Integrated services digital network ( ISDN ) was developed by ITU-T in 1976. It is a set of protocols that mixes digital telephony and data transport services.
The whole idea is to digitize the telephone network to allow the transmission of audio, video, and text over exiting telephone lines.
ISDN is an attempt to standardize subscriber services, provide user/network interfaces, and facilitate the web working capabilities of existing voice and data networks.
the goal of ISDN is to make a wide area network that gives universal end-to-end connectivity over digital media.
This can be done by integrating all of the isolated transmission services into one without adding new links or subscriber lines.
ISDN provides a totally integrated digital service to users. These services fall under 3 categories- bearer services, teleservices, and supplementary services.
Bearer Services:– Transmission of data (voice, data, and video) between users without the network manipulating the content of that information is provided by the bearer network. There is no need for the network to process the information and therefore doesn’t change the content.
Bearer services exist in the first three layers of the OSI model. They are well defined in the ISDN standard. They can be given using Network Switching circuit-switched, packet-switched, frame-switched, or cell-switched networks.
Teleservices:– In this, the network may change or process the contents of the data. These services correspond to layers four-seven of the OSI model. Teleservices believe in the facilities of the bearer services and are designed to accommodate complex user needs.
The user need not be aware of the details of the process. Teleservices incorporate telephony, teletex, telefax, videotex, telex, and teleconferencing. Though the ISDN defines these services by name yet they have not yet become standards.
Supplementary Service:– Additional functionality to the bearer services and teleservices are provided by supplementary services. Reverse charging, telephone, and message handling are examples of supplementary services that are all familiar with today’s telephone service services.
Subscriber Access To The Integrated services digital network
To allow flexibility, digital pipes between customers and the integrated services digital network office (the subscriber loops) are organized into multiple channels of disparate sizes.
The ISDN standard defines three channel types, each with a disparate transmission rate:-
- Bearer channels
- Data channels
- Hybrid channels
|CHANNEL||DATA RATE (Kbps)|
384, 1536, 1920
B Channels:- A bearer channel (B channel) is defined at a rate of 64 Kbps. It is the essential user channel and can carry any type of digital information within the full-duplex mode as long as the required transmission rate does not exceed 64 Kbps.
For example- a B channel can be used to carry digital data, digitized voice, or other low data-rate information several transmissions can be accommodated at once if the signals are multiplexed first. Multiplexing transmission of this sort, however, must be destined for a single recipient.
D Channels:- A data channel (D channel) can be either 16 or 64 Kbps, depending on the requirements of the user. Although the name says information, the primary section of a D channel is to carry control signaling for the B channels.
Up to this point, the transfer protocols we’ve examined all use in-channel (in-band) signaling. Control information (such as call establishment, ringing, call interrupt, or synchronization) is carried by an equivalent channel that carries the message data.
The ISDN separate control signals onto a channel of their own, the D channel. A D channel carries the control signaling for all of the channels during a given path, using a method called common channel (out of band) signaling.
H Channels:- Hybrid channels (H channel) are available with a data rate of 384 Kbps (H0), 1536 Kbps (H11), or 1920 Kbps (H12). These rates suit H channels for high data rate applications such as video, teleconferencing, and so on.
Types of Integrated services digital network
The following are the interfaces of ISDN:
- Basic Rate Interface (BRI)
- Primary Rate Interface (PRI)
Basic Rate Interface (BRI):–
There are 2 data-bearing channels (‘B’ channels) and one signaling channel (‘D’ channel) in BRI to initiate connections. The B channels engage at a maximum of 64 Kbps while the D channel operates at a maximum of 16 Kbps. The 2 channels are independent of each other.
For example, one channel is used as a TCP/IP connection to a location while the opposite channel is used to send a fax to a remote location. In Series, Integrated services digital network supports a basic rate interface (BRI).
The basic rate interface (BRI) specifies a digital pipe consisting of two B channels of 64 Kbps each and one D channel of 16 Kbps. This equals a speed of 144 Kbps. In addition, the BRI service itself desires an operating overhead of 48 Kbps. Therefore a digital pipe of 192 Kbps is desired.
Primary Rate Interface (PRI):–
Primary Rate Interface service consists of a D channel and either 23 or 30 B channels back on the country you’re in. PRI is not supported on the PRI Series. A digital pipe with 23 B channels and one 64 Kbps D channel is being within the standard Primary Rate Interface (PRI).
Twenty-three B channels of 64 Kbps each and one D channel of 64 Kbps same 1.536 Mbps. The PRI supply uses 8 Kbps of overhead also. Therefore PRI desires a digital pipe of 1.544 Mbps.
Broadband-ISDN (B-ISDN) – Narrowband ISDN has been designed to figure over the being communications infrastructure, which is heavily hoked into the copper cable however B-ISDN relies mainly on the evolution of fiber optics.
According to CCITT B-ISDN is best described as a service desiring transmission channels capable of supporting rates greater than the primary rate.
Advantages of Integrated services digital network
ISDN may be a telephone network-based infrastructure, which enables the transmission of both voice and data simultaneously. There are many advantages of ISDN like −
- As the services are digital, there’s less chance for errors.
- The connection is quicker.
- The bandwidth is higher.
- Voice, data, and video − all of those are often sent over one ISDN line.
Disadvantages of Integrated services digital network
The disadvantage of ISDN is that it desires specialized digital services and is costlier. However, the arrival of ISDN has brought great advancement in communications. Multiple transfers with greater speed are being achieved with higher levels of accuracy.
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