synonymisdn(isdn) generally refers to integrated services digital network
Integrated Services Digital Network (ISDN) is an international standard for digital telephone network and a typical circuit switched network system.In ITU's proposal, ISDN is a communication network developed on the basis of digital telephone network IDN. ISDN can support a variety of services, including telephone services and non telephone services.
Chinese name
Integrated Services Digital Network
Foreign name
Integrated Services Digital Network
Abbreviation
ISDN
Commonly known as
"One line connection"
Purpose
Telephone, video phone, conference television, etc
In modern society, people have higher and higher requirements for communication. In addition to the original voice, data and fax services, they also require comprehensive transmission of broadband services such as high-definition television, broadcast television, high-speed data fax, etc.The development of computer technology, microelectronics technology, broadband communication technology and optical fiber transmission provides a good foundation for meeting these growing communication needs.
The earliest attempt in network integration began in the early 1980s.Firstly, the concept and technology of ISDN (Integrated Service Digital Network) are proposed.In ITU's proposal, ISDN is a communication network developed on the basis of digital telephone network IDN (which can provide end-to-end digital connection). ISDN can support a variety of services (including telephone services and non telephone services).The most important feature of ISDN is that it can support end-to-end digital connection, and can realize the integration of traditional voice services and packet data services, so that data and voice can be transmitted in the same network.ISDN has a very close connection with the digital public telephone switching network (PSTN), which can be regarded as formed to support the expansion of data services on PSTN.The most basic function of ISDN is the same as PSTN, which provides an end-to-end 64kbps digital connection to carry voice or other services.On this basis, ISDN also provides N * 64kbps circuit switching function with higher bandwidth.ISDN integrated switching node shall also have packet switching function to support data packet switching.The signaling structure is also the same as that of PSTN. The No. 7 signaling system is adopted, and the user part is ISUP protocol.[1]
1. Development of ISDN abroad
There were 21 countries in the world that opened ISDN commercial services in 1993 and 30 in 1995. Many countries in the world have been able to provide ISDN services.In 1994, the number of ISDN subscriber lines was 1.7 million and increased to 3.95 million in 1995.According to the data, in 1998, the number of ISDN users in Germany reached 2.8 million, with a penetration rate of about 6%;The number of subscriber lines in the United States, Germany and Japan ranks among the top three in the world, with 3.5 million, 3 million and 3.6 million basic rate interfaces respectively.Small businesses and residential users in France are the main users of ISDN, accounting for 74% of the market.At first, Deutsche Telekom mainly provided ISDN services for commercial users, and later began to turn to small businesses and residential users.France is the first country in the world to provide national ISDN connection, and its number of users ranks second in Europe.The number of ISDN users in Japan has reached more than 3 million, and the penetration rate of ISDN has reached 5% to 6%, but all are below 10%.According to the statistics in 1999, the number of basic rate interface (BRI) users in the world reached 14.2 million.
The development of ISDN in Asian countries is also encouraging. In March 1995, ISDN services in Japan spread to all cities in the country, and 98% of telephone users have already met the network conditions for using ISDN.Due to the rapid development of the Internet, the growth momentum of ISDN services abroad has been very strong.The development strategies adopted by foreign operators mainly include: (1) adopting preferential service prices, and charging the same amount for ISDN calls and ordinary telephone calls;(2) Accelerate and increase the coverage of ISDN network;(3) Pay attention to system integration, develop ISDN services and applications, and provide convenient ISDN services.
