lecture2:OSI&TCP Model

The most widely-known TCP/IP Application layer protocols are those that provide for the exchange of user information. These protocols specify the format and control information necessary for many of the common Internet communication functions. Among these TCP/IP protocols are:
• Domain Name Service Protocol (DNS) is used to resolve Internet names to IP addresses.
• Hypertext Transfer Protocol (HTTP) is used to transfer files that make up the Web pages of the World Wide Web.
• Simple Mail Transfer Protocol (SMTP) is used for the transfer of mail messages and attachments.
• Telnet, a terminal emulation protocol, is used to provide remote access to servers and networking devices.
• File Transfer Protocol (FTP) is used for interactive file transfer between systems.
Domain Name Service (DNS) :In data networks, devices are labeled with numeric IP addresses, so that they can participate in sending and receiving messages over the network. However, most people have a hard time remembering this numeric address. Hence, domain names were created to convert the numeric address into a simple, recognizable name. on the other hand DNS protocol is used to resolve Internet names to IP addresses.

DNS The Domain Name System uses a hierarchical system to create a name database to provide name resolution. The hierarchy looks like an inverted tree with the root at the top and branches below.
At the top of the hierarchy, the root servers maintain records about how to reach the top-level domain servers, which in turn have records that point to the secondary level domain servers and so on.
The different top-level domains represent the either the type of organization or the country or origin. Examples of top-level domains are:
.au – Australia
.co - Colombia
.com - a business or industry
.jp - Japan
.org - a non-profit organization
After top-level domains are second-level domain names, and below them are other lower level domains.