Integrated services digital network
A integrated services digital network ( ISDN , in English ISDN for Integrated Services Digital Network ) is a connection authorizing a better quality and speeds being able to reach 2 Mbit/s (S2 access) against 56 kbit/s for a traditional modem.
One can see architecture ISDN like an entirely numerical evolution of the existing phone networks, conceived to associate the voice, the data, it video and any other application or service. ISDN is thus opposed to the phone network commutated (STN) traditional.
Name in the French-speaking countries
- the abbreviation ISDN is used in Belgium and Suisse.
- the abbreviation ISDN is used in France and with the Canada. However, network ISDN of France Telecom is more known under its Numéris trade name.
Presentation
A connection ISDN gives access to several numerical channels: channels of the type B (64 kbit/s in Europe, 56 kbit/s in North America) and channels of the type D (16 kbit/s). The channels B are used with transport as data and can be agglomerated to increase the band-width. The channels D are used for indication of the communications.
Networks ISDN Baseband provide services to low flow: of 64 kbit/s to 2 Mbit/s. Current technology ATM dedicated to the networks long distances (WAN) made in the beginning left definitions ISDN under broad band denomination ISDN for the services with high banc: of 10 Mbit/s to 622 Mbit/s.
With ISDN, the regional and international sites of small size can connect itself to the corporate networks at a cost adapted better to real consumption than with specialized lines. The connections with request ISDN can be used either to replace the specialized lines, or in complement to increase the band-width or to ensure a redundancy. With these same connections, the distant sites or users can reach effectively the critical resources in full safety through Internet.
The development of networks ISDN
The International union of telecommunications (UIT) defined technology ISDN like a network providing a numerical connectivity from beginning to end with a large variety of services. Two important characteristics of networks ISDN distinguish them from the traditional phone networks:
- connections are numerical from one end to another;
- ISDN defines a play of protocol standard S of user interface/network. In this way, all equipment ISDN uses same physical connections and the same protocols of indication to reach the services.
ISDN combines the broad geographic coverage of a phone network with the transport capacity of a data network simultaneously supporting the voice, the video data and it.
In France and Belgium, the domestic network of telecommunications was entirely digitized and the established access protocols are in conformity with the standard Euro-ISDN published by ETSI and UIT.
Operation
In an analogical phone network, a loop on a Twisted pair of copper wires between the central switch of the company of telecommunications and the subscriber support a single transmission channel. This channel treats one service simultaneously: the voice or data. With an Integrated services digital network, the same twisted pair is divided into several logical channels.
Logical channels ISDN
ISDN defines two types of logical channels that one distinguishes by their functions and their flows. The channels B transmit to a flow of 64 kbit/s in package or circuit switching the user news: voice, data, fax. All the services network are accessible starting from the channels B. the channels D transmit to a flow of 16 kbit/s in basic access and 64 kbit/s in primary education access. They support information of indication: calls, establishment of connections, requests for services, routing of the data on the channels B and finally release of connections. This information of indication was conceived to walk on on a network completely distinct from the channels B. It is this indication except band which gives to networks ISDN times of establishment of connection rapids (approximately 4 seconds) relative to the analog networks (approximately 40 seconds). It is also possible to transmit user data through the channels D (X.31b protocol), but as the flow of these channels is limited this type of use is rare.
Standard interfaces ISDN
An interface of access to a network ISDN is an association of channels B and D. There exist two standard interfaces. They correspond to two distinct categories of use:
- Residential: simultaneous use of the phone services and a connection Internet.
- Professional: use of a telephone switch (PABX) and/or of a router of agency.
; Basic access: The basic access or BASIC Misses Interface (BRI) includes/understands 2 channels B and a channel D for indication: 2B+D.
; Primary education access: The primary education access or Primary Spleen Interface (PRI) includes/understands 30 channels B and a channel D with 64 kbit/s in Europe: 30B+D. In the United States, Canada and Japan the definition is different: 23B+D. Seule the protection of the markets explains the differences in definition between Europe, the United States, Canada and Japan. This access is equivalent ISDN of connections T1/E1 to 1,544 Mbit/s and 2,048 Mbit/s.
The adaptation of the flows
Equipment not-ISDN does not have necessarily flows compatible with the definition of channel b: 64 kbit/s. In this case, the adapters of terminal (TA) carry out an adaptation by reducing the effective flow of the channel B up to a value compatible with device not-ISDN.
There exist 2 protocols of management of adaptation: V.110 very much used in Europe and V.120 in the United States. These 2 protocols manage the synchronous and asynchronous transmissions. The V.110 protocol can function with subsystem ISDN Linux (3rd part) and a Cell phone GSM for example. It is to the cellular person receiving benefits of Téléphonie to provide footbridge RNIS/V.110.
The dynamic allocation of band-width
The dynamic band-width or the allowance of channels is obtained by the aggregation of the channels B. One thus obtains a maximum band-width of 128 kbit/s for the basic access (BIS) and of 1,875 Mbit/s for the primary education access in Europe.
This functionality makes it possible to adapt the flow and thus the cost of communication to the effective needs for entering and outgoing flows. According to the hours of the day or the days of the week, the needs for connectivity strongly vary. It is possible that the contractual cost of use of a specialized line is higher than the cost in times of communication of a connection ISDN, when the latter correctly uses the band-width at the request of opening/closing connections to the selected hours.
There exist two techniques to incorporate the channels B called bonding and bundling .
The bonding works on level 1 (physical Layer) of OSI model. It ensures a synchronization at the level bit. This technique thus requires a specific material. It is especially used in the dedicated equipment of videoconference and very little in the equipment of data networks.
The bundling is a generic technique which works on level 2 (Course binder) of OSI model. In the case of a connection ISDN, it makes it possible to open simultaneously several channels B between 2 systems. Standard ML-PPP (established in subsystem ISDN Linux) described how to separate, recombine and séquencer Datagram S on several channels B to create a single logical connection. This standard is dedicated to the Protocole PPP, the standard of level connection of model TCP/IP for the telephone accesses to the lans (LAN) and Internet. The documents RFC 1717 then RFC1990: The PPP Multilink Protocol (MP) describes the software of level connection associated to PPP.
See too
Related articles
External bond
- ISDN
---- This article, or a previous model of this article, is based on the Guide ISDN Linux of Philippe Latu, published on the site Linux France under license GFDL.
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