Access network concept
"Access Network"? ? ? - Maybe many people are a strange noun, but in fact it is around us, except for general terminal equipment (such as phones, mobile phones, computers ...), and our "distance" "The nearest is it -" Access Network ", which is determined by the access network in the entire telecommunications network (directly for users).
In the telecommunications bureau, the speed of the telecommunication backbone is getting faster and faster; however, the connection speed between the user terminal and the switch network is "bottleneck" ... There is a new technical concept in the telecommunications - access network……
The emergence of the access network makes the development of the entire telecommunications network more reasonable, and the utilization of network resources is more sufficient.
"Access Network" is developed by traditional user loops and is an upgrade of user loops. The access network is part of the telecommunications network. The access network is directly for users to provide users with a variety of services through various transport media.
The ITU Standard Ministry (ITU-T) proposes the concept of an access network (the purpose of the purpose is to consider the resolution of local switches, user loops, and interrupt equipment through limited standardized interface, will connect various users. Enter the problem of business nodes.
From the exchange bureau or business node to the user terminal in most cases, the distance is not more than 4km, and in most cases in the city, there may be only 1km, the access network is the bottleneck of business access, which is the last paragraph of network digitization. "The last kilometer "The title is here. Since the access network is wide, it has become the most important part of the network construction and operating costs, and the performance price of access network technology is high, the development task of access network technology is also heavy, access network digitization It is still a long way to go, so some people say that the access network is "difficult last km" or "long last kilometers".
In general, the communication network includes two parts: core network (also backbone, backbone) and access network (Access NetWork). For example, a large city, there must be a city communication network (often known as the city telephone network, Local Telephone Network), which sets a number of exchange bureaus (Co, Central Office) (i.e., Exchange) as a network. These switches are connected to each other with interhousing lines, transmitting a group of signals, and constitute the core network of the city.
At the same time, each communication user terminal is each passing through such or such a wired transmission line, and is connected to the area of the area. Such a subscriber line, the English is called sub-scriber line or local loop, recently called AccessLine, translated into an access line. When the user calls, the signal is connected to the switch through this access line; when the user is called, the signal is connected from the switch to the user. This type of access is both the last mile of the entire communication network and the first mi. Thus, a large number of users within a market communication network constitutes an access network.
From the entire communication network, the core network assumes that the city communicates, the relationship is high, and each pair of access lines of the access network involves only one user, which has little effect. However, there are many users, and the lines of access lines are large. Therefore, for communication network investment enterprises, the access network needs to spend more funds than the core network. "Access" in English noun, soon, in the English literature in communication technology, we translated as "access". It may represent two meaning. First, like the previously said, the signal of the user calls to the node of the communication network, ready to exchange. The second is to send the user's voice, data or video information services into the communication network, or from the communication network to the user. The communication network can be a wired fixed or fixed communication with a wireless mobile communication. For wireless, it is called "WiFi Access".
Recap history
1, a network concept of reducing the investment of the access section
1975 British Telecommunications (BT) held the concept of access network at a seminar held in Scotland (Glasgow).
Experimental time - In 1976, a network feasibility test was conducted in (Manchester). In 1977, there was a large-scale promotion application in Scotland and London;
Summary Time - In 1978, he officially affirmed this networking method in the Glasgow meeting and named "Access Network Network" technology, and then edited by Willesm et al. To the documentation of the meeting - "Telecom Network Technology" .
2, international telecom technology industry identity
1978 BT officially proposed access network network concept at CCITT related meetings;
In 1979, CCITT is a framework description to a device with similar performance with a remote user hub (RSC) naming manner.
Rolling the Yangtze River
1) Digital program-controlled switch (SPC) began mass-large-scale commercialization at the end of the 1970s, which develops the concept of RSC to RSU (without local exchange), RSM (with local exchange).
2) Since the access network concept is generally accepted by telecom operations and equipment suppliers, plus the number of / mold mixed network age, PCM digital multiplexing equipment has reduced RSU (or RSM) and master device from higher degrees. The number of practical connections and a transitional gateway interface device better solves the interconnect interconnection between the simulation equipment and the digital devices in the digital / mode mixed network.
3) Some newly-rising SMEs began to build the production and manufacture of RSU and PCM multiplexing equipment, and launched a competition with traditional large telecom equipment suppliers with monopoly status. Operators noticed that this competition will bring yourself a considerable economic benefit and can get rid of the conventional equipment supplier to a certain extent, so it will openly support this competition on CCITT and hope to get it through standardization procedures. development of.
4) The CCITT-related working group has proposed a general recommendation for the four digital interfaces of V1, V2, V3, and V4 in the early 1980s.
