{{Unreferenced, date=June 2019, bot=noref (GreenC bot) In-band control is a characteristic of

network protocols A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchroniza ...

with which data control is regulated. In-band control passes control data on the same connection as main data. Protocols that use in-band control include

HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, ...

and

SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typical ...

. This is as opposed to

Out-of-band control Out-of-band control is a characteristic of network protocols with which data control is regulated. Out-of-band control passes control data on a separate connection from main data. Protocols such as FTP use out-of-band control. FTP sends its contr ...

used by protocols such as

FTP The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and data ...

Example

Here is an example of an

client-server interaction:

Server: 220 example.com  
Client: HELO example.net  
Server: 250  Hello example.net, pleased to meet you  
Client: MAIL FROM:   
Server: 250 jane.doe@example.net... Sender ok  
Client: RCPT TO:   
Server: 250 john.doe@example.com ... Recipient ok  
Client: DATA  
Server: 354 Enter mail, end with "." on a line by itself  
Client: Do you like ketchup?  
Client: How about pickles?  
Client: .  
Server: 250 Message accepted for delivery  
Client: QUIT  
Server: 221 example.com closing connection

is in-band because the control messages, such as "HELO" and "MAIL FROM", are sent in the same stream as the actual message content.

Example

See also