What is the plain old telephone system (POTS)?
POTS was created in the early 1900’s at which time its primary function was to carry analog signals for supporting voice conversation that is until the early 1970’s where it could carry voice and computer data signals. The computer data signals eventually far surpassed the analog signals towards the end of the 20th century but POTS is still basically a voice carrying medium.
What is the typical frequency range for the human voice?
The average frequency range for a human voice which usually is comprised of multiple frequencies is no lower than 300 Hz and no higher than approximately 3400 Hz a bandwidth of 3100 Hz. The telephone system network was designed to transmit signals of around 3100 Hz but allocates 4000Hz per channel.
The local loop connects what to what?
The local Loop is the telephone line which is comprised of either 4 or 8 wires that leaves your business or house and connects to the telephone company’s central office (CO) which has the necessary equipment to generate a dial tone, interpret the telephone number dialed, see if special services are required and that it connects the receiving call to the next point. From the CO the signal can go over another local loop to a house in your neighborhood to another CO in the neighboring community but the call is not long distance or finally to a long distance provider.
What is a LATA?
A LATA stands for local access transport area which is where a telephone call remains in a geographic area such as a large metropolitan area or a part of a large state. LATA sometimes referenced as an intraLata call is local and will be handled by the local telephone company but if the call resonates to another LATA it than must be handled by a long distance company. However due to cellular companies and now even wired lines offering one rate plans for local and long distance calls many believe the LATA function will eventually be unnecessary one day. Calls that pass from one LATA to another are inter-LATA, or long distance
How does a trunk differ from a telephone line?
A telephone line which is comprised of a subscriber loop has a unique telephone number associated with it and typically transmits analog signals which require amplifiers every few kilometers. This is not the case with a trunk which is usually not associated with a particular telephone number but is also a telephone connection that carries multiple telephone signals usually digital and high speed. A trunk carries hundreds of voice and data channels usually from CO’s and other telephone switching centers and require repeaters every few kilometers.
List the most important results of the Modified Final Judgment of AT&T.
The Modified Final Judgment of AT&T which was a court ruling that basically labeled AT&T a monopoly as it controlled all the long distance telephone lines in the U.S. and a majority of the local telephone systems therefore AT&T was ordered to break up AT&T into separate companies. The results of the divestiture was that 23 of the bell operating systems that were once controlled by AT&T were now separated into seven regional bell companies (RBOCs)to compete with the14,000 local carriers but as a result due to the RBOCs size the number of local companies dropped and due to merger & acquisitions (M&A)left only 3 RBOCs remaining which are now known as AT&T, Qwest and Verizon. Another result of the court ruling was the U.S. was now divided into LATAs and also allowed more competition in the long distant market with MCI and Sprint now offering long distance along with AT&T. Also the local carriers were now required to allow the long distance companies to have equal access to LATAs and people were now able to buy their own telephones whereas before they had to lease them from the telephone company. Local carriers where now known as local exchange carriers (LECs) and long distance companies were called interexchange carriers (IECs or IXCs).
7. What is the difference between a local exchange carrier and an interexchange carrier?
The difference between local exchange carriers (LECs) and an interexchange carrier (IECs) is that LECs are local telephone companies that provide local telephone service and IECs are long distance carriers that provide domestic U.S. long distance services between the LEC and the LATA. A LEC offers a number of services such as Centrex (a service in which up to date phone facilities at the phone company's local office are offered to business users so that they don't need to purchase their own facilities, private and tie lines (a private telephone channel, leased from a telephone company, that connects two or more Private Branch Exchange (PBX) systems which is a computerized self-contained telephone system that sits in a telephone room on a company’s premises) and a multitude of other services such as call waiting and conference calls. An IEC can also offer a multitude of services including credit card and calling card dialing; 700, 800, 888 and 900 numbers; and operator and directory assistance.
List the most important results of the Telecommunications Act of 1996
The Telecommunications Act of 1996 passed by congress paved the way for anyone to offer local telephone service in homes and businesses. New providers were now called competitive local exchange carriers (CLECs) which could include IECs, cable companies, small companies with virtually no equipment and electric companies. For example it was a distinct advantage for cable companies to offer bundled services and since they already had cable laid down across most of the country it was easy to offer telephone service through these lines but it was much more difficult for new companies entering into this space because they did not have the infrastructure in place and in order to rollout that type of infrastructure the costs would have been astonishing. Therefore another mandate in the 1996 act due to these constraints was that the already positioned local phone companies known as incumbent exchange carriers (ILECs), all local exchange carriers before the 1996 act, were now required to give CLECs access to their infrastructure but the CLECs were still forced to pay more or full price for access to ILECs local lines. LECs can also provide long distance service if they can show there is sufficient competition at the local service level.
Why are the 56 kbps modems faster than the older 33,600 bps modems?
The 56 kbps is faster than older 33,600 bps modems because it achieves its speed due to digital signaling through its downstream link however it is a hybrid which means analog signaling is also inclusive as opposed to the 33,600 bps modem using just an analog modulated connection. In a standard call between two modems, your data must be translated into analog before it can be transmitted across the telephone network. This translation is the digital to analog conversion. Once your data reaches a telephone company's Central Office (CO), it's translated back to digital form by a coder/decoder (CODEC) for transmission across the phone company's digital backbone. Unfortunately, because the telephone network contains some random noise, the analog to digital conversion is only an approximation of the original digital signal. However, because most Internet Service Providers (ISPs) connect directly to the phone company's digital backbone using routers, data coming from an ISP never needs to undergo an analog to digital conversion. Instead, the data can be encoded using pulse code modulation (PCM) which we learned about in chapter 2, so that it remains entirely digital until it gets to the CO. Once it arrives, the data is put through a digital to analog conversion before being sent across the analog phone lines to your modem. It was really the introduction of the V.92 modem standard that supported 56,000 bps dial up modems being capable of supporting connections up to 48 kbps as opposed to the 33,600 bps depending on line conditions such as low noise. Unfortunately sometimes there are regulatory constraints that will not allow speeds to exceed a certain levels. Although your modem is a 56k you won't get throughput that fast, thanks to a speed limit set by the Federal Communications Commission (FCC). Sending a signal down a telephone wire requires electrical power so the more power you apply, the greater the chance of a problem called crosstalk. To help prevent crosstalk, the FCC limits the amount of power that phone companies can use to send signals over the network and this cap on signal strength limits data throughput to a maximum of 53 kbps, regardless of what your modem can actually deliver.
Why don’t the 56 kbps modems transmit at 56 kbps?
The reason 56 kbps modems do not transmit 56 kbps is because during transmission in both directions an analog signal is converted to a digital signal where noise is introduced reducing the transmission rate even though it is possible a small data stream can transmit 56k kbps. Also as talked above throughput of 56k cannot be achieved due to a speed limit set by the Federal Communications Commission (FCC). Sending a signal down a telephone wire requires electrical power so the more power you apply, the greater the chance of a problem called crosstalk. To help prevent crosstalk, the FCC limits the amount of power that phone companies can use to send signals over the network and this cap on signal strength limits data throughput to a maximum of 53 kbps, regardless of what your modem can actually deliver. Another reason besides noise degrading a signal and slowing it down is the distance. The further you are from the CO the greater your chance for experiencing noise and the slower the transmission rate. You may at best receive data in the upper 40,000 bps range if your location is close to the CO.
