The Application Layer
Learn about the purpose of the application layer and the two main protocols that it follows.
The application layer relies on the transport layer for the data transfer and is responsible for defining the syntax and semantics of this data as well as the protocol of exchanges between the two sides.
This is probably the most crowded layer with a vast number of protocols. In this lesson, we will explore two of the protocols that form the foundation of the world wide web, namely: Domain Name System (DNS) protocol and the Hypertext Transfer Protocol (HTTP).
Domain name system
DNS is a system used to map human-friendly names, called domain names, to IP addresses. This is useful because these domain names are easier for humans to remember and use, and they can also be agnostic to the actual network topology of an application, making them a better addressing scheme for applications, unlike IP addresses.
Users of DNS
The users of the DNS system can be classified into two broad categories.
Clients that want to resolve a domain name into an IP address in order to send a data packet, and servers that store and serve this information to clients.
The DNS specifies a protocol, which defines the data structures that the servers can maintain and how clients can request the data they need. ...