ISDN basics Tutorial
“Integrated Services Digital Network (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” - Source Put simply your standard telephone line is used to send voice and data over the same line. ISDN (Integrated Services Digital Network) is a set of CCITT/ITU standards for circuit-switched transmission of data over various media, including ordinary telephone-grade copper wire. ISDN is a telephone network based infrastructure, which enables the transmission of both voice and data simultaneously. There are many advantages of ISDN such as − As the services are digital, there is less chance for errors. The connection is faster. The ISDN Network Side for ETSI Net5 PRI feature enables Cisco IOS to replicate the public switched network interface to a PBX that is compatible with the ETSI Net5 switch type. Routers and PBXs are both traditionally CPE with respect to the public switched network interfaces. ISDN lines however are digital communication system. ISDN stands for INTEGRATED SERVICES DIGITAl NETWORK. ISDN networks are capable of generating higher transmission speed of 1.4Mbps. Although 128Kbps speed is more of standard in digital technology. The medium used by ISDN lines are unshielded twisted pair cables (UTP) for communication.
This page on ISDN tutorial covers ISDN types, ISDN architecture and more.
Telephone and mobile growth has increased through out the world.To provide better quality and to combine digital telephonywith data transport services ISDN was introduced in 1979along with ITU-T. ISDN is the set of protocols which helpsdigitize existing telephone network so that video,voice and text can betransmitted over these telephone lines.It is referred as Integrated Digital Services Network.
ISDN services are categorized into bearer services,teleservices and supplementary services.
• Bearer services in which network does not manipulate user information.Voice,data and video utilize this service. It operates on OSI layer 1 to layer 3. Theseservices are provided with the help of circuit switched,packet switched , cell switched and frame switchednetworks.
• Teleservices in which network change the information contents.It operates on layer 4 to layer 7 of the OSI model. Telex,telephone and teleconferencing utilize thisservice.
• Supplementary services utilize features of both bearer and teleservices. The applicationsare call waiting,message handling and reverse charging.
There are three main types of channels used in the ISDN network viz. bearer(B), data(D) and hybrid(H)channels.Different data rates can be obtained by the user with combinations of these channels.One bearer channel supports 64 kbps, one data channel supports between 16 to 64 kbps.One hybrid channel supports 384 or 1536 or 1920 kbps data rates.There are two main types of digital subscriber loops supported in ISDN to fulfilluser requirements.
Basic Rate Interface(BRI): Supports two B channels and 1 D channel.Hence supports about 192 kbps with 64 kbps B channel, 16 kbps D channel and 48 overhead.
Primary Rate Interface(BRI):Supports 23 B channels and 1 D channel.Hence supports about 1.544 Mbps with 64 kbps B channel, 64 kbps D channel and 8 overhead.
Refer ISDN BRI vs ISDN PRI➤ interface types.
As shown in the figure,TE1,TE2,TA,NT1 and NT2 are components used in a typicalISDN network with functions as described below.
• Terminal Equipment-1 or TE1 is used to interface ISDN terminal with the network.
• Terminal Equipment-2 or TE2 is used to interface Non-ISDN terminal with the networksuch as Plain Old Telephony.
• Terminal Adapter or TA Allows non ISDN devices to be interfaced with ISDN network.
• Network Termination-1 or NT1 is physical layer device which separates userpremises from phone company.
• Network Termination-2 or NT2 functions as per OSI layers 2 to 3.PBX and LAN are considered as NT-2 devices.
• Reference points are used to identify interfaces between two ISDN elements.
15 digits are used in ISDN addressing as defined in E.164.
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