Information Technology Reference
In-Depth Information
Addressing Digit Signaling
There are two methods for submitting analog address
digits to place a call:
Pulse or rotary dialing
■
Dual-tone multifrequency (DTMF) dialing
■
Pulse dialing uses the opening and closing of a switch at the telephone set. A rotary regis-
ter at the CO detects the opening and closing of the loop. When the number 5 is dialed on
a rotary phone, the dial mechanism opens and closes five times, each one-tenth of a sec-
ond apart.
DTMF uses two tones simultaneously to indicate the dialed number. Table 14-3 shows the
phone keypad and the frequencies used. For example, when the number 5 is dialed, the
frequencies 770 Hz and 1336 Hz are sent to the CO.
Ta b l e 1 4 - 3
DTMF Frequencies
Frequency
1209 Hz
1336 Hz
1477 Hz
697 Hz
1
ABC
2
DEF
3
770 Hz
GHI
4
JKL
5
MNO
6
852 Hz
PRS
7
TUV
8
WXY
9
941 Hz
*
OPER
0
#
PSTN Numbering Plan
The PSTN uses the ITU E.164 standard for public network addressing. The E.164 standard
uses a maximum of 15 digits and makes each phone unique in the PSTN. Examples of
E.164 addresses are the residential, business, IP phones, and cell phones that you use
every day. Each country is assigned a country code to identify it. The country codes can
be one to three digits in length. Table 14-4 shows some examples of country codes.
Ta b l e 1 4 - 4
E.164 Country Codes
Country Code
Country
1
United States, Canada
1-787, 1-939
Puerto Rico
55
Brazil
39
Italy
