- Public Switched Telephone Network (PSTN):- The feature of the PSTN are its low speed, the analog nature of transmission, a restricted bandwidth and its widespread availability. PSTN is designed for telephone, modems. These are used for data communication. It is also used for FAX.
- Public Switched Data Network (PSDN):- The term PSDN covers a number of technologies. The main feature of PSDN are their high level of reliability and the high quality of the connection provided. It can support both low and high speeds at appropriate costs. It can also be used to link computer system and networks of one organisation to several other organisation. PSDN is very popular for connecting public and private mail system to implement electronic mail services with other companies.
- Value added Services/Network (VAN/VAD):- In CAN, the provider of such services must process, store and manipulate the data that is carried on the network. The technique is used in specific types of business in which it is advantageous to be able to share information with other companies in the same line. Electronic Data Interchange (EDI) is one area for value added services in which two trading partners exchange trading documents such as purchase orders, invoices, transportation etc using electronic means. In india, Videsh Sanchar Nigam Ltd (VSNL) is a service provider.
- Integrated Services Digital Network (ISDN):- The ISDN is a networking concept providing for the integration of voice, video and data services using digital transmission media and combining both circuit and packet switching techniques. Uses can use their digital connection to telephone company for transmitting both voice and data over the same twisted pair cable which connects their telephone.