According to the news on March 7, broadband access technology is one of the most active areas in communication technology. In the telecommunication network, the access network connects users and service nodes, and mainly solves the problems of transmission, multiplexing / demultiplexing, and resource sharing. With the increase of bandwidth requirements, optical fiber continues to extend to users. FTTB (fiber to the building), FTTC (fiber to the roadside), FTTCab (fiber to the pavilion) and FTTZ (fiber to the cell) have been implemented, but the realization of FTTH (fiber To the household) is currently more difficult. Therefore, there are technically the following two problems to be solved: one is what technology should be used between the ONU (optical network unit) and the OLT (optical line terminal) to transmit information; How to access ONU. There are many technologies to solve these two problems (especially the latter). They have different transmission characteristics, market positioning, physical location and problems to be solved. It is likely to be more in the actual access network in the future This technology coexists. This article will introduce some of the main wired broadband access technologies.
At present, the main wired broadband access technologies include: ordinary Modem, N-ISDN (narrowband integrated service digital network), Cable Modem and HFC (hybrid fiber coaxial cable), HDSL (high-speed digital subscriber loop) and SDSL (symmetric digital subscriber Loop), ADSL (Asymmetric Digital Subscriber Loop) and G.lite (ADSL without Splitter), VDSL (Very High Speed ​​Digital Subscriber Loop), HomePNA (Home Telephone Line Networking Alliance), Ethernet, SDH (Synchronous Digital Serial), PON (Passive Passive Optical Network) and APON (ATM Passive Optical Network), IM-DSL (Reverse Multiplexing Digital Subscriber Loop), etc. Generally speaking, any broadband access technology has corresponding CO (office end equipment) and RT (customer end equipment), but the latter is more diverse.
1. Ordinary Modem
Ordinary Modem is one of the main ways to achieve narrowband Internet access. The technology is mature and the highest transmission rate is 56kbps. Technically it does not depend on the optical access network; the product includes the modem used by the user and the modem pool placed in the telecommunications room. Due to its low rate, it is gradually being replaced by N-ISDN and other technologies.
2.N-ISDN
N-ISDN, also known as "one-line communication" is also a mature, narrow-band access copper wire technology that relies on optical access networks. Currently, 2B + D is mainly used to achieve telephone and Internet access, and the typical download speed can reach 64kbps Basically, it can meet the needs of current narrowband browsing, and it is an economical and effective choice for the majority of Internet users to increase the speed of Internet access. At present, it has been opened in various cities in China, and users have responded well, gradually replacing the trend of ordinary Modom. ISDN equipment includes switches and terminal equipment. There are many types of terminal equipment, but from a functional point of view, it is mainly a free combination of ISDN network terminals, terminal adapters, routers and video phones, and provides different interfaces (such as: ISA, PCI , RS232, USB, analog phone port, Ethernet port, etc.) to meet different needs.
3. Cable Modem and HFC
Cable Modem (cable modem) is a method of using cable TV network to achieve user broadband data access, and is also one of the key technologies in the hybrid fiber coaxial network. HFC is the earliest type of broadband access technology that has matured and entered the market. It has the characteristics of broadband and relatively economical. HFC can provide 60 analog broadcast TVs, at least 2 telephones per household, and data services with a rate of at least 10 Mbps in an optical node coverage area of ​​around 500 households (the mature 40 Mbps Cable Modem is currently available). In the future, using its 550M ~ 750MHz spectrum can also provide at least 200 MPEG-2 on-demand TV services and other two-way telecommunications services. In the long run, the HFC network plan provides the so-called FSN (Full Service Network, full service network), that is, to provide various types of analog and digital services in a single network, and gradually transition from multi-user sharing of the above bandwidth to a single user exclusive .
4. HDSL and SDSL
HDSL is a non-relay user loop network, which transmits information symmetrically at high speed with no-load telephone lines, with a typical rate of 2Mbps and a distance of 3 to 5km. Two or three pairs of twisted-pair copper wires are used. Low bit error rate, line code, and good spectrum compatibility. At present, HDSL technology has developed relatively maturely, mainly used to replace the traditional T1 / E1, to solve the broadband access technology of decentralized users, lease lines for users, and transmit multiple channels of voice, video and data. SDSL is a simplified version of HDSL. It uses a single twisted pair cable to provide a bidirectional high-speed variable bit rate connection with a rate ranging from 160Kbps to 2.084Mbps. On a 0.4mm twisted pair cable, the maximum transmission distance is 3 kilometers. HDSL / SDSL can be combined with FTTB / FTTC. In terms of function, there are not many types of HDSL equipment, and the compatibility of equipment of various manufacturers is poor; SDSL matures later and the product types are not too rich.
