Talk:Digital Signal 1
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I'm a first time editor here, so I hope I'm going about this in the right way. I'm a jack of all trades but a master of only 1, T1 that is. As one of the original 5 T1 carrier sales engineers beginning in 1966, there are many things I can clear up that are anything but clear as we view things today. T1 is truly an amazing resource, less appreciated than it should be, and still capable of achieving more than any other available means of serving the public hunger for integrated services by digital network means. Why ISDN has been so poorly promoted is the primary reason why it hasn't been more popular with the public.
In the early days of T1 deployment it represented an enormous leap forward to applications engineers, cutting the inplace cost of comparable analog systems by a factor of 3, a gap that preceded what we are accustomed to with silicone based modular systems technologies like PCs and home media equipment that gets better and cheaper with each new model that comes along. Meanwhile, analog systems were less well suited to large scale integration of functionality, and by comparison their manufacture escalated costs while the T1 alternative products got cheaper and better day by day.
There were also very significant operational benefits to T1 so long as it was properly deployed, and it took a few years for expertise to catch up with feasibility. But it didn't take to learn that T1 was worth the effort. By 1970 T1 was among the hottest commodities being sold in the telecom hardware biz, and the rapid evolution of technology and newly learned techniques accelerated acceptance, but leapfrogging became a problem that lingers to this day....
Designers foresaw the need for an aggregation hierarchy which theoretically became known as T2, T3, T4/5, etc. As T1 became the popular choice of technologies the plan was to design and build new cables that would be installed to support T2, a signal that presented a much more difficult transmission challange than the 772 kilohertz wave envelope emitted by T1. Before these cable designs could be mastered the engineering labs were already making noise about optical fiber, so the future seemed headed in that direction and away from copper twisted wire. Interim experimentation with coax and broad guage twisted pairs was conducted during the '70s. The original T2 thru T5 hierarchy was expected to be as follows:
T2=T1x2= 48channels=3.152MBS= 1.5Megahertz
T3=T2x2= 96channels=6.312MBS= 3.2Megahertz
T4=T3x2=192channels= 13MBS= 6.5Megahertz
T5=T4x2=384channels= 26MBS= 13Megahertz
Back when these projections were being contemplated the highest bundling of 4Khz VF channelized multiplex bundles were conveyed either on coaxial tubes or microwave basebands, with the largest bundles known to man at the time being were Master Channel Groups of 300 channels each. As pragmatists began to attempt to configure twisted wire cables that could support the first aggregating step, T2, they struggled with the regenerator capability to pass analog signal envelopes of 3MHz or better through repeaters spaced far enough apart to make be operationally and economically feasible. Meanwhile GTE's transmission manufacturer Lenkurt Electric produced an optical T2 array for electric power companies that operated on fiber optic cable, and Collins Radio installed beta tests of a comparable system using 2 parallel coaxial cables of the kind being used by the fledgling cable TV industry.
Frustration offset success and the industry at large began to recognize that the digital future was optical, and that it was quite a ways off. In the interim T1 popularity continued to grow for a broadening set of reasons, not the least of which was the elimination of frequency sensitive channelizing elements. This in turn allowed channel differentiation to be reassigned to a broadening array of signal interface types, which meant that a T1 channel bank could be configured to host many types of circuit applications on a plug and play basis. The economic and operational impact of this was enormous, but is seldom mentioned by writers of T1 history.
The frame packaging of the 1.544MB 24 CH T1 bundle underwent refinements during this evolutionary period, and channel bank packaging nomenclature known as D types became intermingled with framing definitions. There has been considerable discussion of D1, D1A, D1B, etc., but little mention of the fact that channel bank configuration changes were also part of the ID meaning. By the time we got to D3/D4 we understood SuperFrame bitstream references but much confusion remains about the fact that D4 also implies twin channel banks, or 2xT1 bundles with latest bit frame organization. Not many people realize that ESF is D5 framing. These subtleties only matter if you really want to know why T1 history can be so confusing to people who didn't actually deal with it daily.
My best attempt to curtail this longwinded dissertation will be done here. T1 is arguably the most signficant network transmission protocol in the development of the internet, not to say that TCP/IP is less important, but to simply suggest honest assessment of how digital media have actually evolved. It is also important to recognize that T1/E1 continue to hold great future potential for those who want to delve into how to take a couple of megabits of data transport capacity and find the most practical ways to do positive things by available means. Thanks for your attention; there's a lot more detail in this history if people are interested.
I just have a minor issue about the "Trivia" Section. Yes, T1 and DS1 are quite often used in an interchanble manner. However; T1 actually identifies the physical interface while DS1 is in reference to singnaling. It may be common, but to be blunt; it is more telco slang than anything else to use them in an interchangable manner.
Sorry, don't know who posted the orginal commented here, it wasn't signed.
I see your point, but many companies (Avaya being one of them) use DS1 as their interface indication, it's not so much slang as the context in which it is used.
What I do have a problem with are the pictures in this article, they are very confusing to non telco people, please have a better description of them within the article or find some better easier to understand pictures. Also, would someone mind adding an alarm section or reference an article to the various alarms (red, yellow, blue).
Thanks!
63.87.170.72 17:28, 7 February 2006 (UTC)
[edit] Physical Medium
How does the physical medium look like? I think its good to have a distict photo of the cross section and terminator jacks, male and female sides. Over what max distance the signal can be tranmitted through such cables?
[edit] Formal Tone
22-Aug-2006: This important, technical article (about common Internet technology DS1) was quickly reworded in formal tone by removing "you" and replacing prepositions them/they with nouns, replacing "where as" with "whereas" and using formal grammar and punctuation. The Notes section was added to cite sources in "<ref\>" tag footnotes, per Wikipedia:Guide_to_layout (The "References" section is more tedious, requiring alphabetic by authors). The alternate abbreviation "T-1" was changed to match "T1" wherever used. The diagram errors in Figure 2 ("DS1 SF Frame") were image-edited/uploaded to correct final Terminal bits as "01" + new caption. Beware of other grammar or punctuation problems still in this complex article. -Wikid77 18:33, 22 August 2006 (UTC)
