PUBLIC TELEPHONE NETWORK
Communication must occur between distinct point but few organization can justify the cost required.
LAN is characterized by high bandwidth and that company controls and maintain all the connectivity of devices as well as the transmission media (wire).
The company could have transmission media like infrared or satellite communication to establish connectivity.
Another possibility is different kind of cables can be used for connectivity
A variety of commercial options are available that enable organization to pay per only the level of service they require.
It has two main types
1. PSTN [PUBLIC SWITCHED TELEPHONE NETWORK]
This commercial network has its own existing infra structure supplied by the Telephone Company or Cable Company.
The feature of PSTN is its low speed, analog nature of transmission, a restricted bandwidth and also wide spread availability.
It is designed for telephone network but if we want it for digital communication than modem is required.
When the link setup is unreliable and can terminate without warning.
At that time PSTN communication medium is advisable.
This connects are easy to get at short notice. This is widely available and covers almost every location where people live and work.
PSTN is mostly useful for occasional users or as a backup to the private services
Fax machines can also operated in this network.
2. PSDN [PUBLIC SEITCHED DIGITAL(DATA) NETWORK]
It covers number of technology available for public telephone network.
The main feature is its high level of reliable and high quality of connection.
They can support both low and high speed at appropriate cost.
It can also use to link computer and system and network of one organization to several other organizations.