Editing 56 kbit/s line

{{Short description|Digital connection matching the data rate of a digital telephone line}}
A '''56&nbsp;kbit/s line''' is a digital connection capable of carrying 56 [[kilobit]]s per second ([[kbit/s]]), or 56,000&nbsp;[[bit/s]], the [[data]] rate of a classical single channel [[digital telephone]] line in [[North America]]. Since the wide deployment of faster, cheaper technologies, 56&nbsp;kbit/s lines are generally considered to be an [[obsolete]] technology.

==Speed derivation==
The figure of 56&nbsp;kbit/s is derived from its implementation using the same digital infrastructure used since the 1960s for [[digital telephony]] in the [[public switched telephone network]], which uses a [[sampling rate]] of 8,000&nbsp;Hz for [[Pulse-code modulation|PCM]] audio with 8-bit [[audio bit depth]] to encode [[analogue signal]]s into a digital stream of 64,000&nbsp;bit/s. However, in the [[T-carrier]] systems used in the US and Canada, a technique called [[bit-robbing]] uses, in every sixth [[frame (telecommunications)|frame]], the [[least significant bit]] for [[Channel Associated Signaling]] (CAS). This effectively renders the lowest bit of the 8 speech bits unusable for data transmission, and so a 56&nbsp;kbit/s line uses only 7 of the 8 data bits in each sample period to send data, thus giving a data rate of {{nowrap|8 kHz ×}} {{nowrap|7 bits {{=}}}} {{nowrap|56 kbit/s}}.

== See also ==
*[[Modem#56 kbit/s technologies|56 kbit/s modem]]
*[[DS0]]
*[[Integrated Services Digital Network|ISDN]]
*[[ITU-T V.90]]
*[[Switch56]]

== References ==
{{Reflist}}

{{DEFAULTSORT:56 Kbit S Line}}
[[Category:Computer network technology]]
[[Category:Telecommunications standards]]
[[Category:Obsolete technologies]]
[[Category:Telecommunication protocols]]

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