Editing Multiplexing (section)

===Time-division multiplexing===
[[File:Telephony multiplexer system.gif|right|thumb|400px|Time-division multiplexing (TDM)]]
[[Time-division multiplexing]] (TDM) is a digital (or in rare cases, analog) technology that uses time, instead of space or frequency, to separate the different data streams. TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver. If done sufficiently quickly, the receiving devices will not detect that some of the circuit time was used to serve another logical communication path.

Consider an application requiring four terminals at an airport to reach a central computer. Each terminal communicated at 2400 [[baud]], so rather than acquire four individual circuits to carry such a low-speed transmission, the airline has installed a pair of multiplexers. A pair of 9600 baud modems and one dedicated analog communications circuit from the airport ticket desk back to the airline data center are also installed.<ref name = "Bates" /> Some [[Proxy server#Web proxy servers|web proxy servers]] (e.g. [[polipo]]) use TDM in [[HTTP pipelining]] of multiple [[HTTP]] transactions onto the same [[Transmission Control Protocol|TCP/IP connection]].<ref>{{cite journal|title = rfc2068 - HTTP/1.1 |year = 1997 |doi = 10.17487/RFC2068 |url = http://tools.ietf.org/html/rfc2068 |access-date = 2010-09-23 |last1 = Fielding |first1 = R. |last2 = Gettys |first2 = J. |last3 = Mogul |first3 = J. |last4 = Frystyk |first4 = H. |last5 = Berners-Lee |first5 = T. }}</ref>

[[Carrier-sense multiple access]] and [[multidrop]] communication methods are similar to time-division multiplexing in that multiple data streams are separated by time on the same medium, but because the signals have separate origins instead of being combined into a single signal, are best viewed as [[channel access method]]s, rather than a form of multiplexing.

TD is a legacy multiplexing technology still providing the backbone of most National fixed-line telephony networks in Europe, providing the 2&nbsp;Mbit/s voice and signaling ports on narrow-band telephone exchanges such as the DMS100. Each E1 or 2&nbsp;Mbit/s TDM port provides either 30 or 31 speech timeslots in the case of CCITT7 signaling systems and 30 voice channels for customer-connected Q931, DASS2, DPNSS, V5 and CASS signaling systems.<ref>{{Cite book|title=Breakthroughs in telephone technology: from Bell to smartphones|date=2012|publisher=Britannica Educational |editor=Curley, Robert |isbn=978-1-61530-724-1 |location=New York |page=69|oclc=769190186}}</ref>