Ntc360

Course: NTC 360

Use short answers to explain the difference between:

* Rotary and Dual Tone Multi-frequency (DTMF)

* Wide Area Telecommunications Service (WATS) and leased lines

* Private Branch eXchange (PBX) and Centrex

* The layers of the International Standards Organization-Open Systems Interconnection (ISO-OSI) model

1. Explain the difference between Rotary and Dual Tone Multi-frequency.

The major difference between Rotary and Dual Tone Multi-frequency(DTMF) is the method by which they are executed to the phone system. Rotary uses interrupted pulses to communicate the characters or digits on the rotary dial. Rotary systems were different depending on the country in which it was used having certain amounts of pulses to represent certain digits on the rotary dial. For example, in the United States, dialing a number five on a rotary dial set would open and close electrical contacts on the phone five times thus sending five pulses. Dual Tone Multi-frequency(DTMF) also know as touch tone dialing is used by sending a combination of two tones over the phone system. An example of how these two tones are sent can be illustrated by these two tables taken from http://www.answers.com/topic/dual-tone-multi-frequency:

DTMF keypad frequencies (with sound clips)

1209 Hz 1336 Hz 1477 Hz 1633 Hz

697 Hz 1

2

3

A

770 Hz 4

5

6

B

852 Hz 7

8

9

C

941 Hz *

0

#

D

An example of a combination of tones could be illustrated by selecting the number five on the keypad. In this example, when someone would dial the number five, two tones at 770 Hz and 1336 Hz would be sent.

DTMF Event Frequencies

Event Low frequency High frequency

Busy signal

480 Hz 620 Hz

Dial tone

350 Hz 440 Hz

Ringback tone (US)

440 Hz 480 Hz

An example from this table shows that when someone picks up their phone and hears a dial tone, two frequency are actually heard at 350 Hz and 440 Hz.

References:

http://www.answers.com/topic/rotary-dial

http://www.answers.com/topic/dual-tone-multi-frequency

2. Explain the differences between Wide Area Telecommunications Service (WATS) and leased lines.

A Wide Area Telecommunications Service or WATS is "a special direct distance dialing (toll) service whereby a subscriber installs a dedicated line arranged for either inward or outward calls (not both) between the customer's premises and a specific geographic area. Monthly charges are based on the size of the area in which the calls are placed, not on the number or length of calls." (http://www.isg-telecom.com/telco_glossary.htm#W) This type of service is typically used for inbound toll-free service such as an 800 number. A leased line or private line is "any communication channel leased for exclusive use from a common carrier". (http://www.isg-telecom.com/telco_glossary.htm#L) This was pretty much a dedicated line between two locations. Many companies used this type of line between two or more locations for dedicated inter office communication. The key difference between the two are that a WATS is a specialized line set up to receive long distance communications to a specified area or to allow long distance communications to a specified area while a leased line is a dedicated line set up between two distinct locations.

3. Explain the difference between Private Branch eXchange (PBX) and Centrex.

Private Branch eXchane (PBX) is "a telephone system within an enterprise that switches calls between enterprise users on local lines while allowing all users to share a certain number of external phone lines." (http://searchvoip.techtarget.com/sDefinition/0,,sid66_gci214278,00.html) A PBX is managed by the company or organization that uses it and is responsible for its own upgrades and system configurations. A Centrex (central office exchange service) is "a service from local telephone companies in the United States in which up-to-date