5) Operators, traditional equipment suppliers, the intricate economic interest relationship between new competitors, so that the above four digital interface recommendations will eventually achieve extensive recognition.
6) In the mid-1980s, the anti-monopoly calls were high, and the newly born SMEs have become increasingly dissatisfied with the development of the development of traditional large suppliers, and the introduction of anti-monopoly law in developed countries has led to the telecommunications industry. The standardization and standardization requirements of the network interface are proposed.
7) In the late 1980s, under various aspects, ITU-T began to set the standardized digital interface specification - V5.x with a higher standardization, and a more scientific definition of the access network (although there are still many A question worth discussing and obviously omissions).
8) V5.X causes the access network equipment to have crashing in the long-term manufacturer of monopoly status, and the operations can get more benefits from the competition between equipment suppliers (including economy, technology. of). However, with the rapid expansion of the network, the network management of the operation industry (especially due to the significant increase in physical nodes in the connection network) and many related problems are increasingly complex, the network management crisis begins. 9) The concept of TMN (Telecom Management Network) is that the operational industry is a new effort to solve the network management problem in the multi-equipment vendor environment.
10) Due to historical reasons, large manufacturers are reluctant to remain silent for the loss of market share and profitability, and have adopted all-round counterattacks from technical standards to competition strategies on the network management issue. The direct result is It is difficult ITU-T to make difficulties in the development of ITU-T in the formulation of access network management, in order to reach the network management to make operators lose their unconsciously resistant to other supplier products based on V5.x standards (due to network management will make operators The access network of the standard interface generates management barriers and psychological obstacles).
11) Competitive companies entering the telecom product market can only rely on the continuous introduction of new technical concepts and advocating benefits that may bring to the operation industry to obtain support from the market.
12) The development of broadband and wireless technology since the 1990s, especially people, generally believe that the B-ISDN era is coming, access network may provide development opportunities for new operations, providing value-added services for old operating companies, so ITU- T finally completed the formulation of VB5 recommendations in 1998.
13) At the same time, the monopoly behavior of the operation industry is also being unstoppable by developed countries. The new operators must use a more advanced technical means (such as broadband, wireless access, etc.) to decrease or decrease as much as possible. Investment risk of ground lines.
14) Nii (National Information Infrastructure), GII (Global Information Infrastructure) Concepts and Revolutionary Progress in Fiber Transport Technologies, enabling access to access networks into a separate product and operational market.
The above driving force makes access network technologies continue to develop in a strong momentum.
Access network definition
The access network is a system that consists of a transport entity that provides a telecommunication service between the service node interface (SNI) and each of the user network interfaces (UNIs) associated therewith.
SN (Business Node) is a network element that is access to various exchanges and / or non-exchange telecommunications services. The SNI (Business Node Interface) is an interface to which the user is accessible to the SN. UNI (User Network Interface) refers to an interface between the terminal device and the network terminal of the application access protocol.
Interface configuration
In the case of switching services, the SN is a local switch (LE), which provides access calls and connection control signaling and the ability to access connection and resource processing. At this time, the access network is a system between the local switch and the user terminal, that is, all or part of the local line allocation network referred to. The simplest access network is a metal user line. At this time, UNI is the interface of the telephone and the user line, and the SNI is the analog subscriber line interface (Z interface) of the telephone switch. Obviously there is an access network since the telecommunications network, as digitization extends from the core network to user access, SNI and UNI are diversified, and the transfer entities between them have become more complicated. The International Telecom Alliance starts with access. The network defines the transfer system between SNI and UNIs. The SNI for the switch digital user access is a V interface. According to the frame format, the V1 to V5 is distinguished, where V5 is divided into V5.1 and V5.2 in accordance with the line capacity, and the broadband is called VB5.1 and VB5. .2. The type of Uni is also a lot, ITU-T has ISDN T interface and B-ISDN TB interface, in fact, there are also 10MB / s and 100MB / s Ethernet interfaces, and 1000MB / s Ethernet will Net port. The user terminal is not just TE, but instead of TE may be a network, ie CPN (user station). With IP and video business development, routers, access servers, video servers, etc. As SN appear in telecommunications network, the SNI can be the same V5 or VB5 class interface as the exchange service, or may be different interfaces, the latter ITU-T is currently not standardized.
Access network function
The access network now told that it includes cable facilities and transmission devices, which can be multiplexed, cross-connect, etc., as well as user port features related to UNI, service port features related to SNI, and core Functions (such as lines, circuitry, and path selection), which are distributed in OLT (optical terminal) and ONU (optical network unit). It is necessary to point out that even if the access network itself does not interpret user signaling even in the case of switching service access, in other words, the access network is not controlled by the user signaling. For the access network of the SNI is the V5 and VB5 interfaces, the function related to the V5 and VB5 type interfaces is configured by the network management system through the Q interface managed in AN.
