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Broadband - the only way to develop telecommunications

With the rapid development of social economy and technology, the communication network is undergoing profound changes. The telecommunication service is gradually developing from the traditional narrowband service based on telephone service to the multimedia broadband service integrating voice, high-speed data and image. . Multimedia communication has become the main driving force for the establishment of public broadband networks. The traditional telephone network will inevitably have to transition to the next-generation telecommunication network centered on data services, especially IP services, which have placed urgent demands on the broadbandization of telecommunication networks. Broadband networks are network systems built on broadband technology. It is well known that the data content of multimedia information far exceeds the amount of data previously transmitted in a single form. In the case that the transmission rate cannot be reduced and the information capacity is increased at the same time, the telecommunication network must strive to increase the capacity and speed of the transmission channel, otherwise it is inevitable Information cannot be guaranteed to be delivered in a timely, accurate and complete manner. Therefore, to achieve multimedia information, we must rely on broadband technology. Broadband networks can be divided into three parts: broadband transmission network, broadband switching network and broadband access network according to their technical structure. The transmission network is the basic channel for the transmission of all information elements. The information unit and data are transferred from the source address to the destination address through the transmission network. The broadband switching network realizes the process of information exchange through the process of receiving, sorting and forwarding information; the access network is the last segment connected to the user in the entire broadband network, and the user connects to the broadband through the access network. Online. The construction of the broadband access network access network accounts for a large proportion of the investment in the whole network, and it is the most complicated part of the technology, the most difficult to implement, and the most extensive part of the impact. It is necessary to adapt to local conditions, adapt to the time, and develop the access network as reasonably as possible. The development of advanced fiber access networks should consider the compatibility of the fiber access network with the original cable access network topology, and the direction of the full fiberization of the access network. It is necessary to save investment costs and maintain a high starting point. The principle of implementation by stages. Therefore, in the process of building the access network, we should proceed step by step, starting from low-speed services and gradually developing into high-speed services. The currently used narrowband access technology has a band Modem technology, and the Modem downlink rate of the V.90 standard is 56 kbps; the narrowband ISDN access technology can provide users with end-to-end full numbers on a pair of ordinary telephone lines through a basic rate interface. A variety of telecommunications services connected. At present, broadband access technologies mainly include the following: Digital subscriber line access technology based on telecommunication network subscriber line DSL technology is a series of high-speed subscriber line transmission technology based on twisted pair copper wire, including HDSL, SDSL, ADSL, RADSL and IDSL, etc., collectively referred to as xDSL. ? ADSLADSL technology, its downlink rate of 8Mbps, uplink speed of 640kbps, can transmit distance of 3 ~ 5km. The main services supported by ADSL are the Internet and telephone. The access speed of this technology can meet the broadband Internet access and some broadband applications. More importantly, it can support broadcast-quality video distribution and VoD in combination with broadband trunking network technologies such as ATM. The advantage of using ADSL technology to carry out broadband access services is very obvious. First, you can make full use of the existing copper resources of the telecommunication network to protect this huge investment and give full play to the potential of copper wire. Secondly, users can access the Internet at any time without having to re-establish the connection every time, and it will not affect the use of the phone. Each user can enjoy the high-speed channel without blocking problems. The main disadvantage is the stringent requirements of the pair. Currently, only about 30% of the pairs can open the ADSL service. A simplified, splitterless ADSL standard is now available, called G.Lite. The basic characteristics are two points: the first is that the rate is reduced to about 1.5 Mbps, and the second is that the user does not need a telephone splitter, the price can be lowered, and the installation is more convenient. It has adaptive rate adaptation capability and is more resistant to radio frequency interference than ADSL. Its main services are Internet access, Web browsing, IP telephony, distance education, home work, videophone and telephone. The second trend in the development of ADSL systems for VDSL systems is to further increase the downstream bandwidth of the system, which evolves into a very high-speed digital subscriber line system. This technology can extend the downlink transmission rate on the twisted pair to 25Mbps to 52Mbps, while allowing the uplink rate