ISDN:
ISDN (Integrated Service Digital Network) is a digital telephone link system that has been in use for 10 years. This system allows point-to-point connections throughout the world to transmit data simultaneously. ISDN was the first accepted form of broadband Internet access, and in addition to its 128Kbps transmission rate, ISDN also allows users to talk on the phone while surfing the Internet. This is a great attraction for users who are Internet addicted but also have a lot of phone calls.
The earliest concept of ISDN was formally proposed by the CCITT (Consultative Committee for International Telephone and Telegraph) organization in 1972, and its widespread adoption took place over the next four or five years. Its purpose is to use the same communication network to provide users with diversified services and to solve the problem of synchronization and parallelism of multiple services. Simply put, it allows users to use a single ISDN line to simultaneously access the Internet, make phone calls, or send video, and so on. Because of its moderate price, ISDN can be considered the first service to enter the personal broadband Internet.
The biggest difference between an ISDN phone line and a regular home phone is that it is "digital", whereas a regular home phone line is "analog". Because of the use of "digital" transmission, in addition to having a faster transmission rate than the average home phone line, even when making general voice calls, you can enjoy more additional services, such as caller ID, airtime, multi-party calls, etc. ISDN provides two digital channels, called the B-channel. Each B-channel can provide a transmission rate of 64Kbps. When used separately, a user can use one B-channel to connect to the Internet and use the other B-channel to make phone calls, send and receive faxes, etc. If the two B-channels are used together, the user can use the other B-channel to send and receive faxes. If the two B-channels are used together, it can provide a transmission rate of 128Kbps, which is also the fastest transmission rate of ISDN. Note that in the ISDN technical vocabulary, the "K" stands for 1000, not 1024 (210) as in the usual computer vocabulary. Thus, a channel with 64 Kbps bandwidth represents a data rate of 64,000 bps (bits per second).
Strictly speaking, ISDN can't be considered a popular solution to the lack of bandwidth available to users, since the fastest transmission rate is only 128 Kbps. However, in addition to Internet access, more ISDN users are interested in the simultaneous use of voice and data transmission. Therefore, point-to-point communication is a very popular area for ISDN, such as video conferencing systems for cross-county companies, telemedicine systems for hospitals, or distance learning for schools
The most important feature of ISDN is that it supports two communication channels and one control channel, which is called B-channel in the terminology of communication channels, and D-channel in the terminology of control channels, and this is often referred to by professionals as 2B + D. For ordinary users, there is no need to consider the D-channel at all. For ordinary users, there is no need to consider the D-channel at all, and only the B-channel can be used. The D-channel is reserved for adapters or professional programmers.
Let's take a look at what two B-channels can do for us. You can think of the two B channels in an ISDN as two normal analog phone lines. What you can do with two normal analog lines can be done with one ISDN line. The simplest example is that you can make two calls and answer two calls with one ISDN line. ISDN not only provides us with convenience in the way of communication, but also provides us with a high-quality communication environment by its inherent digital technology. ISDN lines use all-digital signals for communication, which converts all kinds of information into digital signals. Because digital signals are used for transmission, the correctness of the information is ensured when it is transmitted.
"One line through (i.e., ISDN)" service to provide users with the basic rate (2B + D, 144kbps) and a group rate (30B + D, 2Mbps) two interfaces. The basic rate interface consists of two independently working B channel (64Kkbps) and a D channel (16Kkbps), of which the B channel is generally used to transmit voice, data and images, and the D channel is used to transmit signaling or packet information.
B-channel: ISDN's support channel that provides 64kbps bandwidth to carry voice or data information.
Channel D: ISDN's control signaling channel, transmits sideband signals between the ISDN network side and the subscriber side. This channel can also be used to transmit X.25 information, provided that the switch is capable of providing this service.
2B+D: Also known as Basic Rate Interface (BRI), this is a standard ISDN subscriber circuit. It contains two B-channels and one D-channel, each B-channel is capable of transmitting data at 64Kbps, and the D-channel is capable of transmitting at 16Kbps, supporting packet-switched data (usually X.25) with a throughput of up to 144Kbps.
