This question appears in Mumbai University > Mobile Communication and Computing subject

Marks: 5 M

Year: Dec 2015

• In a cellular system, a cell is a local area of coverage served by a base station. These base station are connected to an MSC. Since communication may occur over multiple such MSCs, the MSCs provide connectivity between the PSTN and multiple base stations.

• PSTN stands for Public Switched Telephone Network.

• The PSTN forms the global telecommunications grid which connects conventional (landline) telephone switching centers (called central offices or exchanges) with MSCs throughout the world.

• A typical MSC is responsible for connecting around 100 base stations to the PSTN.

• The information transfer in PSTN takes place over landline trunked lines (trunks) comprised of fiber optic cables, microwave links and satellite links.

• The network configuration remains static as it needs to be changed only when the user changes residence and a reprogramming happens at central office.

• The bandwidth for a fixed landline network can be changed by altering the type of material (co-axial cable/fiber-optic).

• It is estimated that there are around 1 billion fixed landline subscribers in whole world )as compared to 600 million mobile subscriber)

• Depending on individual country, the rules for usage of such PSTN systems change. In some countries, certain private parties too are allowed to be part of it.

• In PSTN, each city or a geographical grouping of towns is called a local access and transport area (LATA).

• The various nearby LATAs are connected by a local exchange carrier (LEC).

• Interexchange Carriers (IXC) have a large network of fiber-optic connections connected to LEC throughout a country or continent. Extra fees need to be paid for accessing such connections.

• The figure below is an illustration of a local telephone network called a local exchange.

• As seen in the figure, each CO provide connectivity to

1. Customer Premises Equipment (CPE) kept at residences.
2. Private Branch Exchanges (PBX) kept at business organizations (e.g. extension lines as in colleges)