Integrated Services Digital Network (ISDN) is a digital version of switched-circuit analogue telephone service. It was and developed to use the existing telephone wiring system is provided by local phone companies or PTTs
ISDN was specifically designed to solve the low bandwidth problems that small offices or dial-in users have with traditional telephone dial-in services. When a data call is made using ISDN, the WAN link is brought up for the duration of the call and is taken down when the call is completed.
ISDN is generally viewed as an alternative to leased lines, which can be used for telecommuting and networking small and remote offices into LANs as shown in Figure 1.
Telephone companies developed ISDN as part of an effort to standardise subscriber services including the User-Network Interface (UNI). The ISDN standards define the hardware and call set-up schemes for end-to-end digital connectivity.
ISDN's ability to bring digital connectivity to local sites has many benefits, including the following:
ISDN has been developed by the International Telecommunication Union Telecommunication Standardisation Sector (ITU-T) and as such has become a worldwide industry standard, which helps achieve the goal of worldwide connectivity by ensuring that ISDN networks easily communicate with one another.
This means multinational corporations can deploy ISDN technology in their facilities located throughout the world. and standards-based Customer Premises Equipment (CPE) will be easier to install and will cost less as manufacturer pass on the savings of economies of scale
Because ISDN is a digital communications technology it is not subject to the same noise interference that analogue modem technologies suffer. Lower error rates result in fewer re-transmissions, greater network reliability and hence higher throughput.
ISDN can carry a variety of user traffic signals. ISDN provides access to digital video, circuit-switched data, and telephone network services by using...