Access network service
To date, the main business of the telecommunications networks in various countries is still a telephone, accounting for 70% to 90% of the total traffic, so the main goal of the access network planning and design is still aimed at the telephone business, and is mainly 2Mbit the following rate. In addition to the telephone service, the access network should at least support all services that can be supported by the existing copper cable users, such as various low-speed data services, N × 64kbit data leased business, analog lease lines, ISDN basic access and once Group access, non-locally exchanged business, etc.
For small business users and resident users, the recent main broadband business needs mainly have the following 5 categories:
1 Oncast Television (VOD) or difficult to broadcast TV (NVOD), also known as film and television on demand services or quasi-film on demand services, especially on movie programs. Such services allow users to select any movie in the center movie library and have a short delay. Such business will be the fastest growing broadband business in small enterprises and residential users.
2 interactive image game. Such business allows users to play electronic image games through existing public telephone networks, and electronic image gaming libraries can have a large number of rich programs available. This type of business will have a considerable market.
3 interactive image service. Such services allow user control to control the program, such as the user can control the angle of the camera, participate in the game program, get additional information of the news or sports program.
4 Distance education. Such business allows users to distribute users to participate in the field or video education course. Such business is expected to have a large development potential.
5 multimedia library. Such services can be seen as one of the distance education programs, which is characterized by allowing users to interactively search, and can read, read, listen to multimedia information, that is, have audio-visual capabilities. The medium and long-term broadband business needs mainly have the following categories:
1 Radio TV. Such business allows users to use radio and television. Such services allow users to access and quickly select broadcast TV programs.
2 transaction business. Such services allow users to participate in interactive transactions, such as banks, shopping, request services, pre-order tickets, booking hotels, etc. "
3 Target type advertisement. Such business allows companies to choose from to choose a certain type of person or group to see their advertisements, or select the type of advertisement for a particular individual or group.
Other image mailbox services and video telephony services, etc.
Access network family
There are many types of access to the access network, for example, according to the transfer medium, according to the topology, according to the technical points, according to the interface standard, according to the service bandwidth, according to the business species, etc. Take these factors into walk in, the pattern of access to the network is natural, but the main use mainly has the following categories, they can be used or mixed alone:
XDSL on the metal subscriber line can also be divided into IDSL (ISDN Digital User Loop), HDSL (High Speed Digital User Loop 2MB / S), SDSL (Single Normal Symmetry Transmission 2MB / The digital user loop of S, the transmission distance is slightly short than HDSL), VDSL (very high speed digital user loop), ADSL (asymmetric digital user loop). The topology of the above system is point-to-point.
HFC (bidirectional mixed fiber coaxial cable access transmission system) on coaxial cable, SDV (exchangeable digital video access system, is also based on mixed fiber coaxial cable, but only passing the row signal on the same shaft).
Topological structure is a tree or bus type, and the downstream is usually broadcast. Compared with other access methods, HFC / SDV is that the downlink can be mixed and transmitted and digital signals.
Optical fiber access system: It can be divided into active and passive systems. The active system is based on PDH and SDH, and the topology can be a ring type, a bus type, a star or a mixed, and a point-to-point application.
Passive is PON (passive light network), with narrowband and broadband, current broadband PON has been normalized based on ATM-based PON, namely APON. PON itself is downtown to a multi-point system, and the active behavior is multi-point, and you need to solve the problem of multi-user contention when uplink. At present, most of the TDMA (Time Multiple Access) technology is currently available.
Wireless access system: Usually refers to fixed wireless access (FWA), according to its technology from cordless phones, cluster phone, cellular mobile communication, microwave communication, or satellite communication can be divided into many classes, corresponding to different frequency bands, capacity , Business bandwidth and coverage are different. The main way of wireless access is to point to a multi-point. The upstream solves the technology of multi-user contention has FDMA (frequency division multiple access), TDMA (time division multiple), and CDMA from spectrum efficiency. It is best, TDMA followers. Among them, CDMA can have several spectrum (DS), frequency hopping (FH) and synchronous (S-CDMA).
Access network tide
With the appearance of digital and broadband services, communication medium with longer transmission distance and greater capacity is used to become the development direction of today's access network technology.
