The entire idea of ISDN is to digitize the telephone network to allow the transmission of video, audio and text over existing telephone lines. The reason of the ISDN is to provide fully integrated digital services to users.
For accessing the Internet the use of ISDN has breathed new life into ISDN service. ISDN's slow acceptance owed mostly to a lack of need for its capabilities. Being a digital interface, ISDN has provided a means for accessing web sites rapidly & efficiently. In response to this new demand, telephone companies are adding ISDN services rapidly.
The ISDN standard described three channels types, each with the distinct transmission rate: data channel (D), bearer channel (B) and hybrid channel (H)
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Channel
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Data Rate (Kbps)
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B
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64
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D
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16, 64
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H
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384, 1536, 1920
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The B channel is described at a rate of 64 Kbps. It is the basic user channel & can carry any type of digital information in full duplex mode as long as the needed transmission does not exceed 64 kbps. A data channel can be either 64 or 16 kbps based on the needs of the user used to carry control signals for B channels.
Of the two basic rate B channels, one is utilized to upload data to the Internet & one to download from the Internet. The D Channel assists into setting connection & maintaining flow control. There are three ways ISDN can be utilized to interface to the Internet, by using adaptor, modem or bridge/router. ISDN modems & adaptors limit access to a single user. Both terminate the line in an ISDN service. The difference among them is that the ISDN modem takes the Internet traffic and pushes it by the computer serial port, whereas, the faster ISDN adaptor connects to the computer's buses directly.
ISDN bridge/routers let for local network connections to be made through ISDN to the Internet. The ISDN termination is built into an Ethernet-type LAN so that multiple users can attain access to the Net through a single access address. Transfer rates among user and the Internet are between 56 and 128 Kbps.