5. ADSL and G.lite
ADSL uses a loaded telephone line to transmit information asymmetrically at a high speed on a subscriber loop network without relays. Compared with HDSL / SDSL, it avoids user-side interference, improves the transmission rate, and extends the transmission distance. ADSL adopts DMT (Discrete MulTItone, Discrete Multi-Tone) line code. The rate that downlink communication can support is 1.5Mbps ~ 8Mbps or higher, and the rate of uplink communication is 16K ~ 640Kbps or higher. The analog user's voice path is independent. The 0.5 core diameter twisted pair will transmit 6Mbps signal 3.6 kilometers away. G.lite is a simplified ADSL to reduce costs and facilitate the installation of user equipment. The maximum downlink speed is 1.5Mbps and the maximum uplink speed is 512Kbps, without the use of a telephone splitter, and the maximum transmission distance can reach 5 kilometers.
ADSL (including G.lite) CO terminal equipment DSLAM (Digital Subscriber Loop Multiplexer) mainly realizes the function of multiplexing / dropping, which can be placed in the local office or cell of the local telephone, and the purpose of the cell is to increase the transmission rate And can enable more general users to use ADSL, which requires the cooperation of the optical access network; there are many user-end equipment, from a functional perspective, including: ADSL Modem with different interfaces (PCI, USB, Ethernet), adapt to different needs ADSL routers, integrated gateways, splitters or low-pass filters that provide both data and voice. At present, the difference between G.lite and ADSL in the price of terminal products is not too big, mainly due to the difference in DSLAM prices, but because telecom operators prefer the full-rate ADSL DSLAM, and the current ADSL chips and equipment support both ADSL with speed also supports G.lite, so pure G.lite products are rare in practice. In China, ADSL experiment networks have been opened in Guangdong, Shanghai, Fujian and Wuhan. However, due to the need to pay expensive installation fees and user fees, it is difficult for ordinary home users to bear.
6.VDSL
In the development of ADSL, it was found that properly reducing the distance will greatly increase the transmission rate, which appeared VDSL. The frequency spectrum of the upper and lower channels in the VDSL system is separated by frequency division multiplexing technology, and the coding methods are CAP (no carrier amplitude and phase modulation), DMT and DWMT (discrete wavelet multi-tone). The upstream and downstream rates of VDSL are also asymmetric, and its downstream rate has 3 files: 13Mbps, 26Mbps and 52Mbips, and the corresponding transmission distance is 1500m, 1000m and 300m; the upstream rate also has 3 files: 1.6Mbps, 2.3Mbps and 19.2Mbps. VDSL must be used in combination with FTTB, FTTC, FTTCab, and FTTZ. In terms of products, VDSL is similar to ADSL, but due to the late appearance of VDSL technology, there are not many formal products.
7. HomePNA
HomePNA is a technology that uses a telephone line to form a local area network to solve the problem of connecting multiple devices for home users. It cannot be viewed as an independent broadband access technology. From the spectrum point of view, HomePNA physical layer signals are distributed between 5.5MHz and 9.5MHz, the center frequency is 7.5MHz, and the data transmission rate is 1Mbps; on the media access control layer, HomePNA uses the existing Ethernet protocol; in the connection mode The HomePNA technology allows all nodes in the network to be connected in a daisy-chain manner without the need for a central tandem connection or exchange. This connection method helps simplify installation and subtly changes the random topology of the home phone wiring.
In terms of products, HomePNA's terminal equipment is developing from independent network interface cards and embedded network cards on PC motherboards to integration into 10 / 100M fast Ethernet cards; in order to solve the problem of accessing the Internet, HomePNA is combined with xDSL and ordinary modems. Form a smart residential gateway.
8.Ethernet
Because 10M / 100M Ethernet has been popularized, 1000M Ethernet technology is mature, the price is low, people only need IP services and QOS requirements are not very urgent, etc., all Ethernet access solutions are widely concerned, and the basic concept is : Establish 1000M Ethernet as the backbone network, realize 1000M Ethernet to the building, roadside, and residential area, then use 100M Ethernet to the floor of the building, or small buildings and residential buildings, and then use 10M Ethernet to the semi-public office and desktop . At present, users use Ethernet cards and Category 5 lines to connect to the equipment in the floor; the floor is a switch working on the second floor (using VLAN technology), which implements out-of-band management through a common Modem and uses remote power supply; the cell equipment is more High-throughput second-layer switch (using VLAN technology), which manages and supplies power to the switches in the floor through hybrid optical cables and modems; multiple cells share a gigabit router and NAT (network address mapping) through fiber; backbone network Connect multiple routers to form a broadband IP metropolitan area network. Access between users should be through a router, and user management is also done at the node where the router is located.
