In-band/Sideband/Out-of-band

[wiki] In-band signaling
http://en.wikipedia.org/wiki/In-band

In telecommunications, in-band signaling is the sending of metadata and control information in the same band, on the same channel, as used for data.

如PCI中的MSI，不用到額外訊號線，只用現有傳資料的線路來傳送interrupt/control

[wiki] Out-of-band
http://en.wikipedia.org/wiki/Out-of-band

It refers to communications which occur outside of a previously established communications method or channel.

通常相對In-Band signaling而言,有其他訊號線專門傳送interrupt/control

[wiki] Sideband
http://en.wikipedia.org/wiki/Sideband

In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, somehow containing power as a result of the modulation process. The sidebands consist of all the Fourier components of the modulated signal except the carrier. All forms of modulation produce sidebands.