Untitled Essay Research Paper By Scott CrandellTelecommunications
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Untitled Essay, Research Paper By: Scott CrandellTelecommunications – T1’sDigital transmission is what T1s are all about. T1s are the wanted access in the local loop. They provide multiple services simultaneously over the same medium with the ability to have WATS, international, virtual networking, private networking and switched data services. T1 circuits have grown from point to point links for private networks to switched and dedicated access services. T1s have been used for decades with their attributes and functionality keeping them still in use in the industry today. Starting in 1960 multiplexing started with only two users that were multiplexed on one “carrier facility.” More and more copper was added to the local loop till 1970 when a line per subscriber became too expensive and industry turned toward the technology of the T1. The name T1 came from AT&T in the 1960’s and was something just to name the technology till the name was picked up to describe the digital transmission line. What the T1 did was allowed “24 voice channels onto a single four-pair wire”(Minoli). The industry decided to switch to T1s because the cost savings of having 24 channels with less lines used and the room for expansion. Though the switch between massive amounts of copper to T1 solved some problems the lines were not very usable due to technology still using analog signals. Digital finally started being used in the 1970’s because it helped eliminate noise in the circuit followed quickly by PBX that realized the potential of the digital technology. Multtiplexing for analog and digital were both used but analog used space division where digital used time division. Since price between the two types of multiplexing was similar industry started to switch to digital time division multiplexing. Instead of using cross-point technology with analog digital multiplexing was used which allowed an eight contact circuit connection be converted to a single serial datastream and transmitted over the same copper wire (Minoli). Digital multiplexing uses something called pulse coke modulation. The signal is sampled 8,000 times per second and made into 8 bits. Every channel contains 64K bps with is figured by 8000 X 8. Transmission can go as high as Gigabits per second and have two or more conversations happening at once. T1 have capable speeds of 1536 Kbps due to the 24 channels multiplexed into 64K bps channels. Synchronous and asynchronous are two types of time division multiplexing. Synchronous multiplexing has a system where a mechanism determines where each bit belongs whereas asynchronous has information in packets that have a label as to where to send the data. One data bit has to be used to determine the end and beginning of each packet. Multiplexing is used for data, voice and a combination of both. T1 transmits over a copper wire and is DS1 formatted. It can be transmitted over fiber and is better for longer runs to eliminate noise and repeaters on the line. 672 channels can be achieved with a T3, which is equivalent to 28 T1s. So during the 1970’s and the 1980’s T1s and T3s were used for the backbone of the transmission network (Bezar 200). In the CO either one or two interface cards are used to receive the 24 individual telephone circuits. The T1 cards have the ability to convert the analog to digital with the 8.000 per second sampling required to fit the 8 bit compressed sample. After it is converted to digital and it is transmitted it has to be converted back to analog in order for the DTMF signaling to be effective. If the conversion of analog to digital and vise versa does not want to be made 7 bits instead of 8 can be used which only transmits 56K bps opposed to the 64K bps with 8 bits. Other types of signaling are also possible. T1 cable gauge ranges anywhere between 16-26 and is transmitted with repeaters put roughly every mile to preserve the signal.