THE TELEPHONE SYSTEM

Transmission Deteriorations

Three transmission problems:

• Attenuation. Loss of energy as the signal propagates towards its destination.
• Delay distortion. Different components have different speeds. The signal arrives later and distorted.
• Noise. Types: thermal, crosstalk, and impulsive.

Another problem is echoes. When a part of the signal is reflected.

• One solution for voice is an echo suppressor,
• Change the line from full-duplex to half-duplex.
• Change the direction of transmission quickly.
• On lines of more than 2000 km.
• Can react in 2 to 5 ms
• Detects the voice from one end and eliminates those going the other way
• They are deactivated when they detect a tone at 2100hz (in-band signaling)

An alternative is an echo canceller,

• Preserve full-duplex transmission
• Subtracts an echo estimate from the signal.
• They replace suppressors.

In the long term, it is necessary to convert the local loops to fiber, due to the advancement of technology that at one point will allow not only voice transmission but also video, but it is very expensive to change the entire twisted pair for fiber optics; this solution is called FTTH (fiber to the home, fiber to homes).

An intermediate solution is to first install fiber only in the streets and continue to use the twisted pair for the connection to the home (called FTTC, Fiber to the curb, fiber to the sidewalk).