Mumbai University > Computer Engineering > Sem6 > Mobile Communication and Computing

Marks: 5M

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

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