The European IT Watch is the most optimistic about the development of ISDN: in 1999, it predicted that the number of global ISDN users would reach 104 million in 2001, breaking through 100 million for the first time;The number of ISDN users will be 123 million in 2002 and 139 million in 2003.However, the development of ISDN is restricted by other competitive technologies, such as ADSL, which is difficult to achieve.Table 1 shows the statistics of global ISDN users reported by ISDN newsletter in July 1999
Table 1 Statistics of global ISDN users in July 1999
(Source: Operators,industry and FT Media &Telecoms estimate)
countries and regions
Operator
Number of basic rate access users (pcs)
Number of primary group rate access users (pcs)
Europe
Austria
Austrian PTT
30 000
7 500
Belgium
RTT Belgacom
67 000
3 500
Denmark
TeleDanmark
35 000
2 000
Finland
TelecomFinland
20 000
1 500
Finnet Group
10 500
five hundred
France
France Telecom
1 275 000
35 000
Germany
Deutsche Telecom
3 000 000
50 000
Hungary
Matav
seven hundred and fifty
one hundred and fifty
Iceland
PTIIceland
9 433
two hundred and twenty-six
Ireland
Telecom Eireann
25 300
2 000
Israel
Bezeq
20 000
eight hundred
Italy
Telecom Italia
155 000
6 500
Luxembourg
Enterprise des P&T
forty-five
Europe
Netherlands
PTT Telecom
185 000
Norway
Telenor
35 000
7 000
poland
TP
five hundred and fifty
2 100
Portugal
Portugal Telecom
45 060
2 785
Spain
Telefonica
42 000
1 000
Sweden
Telia
55 000
3 000
Switzerland
Swiss PTT
160 000
6 100
britain
BT
1 600 000
90 000
Cable& Wireless
36 000
Cable Companies
5 000
two hundred
Asia
India
5 000
Japan
NTT
3 600 000
41 000
KDD
4 000
three hundred
Macao China
one hundred and forty
Malaysia
5 000
five
Singapore
Singapore Telecom
5 000
three hundred and fifty
the republic of korea
KTA
5 000
two hundred
Taiwan, China
Taiwan PTT
12 300
five hundred
Thailand
TOT
2 000
America
U.S.A
AT&T
30 000
Sprint
6 000
MCI
7 000
Regional Bells
3 000 000
11 000
Canada
Bell Canada
38 000
1 000
Chile
2 200
Columbia
3 100
Oceania
Australia
Telstra
110 000
7 000
Africa
South Africa
Telkom
five hundred
one hundred
2. Development of ISDN in China
Shanghai was the first city in China to conduct ISDN commercial test.In 1995, Shanghai began the construction of a commercial pilot network, which is independent of PSTN.Later, Beijing and Guangzhou began to build small-scale commercial test networks.In the absence of an ISDN local network, Beijing boldly started with the International Bureau, set up independent ISDN bureaus and eight module bureaus, and took the lead in opening international ISDN services for domestic foreign enterprises and commercial users.In 1996, the ISDN service was officially named "One Line Communication", which vividly summarized the basic characteristics of ISDN.During the 1996 Olympic Games, it provided 384kbit/s ISDN video conference service, which was well received by the society.However, due to the impact of their coverage and business functions, these pilot networks developed slowly at the initial stage.
During the "Seventh Five Year Plan" and the "Eighth Five Year Plan", ISDN was a key scientific and technological project.From 1985 to 1995, China established an ISDN model network and a pilot network to carry out research on ISDN practical technology.Based on these research results and international recommendations, the former Research Institute of Telecommunication Transmission of the Ministry of Posts and Telecommunications formulated a series of technical standards related to ISDN, laying the foundation for the commercial use of ISDN in China.
After gaining the operation experience of ISDN, the original China Telecom has continuously strengthened its ISDN construction. The original China Telecom has carried out the transformation of the domestic long-distance network and the international bureau since 1996. By 1998, 26 original PSTN long-distance switches in 26 provincial capital cities nationwide had ISDN functions through version upgrading and hardware transformation, including Beijing, GuangzhouLong distance ISDN services were opened between Nanjing and Shanghai. Zhengzhou, Jinan, Chengdu and Tianjin joined the national network in June 1998. ISDN services in other provincial capitals began to open gradually.At the same time, three international bureaus in Beijing, Shanghai and Guangzhou opened ISDN international services.Among them, the Beijing International Bureau opens ISDN services with the United States, Germany, Singapore, Japan, the United Kingdom, Australia, South Korea, Switzerland, Finland and other countries, as well as Hong Kong, Macao and Taiwan in China.At the end of 1998, ISUP signaling was opened with Belgium, Italy, France, Sweden, Spain and other countries.ISUP signaling has been opened between Shanghai International Bureau and Japan, Taiwan, Hong Kong, Macao and other countries and regions in China, and between Guangzhou International Bureau and Taiwan, China, and the United States.
