in-band control
{{Unreferenced|date=June 2019|bot=noref (GreenC bot)}}
In-band control is a characteristic of network protocols 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 and SMTP. This is as opposed to Out-of-band control used by protocols such as FTP.
Example
Here is an example of an SMTP 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
SMTP is in-band because the control messages, such as "HELO" and "MAIL FROM", are sent in the same stream as the actual message content.