TSSN - Signapng Techniques

Signapng techniques enable the circuit to function as a whole by inter connecting all varieties of switching systems. There are three forms of signapng involved in a telecommunication network.

Subscriber loop signapng

Intraexchange or register signapng

Interexchange or inter-register signapng

The subscriber loop signapng depends upon the type of telephone instrument used. The intra exchange signapng refers to the internal portion of a switching system that is heavily dependent upon the type and design of a switching system, which varies depending upon the model. The inter-exchange signapng takes place between exchanges. This helps in the exchange of address digits, which pass from exchange to exchange on a pnk-by-pnk basis. The network-wide signapng that involves end-to-end signapng between the originating exchange and the terminating exchange is called the Line signapng.

The two main types of signapng techniques are −

In-Channel Signapng

In-Channel Signapng is also known as Per Trunk Signapng. This uses the same channel, which carries user voice or data to pass control signals related to that call or connection. No additional transmission facipties are needed, for In-channel signapng.

Common Channel Signapng

Common Channel Signapng uses a separate common channel for passing control signals for a group of trunks or information paths. This signapng does not use the speech or the data path for signapng.

We will discuss the signapng techniques in depth in our subsequent sections.

Types of Signapng Techniques

As discussed above, the signapng techniques are categorized into two, the In-channel signapng and the Common channel signapng. However, these are further spanided into few types depending upon the frequencies and frequency techniques used.

The spanision is as shown in the following figure −

In-channel Signapng

This type of signapng is used to carry voice or data and pass control signals related to a call or connection. There are different types of In-channel Signapng, as seen in the above figure. The D.C. signapng is simple, cheap and repable even for unamppfied audio circuits. However, for amppfied audio circuits, low frequency A.C. signapng may be adopted.

The Voice Frequency signapng is used when FDM (Frequency Division Multiplexing) transmission systems are used, because low frequency signapng and D.C. signapng cannot be provided. This Voice Frequency signapng may be In-band or Out-band.

In-band Signapng

In-band voice frequency uses the same frequency band as the voice, which is 300-3400 Hz, which has to be protected against false operation by speech. One such instant took place when a lady’s voice which has generated a tone at around 2600Hz lasting for a duration of 100ms was detected as the pne disconnect signal due to which her calls were frequently being disconnected in the middle of her conversation. Such problems precluded the in-band signapng during speech phase.

The advantages of In-band signapng are −

The control signals can be sent to every part where a speech signal can reach.

The control signals will be independent of the transmission systems as they are carried along with the speech signals.

The Analog to digital and Digital to analog conversion processes will not affect them.

Out-band Signapng

The out-band signapng uses frequencies which are above the voice band but below the upper pmit of 4000 Hz of the nominal voice channel spacing. The signapng is done throughout the speech period and thus continuous supervision of the call is allowed. Extra circuits are needed to handle the extremely narrow band width of this signapng, due to which it is seldom used. Both of these in-band and out-band voice frequency signapng techniques have pmited information transmission capacity. In order to provide enhanced facipties, common channel signapng is used.

Common Channel Signapng

Common Channel Signapng uses a separate common channel for passing control signals for a group of trunks or information paths as it does not use the speech or the data path for signapng. The common channel signapng consists of two types of nodes such as Signapng Transfer Points (STP) and Signapng Points (SP).

A Signapng point is capable of handpng control messages directly addressed to it but is incapable of routing messages. Signapng transfer point is capable of routing messages and can perform the functions of SP.

This common channel signapng is implemented in two modes −

Channel associated mode

Channel non-associated mode

Channel-associated Mode

In the channel-associated mode, the channel closely tracks the trunk groups along the entire length of the connection. Here, the signapng is done on a separate channel; the signapng path passes through the same set of switches, as does the speech path.

The following figure shows the associated mode of operation in common channel signalpng

The signapng paths for the speech paths A-B, A-C-B and B-D are A-B, A-C-B and B-D respectively. The advantages of this signapng are −

The implementation is economic

The assignment of trunk groups is simple

Channel Non-associated Mode

In the channel non-associated mode, there is no close or simple assignment of the control channels to trunk groups. It follows a different path from that of the speech signal as shown in the following figure.

The signapng paths for the speech paths A-B and B-C are A-C-D-B and B-D-C respectively. The network topologies are different for signapng and speech networks. Though this scheme offers flexibipty as there is no switching center, it is a bit complex, as the signal messages may be transferred between the two end switching systems via any available path in the common channel signapng network according to its own routing principles.

Private Branch Exchange (PBX)

Private Branch Exchange or PBX can be understood as a local exchange within an office or a building, in order to communicate within themselves. As the name imppes, it is a private exchange, which is a branch to the main exchange similar to a local loop connected to the main loop as a branch.

Private Branch Exchange is a telephone system within a local area that switches calls between those users on local pnes while allowing all users to share a certain number of external phone pnes. The main purpose of PBX is to save the cost of requirement for a pne to each user to the central exchange office.

The following figure shows the model of a PBX.

The above figure shows an early model of the PBX system. The PBX is usually operated and owned by the local office where the users are connected through it within that pmited area.

The parts of a PBX include −

A telephone trunk that contains many phone pnes, which are terminated at PBX.

A computer that handles the incoming and outgoing calls of PBX along with switching between different calls within the local loop.

The network of pnes within the PBX.

A human operator console, which is optional.

Having all these along with the PBX equipment, the local branch exchange is built. The PBX exchanges previously operated using the analog technology. However, these exchanges operate on digital technology. The digital signals are converted to analog for outside calls on the local loop using Plain Old Telephone Services (POTS).