To serve the request, the client must first resolve the host name using the domain name service (DNS) protocol, which in turn relies on the user datagram protocol (UDP) and the internet protocol (IP) at a still lower layer. Once the hostname is converted to an IP address, the client opens a transmission control protocol (TCP) connection to the server, again using IP at a lower layer.
The browser transmits a hypertext transmission protocol (HTTP) request, which the server interprets before sending an HTTP reply.
This is the total scenario , what is happening actually when you type google.com in your browser .
At no point during this whole process the Simple mail transport protocol (SMTP) play any important role .
The top layer of protocols is the application layer. Typical application layer protocols are HTTP (for web content), HTTPS (for secure web content), FTP (for file transfer), SMTP (for sending mail), telnet (for text based logins), and SNMP (for managing networks).
The next layer is the transport layer. The two crucial protocols in this layer are TCP (for reliable, in-order delivery of packets) and UDP (for unreliably transmitting short snippets of information).
The next lower layer is the network layer. The crucial protocol in this layer is IP (for addressing of datagrams over the internet).
The next lower layer is the data link layer. The crucial protocol in this layer is Ethernet (mainly for sending data over twisted-pair cables), but another is FDDI (for sending data over fast fiber channels).
The lowest layer is the physical layer.
