Integrated Services Digital Network

ISDN or Integrated Services Digital Network which was developed by Consultative Committee on International Telegraph and telephone on early 1980s was dealt by some North American carriers but few were really in doubt to it due to faults and fails on data network. ISDN sets protocols for data transmission such as voice, data and video over our traditional circuits in public switch telephone network. With ISDN, transmission for data, video, and voice can be performed at the same time.

ISDN has three basic access interfaces: Basic Rate Interface, Primary Rate Interface and Broadband ISDN.

Let’s discuss Basic Rate Interface.

BRI-ISDN uses 2 bearer channels running at 64Kbps and a data channel of 16Kbps. This is a payload of 128kbps service delivered over a four wire bus. This is the reason why it is sometimes called 2B+D. BRI-ISDN specifies the bandwidth allocated to the user. With 64kbps for bearer channel and different bandwidth for signaling, it gives user full-pledge bandwidth for users. BRI-ISDN is created by a Network Terminal Type 1 (NT1). An ISDN device is connected to the NT1 which provides the ISDN network with Echo Cancellation which terminates echoes from different noise and discontinuities. Echoes are noise that is disastrous to your network. With NT1, it removes echoes by reading what has being sent and monitoring the transmission. NT1 also provides timing for all devices. NT1 serves as switch or a traffic controller to which bearer channel to connect. The ISDN only serves the 1^st three layers of the OSI model the physical, network, and data-link layers. The higher layer of services could be video-conferencing, internet and other services.

Physical Interface of BRI

a.)S-bus or S/T interface from the ISDN terminal up to the NT

The S/T Interface (S₀) uses four wires; one pair for the uplink and another pair for the downlink. It offers a full-duplex mode of operation. It is define in I.430 by the International Telecommunications Union(ITU).

b.) U reference point from NT to central Office

The U Interface uses two wires. The U interface uses one wire pair with echo cancellation for the long last mile cable between the telephone exchange and the network terminator. The maximum length of this BRI section is between 4 and 8 km.

Primary Rate Interface

Primary Rate Interface provides 23B+D and all of these channels provide 64Kbps. The PRI uses T1 as physical interface with extended superframe framing. Since it is now a T1 line NT1 perform as Channel Service Unit and NT2 as private branch exchange. A T1 Primary Rate Interface user would have access to a 1.472-Mbit/s data service.  But PRI-ISDN isn’t limited to one T1 line but it could also add multiple T1 lines and a D channel could handle or control all the channels. That is the reason why PRI is used in big companies who handles lots of calls and data transmission while BRI is used in small offices.

Broadband ISDN

Any service that has a speed greater than 1.544Mbps is considered as broadband. This was according to John T. Gorgone. Therefore with that definition, Broadband ISDN is basically means a transmission channel that caters a speed greater than those of the primary rate interface. It is only an extension of the term ISDN by name and it all includes the protocols, services, architectures and technologies that have been improved.

B-ISDN Services

Interactive Services

Two-way exchange of information (other than controlsignaling information) between two subscribers or between a subscriber and a service provider.

Distribution Services

Primarily one way transfer of information, from service provider to B-ISDN subscriber.

Conclusion

ISDN was a great technology developed by CCITT. It covered some solutions for business problems mainly by providing dynamic bandwidth are guaranteed over non-shared lines with wide range at one standard cost. But it can’t compete with other technologies in terms of providing high speed internet and other specialized services. It also requires specialized digital devices just like Telephone Company.

sources:
http://en.wikipedia.org/wiki/Integrated_Services_Digital_Network
http://cis.bentley.edu/jgorgone/cs340/C/pdf/BISDN.pdf
http://www.t1everywhere.com/isdn-pri.html
http://www.freewimaxinfo.com/isdn.html
http://networking.ringofsaturn.com/Telecommunications/fig2c.gif