The fastest growing city of ISDN in mainland China is Shanghai.In 1997, an ISDN covering the urban area and overlapping with PSTN was built in Shanghai and put into commercial use. Since then, ISDN has entered the track of healthy and rapid development.In 1997, there were only 645 ISDN users in Shanghai;By 1998, the number of ISDN users had reached 17000, an increase of 25.3 times over the previous year;In 1999, the number of ISDN users in Shanghai reached 78000, an increase of 3.59 times over the previous year;In 2000, the net increase of ISDN users in Shanghai reached 100000, exceeding the total number of users developed in the previous three years. The cumulative number of users reached 179000, and the penetration rate of ISDN reached 3.26%.In 1996, Germany had the highest ISDN penetration rate, 3.5%, and in 2000, the penetration rate in Shanghai reached 3.26%, indicating that the development level of Shanghai's ISDN is close to that of some developed countries and regions.
At the same time, ISDN services in other regions of the country are also developing rapidly.The successful development of the former China Telecom "First Line Communication" has greatly promoted the development of narrowband integrated services in China.In 2000, the number of ISDN users in China (excluding Taiwan, Hong Kong and Macao) reached nearly 690000, an increase of 520000 over the end of last year, three times that of previous years, and achieved good social and corporate benefits.As of June 2001, China (excluding Taiwan, Hong Kong and Macao) had 937838 ISDN basic interface users and 2830 primary group interface users.
significance
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ISDN is a network developed from IDN, which provides end-to-end digital connections to support a series of services (including voice and non voice services), and provides users with multi-purpose standard interfaces to access the network.The integration of communication services can be provided by one subscriber lineTelephone、Fax、Videotexanddata communicationAnd other businesses.
In addition to making phone calls, ISDN can also provide multiple services such as video phone, data communication, conference television, etc., so that multiple services such as telephone, fax, data, image, etc. can be integrated in a unified digital network for transmission and processing, which is the origin of the name of "ISDN".
Due to the ISDN coverage ratioADSLAnd LAN access is much more extensive, so for those users who do not have broadband access, ISDN seems to be the only solution to high-speed Internet access. After all, 128kbps is much faster than dial-up;ISDN is charged according to time just like the telephone, so for some users with less Internet time (such as users with less than 20 hours per month), it is still better than usingADSLIt's much cheaper.In addition, because ISDN line belongs to digital line, the effect of using it to make phone calls (including network phone) is much better than ordinary phone calls.
It transmits voice and data at a higher rate and quality through ordinary copper cables.ISDN is a popular form of telephone network in Europe.The GSM mobile phone standard can also transmit data based on ISDN.Because ISDN is a fully digital circuit, it can provide stable data services and connection speed, unlike analog lines, which are more obvious for interference.It is easier to carry out more digital information services on digital lines that are unable or difficult to prove the quality of analog lines.For example, in addition to the basic telephone function, it can also provide video, image and data services.ISDN needs a fully digital network to carrydigital signal(There are only two statuses: 0 and 1). This is the biggest difference between the analog phone and the ordinary analog phone.
In addition, ISDN also refers to the protocol set for maintaining and disconnecting circuit switching using this technology or the abbreviation of isosorbide dinitrate.
(1) Realize high reliability and high-quality communication.Because the channel between terminals is completedigitization，noise、CrosstalkAnd the signal fading distortion is very little affected by the increase of distance and link number, so the communication quality is very high.
(2) Easy to use.Information channel and signal channel are separated.Eight terminals can be connected to a subscriber line of approximately 2B+D, and three terminals can work simultaneously.
(3) Low cost.
characteristic
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1. Analyzing the characteristics of ISDN from the perspective of definition
(1) ISDN is an all digital network, which realizes end-to-end digital connection.In modern telephone network, digital program-controlled exchange and digital transmission system are used. All the processing within the network has been digitized, but analog signals are still used to transmit voice services on the user interface.In ISDN, the user loop is also digitized. No matter the original information is voice, text, or image, the terminal equipment converts the information into digital signals first, and then the network transmits them.
(2) ISDN is an integrated service network because it realizes end-to-end digital connection and can support various services including voice, data and image.Theoretically, any form of original signal, as long as it can be converted into digital signal, can be transmitted and exchanged using ISDN to achieve information exchange between users.
(3) All kinds of service terminals use a standard interface to access ISDN.Multiple user terminals can be connected to the same interface, and different terminals can be used at the same time.In this way, users can use different services with only one interface.