30B+D: Also known as Primary Rate Interface (PRI), this is a standard ISDN service carried over T-1 (E-1) circuits.PRI provides transmission rates of up to 2.048Mpbs over 30 discrete or combined 64Kbps channels and a 16Kpbs D channel.
Principle:
Different layers and protocols
ISDN uses circuit-switching to establish a physical, permanent, point-to-point connection from the source of the signal to the destination.ISDN has a standard defined by the International Telecommunication Union (ITU). This standard includes the OSI, the bottom three layers, the physical layer, the data link layer, and the network layer (see table below). At the physical layer, the ITU-defined standards for user network interfaces include the 1.430 Basic Rate Access Interface and the I.431 Primary Rate Access Interface.ANSI has defined the standard for user network interfaces as T1.601 As noted above, this physical layer uses the same normal telephony wiring that is used for its physical wiring structure.
ISDN B channels generally market point-to-point protocols such as HDLC (High Level Data Link Control) or PPP (Point-to-Point) framing protocols at Layer 2. However, you can sometimes see other encapsulations such as Frame Relay. As you might expect, you will usually see IP packets at Layer 3. ISDN operates in full duplex. Full duplex is the ability to send and receive traffic at the same time.
ISDN D-channels will use different signaling protocols at layers 3 and 2 of the OSI model. Generally speaking, LADP-D (Link Access Protocol-D channel) is using Q.921 signaling at layer 2 and DSS1 (Digital Subscriber Signaling System 1) is using Q.931 signaling at layer 3. It is easy to remember which signaling works at which layer by simply remembering that the middle number corresponds to the layer it works at.
Differences in ISDN components
As part of the ISDN standard, there are a number of types of equipment that are used to connect to an ISDN network. This equipment is called Terminal Equipment (TE) or Network Terminal Equipment (NT). You also have a number of reference points used to define the connections between the various parts of the equipment in an ISDN network.
Definition of Terminal Equipment and Network Terminal
Terminal Equipment Type 1 (TE1) is a device that has direct access to the ISDN network and understands the ISDN standard.
Terminal Equipment Type 2 (TE2) is equipment that predates the release of the official ISDN standard and requires the use of a terminal adapter to access the ISDN network. This type of device can be a router with only one serial interface, rather than an ISDN Wide Area Network Interface Card (WIC). This terminal adapter is able to plug into this serial interface, allowing the use of a router to connect to this ISDN network. Another example is a computer.
Network Terminal 1 (NT1) is typically a customer's device used to implement the physical layer on an ISDN network (or NT2 device). This is the U reference point for connecting to the telco. It works at layer 1 of the OSI model.
Network Terminal 2 (NT2) is typically the telco's device (it is rare to see this device at a customer site) used to terminate the user's NT1 device before the communication reaches the ISDN network. This device works at layers 2 and 3 in the OSI model and is an intelligent device that performs this conversion.
A terminal adapter (TA) is a device that converts TE2 device signaling to signaling used by ISDN switches.
A terminal adapter is a device that converts TE2 device signaling to signaling used by ISDN switches.
isdn-logic-characteristics
Pulse standard
ISDN in Germany originated in 1TR6 and since 1991 has resulted in a harmonized European Common Standard (E-DSS-1). Other implementations exist outside of Europe.
ISDN in the United States is called NI-1 (National ISDN Phase 1) and NI-2, which corresponds to the DSS1 standard, which does not have its own signaling channels (D-channels), but instead the signaling data is transmitted over the subscriber channels (B-channels), with a corresponding drop in capacity to 56 kbit/s.
Japan and Hong Kong's ISDN system name is INS-Net64, and in Australia it is called TPH1962.
Voice conversion
The voice data is modulated by the ISDN system's 8K Hertz digitizing (PCM) encoder, which utilizes a logarithmic characteristic curve (ITU-T-Standard G.711,? -law/a-Law) the signal is compressed from 12 to 8 to take into account specific human behavioral characteristics. The occupied bandwidth is 300 to 3400 Hz.
Data conversion
The B-channel is used for control and synchronization, for the purpose of using different transmission protocols. In order to achieve the effect of doubling the transmission rate, these two B-channels connected to the basic interface also gebündelt. The system can be called a success (e.g. videoconferencing system) if the end devices can eventually be synchronized.