9.SDH
SDH suitable for access network has high reliability, flexibility, high compactness, low power consumption and low cost. In general, when the bandwidth of 155Mbps or higher is required, the SDH system can be directly connected to users in a point-to-point or ring topology; when the bandwidth is greater than 34Mbps, the SDH ADM (Add / Drop MulTIplexer, add-drop multiplexer) Device) Set up at the user to connect to the STM-N service node with the STM-1 channel. This connection can be either point-to-point or through a ring structure; for bandwidth requirements far less than 34Mbps, use a lower rate The multiplexer or ADM sharing method is more cost-effective; for most ordinary enterprises and users, the terminal multiplexer located on the roadside (DP point) can be used to provide a large number of users with a bandwidth of 2Mbps as the basic unit, which needs to be less than 2Mbps Users of bandwidth services can be resolved by a service multiplexer or a PON. The use of STM-0 sub-rate connection (Sub STM-0) is a cost-effective solution for small-bandwidth users while maintaining all SDH management capabilities and functions. ITU-T G.708 specifies such an interface.
Although SDH can allocate different bandwidths to different nodes during construction, it cannot achieve the dynamic adjustment of the total node rate. At present, there are many kinds of SDH equipment (especially SDH ADM) applicable to the access network, which will not be detailed in this article.
10.PON and APON
Passive optical networks (PON) include narrowband passive optical networks and ATM-based broadband passive optical networks—APON. The former is used to provide data transmission channels at 2Mbps and below, while the latter can provide up to 622Mbps Downstream transmission channel. APON mostly adopts passive double-star or tree structure, and uses a special point-to-multipoint multiple access protocol, so that many ONU / ONT (OpTIcal Network terminaTIon, optical network terminal) share OLT, and many users share ONU to reduce the initial construction cost. At present, there are official APON products, but the variety is limited, and the integration of components still needs to be further improved.
11.IM-DSL
The basic idea of ​​IM-DSL is to establish multiple xDSL links, form a high-speed physical link through inverse multiplexing technology, and then use ATM's statistical multiplexing technology to enable many users to share this physical channel. Obviously, the transmission distance of IM-DSL is limited to less than 2 kilometers, in order to solve the contradiction between the current broadband DSL technology relies on broadband access technology due to the limited transmission distance and the widespread implementation of FTTB, FTTC and FTTZ is still quite difficult. The IM-DSL technology makes full use of existing telephone lines, with small engineering, good capacity scalability, and low investment. However, it currently lacks industry standards and is under pressure from HFC and fiber to further extend to users. At present, it is difficult to see mature and formal products of this technology.
summary
With the development of data and multimedia services, the research and development of broadband access technology will become more and more obvious. Broadband and optical fiber of the network will become a hot spot in the current communication field. From the current development point of view, three different systems of broadband access technology: xDSL (especially ADSL), Cable Modem and HFC, Ethernet will be the third in recent years, and APON and SDH as broadband access technologies also Will be developed in the corresponding field.
Programmable DC Power Supplies
The CSP series Programmable DC Power Supply is upgraded and developed on the basis of iDealTek-Electronics' mature IGBT high frequency switching power topology and all-digital signal control loop. Featured with high precision, low ripple and fast response speed.
The Programmable DC Power Supply is different from the traditional DC power supply that can only control the output voltage and current values. The programmable DC Power Supplies can realize the programming of multiple parameters through adding the microprocessor unit with built-in control program, such as parameters like operating time, output rise time, protection response time, OVP and OCP etc. All can be set and programmed.
At the same time, the microprocessor unit also adds more functions to the power monitoring system, which can realize the query of the historical data of the test results, making the programmable DC power supply the best choice for laboratory test, production line manufacturing test, photovoltaic plate aging test and various cutting-edge applications with Programmable DC power supplies.
This series of Programmable Power Supplies have a total of 4 standard rated power levels, ranging from 1KW Desktop Programmable Laboratory power supplies to 3KW / 6KW / 10KW Rack-mounted Programmable DC power supplies. The maximum output voltage ranges from 600V to 1000V under different rated powers.
Beautiful appearance design with small and compact size, the whole series power supplies adopt silicone buttons, stepless knobs and LCD display on control panel layout. The output voltage, current, start / stop time, output rising rate, OVP, OCP and other parameter setting programming and reading of the Programmable Power Supplies can be easily and quickly completed through the front panel man-machine interface, up to 5 digits of high-precision programming and monitoring levels make the measurement results of the programmable DC power supply accurate and reliable, almost no need to use external power meters.
At the same time, the whole series of programmable DC power supplies are equipped with RS485 interface as standard, following the MODBUS-RTU international protocol, which can realize remote control programming, test results save and uploading to the master unit and status monitoring of the power supply.
Programmable Power Supplies, DC Programmable Power Supplies, Programmable AC - DC Power Supplies, Programmable AC DC Power Supplies, Programmable Laboratory Power Supplies
Yangzhou IdealTek Electronics Co., Ltd. , https://www.idealtekpower.com