7.3
SIGNALING TECHNIQUES
155
appropriate, some supervisory techniques are also reviewed. Common-channel signaling
is discussed in Chapter 13, where we describe the CCITT No. 7 signaling system.
7.3.2.2.1
Multifrequency Signaling
. Multifrequency (MF) signaling has been in wide
use around the world for interregister signaling. It is an in-band method using five or
six tone frequencies, two tones at a time. It works well over metallic pair, FDM, and
TDM systems. MF systems are robust and difficult to cheat. Three typical MF systems
are reviewed in the following:
MULTIFREQUENCY SIGNALING IN NORTH AMERICA--THE R-1 SYSTEM
. The MF signaling
system principally employed in the United States and Canada is recognized by the CCITT
as the R-1 code (where R stands for "regional"). It is a two-out-of-five frequency pulse
system. Additional signals for control functions are provided by frequency combination
using a sixth basic frequency. Table 7.2 shows the ten basic digits (09) and other com-
mand functions with their corresponding two-frequency combinations, as well as a brief
explanation of "other applications." We will call this system a "spill forward" system.
It is called this because few backward acknowledgment signals are required. This is in
contraposition to the R-2 system, where every transmitted digit must be acknowledged.
CCITT NO. 5 SIGNALING CODE
. Interregister signaling with the CCITT No. 5 code is very
similar to the North American R-1 code. Variations with the R-1 code are shown in
Table 7.3. The CCITT No. 5 line signaling code is also shown in Table 7.4.
Table 7.2
North American R-1 Code
a
Digit
Frequency Pair (Hz)
1
700
+ 900
2
700
+ 1100
3
900
+ 1100
4
700
+ 1300
5
900
+ 1300
6
1100
+ 1300
7
700
+ 1500
8
900
+ 1500
9
1100
+ 1500
10 (0)
1300
+ 1500
Use
Frequency Pair
Explanation
KP
1100
+ 1700
Preparatory for digits
ST
1500
+ 1700
End-of-pulsing sequence
STP
900
+ 1700
ST2P
1300
+ 1100
Used with TSPS (traffic service position system)
ST3P
700
+ 1700
Coin collect
700
+ 1100
Coin control
Coin return
1100
+ 1700
Coin control
Ring-back
700
+ 1700
Coin control
Code 11
700
+ 1700
Inward operator (CCITT No. 5)
Code 12
900
+ 1700
Delay operator
KP1
1100
+ 1700
Terminal call
KP2
1300
+ 1700
Transit call
a
Pulsing of digits is at the rate of about seven digits per second with an interdigital period of 68
± 7 msec. For
intercontinental dialing for CCITT No. 5 code compatibility, the R-1 rate is increased to 10 digits per second. The KP
pulse duration is 100 msec.
Source: Ref. 4.
Summary :
Table 7.2 North American R-1 Code a Digit Frequency Pair (Hz) 1 700 + 900 2 700 + 1100 3 900 + 1100 4 700 + 1300 5 900 + 1300 6 1100 + 1300 7 700 + 1500 8 900 + 1500 9 1100 + 1500 10 (0) 1300 + 1500 Use Frequency Pair Explanation KP 1100 + 1700 Preparatory for digits ST 1500 + 1700 End-of-pulsing sequence STP 900 + 1700 ST2P 1300 + 1100 Used with TSPS (traffic service position system) ST3P 700 + 1700 Coin collect 700 + 1100 Coin control Coin return 1100 + 1700 Coin control Ring-back 700 + 1700 Coin control Code 11 700 + 1700 Inward operator (CCITT No.
Tags :
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