2. Analyze the characteristics of ISDN from the perspective of application
(1) Multiplexing.For most users, one of the greatest advantages of ISDN is its multiplexing.ISDN users can provide two B channels (64 kbit/s each) and one D channel (16 kbit/s) on a pair of twisted pairs, and use multiple services at the same time.
(2) High transmission quality.ISDN uses end-to-end digital connection, unlike analog lines, which are subject to static electricity and noise interference, so the transmission quality is very high.Due to the adoption of error correcting codes, the error code characteristics of ISDN transmission are at least 10 times better than those of data transmission over the telephone network.
(3) Comprehensive.ISDN provides various services. Users can use various services provided by the network with only one network access interface. For example, users can access devices such as telephones, computers, conference televisions and routers on a basic rate interface.
(4) High speed data transmission.With ISDN, the highest data transmission rate can reach 128kbit/s, and it is full duplex, more than twice the theoretical uplink rate of the general V.90 modem.
Main types
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ISDN is available in narrowband and broadband.Narrow band ISDN has two interfaces: basic rate (2B+D, 144kbps) and primary group rate (30B+D, 2Mbps).The basic rate interface includes two independent B-channels (64kbps) and one D-channel (16kbps). B-channel is generally used to transmit voice, data and images, and D-channel is used to transmit signaling or packet information.B stands for bearing and D stands for control.
Broadband can provide users with communication capability of more than 1.55Mbps.However, due to the complexity of broadband integrated services digital network technology and huge investment, it is unlikely to put a lot of use, while narrowband integrated services digital network has been very mature, fully equipped with the conditions for commercial promotion, so the ISDN opened everywhere refers to the integrated services digital network, which is actually narrowband ISDN.The bit error characteristic of digital line data transmission is at least 10 times better than that of telephone line.ISDN is widely used, but for ordinary people, only surfing the Internet is the most commonly used.
ISDN function group
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The user network interface is the entrance for ISDN users to access ISDN.This interface must meet the requirements of service integration, that is, the interface must be universal and can accept circuit switching services and packet services at different rates.An ISDN user network interface can support multiple terminals. The system model of user access to ISDN can be defined by the reference model of user network interface.The concept of user function group is used in the reference configuration.A function group is a combination of a set of functions on an interface. It can be a physical functional part required by an interface or an abstract concept.The ISDN user network interface includes the following functional groups:[1]
(1) Terminal Equipment (TE).Terminal equipment can be divided into two categories: TE1 for digital terminals that meet the requirements of ISDN user network interface standard, and TE2 for terminals that do not meet the requirements of user network interface, such as analog telephones, X.25 terminals, etc.
(2) Terminal adapter (TA,Terminal Adaptor）。Its function is to connect the non ISDN terminal (TE2) to the ISDN network.TA functions include rate adaptation and protocol conversion.
(3) Network terminal equipment (NT).Network equipment is also divided into two categories: NT1 and NT2.NT1 is a subscriber line transmission service, whose functions include line maintenance, monitoring, timing, feeding, multiplexing, etc.NT2 performs the functions of PBX, LAN and middle section control equipment.
(4) Line terminal equipment (LT).LT enables the interface equipment connected between the user loop line and the exchange office end to realize the interface function between the exchange equipment and the line transmission end.
The connection points between different user function groups are called access reference points.The reference points defined in the ISDN user network interface include R, S, T, U, etc. The S and T reference points are the standard reference points of the ISDN user - Wang Kuo interface, and are directly connected to the ISDN standard terminal.Generally, when PBX is not used, S and T references can be combined and called S/T reference points.On the user network interface, ISDN defines different channels for transmitting information.The B channel is used to transmit user information, and the channel bandwidth is 64kbps.D channel is used to transmit control signaling required by circuit switching, and also to transmit packet switched information.The H channel is used to transmit high bandwidth user information greater than 64kbps. According to its transmission rate, it can be divided into H0, H1 (2.048Mbps), H3, H4 (130.264Mbps), etc.The standard interfaces defined in ISDN mainly include basic rate interface (PRI) and basic group interface.The basic rate interface consists of two 64kbps B channels and one 16kbps D channel, which is usually called 2B+D.The B channel is used to transmit voice or other types of data services;D channel is used to transmit signaling or packet data.The base group interface is used for the communication of large traffic users. It is usually composed of multiple B, D and H channels, such as 30B+D (where the bandwidth of D channel is 64kbps).
