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. 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 suppressers proper grounding

and the elimination of load coils. T1’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.

T1s can be used for analog voice, data command and control, video teleconferencing or

anything else that can be transmitted as digital data (Minoli). T1s 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 T1s might be the solution to the

problem. The technology of fiber, prices of T1s 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.