In Band and Out of band signaling

In Band signaling - In-band signaling is the sending of voice data and control information in the same voice band (300Hz to 3.4 kHz) on the same channel, as used for data.

           Ex- When we dial a number this number is encoded and transmitted across the telephone line as Dual-Tone Multi-Frequency (DTMF) tones. This tone is handed by the telephone exchange switch. Then the switch is routed the call according to the Dual-Tone Multi-Frequency (DTMF) tones. When the trunk circuits were in idle (not in use), it would have a 2600 Hz signal (single tone).A failure in the trunk circuit facility would cause the absence of 2600 Hz tone. This control toned is gone through same channel which voice data is going.

Out of band signaling - Out-of-band signaling is the exchange of call control information in a separate band from dedicated channel (as in Common Channel Signaling). Out-of-band signaling establishes a separate digital channel for the exchange of signaling information. This channel is called a signaling link. Then the signaling links are used to carry all the necessary signaling messages between nodes.

Ex- When we take a call by dialing numbers, there is a trunk selected, and other pertinent information are sent between switches using their signaling links, rather than the trunks which will ultimately carry the conversation.

Digital Transmission

The fundamental transmission concept is to transmit the minimum possible frequency or the bandwidth with maximum possible number of channels or the bit rate.

When we consider the analog transmission we can’t transmit much distance than digital transmission. Therefore we need to use small bandwidth. Using that small bandwidth can transmit much distance. Therefore we use modulation techniques to reduce the bandwidth. FDM multiplexing system is combining number of channels to convey over common transmission medium. Major advantage of analogue transmission is occupied band width is low When we use frequency modulation in low pass filter there are two, out come upper side bandwidth and lower side bandwidth. By choosing the lower side bandwidth we can reduce bandwidth of the signal.

In digital transmission we can have more than solutions compare to analog.

Theoretically we know Nyquist Theorem, it tells us relationship between bandwidth and channel capacity.

                             C = 2Blog₂M

C- Channel capacity   ,    B – Bandwidth       ,    M – signal levels 

If we want increase channel capacity for a value of bandwidth need to increase signal levels.

In digital transmission we can use time division multiplexing (TDM).using this technique we can reduce bandwidth. In this TDM large numbers of channels are put into one line and transmit. . In the digital transmission can use the available bandwidth of the channel much more efficiently as compared to analogue system.