Sudarshan S
3 min readMar 22, 2022


Are you online? Of course you are! And that’s how you are reading this blog right now. Would you like to know how this is possible? This series is all about what it takes to be online and access internet!

Hey peeps, so far in this series we have discussed a lot about networking and different layers. Now, we’ll be discussing about the “application layer” in this blog and in a few following blogs.

Network Application Services

The first thing to do before moving into this topic is, remember what are you doing on the internet? Yeah!, you’ll be visiting a web page, sending an email or sending/receiving files with someone. All these tasks are possible because of the application layer services. There is a lot to know about application layer services. Without any delay, let’s jump into the topic!

Photo by imgix on Unsplash

The common internet services that we use on a regular basis like internet searches, social media sites, video and audio streaming, online shopping sites, email and messaging relies on protocols from TCP/IP protocol suite to reliably communicate the information between clients and the servers.

There are some of the most common servers that provide the above mentioned services. Let’s discuss them!

Domain Name System (DNS)

This server is used to resolve the internet names or the URL into IP address.

Secure Shell (SSH)

SSH server is used to provide remote access to servers and networking devices.

Simple Mail Transfer Protocol (SMTP)

This server sends email messages and attachments from clients to the servers and from servers to other email servers.

SMTP is used to send messages to its local email server. Then the local server decides if the message to be delivered to a local mailbox or to a mailbox on another server. If the server has to to send the message to different server, then SMTP is used between those two servers as well.

SMTP requests are sent to port 25

Post Office Protocol (POP)

This is used by the email clients to retrieve email and attachments from a remote server. A server that supports POP clients receives and stores messages addressed to its users. When the client connects to the email server, the messages are downloaded to the client, then they are not kept on the server after they have been accessed.

POP3 servers are contacted on port 110

Internet Message Access Protocol (IMAP)

This is similar to POP. This too used to retrieve email and attachments from a remote server. A server that supports IMAP also does the same thing like receiving and storing messages addressed to its users. But, unlike POP, IMAP keeps the messages in the mailboxes on the server, unless they are deleted by the user.

IMAP listens on port 143

Dynamic Host Configuration Protocol (DHCP)

DHCP servers are used to configure IP addresses and other necessary networking information to devices so that it enables them to communicate over the internet.

Hypertext Transfer Protocol (HTTP)

The HTTP is used by the web browsers to request web pages and web servers to transfers the files that make up the web pages of the World Wide Web (WWW).

File Transfer Protocol (FTP)

The FTP server is used for interactive file transfer between systems.

And there are many other servers which are involved in the internet and provide some important services. We’ll be discussing elaborately about the above mentioned servers and their functions and how they are configured. I’ll catch you up in the next blog.

Until then, Stay connected!!

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Sudarshan S

Tech enthusiast | Developer | Machine learning | Data science | Cybersecurity