(Teletech 1996)

Md. Habibur Rahman

Signaling is the extra electrical information other than the traffic. The primary purpose of Signaling system in a Telecommunication network is to enable the network to exchange information needed for the handling of Telecommunication traffic.

TA,TB :terminal of users equipment

LA,LB :Local Subscribe network

E1,2,3,4 :Switching equipment

J1,2,3,4,5,6,7,8 :Trunk or Junction Circuit

Fig-1: A Typcle Telecom Network

The idea of signaling is so wide that it is not possible to clarify about signaling in such a short article. CCITT or ITU-T circulated a large volume of Recommendations in its periodicals, Journals etc. However a few of them which are closely related in our known systems shall he discussed here. Two different signaling philosophies are employed for Telecommunication Signaling.

(1) Channel Associated signaling Where (he signals and traffic are carried in the same channel or in a signaling channel permanently associated with it.

(2) Common Channel Signaling Where the signaling intonation carried independently on a network by the labeled message, Relating o end users, the signaling are of two types.

i) Line Signaling Where Seizure, Acknowledge Supervision, Clear forward, Release guard, Connect disconnect etc. are considered,

ii) Register Signaling Where the information about the users such as terminal number, network number or other information having numerical value are considered.


Methods or transmission of signals

1. Alternating current Loop make-break, Polarity change, Eart1~ or Battery Connect - Disconnect

2. Alternating Current (1) Inband - 2400, 2600 Hz.
(2) Out hand -3825 Hz
(3) TS16 in PCM.

Due to the type Equipment separated versions of signaling have been introduced.

(I) Analogue version (2) Digital Version.

Register signals generated in common Telephone sets are of two type.

(I) Decade Pulse DC make-break ratio 1:2 usually 10 pps for example

(2) Dual Tone Multifrequency (DTMF) : Where combination of two frequencies are selected out of 7 or 8 frequencies such as:

Register signaling in CCITT, No,5 signaling system.

Multifrequency (MF) : Combination of 2 frequencies out of six frequencies as follows:

Register signaling in R2 Analogue Version. Multi frequency Compelled.

There are two groups of frequencies.

(1) Higher group for forward direction. Frequencies are 1380, 1500, 1620, 1740, 1860, 1980 Hz.

(2) Lower group for forward. Frequencies are 1140, 1020, 900, 660, 540 Hz.

Duration signaling each group compelled to transmit each other for confirmation and Proceeding. MFC Higher group:

MFC Lower Group.

Signaling in PCM System


R2 Digital Version


TS1o (in 30 channel PCM system) is used for signaling. TS16 of each frame in a multi frame is assigned to carry signals of 2 traffic channels Fe. 4 hit is used for signaling in one channel i.e. n 2nis In practice only 2 hits are used as follows.

It is important to note that 2 hit in 2ms is sufficient for signaling in one channel, Thus the signaling hit rate is 161KHz which is also used in common channel signaling.

TA: Terminal A. Any Telecommunication Terminal, which generates Traffic.

MTP (Message Transfer part): Bi-directional transmission Path comprising two data channels operating together in opposite direction in same data rate (layer-I). Signaling link for reliable transfer of signaling messages between two directly connected signaling points (Layor-2). Reliable transfer path for messages between origination and destination signaling points (Layer-3).

SCCP (Signaling Connection Control Part) : Logical signaling connections within The CCS network.

AP Application Part, UP = User part.

Advantages of common channel signaling.

1) Faster transport of information

2) More types of information transported,

3) Information transported without traffic circuit connection

4) High availability, reliability and quick recovery

5) High accuracy, low delay

6) Flexible, Layered Protocol and ISO - 051 standard.

Engr Mr. Habibur Rahman is a Divisional Engineer in Bangladesh Telegraph & Telephone Board and presently working at Telecom Staff College, Gazipur.