Using special routers it is possible to combine all 30 available channels into a single logical interface, which provides a bandwidth of 2.048kb. This technology is primarily used for accessing the Internet from a large number of computers in an organization.
ISDN addressing
The ISDN-address is determined by the ITU-T-strategy E.164. This ISDN-address consists of an ISDN-call sign and a sub-address. For example, an ISDN call sign is used by a participant to connect a base interface. The sub-address is a maximum of 32 characters in length and provides, for example, an address to a host in a LAN (which must be connected to the ISDN network via a gateway). The subaddress is transparent to the ISDN network and can only be recognized by the participant in use.
isdn-network system
ISDN equipment refers to the various types of equipment required by an ISDN network to provide ISDN services to users, including ISDN switches, ISDN subscriber switches, network terminals, access units, and various types of ISDN terminals and terminal adapters.
First, the ISDN network composition
Usually, the ISDN network consists of three parts, namely: user network, local network and long-distance network.
The user network refers to the user equipment and wiring at the user's location. It refers to the machine line equipment contained from the subscriber terminal to the T reference point. In the ISDN environment, the user's access to the network is much more complex than the telephone network users, the general user network can be used in the following three types of structure:
(1) bus structure
When the same user has a variety of terminals, you can use the bus structure, this time more than one terminal is connected to a passive bus, enjoying the same subscriber number. This way in a 2BD basic rate subscriber line can be opened at the same time telephone, data, fax and other services, and can be connected to more than eight terminals. Because the passive bus mode user terminals can be configured as needed, without network control, so this mode has the shortest connection cable, can achieve a variety of functions and other features.
(2) Star structure
The star structure is a way to connect multiple ISDN terminals to the network directly through the S reference point through the subscriber switch, i.e. NT2. This way is suitable for the synthesis of voice and data services, with a variety of user terminals used independently, centralized control, maintenance and management, real-time transparency and network expansion is easy and so on. It is suitable for organizations, companies and other group users with ISDN requirements into the network.
(3) mesh structure
The mesh ring structure consists of a set of ring digital nodes and ring links, with a simple network interface, decentralized control and equal distribution of capacity, even if overloaded with its system function is also more stable and so on. However, when a node fails, it will affect the normal operation of the whole system, and even if the system is lightly loaded, its average delay is longer. So currently this approach is limited to the use of LAN and MAN.
The construction of a local ISDN network is based on the ISDN end office, which is the most important part of the ISDN service for the subscriber, and the realization of the ISDN function requires the use of ISDN subscriber signaling between the subscriber and the end office, i.e., DSS1, and the use of **** road signaling between the ISDN end offices, or between the end office and the sink.
A long-distance network is a group of devices used to interconnect all local networks. Therefore, the digitization of the long-distance network, i.e., the introduction of digital long-distance transmission equipment and digital long-distance switching equipment, as well as the opening of the long-distance network 7 signaling has become the basis for the realization of ISDN long-distance transmission and service.
Second, ISDN inter-office signaling
(1) Message Transfer Part (MTP) to complete the signaling network to provide reliable signaling transmission function. It includes three functional levels: signaling data link, signaling link function and signaling network function. It corresponds to the lower three layers of the OSI reference model.
The first level of MTP is the signaling data link, a bi-directional transmission path used to deliver signaling, consisting of two data paths operating in opposite directions using the same data rate, which meets the requirements of the OSI physical layer definition. This is 64 kbit/s in the case of digital data links and 4.8 kbit/s in the case of analog data links.
The second level of MTP is the signaling link function, which completes the functions required to provide a reliable signaling link for the transmission of signaling messages between two directly connected signaling points.
The third level of MTP is the signaling network function. This function provides the functionality and procedures required for message passing between signaling nodes of a signaling network. Reliable delivery of signaling messages is ensured in the event of signaling link and signaling transfer point failures. Signaling network functions include signaling message processing and signaling network management functions in two parts.
Signaling message processing consists of three functions: message routing, message identification, and message distribution. Signaling network management refers to the function of reorganizing the network structure in case of signaling link or signaling transfer point failure and controlling the service volume in case of congestion. Including signaling service management, signaling route management and signaling link management three functions and procedures.
(2) The Telephone User Part (TUP) specifies the functions and procedures for signaling telephone calls necessary for international and domestic telephone calls.
