Which of the following protocols uses separate control and data connections between the client and server applications?

A.
HTTP

B.
FTP

C.
SMTP

D.
SCP

Explanation:
File Transfer Protocol (FTP) is a standard network protocol used to copy a file from one host to another over a TCP/IP-based network, such as the Internet. FTP is built on the client-server architecture and utilizes separate controls and data connections between the client and server applications which solve the problem of different end host configurations (i.e. Operating System, file names). FTP is used with user-based password authentication or with anonymous user access. Applications were originally interactive command-line tools with standardized command syntax, but graphical user interfaces have been developed for all desktop operating systems in use today.

Answer A is incorrect. Hypertext Transfer Protocol (HTTP) is a client/server TCP/IP protocol used on the World Wide Web (WWW) to display Hypertext Markup Language (HTML) pages. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. For example, when a client application or browser sends a request to the server using HTTP commands, the server responds with a message containing the protocol version, success or failure code, server information, and body content, depending on the request. HTTP uses TCP port 80 as the default port.

Answer C is incorrect. Simple Mail Transfer Protocol (SMTP) is a protocol for sending e-mail messages between servers. E-mailing systems use this protocol to send mails over the Internet. SMTP works on the application layer of the TCP/IP or OSI reference model. The SMTP client typically initiates a Transmission Control Protocol (TCP) connection to the SMTP server on the well-known port designated for SMTP, port number 25. However, e-mail clients require POP or IMAP to retrieve mails from e-mail servers.

Answer D is incorrect. The SCP protocol sends data in encrypted format. It is used to prevent potential packet sniffers from extracting usable information from data packets. The protocol itself does not provide authentication and security; it relies on the underlying protocol, SSH, to provide these features. SCP can
interactively request any passwords or passphrases required to make a connection to a remote host, unlike rcp that fails in this situation. The SCP protocol implements file transfers only. It does so by connecting to the host using SSH and there executes an SCP server (scp). The SCP server program is typically the same program as the SCP client.
Reference.http.//searchenterprisewan.techtarget.com/sDefinition/0,,sid200_gci213976,00.html