From the perspective of application and promotion, ISDN did not achieve the expected results.The main service of ISDN is still voice telephone switching service, and the support for data service is limited to the channel bandwidth of 64kbps.Therefore, ISDN actually provides a narrowband switching service, which cannot meet the requirements for higher bandwidth data communication, such as high-definition image data transmission.Compared with the proposed ATM based bandwidth ISDN, ISDN is usually called narrowband ISDN (N-ISDN).ISDN is not really comprehensive in structure, because it uses both circuit switching technology and packet technology internally, which are used for voice services and data services respectively. The so-called integration is only realized on the user interface, and the ability to adapt to new services and new technologies is poor.
Access mode
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Integrated Services Digital Network
ISDN has two access modes: the basic rate interface (BRI) consists of two B channels, each with a bandwidth of 64kbps and a D channel with a bandwidth of 16kbps.The three channels are designed as 2B+D.
Primary Rate Interface (PRI) - consists of many B channels and a D channel with a bandwidth of 64Kbps. The number of B channels depends on different countries:
North America, Hong Kong, China and Japan: 23B+1D, total bit rate 1.544 Mbit/s (T1)
Europe, Mainland China and Australia:30B+D, total bit rate 2.048 Mbit/s (E1)
Voice calls are transmitted through the data channel (B), and the control signal channel (D) is used to set and manage the connection.When a call is established, a 64K synchronization channel is established and occupied until the call ends.Each B channel can establish an independent voice connection.Multiple B channels can be combined into a single data channel with high bandwidth through multiplexing.
D channel can also be used to send and receive X.25 packets and access X.25 message network.(In fact, it is seldom widely used).
Advantages and disadvantages analysis
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Benefit analysis
1. Comprehensive communication service: using one subscriber line, you can make calls, receive and send faxes while surfing the Internet, just like two telephone lines.
2. High transmission quality: the transmission quality is significantly improved due to the end-to-end digital transmission.
3. Flexible and convenient use: just one network access interface and a unified number can be used to get various services needed from the network.Users can connect multiple terminals of different types on this interface, and multiple terminals can communicate at the same time.
4. The Internet access speed can reach 128kbps.
Disadvantage analysis
1. Compared with ADSL, LAN and other access modes, the speed is not fast enough.
2. Long time online costs will be high.
3. The equipment cost is not cheap.
Application development
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Since ISDN is not satisfactory in practice, people began to seek a new network architecture from the mid-1980s to overcome the problems existing in ISDN.When designing the new network architecture, we hope that it can really realize the integration of various services (voice, data, image, and even future new services), and can support the different characteristics of various existing services and future services;It can flexibly support the efficient transmission of services with different transmission rates, bursts and time characteristics in a unified network.Obviously, since broadband and service integration are the main features of this new network architecture, it is named Broadband Integrated Services Digital Network (B-ISDN) to distinguish it from the original ISDN.[1]
The development from narrowband ISDN to broadband ISDN can be divided into three stages.
The first stage is to further realize the integration of voice, data, image and other services.The preliminary integrated B-ISDN is composed of three independent networks.Consisting of ATMBroadband switching networkRealize voice and high-speeddataAnd activitiesimageSynthesis oftransmission。
The main characteristics of the second phase are that B-ISDN and user network interfaces have been standardized, optical fiber has entered the home, and optical switching technology has been widely used. Therefore, it can provide broadband services including multi-channel HDTV (High Definition Television).
The main feature of the third stage is the introduction ofIntelligent management networkThe intelligent network control center manages the three basic networks.The intelligent network can also be called intelligent broadband ISDN, in which smart phones, intelligent switches and various intelligent expert systems for engineering design or fault detection and diagnosis may be introduced.
The transmission modes adopted by B-ISDN mainly include high-speed packet switching, high-speed circuit switching, asynchronous transmission mode ATM and optical switching.
High speed packet switching uses the basic technology of packet switching, simplifies the X.25 protocol, adopts connection oriented services, has no flow control and error control on the link, and integrates the advantages of packet switching and synchronous time-division switching. Several experimental networks have been put into operation.
