A phone network is a telecommunication network that is used for the communication between two or more parties. This may be a wired network or a wireless network. There are different types of telephone networks:
A fixed line network where the telephones are directly wired in a single telephone exchange is known as public switched telephone network or commonly known as PSTN.
A wireless network is a network where the telephones are mobile and can move remotely. In this network there is no wired connection between the mobile phones. In this network the communication is done through microwave in a specific band and the range is also specified by the ITU(International Telecommunication Union).
A private telephone network is a network where a small group of telephones are connected to each other for communication through a gateway which connects the network to the out side world. This is basically used in a company where a good number of telephones are needed to communicate between each other, in a call center. This is called Private Branch Exchange (PBX).
Public Switched Telephone Network:
The public switched telephone network is a network for the public and it is a circuit switched network. This public switched network consists of telephone lines, fiber optic cables, microwave transmission, mobile network, LEO Satellites and Geostationary satellites and under sea telephone cables. These all are inter connected to each other so that any one from any country can communicate between each other.
Originaly a PSTN is a wired analog network but PSTN is now almost digital in the core level and can support both mobile and fixed telephone. The telephone network like PSTN is standardized by the ITU(International Telecommunication Union).
The first telephone did not have any network but was in private use.This was wired through pairs.A user who had the wish to talk with another person whistled in the transmitter and whistled until the other party heard.
The task of building the network and selling the service to the subscriber was first taken by the Bell Telephone Company. Which is a United States based company.
Network Topology for PSTN :
The network topology for PSTN has to be upgraded and changed many times to provide the increasing need subscribers call, connections to other countries, direct dialing and other facilities. The network topology made by US and Canada are adopted by other countries.
Now a days most of the PSTN uses digital switching rather than mechanical or analog switching. In PSTN the analog video signal is digitized in 8KHz sample rate using 8-bit pulse code modulation. Then the pulse is transmitted through the wired connection and exchange to other end. The call is carried over the PSTN channel by dint of a 64 kbit/sec channel which is designed by Bell Labs.
A wireless network is a network where the radio network is distributed among land areas which are called as cells. Each cell is fed by a BTS(Base Transreceiver Station).When these BTS are accumulated they provide signal of a large area.
Wireless network has some important advantage over other services. The advantages are like-
- Increased Capacity
- Users are not fixed, have the mobility
- Reduced Power Use
- Large Coverage Area
- Reduced Interference.
Basic Concept in Wireless Communication:
In a regular wireless communication system, a land area is divided into some regular cells. These cells can be in regular shapes like hexagonal or any other shpes.But the most conventional shape is hexagonal shape. These cells are assigned some multiple frequency like f1 to f2.
These frequencies are reusable which is usable in other cells. But the problem is the same frequency is not usable in neighboring adjacent cells. The increased capacity in the wireless communication is because the frequency is reusable to different cells for a completely different transmission. In a standard FDMA system there must one cell gap between the cells.
To distinguish between the signal from different transmitter the techniques Code Division Multiple Access (CDMA) and Frequency Division Multiple Access (FDMA) these techniques are developed.
With the use of FDMA this gets confirmed that the frequency used in the neighboring cells are not same like the frequency in the different transmitter and receivers.
The principle of CDMA is to generate different codes to distinguish between the frequency of the neighboring cells and the frequency of transmitter and receiver.
The magical characteristics in a cellular network technology are the frequency reuse. Through this frequency reuse the capacity and the coverage are is covered enormously. The adjacent cells must reuse the same frequency otherwise interference will be there.So,to avoid interference the elements that define the successful frequency reuse is the reuse distance and the reuse factor. The reuse distance D can be formulized as ,
Where R is the cell radius and N is the number of cells per cluster.
The frequency reuse factor is the rate at which rate the same frequency can be used in the network.
Code division multiple system uses a wide frequency band to achieve the same rate of transmission as the Frequency Division Multiple Access (FDMA) does. In this topology the adjacent cells use the same frequency but the other cells are differentiated by codes but where in GSM those are separated by frequencies.
Recently Orthogonal Frequency Division Multiple systems are also developed for the service like LTE(Long Term Evolution).
The most common phone network is a mobile phone network. A mobile phone is a portable telephone which makes call from a particular cell by transmitting the power from the mobile phone device. In urban area the cell size in a mobile phone communication is .5 kilometer but in rural areas the range could be up to 10 kilometer. Though it is possible that a mobile can get signal from a distance of 25 miles away base station if the line of sight is clear and the area is open enough.
A cellular phone mobile network consists the following things:
- Base station to form the base station subsystem.
- Circuit Switched network(to handle the voice communication) and Packet network(To handle the data communication) to form the Switching Subsystem.
- The public switched telephone network to connect the subscribers to the outside telephony network.