TUP can meet the requirements of telephone service functions of digital telephone network, but it cannot fully meet the business requirements of ISDN, therefore, when carrying out ISDN services, ISDN user part (ISUP) should be used to replace TUP.
(3) ISDN user part specifies the signaling functions and procedures required for telephone or all kinds of non-talking exchange services. It not only provides users with basic and supplementary services, but also supports a variety of bearer services such as 64kbit/s and n×64kbit/s. ISUP can be used for international and domestic requirements for the connection of various communication services.
(4) Signaling Connection Control Part (SCCP) extends the business functions of MTP to transfer circuit-related and non-circuit-related signaling information and other types of information between switching offices and private centers, and to establish connectionless and connection-oriented network services. Compared with MTP, addressing functions utilizing full address (GT) and subsystem number (SSN) are added.
(5) Transaction Capability (TC) is a communication application protocol for the 7th signaling method. It only specifies the protocol (TCAP) of the seventh layer (application layer) of OSI. TCAP mainly includes the mobile application part (MAP) and the operation, maintenance and management part (OMAP). MAP specifies the procedures such as roaming and channel over-the-horizon transfer in the mobile service, and OMAP provides only the formal test of the MTP routing and the formal test procedure of the SCCP routing.
Third, ISDN inter-network interoperability
ISDN is with the existing various types of telecommunications networks **** exist, so it is necessary to consider the interoperability of ISDN and other business networks. The so-called inter-network interoperability refers to the interoperability between ISDN and ISDN, but also includes the interoperability between different ISDN networks. Non-ISDN interoperability with ISDN includes various networks that are currently providing services, such as existing telephone networks, packet data networks, private networks, other ISDN and ISDN outside the service provider.
Since ISDN is based on the development of the digital telephone network, ISDN and the telephone network should be regarded as a whole, only to complete different functions. The telephone network only has the function of transmitting audio signals at the user's end, while ISDN can handle the business and capabilities far beyond this scope. So when there is a telephone call, can be freely routed in the ISDN and telephone network, that is, in the ISDN terminal and the existing telephone network between the terminals can be free to voice communication.
In order to accomplish the communication between ISDN users and users of the existing telephone network, the following technical problems mainly need to be solved:
(1) Interoperability between signaling systems
The inter-office signals of the telephone network may use the China signaling No. 1 or No. 7 telephone user portion of the signaling No. 7 (TUP), whereas the inter-office signals of the ISDN will use the No. 7 signaling ISDN user portion ( ISUP), so inter-office signaling needs to be completed to match.
The ISDN subscriber signaling is DSS1, so it is also necessary to complete the interworking of ISDN subscriber signaling and telephone network subscriber access signaling.
(2) Interoperability indication
When telephone network users talk to ISDN users, the ISDN local switching office is required to indicate the interoperability situation to ISDN users to facilitate user communication. Moreover, both the telephone network and ISDN are required to provide various in-band signaling tones to users.
When a packetized terminal needs to communicate with another packetized terminal in the PSPDN over the ISDN, there are two ways to do this: Way A - circuit-switched access to public *** packet data network (PSPDN) services; and Way B - packet-switched access to ISDN virtual circuit services.
Mode A is to establish a transparent circuit-switched access connection through the access unit (AU) between ISDN and PSPDN. the AU has an interworking function, equivalent to the IWF (Interworkingfunction). This connection can be established by the user or by the AU. Use the D-path circuit-switched call control program. With this method, only the B-path is used to pass messages for user communication. Mode B establishes a packetized access connection via ISDN's packet processor (PH). Mode A is easier to implement than mode B.
The packet processor access point interface (PHI) is a standard interface between the PH and the switch as defined by ETSI, the European Telecommunications Standards Committee. The interface is based on the CCITTX.31 recommendation, which details the technical specifications of the interface, and supports the types of services described in the X.31 recommendation. The interface signaling is based on the ISDNDSS1 protocol, and uses the structure of a 30BD.