XDSL Digital User Series Technology is a broadband access method provided by the original copper access network, HFC system and asymmetry Cable Modem have great advantages in transmitting simulated CATV signals; but from the perspective of technology development, Fiber-to-Fi-Home (FTTH) is the final solution for access network. The advantage of the fiber to the household is that the bandwidth is not limited to the user, which provides a wide guarantee for the broadband service into the family; in addition, the fiber directly arrives at home, no disclosure of the external interference, Outdoor equipment can do Passive, avoid lightning strike, more reliable performance, low power supply; but its disadvantage is that the cost is too high, and it cannot be promoted. Due to the cost problem of ftth, the fiber can not be home in most cases, but in the case of increasing cost, make the fiber as close as possible to the user, fiber to the roadside / fiber to the building (FTTC / FTTB) is undoubtedly a kind Take care of the current and future better programs. In the access network technology, there are currently several leading trends:
1. Built-in SDH access network. It has strong compatibility and is conducive to the advantages of developing to broadband access.
2. Passive Light Network (APON) based on ATM Technology. It represents the development direction of broadband access technology. Its advantage is that combined with ATM multi-bit rate support capabilities and PON transparent broadband transmission capabilities, the access is very flexible.
3. Use ATM technology to transfer MPEG-2 signals. Implementing video on demand services (VOD) is a central content of ATM Forum, ITU-T, etc. in recent years, and another trend in AN development.
4. Interactive Digital Video Access System (SDV) based on fiber optic loop (Fitl) and ATM technology. At present, the system is experimenting abroad, in addition to supporting traditional voice narrowband services, can also provide users with VOD, digital broadcast video services, and analog broadcast video service services; in addition, information can be performed in different units in the SDV network. Switching between streams (such as images, ATM packets).
5. Local Multiple Allocation System (LMDS) of Broadband Wireless Access. It uses a cellular unit that provides users with millimeter wave 28GHz to users with VOD, broadcast and conference television, video home shopping.
With the advancement of society and technology, the trend of information technology development is the convergence of three technologies, industries and even networks, and three networks. It is manifested as the interoperability of the business layer, and the application layer uses a unified communication protocol, and the network layer is interconnected, and the technological tendency is consistent. Under this tide promotion, the development goal of the access network is to establish a full-service access network (FSAN), which not only supports narrowband, broadband, and interactive broadband services, but also supports some new services that have not yet been defined. Integrate various application techniques to a network to meet the needs of users
Access network application
Access to the network has wired, wireless, etc. In the world, the way to achieve access network is also different due to different national conditions. There is a large number of telecommunications networks, cable TV and computer networks, which have been built in Western developed countries, and coaxial cables in the construction of information infrastructure in developing countries, due to fiber access networks will become world information. The development focus on the network, the fiber access network is being greatly increased.
North America ---- North American countries basically utilize optical cables and original metal twisted pairs and coaxial cables to provide multimedia image services. In the United States, CATV coaxial cables have been connected to more than 93% of families, so it is widely used to achieve CATV in one-way HFC. Some companies use interactive digital video SDV mode in the access network to digitally reuse transfers, and mix access users with analog CATV signals on ONU to achieve high-speed bidirectional services.
European ---- In Europe, there are many digital user loop DLC modes. Britain and Germany, other countries are actively adopting passive optical network Pon, and the ONU's terminal is connected to the user's introduction line to keep the original metal cable, using ADSL and VDSL system, and quickly effectively provide multimedia image service. Japan ---- Japan has realized fiber optics and fiber to the roadside, although it is postponed the plan to promote fiber-to-house households, but some big company's latest system is still to further close the cable to user housing.
my country ---- in my country, with the concept of access network, my country has also developed a series of access network technical systems, standards and test specifications. Since 1996, China Telecom organized 35 experiment points from 17 Chinese and foreign manufacturers and 15 Provincial Posts and Telecommunications Authorities. After nearly 2 years, the results show that the V5 interface can realize the interoperability of different manufacturers access network equipment and switch, access network has strong business support capabilities, in addition to supporting PSTN, ISDN business, also supports N × 64kbps, 64kbps The following types of rates, Internet, X.25, CATV, etc., it is worthwhile to promote public network, and SDH's access devices have also been put into practical. According to the experiment and test results, China Telecom selected in 1998 is strong, and more than 10 access network devices in the public network of 15 manufacturers in China V5 interface norms can be practiced. As a result, the practical application of my country's V5 access network is gradually expanded nationwide. So far, online access network devices are 4 million lines, and the scale exceeds the rest of the world.
With the gradual maturity and development of my country's access network technology, the public multimedia communication access system, ATM access, VOD system, etc. have gradually entered the test network stage, and the HFC system and asymmetric CABLEMODEM will be used to change the special CATV network. Wideband data and voice access network work are also gradually expanded. These are a solid foundation for the construction of various services such as transport images, pictures, data, and voice, etc. - all business access networks.
