Integrated Services Digital Network Prepared By: Muhammad Basheir Omer Tyseer Khalil ISDN

What is ISDN is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network. Before ISDN the telephone system was viewed as a way to transport voice, with some special services available for data

ISDN found major market application for Internet access, in which ISDN typically provides a maximum of 128 kbit/s bandwidth in both upstream and downstream directions. Figure: ISDN Telephone

ISDN Access Interfaces The ISDN standards define several kinds of access interfaces, such as: Basic Rate Interface Primary Rate Interface Narrowband ISDN Broadband Integrated Services Digital Network

Basic Rate Interface Also known as Basic Rate Access is an Integrated Services Digital Network (ISDN) configuration intended primarily for use in subscriber lines similar to those that have long been used for voice-grade telephone service. As such, an ISDN BRI connection can use the existing telephone infrastructure at a business. The BRI configuration provides 2 data (bearer) channels (B channels) at 64 kbit/s each and 1 control (delta) channel (D channel) at 16 kbit/s. The B channels are used for voice or user data, and the D channel is used for any combination of data, control/signaling, and X.25 packet networking.

The 2 B channels can be aggregated by channel bonding providing a total data rate of 128 kbit/s. The BRI ISDN service is commonly installed for residential or small business service (ISDN PABX) in many countries. In contrast to the BRI, the Primary Rate Interface (PRI) configuration provides more B channels and operates at a higher bit rate.

Primary Rate Interface is a telecommunications interface standard used on an Integrated Services Digital Network (ISDN) for carrying multiple DS0 voice and data transmissions between the network and a user. PRI is the standard for providing telecommunication services to enterprises and offices. It is based on T- carrier (T1) transmission in the US, Canada, and Japan, while the E-carrier (E1) is common in Europe and Australia.

Applications of PRI The Primary Rate Interface channels are typically used by medium to large enterprises with digital private branch exchange (PBX) telephone systems to provide digital access to the public switched telephone network (PSTN). The B-channels may be used flexibly and reassigned when necessary to meet special needs such as video conferences. PRI channels and direct inward dialing are also common as a means of delivering inbound calls to voice over IP gateways from the PSTN.

Narrowband ISDN N-ISDN was an attempt to replace the analog telephone system with a digital one. Unfortunately, the standardization process was too long and regarding to the technology progress in this area, once the standard was finally agreed, it was obsolete. It generally uses 64 kbit/s channel as the basic unit of switching. It has a circuit switching orientation. Its major contribution was Frame Relay. It describes telecommunication that carries voice information in a narrow band of frequencies.

Narrowband refers to data communication and telecommunications tools, technologies and services that utilize a narrower set or band of frequencies in the communication channel Narrowband is typically implemented in telecommunication technologies to carry voice data on a limited number of frequency sets. Narrowband is also used in sending audio spectrums that consume a restricted range of frequencies.

Broadband Integrated Services Digital Network: From humble beginnings in 1988, the international standardization of Broadband ISDN (B-ISDN) has progressed rapidly. In 1988 the sum total of B-ISDN recommendations consisted of two I-series recommendations, I.113, “Vocabulary of Terms for Broadband Aspects of ISDN,”and I.121, “Broadband Aspects of ISDN.” By 1990 a sufficient level of detail had been agreed upon to allow for the issuance of eleven new recommendations covering various aspects of B-ISDN along with updated versions of I.113 and I.121. These thirteen recommendations provided the groundwork for B-ISDN and firmly established the Asynchronous Transfer Mode (ATM) as the transfer mode for B-ISDN. Work on standardizing B-ISDN has continued with several new Telecommunications Standards Sector (TSS) 1 recommendations approved in 1992, along with updates to the 1990 recommendations.

ISDN and broadcast industry SDN is used heavily by the broadcast industry as a reliable way of switching low-latency, high-quality, long-distance audio circuits. In conjunction with an appropriate codec using MPEG or various manufacturers' proprietary algorithms, an ISDN BRI can be used to send stereo bi-directional audio coded at 128 kbit/s with 20 Hz – 20 kHz audio bandwidth, although commonly the G.722 algorithm is used with a single 64 kbit/s B channel to send much lower latency mono audio at the expense of audio quality. Where very high quality audio is required multiple ISDN BRIs can be used in parallel to provide a higher bandwidth circuit switched connection. BBC Radio 3 commonly makes use of three ISDN BRIs to carry 320 kbit/s audio stream for live outside broadcasts. ISDN BRI services are used to link remote studios, sports grounds and outside broadcasts into the main broadcast studio.

X.25 Protocol X.25 can be carried over the B or D channels of a BRI line, and over the B channels of a PRI line. X.25 over the D channel is used at many point-of-sale (credit card) terminals because it eliminates the modem setup, and because it connects to the central system over a B channel, thereby eliminating the need for modems and making much better use of the central system's telephone lines. X.25 was also part of an ISDN protocol called "Always On/Dynamic ISDN", or AO/DI. This allowed a user to have a constant multi-link PPP connection to the internet over X.25 on the D channel, and brought up one or two B channels as needed.