Editing Digital Signal 1 (section)

==Origin of name==
The name T1 came from the carrier letter assigned by AT&T to the technology in 1957, when digital systems were first proposed and developed, AT&T decided to skip Q, R, and S, and to use T, for ''time division''. The naming system ended with the letter T, which designated fiber networks. Destined successors of the T1 system of networks, called ''T1C'', ''T2'', ''T3'', and ''T4'', were not commercial successes and disappeared quickly. Signals that would have been carried on these systems, called ''DS1'', ''DS2'', ''DS3'', and ''DS4'', are now carried on T1 infrastructure.<ref name="DCB">{{cite web|title=T1, Where Does the "T" Come From? Some Bell Labs History from Dr. John Pan|url=http://www.dcbnet.com/notes/0103t.html|work=Data Comm for Business, Inc.}}</ref>

''DS-1'' means ''Digital Service{{dash}}Level 1'' and has to do with the signal carried—as opposed to the network that delivers it (originally 24 digitized voice channels over a T1). Since the practice of naming networks ended with the letter ''T'',<ref name="DCB"/> the terms ''T1'' and ''DS1'' have become synonymous and encompass a variety of services including voice, data, and ''clear-channel pipes''. The line speed is always 1.544&nbsp;Mbit/s, but the payload can vary greatly.<ref name="CDE">{{cite encyclopedia|url=http://lookup.computerlanguage.com/host_app/search?cid=C999999&term=ds1&lookup=Go|title=DS definition|publisher=The Computer Language Company|encyclopedia=The Computer Desktop Encyclopedia (CDE)}}</ref>