Computer Science SSS1 Third Term

COMMUNICATION SYSTEM II

Week 2

Performance Objective

The student should be able to:

1. Identify ICT Available Gadget
2. Identify Satellite Dish

 

Content:

What is PSTN? (Public Switched Telephone Network)

PSTN stands for Public Switched Telephone Network or the traditional circuit-switched telephone network. This is the system that has been in general use since the late 1800s.

Using underground copper wires, this legacy platform has provided businesses and households alike with a reliable means to communicate with anyone around the world for generations.

The phones themselves are known by several names, such as PSTN, landlines, Plain Old Telephone Service (POTS), or fixed-line telephones.

PSTN phones are widely used and generally still accepted as a standard form of communication. However, they have seen a steady decline over the last decade.

How Do PSTN Phone Lines Work?

Think of a Public Switched Telephone Network (PSTN) as a combination of telephone networks used worldwide, including telephone lines, fibre optic cables, switching centres, cellular networks, as well as satellites and cable systems. These help telephones communicate with each other.

But simply, when you dial a phone number your call moves through the network to reach its destination – and two phones get connected. To fully understand how a POTS actually works, consider what happens when you dial a number from your own phone.

1. Your telephone set converts sound waves into electrical signals. These signals are then transmitted to a terminal via a cable.
2. The terminal collects the electrical signals and transmits these to the central office (CO).
3. The central office routes the calls in the form of electrical signals through fibre optic cable. The fibre optic conduit then carries these signals in the form of light pulses to their final destination.
4. Your call is routed to a tandem office (a regional hub responsible for transmitting calls to distant central offices) or a central office (for local calls).
5. When your call reaches the right office, the signal is converted back to an electrical signal and is then routed to a terminal.
6. The terminal routes the call to the appropriate telephone number. Upon receiving the call, the telephone set converts the electrical signals back to sound waves.

This may sound complicated, but the thing to remember is that it takes a few seconds for your call to reach its destination. This process is facilitated by using fibre optic cables and a global network of switching centres.

What is PSTN? (Public Switched Telephone Network)

PSTN stands for Public Switched Telephone Network or the traditional circuit-switched telephone network. This is the system that has been in general use since the late 1800s.

Using underground copper wires, this legacy platform has provided businesses and households alike with a reliable means to communicate with anyone around the world for generations.

The phones themselves are known by several names, such as PSTN, landlines, Plain Old Telephone Service (POTS), or fixed-line telephones.

PSTN phones are widely used and generally still accepted as a standard form of communication. However, they have seen a steady decline over the last decade.

PSTN – Understanding the Art of Switching

You could say that PSTNs are all about switching, which forms the backbone of traditional phone networks. When a call is made, switches create a wire circuit between two telephones, with this particular connection lasting as long as the duration of the call.

Now, let’s have a look at each of the four types of switching which take place at different levels.

1. The Local Exchange

A local exchange – which may consist of one or more exchanges – hooks up subscribers to a PSTN line. Also known as a central office or a switching exchange, a telephone exchange may have as many as 10,000 lines.

All telephones are connected to the local exchange in a specific area. Interestingly, if you were to dial the number of your supplier located in the building next to yours, the call won’t leave your local exchange and will be routed to the supplier as soon as it reaches the exchange.

The exchange then identifies the number dialled so it can route the call towards the correct end destination. This process works as follows:

The first three digits of a phone number represent the exchange (the local switch), while the last four digits identify the individual subscriber within that exchange.

This means that when you dial a number and it reaches your local exchange, your call is immediately linked to the subscriber without the need for any further routing.

2. The Tandem Office

Also known as a junction network, a tandem office serves a large geographical area comprising several local exchanges while managing switches between local exchanges.

Let’s say you dialled the number of a client who lives in the same city but in another suburb. In this case, your call will be routed to a tandem office from your local exchange, and the tandem office will route the signal on to the local exchange near your client’s location.

3. The Toll Office

This is where any national long-distance switching takes place.

A toll office is connected to all the tandem offices. For instance, if you have an office in another city you’ll find that, whenever you dial that branch’s number, your call will be switched through a toll office.

4. The International Gateway

International gateways manage international call switching, routing domestic calls to the appropriate countries.

Circuit-Switched Telephone Systems

Circuit Switched Telephone Systems are used by the Public Switched Telephone Network (PSTN). They work with standard analogue telephones where you have one line that allows you to make or receive calls. A circuit-switched telephone system has a single, dedicated connection between two endpoints in a network. This is also referred to as a PLAIN OLD TELEPHONE SYSTEM (POT).

When using a circuit-switched telephone system, once a call has been placed the line is no longer free. The entire bandwidth of the line will be in use and will remain so until the call has been disconnected.

If someone calls you whilst you are already having a telephone conversation, they will receive an engaged signal and the connection will not be made. There will also be no way of telling that someone has tried to call when you hang up the telephone.

A good way of explaining circuit switching is to look at early telephone exchanges where a caller would ask an operator to connect them to a specific number. The operator would physically connect the call by plugging a cord into a jack.

Telephone System itself is indeed still relevant, or whether it too will soon be replaced.

Packet-Switched Telephone Systems

Packet switching is currently the most modern form of the telephone system. Instead of using one line and one communication channel dedicated to a single call, packet switching divides the call data up into small units, known as packets.

These packets are transmitted independently through a network and will find available network space allowing for multiple communication sessions to take place simultaneously.

Each packet will find its own route to the final destination. However, if the network bandwidth is swamped then the quality of the call can suffer.

A Personal Area Network (PAN) is the interconnection of information technology devices within the range of a person, typically within a range of 10 meters. For example, a person travelling with a laptop, a personal digital assistant (PDA), and a portable printer could interconnect them without having to plug anything in, using some form of wireless technology. Typically, this kind of personal area network could also be interconnected without wires to the Internet or other networks.

 In another usage, a personal area network (PAN) is a technology that could enable wearable computer devices to communicate with other nearby computers and exchange digital information using the electrical conductivity of the human body as a data network. For example, two people each wearing business card-size transmitters and receivers conceivably could exchange information by shaking hands.

The transference of data through intra-body contacts, such as handshakes, is known as linkup. The human body's natural salinity makes it a good conductor of electricity. An electric field passes tiny currents, known as Pico amps, through the body when the two people shake hands. The handshake completes an electric circuit and each person's data, such as e-mail addresses and phone numbers, are transferred to the other person's laptop computer or a similar device. A person's clothing also could act as a mechanism for transferring this data.

The concept of a PAN first was developed by Thomas Zimmerman and other researchers at M.I.T.'s Media Lab and later supported by IBM's

What Is WAN? How Wide Area Networks Function

A wide area network (also known as WAN), is a large network of information that is not tied to a single location. WANs can facilitate communication, the sharing of information and much more between devices from around the world through a WAN provider.

WANs can be vital for international businesses, but they are also essential for everyday use, as the internet is considered the largest WAN in the world. Keep reading for more information on WANs, their use, how they differ from other networks and their overall purpose for businesses and people, alike.

What Is a Wide Area Network (WAN)?

As described above, wide area networks are a form of telecommunication networks that can connect devices from multiple locations and across the globe. WANs are the largest and most expansive forms of computer networks available to date.

These networks are often established by service providers that then lease their WAN to businesses, schools, governments or the public. These customers can use the network to relay and store data or communicate with other users, no matter their location, as long as they have access to the established WAN. Access can be granted via different links, such as virtual private networks (VPNs) or lines, wireless networks, cellular networks or internet access.