Understanding Telephone Networks: Technologies and Components
Currently, basic telephone lines are analog, but once the signal reaches the operator, it is digitized and transmitted between different operators in the network core, making it digital. It only changes back to analog when the signal is sent to the receiver.
Today’s RTB (basic telephony network) consists of switching centers and links that unite subscribers. The Integrated Services Digital Network (ISDN) began as an attempt to develop a digital line connecting with power users. The subscriber loop is the link that allows our telephone communication with the telephone network through the local exchange, typically using 2-wire (twisted copper pairs).
Telephone Network Technologies
- Hybrid Fiber-Coaxial (HFC): This technology uses a hybrid of coaxial and copper pair cables, offering telephony, data, TV signal distribution, return channel, and value-added services.
- Wireless: This technology transmits the telephone signal from our homes to base stations using radio waves. The distance from the base station has to be short and free of obstacles. The signal is then transmitted to the telephone system using fiber optics. Each user will contact the local exchange through a base station with adequate coverage.
Advantages of Wireless Technology
- High transmission capacity.
- Much faster network installation because no cable is needed.
- Simple maintenance.
Disadvantages of Wireless Technology
- Difficulty ensuring no obstacles exist between the user’s antenna and the base station.
- Not suitable for urban settings.
Central Phone Systems
To determine the number of lines connecting N phones, use the formula: Number of lines = N (N-1) / 2.
In a Star Network, all phones are connected to a central point, which provides connections between users who want to communicate at all times (Number of lines = N).
Switching Circuits
The switch circuit is responsible for making connections. The phone signal comes through an input line and exits through an output line, carrying the signal to the receiver.
- Space Switches (Spatial Division): These establish a physical path between input and output, so each connection has a different and unique path.
- Time Switches (Division in Time): These assign a time interval for each signal being conveyed.
Telephone Terminals
The telephone is an acoustic transducer that converts electrical energy and vice versa. It converts the voice signal picked up by a microphone into electrical signals suitable for transmission through the phone line to the recipient, and performs the inverse process.
A telephone call has three phases: call setup, communication or information transfer, and call release.
Circuit Components
- Phonics Circuit: Consists of a microphone and a speaker.
- Local Suppressor Circuit: Formed by a transformer, it prevents the person speaking through the microphone from hearing their own voice through the speaker.
- Supply Circuit: Powered by a 48V DC voltage received from the local exchange through the phone line.
- Ringer Circuit: Activates the ringer when receiving a call signal from the central exchange.
Dialing Systems
The dialing system encodes and sends the subscriber number of the phone we want to call through the telephone line. Rotary dial phones produce electrical signal pulses with a number depending on the number selected. Nowadays, DTMF (Dual-Tone Multi-Frequency) or tone dialing is more commonly used.
Telephone Installation
- Base Unit: Part of the terminal where you will find the keyboard and the electronic circuitry that processes the signal corresponding to each voice actor, and the power supply for these circuits.
- Handset or Headset: Contains the speaker and microphone, allowing us to establish voice conversations.
- Spiral Cable: Connects the handset with the base unit. It has 4 wires: 2 for the speaker and 2 for the microphone.
The telephone connects to the user via a rosette, which in turn connects to the phone line.