Technology Of The T 1 example essay topic

By: Scott CrandellTelecommunications - T 1'digital transmission is what T 1's are all about. T 1's 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. T 1 circuits have grown from point to point links for private networks to switched and dedicated access services.

T 1's 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 T 1. The name T 1 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 T 1 did was allowed "24 voice channels onto a single four-pair wire" (Minoli). The industry decided to switch to T 1's 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 T 1 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. Multiplexing 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 64 K 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. T 1 have capable speeds of 1536 Kbps due to the 24 channels multiplexed into 64 K 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. T 1 transmits over a copper wire and is DS 1 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 T 3, which is equivalent to 28 T 1's. So during the 1970's and the 1980's T 1's and T 3's 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 T 1 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 56 K bps opposed to the 64 K bps with 8 bits. Other types of signaling are also possible. T 1 cable gauge ranges anywhere between 16-26 and is transmitted with repeaters put roughly every mile to preserve the signal. When using a pair-gain repeater the requirement is only every five miles. Repeaters are either pole mounted or placed underground accessed through sewer plates. By the signal being digital re-creation is simple compared to analog with noise and distortion kept to a minimum (Bezar 201).

Data transmission needs a clean circuit with the least possible problems on the line. Various problems can be stopped with equipment such as echo suppresses proper grounding and the elimination of load coils. T 1's should fall within the standard of less than 10-6 errors per bit in order to provide good service. Fiber is becoming popular due to the lack of errors and noise. Fiber doesn't need as many repeaters and doesn't provide power do electric induced noise is not a worry. Further more fiber doesn't require as much maintenance but it costs more and instillation has to be properly done including good splices and no bends larger than two inches in the wire which will cause attenuation.

T 1's can be used for analog voice, data command and control, video teleconferencing or anything else that can be transmitted as digital data (Minoli). T 1's are often used to link offices or campuses together or to link private networks over short distances. An interconnection can be made between two businesses PBX's so the telephone system will act like one unit. By doing this cost can be cut with the use of the same outgoing trunk lines.

With the demands of larger capacity transmission lines T 1's might be the solution to the problem. The technology of fiber, prices of T 1's have already decreased. Users are requiring more bandwidth with the use of video conferencing, connection of networks and the desire for faster service. When choosing what to purchase an assessment of the industry need to be made with all the new advancements planning and implementing something new could be a difficult job.