8.1 Signaling for Analog Telephone Networks

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needed for one subscriberto interconnect with any other in that network.

and

then gives the local switch the data necessary to identify therequired distant subscriber and hence to route the call properly.

It also of the call along its path.

Signaling also gives the subscriber certain ,such as , and .

may also be considered a

form of signaling.





There are several classifications of signaling:



A functional breakdown of signaling.



is provided between modern switchingmachines by

The is provided by

The functions inform thecalling subscriber regarding Theinforms the called subscriber of a call waiting or an extended off-hook condition of his or her handset.

Dial tone, Busy tone, Ring backRinging, Paging, Off-hook warning





Intentionally Left Blank

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SUPERVISORY SIGNALING

the

whether a or whether a

How do we know the difference between supervisory and dialing?

Primarily by duration-The and is

(which is transmitted in the same direction for a longer

duration

The switch is sensitized to duration to distinguish betweensupervisory and dialing of a subscriber loop.



SUPERVISORY SIGNALING

E and M Signaling

is ,particularly with

E-lead and M-lead signaling systems are semantically derived

from historical designation of signaling leads on circuit drawingscovering these systems

between theand what we may call

(signaling interface).

which carries signals to theswitching equipment



E and M signaling

E and M Signaling




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Each of these can derive the four E and M signaling states.



Low-Frequency AC Signaling Systems

A n ac signaling system operatingare termed low

frequency.

Low-frequency signaling systems aretypically 50 Hz , 80 Hz , 135 Hz , or 200 Hz

It is such systemsbecause of the excessive distortion and band limitation

introduced.



In-Band Signaling

to signaling systems using an , or

, to conveysignaling information.

Single frequency and two-frequency signaling systems utilize the 2000-

to 3000-Hz portion , where less speech energy is concentrated.



Single-frequency signaling: In-band



Single-Frequency Signaling.



F unctional block diagram of a single-frequency signaling circuit



Two-Frequency Signaling

, supervision is by necessity;

otherwise subscribers would have an annoying 2600-Hz

tone on throughout the call.

Two-frequency signaling is used for bothand .

systems is

The term while



, a to bypass signalingtones may be used.

A typical 2V F line signaling arrangement is thewhere and .

which refers to theby an inadvertent sequence of voice

tones through the normal use of the channel.

Two-Frequency Signaling



Out-of-Band Signaling

W ith out-of-band signaling,

The advantage of out-of-band signaling is that either system,, may be used when

Talk-down cannot occur because all supervisory information ispassed out of band

The preferred CCI TT out-of-band frequency is ,

whereas is commonly used in the United States.

Out-of band signaling is used exclusively oncarrier systems ( F DM), not on wire trunks.




The major advantage of out-of-band signaling is that, whether

, during the entire telephone conversation.

Out-of-band signaling is one method of






Single-frequency signaling: out-of-band.






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ADDRESS SIGNALING: INTRODUCTION

.



Two-Frequency Pulse Signaling

Two-frequency signaling is commonly used as anemploying the for the

transmission of information.

uses and to represent.

It uses a four element code, permitting 16 differentcoded characters.

It may also be used for



Sending duration of binary elements 35 ± 7 ms. Sending duration of blank elements

between binary elements 35 ± 7 ms. Element x is 2040 Hz; element y is 2400 Hz.

CCITT Signal Code System No. 4



with the code is based on.

Each line signal consists of an

followed by a

The P signal consists of both frequencies (2VF),and the suffix signal consists of one frequency ,

where and

Two-Frequency Pulse Signaling



CCITT No. 4 Line Signaling



Multifrequency Signaling

It is an utilizing ,

Multifrequency signaling works equally well over



SOCOTEL

is an used principally in F rance,areas of F rench influence, and Spain with some modifications.

may be dc, 50 Hz, or 2000 Hz. T he samefrequencies are used in both directions.

Basic SOCO TEL MF Signaling Code



Multifrequency Signaling in North America: The R-1 Code

system principally used in theis recognized by the

It is frequency-pulse system.

are provided bycombinations using a .

The R-1 Code a (North American MF)



CCITT No. 5 Signaling Code.

Interregister signaling with the CCI TT No. 5 code is very

CCITT No. 5 Codea Showing Variations with R-1 Code

CCITT No. 5 Line-Signaling Code

Line signaling for CCI TT No. 5 code is2VF, with f1 2400 Hz and f2 2600 Hz



The R-2 Code

The R-2 code is listed by CCI TT ( as a

Taking full advantage of combinations of ,

This number is doubled in each direction by having meaningand



European R-2 System, Address Signaling, D TMF Code



Line Conditions for R-2 Code



Subscriber Tones and Push-Button Codes (North America)

in many places in the world are either dial orpush button.

is more versatile, and more rapid dialingcan be accomplished by a subscriber.

North American Push-Button Codes



Audible Tones Commonly Used in North America

(Call-progress tones presented to the subscriber)




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An important factor to be considered in switching system design thatdirectly affects both and is

*Postdialing delay

T his is the amount of time it takes after the calling subscriber completes

dialing until is received.

Another important consideration isas the setup proceeds from originating exchange to terminating

exchange.

Register occupancy time

By reducing register occupancy per call , we may be able to.



o Link-by-link signaling may be defined as a signaling system where

must be

Link-by-link signaling

o The R-1 system is an example of link-by-link signaling.

o End-to-end signaling abbreviates the process such that tandem/transit exchanges receive only the

End-to-end signaling



o The need beonly between the exchange and theexchange in the call setup.

T hus the signaling process may be carried out much morerapidly, .

Intervening exchanges on the call route ,

to thenext exchange in the sequence.

Leading register:

o The key to end-to-end signaling is the concept of leadingregister.

thatrouting until a speech path is set

before releasing to prepare for another call setup.



345-6789 345-6789 34 45

6789




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, the assignment and use of telephone numbers,

There can be two types of numbering schemes:

1. Uniform numbering

Most in the nontoll or local-area case arebased on , although some are based on six.

Uniform numbering can



1. The with the callbecause it "knows when the last digit has been

received.2. Knowing the number of digits to expect provides

and makes simpler.

For nonuniform numbering,built in. It is the initial digit or digits that will

tell how many digits are to follow, at least in theory.

1. Nonuniform numbering

W ith nonuniform numbering, anacross a network up to the

terminating exchange, and the call setup is released only after

time out has run its course.



W ith nonuniform numbering systems, national andinternational networks are better

with good features of backwardinformation, such as the R-2 system.




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Conventional analog associated channel signaling (upper drawing) versus separate channel signaling (lower drawing).;

. CCS = common channel signaling such as CCI TT Signaling System No. 7.



Separate channel signaling may or may not go on that samemedium or path.

The European PCM system called E1 uses this type of signaling

One separate digital channel covers all supervisory signaling for 30traffic channels.

If it travels on the same medium and path as its associated trafficchannels, it is still associated channel signaling.

That separate channel can follow a different path using, perhaps,different media.

CCITT Signaling System No. 7 is always a separate channel, but canbe associated or disassociated.

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8.1 Signaling for Analog Telephone Networks