In-band control

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.

Here is an example of an SMTP client-server interaction: 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.

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