TDC 461

Homework #1

Spring Quarter 2001

1. I pick up my phone in Chicago and dial "1-212-555-9822", which is the number of my friend, Sam, who lives in New York City. Ameritech is my LEC and Sprint is my IXC.

A. (5 points) There are two methods by which my telephone could have communicated the dialed digits to my local central office switch, depending on what type of phone I have. For each method, tell me how the central office switch determines the digits that have been dialed.

B. (5 points) Describe the sequence of switching offices that this call passes through from Chicago to New York. Tell me who owns each switch.

2. (5 points) What is the difference between a repeater and a regenerator in a transmission circuit?

3. (5 points) In what year did the FCC rule that equipment made by any manufacturer can be attached to any telephone line, as long as it met certain technical specifications? (Before this, only equipment manufactured by Western Electric could be connected to telephone lines in the United States.) What was the name of the company that won this ruling?

4. (5 points) Using standard Frequency Division Multiplexing, how many voice channels can be carried over an analog trunk that can carry a total bandwidth of 40 MHz?

5. (5 points) Voice signals are filtered to remove all frequencies except those in the range 200 Hz to 3300 Hz before they are transmitted over the telephone network. Why is this filtering done?

6. (5 points) Assume that you have specified that the default Interexchange Carrier (IXC) for your telephone service is MCI. That is, if you just dial 1-415-555-3223, your call is passed up to an MCI POP. Now assume that you’d like to make one call that is carried by AT&T rather than MCI. What can you do to specify a different IXC for a single particular call?

7. (5 points) What is the purpose of a Distribution Frame (or the Main Distribution Frame (MDF)) in a switching center building (also called a wire center)?

8. (5 points) When you pick up your phone to make a call, how does your local Central Office know that you want to make a call? In other words, what physical change occurs in your telephone subscriber loop that allows the Central Office to determine that your phone is off-hook?

9. (5 points) Before 1995 the format for area codes was N(0/1)X, where the first digit was in the range 2-9, the second digit was 0 or 1, and the third digit could be anything (0-9). This resulted in 152 possible area codes (there would be 160, but the 8 codes of the form N11 are not allowed). Now that the area code format is NXX, how many possible area codes are there?

10. (15 points) Your company, located in Detroit, is opening an office in San Jose. You want to provide the least expensive calling method between the two offices. You will use approximately 160 hours per month of office-to-office communication services. You need to be able to support 6 simultaneous connections Your choices are a T1, with a flat rate of $1750 month, WATS and INWATS services, each of which costs $42 a month plus $.15 a minute, and remote call forwarding, with a flat monthly rate of $27 per line and $.25 per minute. Create a table that shows the costs of each option and recommend the option that provides the best solution to this need.