ISDN provides integrated services to users with advanced network technologies. As the application of ISDN on public networks gradually expands, some ISDN private networks are also developing. Especially in some sectors and regions, the development of ISDN private networks is likely to exceed that of public ISDN.At present, the CCITT's recommendations on ISDN can be used for public networks as well as local area networks (LANs).
isdn-development
World
The 1970s produced digital technology for telephone networks to replace mechanical switching. This technology gave users better features and better call quality. The standardization organization, the Consultative Committee for International Telegraph and Telephone (CCITT, now the International Telecommunication Union (ITU)), developed technical specifications for the digital telephone network in 1980 under the name "ISDN".
Europe
In 1988, the European Telecommunications Standards Organization (ETSI) EG-Kommission drafted a standard for the establishment of a common digital telephone network. 26 telecom operators from 20 European countries accepted the Euro-ISDN standard on April 6, 1989, which was unified as the national ISDN system for each country. ISDN system and optimize the related technologies. in December 1993 the Euro-ISDN Digest was produced, which is the basis of the Memorandum of Understanding for the European ISDNImplementation.
Germany
Deutsche Post decided in 1979 to digitize all local calls in Germany. At the time there were warnings about the risks of this technology. Some data protection experts from the Green Party commented that ISDN created a "qualitative leap" towards complete data capture, as the technology made it possible to capture and save all connection data.
By May 1994, all the necessary software upgrades at the local level had been completed and Germany had the ability to release lines. From 1995 the entire telephone network was digitized, with ISDN lines running through the streets. By mid-1996, Deutsche Telekom was actively promoting ISDN technology. The cost of a newly installed line is up to DM 300, plus the telephone is about DM 700. 1,063,000 subscribers were using narrowband ISDN at the beginning of 2003 (about one-third of the total installed base), and there are also 120,000 2,500 lines of broadband ISDN subscribers.
Austria
The Austrian telephone system was digitized in 1978 under the auspices of the Ministry of Post and Telegraph.Ab1986wurdedieOES-Technikfl?chendeckendumgesetzt.In February 1992 the Vienna local network voice area " Dreihufeisengasse&" started ISDN trials, by that year more than 200 lines had been installed. By 1999 the total number of digitized lines in Austria was 247,000 247,000 lines, and in 2002 this number reached 438,000 lines.
Switzerland, Japan and France
Switzerland established its first digital ISDN network in 1988 under the name of "Swissnet 1", which totaled more than 250,000 subscribers in 1996, and by 2004 the telephone terminals exceeded 900,000 lines.
In Japan, there were many subscribers between 1999 and [[2001]], but most of them have been reduced since the introduction of ADSL, and NTT, the main Japanese telephone company, still offers ISDN services called INS64 and INS1500.
In France, France Telecom's ISDN service is called Numeris (basic rate). The ISDN service known as RNIS still has a market in France, and ADSL has taken over ISDN's data and Internet access business, but there are still a certain number of subscribers in the suburbs and the countryside.
United States
The United States began deploying an ISDN system in 1992 under the name NI-1, which was very different from DSS1. An improved version, NI-2, was later deployed, and AT&T now has an ISDN system called 5ESS. But because of poor marketing and price advantages, ISDN has basically become known as the chicken ribs in the United States.
China
China's telecom industry is growing rapidly, but when ISDN was deployed on a large scale, the technology was not introduced in China. So when ISDN became common in Europe and the United States, China only began to install local equipment. By this time, ADSL technology had already matured and was being marketed.
So in the mid-nineties, only in Beijing, Shanghai, Guangzhou and a few other pilot cities ISDN installed more, other cities are only a small area of use. The fundamental reason is that operators need to invest a huge amount of money for equipment transformation. At that time, China Telecom provided 2B + D program is a narrow-band ISDN standard, can only provide 128Kbps rate. Users needed to bear nearly 1.5 times the cost of an ordinary phone call. The online business was not really launched, and the services and contents needed by users were not supported.
ISDN is not as easy to separate voice and data as ADSL, so users must use all digital equipment, which creates a situation in which both operators and users have to invest. On the one hand, operators have to meet the rapidly growing demand for network connectivity, and on the other hand, they have to develop fixed-line telephone services. ISDN cannot flexibly adapt to the diversified needs of China's market, and can only fade out of the market competition. DSL's high bandwidth, high capacity and low modification costs allow operators to quickly invest in DSL network construction.
All right, my friend. I hope this solves your problem