Network Time Protocol (NTP)

Network Time Protocol (NTP)

Network Time Protocol (NTP), originally developed by Professor David Mills at the University of Delaware, is used to synchronize (or set) computer clocks to some standard time source, which is
usually a nuclear clock. This protocol (along with synchronization utilities) keeps all computers on a network set to the same time. Time synchronization is important because many transactions
are time and date stamped (in a database, for example). If the time on a server is out of synchronization with the time on two different computers, even by just a few seconds, the server will get confused. For example, one computer can seemingly enter a transaction, but the server will indicate that it occurred before it actually did. Because this time problem will crash the database server, it is important that these servers (and workstations) use NTP.

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Hypertext Transfer Protocol Secure (HTTPS)

Hypertext Transfer Protocol Secure (HTTPS)

Hypertext Transfer Protocol Secure (HTTPS), also referred to as Secure Hypertext Transfer Protocol (which you will see abbreviated as SHTTP or S-HTTP), is a secure version of HTTP that provides a variety of security mechanisms to the transactions between a web browser and the server. HTTPS allows browsers and servers to sign, authenticate, and encrypt an HTTP message.

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Hypertext Transfer Protocol (HTTP)

Hypertext Transfer Protocol (HTTP)

Hypertext Transfer Protocol (HTTP) is the command and control protocol used to manage communications between a web browser and a web server. When you access a web page on the
Internet or on a corporate intranet, you see a mixture of text, graphics, and links to other documents or other Internet resources. HTTP is the mechanism that opens the related document
when you select a link, no matter where that document is actually located.

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Secure Shell (SSH)

Secure Shell (SSH)

The Secure Shell (SSH) protocol is used to establish a secure Telnet session over a standard TCP/IP connection. It is used to run programs on remote systems, log in to other systems, and move
files from one system to another, all while maintaining a strong, encrypted connection. It replaces such utilities as rsh and rlogin as well as Telnet.

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Telnet

Telnet

Telnet is a terminal emulation protocol that provides a remote logon to another host over the network. It allows a user to connect to a remote host over a TCP/IP connection as if they were sitting
right at that host. Keystrokes typed into a Telnet program will be transmitted over a TCP/IP network to the host. The visual responses are sent back by the host to the Telnet client to be displayed.

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Network File System (NFS)

Network File System (NFS)

UNIX systems are unique in the way they access files and are actually fairly elegant. The Network File System (NFS) Application layer protocol was originally designed to allow shared file
systems on UNIX servers to appear as local file systems on UNIX clients.

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Line Printer Daemon (LPD)

Line Printer Daemon (LPD)

Another TCP/IP upper-layer service that is in widespread use is the Line Printer Daemon (LPD). It resides on a network printer or print server and responds to TCP/IP printing requests from the printing clients (known as LPR clients). It was developed as the printing services for UNIX. But, because of the tight marriage between UNIX and TCP/IP, the LPD service became the default
print service used with TCP/IP.

Note:

A daemon is a program that acts like a terminate and stay resident (TSR) application
by loading into memory and lurking there for any trigger that calls upon its services.

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Internet Message Access Protocol, Version 4 (IMAP4)

Internet Message Access Protocol, Version 4 (IMAP4)

Internet Message Access Protocol (IMAP) allows users to download mail selectively, look at the message header, download just a part of a message, store messages on the e-mail server in a hierarchical structure, and link to documents and Usenet newsgroups. Search commands are also available so that users can locate messages based on their subject, header or content. IMAP has strong authentication features and supports the Kerberos authentication scheme originally developed at MIT. The current version of IMAP is version 4.

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Lightweight Directory Access Protocol (LDAP)

Lightweight Directory Access Protocol (LDAP)

In large networks, most administrators have set up some kind of directory that keeps track of users and resources (e.g., NDS, Active Directory). In order to have a standard method of accessing
directories, the Lightweight Directory Access Protocol (LDAP) was developed. It allows clients to perform object lookups with a directory using a standard method. LDAP was originally
specified as RFCs 1487 (version 1) and 1777 (version 2), with RFC 3377 proposing the more commonly used third version, which fixes a number of shortcomings in the protocol.

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Post Office Protocol (POP)

Post Office Protocol (POP)

Post Office Protocol (POP) provides a storage mechanism for incoming mail; the latest version of the standard is known as POP3. When a client connects to a POP3 server, all the messages
addressed to that client are downloaded; there is no way to download messages selectively. Once the messages are downloaded, the user can delete or modify messages without further interaction with the server. In some locations, POP3 is being replaced by another standard, IMAP.

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Secure Copy Protocol (SCP)

Secure Copy Protocol (SCP)

While FTP is easy to use to transfer files, it has a major security problem in that the username and password are sent along with the file request in clear text (i.e., not encrypted). It would be a relatively simple matter for someone to intercept that information and use it for other purposes. 
      Secure Copy Protocol (SCP) was designed to overcome this limitation. It uses SSH to establish and maintain an encrypted connection between hosts. The file transfer can then take place
without fear of password or data interception.

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Simple Mail Transfer Protocol (SMTP)

Simple Mail Transfer Protocol (SMTP)

Simple Mail Transfer Protocol (SMTP) allows for a simple e-mail service and is responsible for moving messages from one e-mail server to another. The e-mail servers run either Post Office
Protocol (POP) or Internet Mail Access Protocol (IMAP) to distribute e-mail messages to users.

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