maximum flexibility at the application layer for software developers.

The TCP/IP protocols that support file transfer, e-mail, and remote login are probably the most familiar to users of the Internet. These protocols include the following applications:

• DNS
• FTP
• HTTP
• SMTP
• SNMP
• Telnet

The next page will discuss DNS.

DNS
11.2.2 This page will describe DNS.


The Internet is built on a hierarchical addressing scheme. This scheme allows for routing to be based on classes of addresses rather than based on individual addresses. The problem this creates for the user is associating the correct address with the Internet site. It is very easy to forget an IP address to a particular site because there is nothing to associate the contents of the site with the address. Imagine the difficulty of remembering the IP addresses of tens, hundreds, or even thousands of Internet sites.

A domain naming system was developed in order to associate the contents of the site with the address of that site. The Domain Name System (DNS) is a system used on the Internet for translating names of domains and their publicly advertised network nodes into IP addresses. A domain is a group of computers that are associated by their geographical location or their business type. A domain name is a string of characters, number, or both. Usually a name or abbreviation that represents the numeric address of an Internet site will make up the domain name. There are more than 200 top-level domains on the Internet, examples of which include the following:

.us – United States
.uk – United Kingdom

There are also generic names, which examples include the following:

.edu – educational sites
.com – commercial sites
.gov – government sites
.org – non-profit sites
.net – network service

The next page will discuss FTP and TFTP.