High speed circuit switching mainly adoptsMulti speed time division switching mode(TDSM), which allows channels to be allocated by time, and its bandwidth can be an integer multiple of the basic rate.Because this is fast circuit switching, its channel management and control is very complex, and there are still many problems that need to be further studied.
The main equipment of optical switching technology is optical switch, which willOptical technologyIntroduce transmission circuit to realize digitalsignalHigh speed transmission and switching.
There is no doubt that the combination of ATM and synchronous optical fiber network (SONFT) will constitute the main body of communication in the 21st century.
B-ISDN (Broadband Integrated Service Digital Network).
B-ISDN refers to ISDN with transmission rate of more than 2Mbit/s on subscriber line.It is developed on the basis of ISDN and can support various types of services with different rates, including not only continuous services, but also burst broadband services.Its business distribution range is extremely wide, including narrowband services (such as voice/fax) with a speed of no more than 64kbit/s, broadband distribution services (broadcast television, high-definition television), broadband interactive communication services (video phone, conference phone), broadband burst services (high-speed data), etc.
Application of B-ISDN
Among several high-speed WAN technologies: SMDS (Switched Multimegabit Data Service), frame relay, and B-ISDN (broadband integrated services digital network),B-ISDN replaces the existing telephone network and various private networks with a new network. This single integrated network can transmit all kinds of information. Compared with the existing network, it needs to provide a very high data transmission rate, and is likely to provide a large number of new services, including on-demand television, television broadcasting, dynamic multimedia e-mailVideophoneCD quality music, LAN interconnection, high-speed data transmission for scientific research and industry, and many other services not even thought of today.
To sum up, these services can be divided into two categories: interactive services and communication services. From the perspective of characteristics, they can be divided into three points:
(1) Not all services require very high transmission rate and bandwidth, but active image transmission services and high-speed data communication have such requirements, such as TV transmission requires 30Mbps, HDTV transmission requires 130Mbps.
(2) Some services have high bursts, such as connection oriented data transmission of 1Mbps~50Mbps, text transmission of 1Mbps~20Mbps, and video conference of 1Mbps~5Mbps.
(3) The requirement of the network is to support services with different rates and burst communication. Information loss sensitive applications and delay sensitive applications should be considered.
ATM and B-ISDN
One technology that makes B-ISDN possible is called asynchronous transfer mode (ATM). The development of ATM technology conforms to the requirements of multimedia transmission.The transmission characteristics of multimedia (voice/image) are different from those of traditional data transmission. The characteristics of data transmission are that delay is allowed, but no errors are allowed. Data errors will lead to different data meanings and wrong results;Voice/image transmission is characterized by large amount of information and high real-time performance, but a small number of errors are allowed. Errors can only affect the quality of voice/image at that time.Although various compression technologies can be used, the amount of multimedia information is still amazing, especially the real-time requirements of multimedia transmission make it difficult for other technologies to adapt, so a new switching technology: ATM switching technology has emerged.
Realize high reliability and high-quality communication.
Easy to use.
Low cost.Compared with independent communication networks, the cost of integrating services in one network is much lower.
ISDN has a wide range of applications, including LAN, multipoint screen sharing, video, voice/data integration, file exchange, remote communication, image, multimedia file access, computer based caller ID recognition, etc.
Industry forecast
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Integrated Services Digital Network
There are mainly two views on ISDN.The most common view is that users want a digital connection from home to telephone and data networks that is better than the performance of ordinary analog modems.The typical end user's Internet connection is based on this point of view, and the comparison of various modems and the products and prices (performance, price) of operators are all based on this point of view.Most of these discussions are based on this point of view, but as a data connection service, ISDN has actually beenDSLTechnology obsolescence.
However, there is another point of view: for the telecommunications industry, ISDN has not yet been sentenced to death.A telephone network can be regarded as a collection of wired connections between different switching systems.It also serves as an intelligent network technology to provide more new services for the Public Switched Telephone Network (PSTN) through end-to-end circuit switched digital services.
ISDN has not been widely used in the telephone network of the United States all the time, and it has become an outdated technology.However, it has some uses in the recording studio, especially when the voice actor and the director are not in the same place, ISDN highlights the advantages of real-time non over the Internet service at this time, and its lifelike language quality is comparable to POTS service.
