Out-of-band

The term out-of-band has different uses in communications and telecommunication. In case of out-of-band control signaling, signaling bits are sent in special order in a dedicated signaling frame. D-channel in ISDN is an example of out-of-band and CCS signaling methods.

The word band originates from the term band as used in radio and other electronic communications.

General Usage

In general language, out-of-band refers to communications which occur outside of a previously established communication method or channel.

Here are two very simple, but illustrative, examples:

• A person is involved in a discussion with a group of people. During the discussion, he decides that some information is best kept between himself and one other member of the group, exclusively, such as by whispering or sending an electronic text message -- whether for privacy reasons, or merely the need to avoid saturating the entire group with information they do not need. His communication with that individual may be considered out-of-band, relative to the group discussion as a whole.
• A person is at his place of work, and he is communicating with someone outside of his work place (for example, by Internet or telephone, using his employer's computer or telephone equipment). He decides that key parts of his conversation are best kept private from his employer, such as if he were discussing plans to change jobs. He would use his personal cell phone to transmit sensitive messages to, and receive related messages from, his external contact, in order to avoid use of his employer's phone or computer network. In this situation, his personal cell phone communications are considered out-of-band, relative to the main conversation method.

Telecommunications

Main article: Signaling (telecommunications)

Out-of-band communication is the exchange of call control information in a separate band from the data or voice stream, or on an entirely separate, dedicated channel (as in Common Channel Signaling).

Computing

In computer networking, out-of-band data (called "urgent data" in TCP) looks — to the application — like a separate stream of data from the main data stream. This can be useful for separating two different kinds of data. Note that just because it is called "urgent data" does not mean that it will be delivered any faster or with higher priority than data in the in-band data stream. Also beware that unlike the main data stream, the out-of-band data may be lost if the application cannot keep up with it. "Urgent data" notifies the receiving connection that the separate stream is more important than the main stream. Therefore it must first check the separate stream in order to process the main stream normally.

In computer administration, out-of-band management refers to system console access provided, even in the event of primary network subsystem (hard and/or software) failure. This can be done via a console server or with a remote access card (RAC) which has its own processor, memory, battery, network connection, and access to the system bus.

In personal communications, methods other than e-mail (such as telephone or snail-mail) are sometimes called "out-of-band".^[1]

See also

• In-band signaling
• Out-of-band agreement
• Out-of-band management
• Ident

References

1. ^ The Jargon File "Out-of-band", def. 3

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.