of 1.5Mbps, and the transmission distance is shortened to 1000m or 300m respectively. Very suitable for fiber-to-cell access. Because it can provide high-speed access bandwidth and meet the requirements of high definition TV and video on demand, it is a realistic and ideal broadband hybrid access solution. Cable Data Access Technology Based on CAV Network HFC Transmission Facility The cable television network is a terrestrial network used to transmit analog TV signals. All users share the downlink bandwidth and are truly broadband networks. HFC technology has promoted the development of CATV networks. HFC networks can not only provide original cable TV services, but also provide voice, data and other interactive services. The Cable Modem solution is based on HFC-based high-speed access technology. Cable Modem users share the downlink data bandwidth, and the data throughput of each sub-channel downlink channel can reach 25Mbps to 40Mbps. The traditional wired network can only transmit one-way services, and must be upgraded to a two-way HFC network to realize two-way broadband transmission of digital information, and can open VoD, distance learning, telemedicine, Internet high-speed access and voice calls. New value-added services. Cable Modem has a high turn-on rate, and there is no problem with ADSL's low turn-on rate due to cable quality and crosstalk. It only reduces the available data bandwidth per user due to the increase in the number of shared users. Broadband optical fiber access technology based on optical cable? Broadband active optical access In various broadband optical access network technologies, access network systems using SDH technology are the most common. Such a system can be referred to as active optical access, primarily for comparison with passive optical network based access systems. SDH technology is a mature, standard technology that is widely used in backbone networks. Apply SDH technology in the access network, which can bring the huge bandwidth advantage and technical advantage of SDH technology in the core network into the access network field, making full use of SDH synchronous multiplexing, standardized optical interface, powerful network management capability and flexibility. The benefits brought by network topology capabilities and high reliability have benefited in the long-term development of access networks. Although the application of SDH technology in the access network is already very common, it is still only the extent of FTTC and FTTB, and the huge bandwidth of the optical fiber is still not available to the household. Therefore, to truly provide broadband service capabilities to users, it is not enough to use SDH technology to solve the widening of feeders and wiring segments. In the lead-in part, FTTB/C+xDSL, FTTB/C+Cable Modem, and FTTB/C+ regional network can be used respectively. Provide services in the same way. Broadband Passive Optical Access Network An ATM-based passive optical network is a broadband platform that provides both traditional services and advanced multimedia services. PON's business transparency is good, and in principle can be applied to any standard and rate signals. APON downlink adopts TDM, and uplink adopts TDMA technology. Its downlink rate is 622Mbps or 155Mbps, and the uplink rate is 155Mbps, which can provide users with flexible high-speed access. The most important feature of ATM PON is its passive point-to-multipoint network architecture. There are no active devices in the optical distribution network, which is simpler, more reliable, and easier to maintain than active optical and copper networks. Especially if the FTTH is used in a large amount, the active device and the power backup system are transferred from the outdoor to the indoor, the environmental requirements for the device and the device can be greatly reduced, and the maintenance cycle can be lengthened. The high degree of standardization of APON makes large-scale production and cost reduction possible. In addition, the characteristics of ATM statistical multiplexing enable ATM PON to serve more users than TDM PON, and the QoS advantage of ATM is also inherited. The use of wavelength division multiplexing technology is an effective means to expand the transmission capacity of optical fibers. Passive optical networks based on wavelength division multiplexing technology have broad prospects for access networks. The high-speed area network access based on Ethernet is connected to the Ethernet network, which is similar to the IP network. It can reach 10/100/1000Mbps in three levels. The use of dedicated collision-free full-duplex fiber optic connection has enabled the transmission distance of the Ethernet network to be greatly expanded, which can fully meet the application requirements of the access network. Ethernet technology encapsulates IP packets directly into Ethernet frames. It is one of the best protocols for cooperation with IP. It transmits variable length IP packets in variable length frames. In the current rapid development of the Internet, Ethernet is transforming into a major access method. Wireless access technology based on wireless transmission technology Fixed wireless access technology has become a new force in the field of access networks because it does not need to lay lines, construction speed is fast, it is less subject to environmental constraints, initial investment, flexible installation, and easy maintenance. There are three main types of broadband fixed wireless access technologies: multi-channel multi-point distribution services already in use, direct broadcast satellite systems, and local multipoint distribution services that are being field tested. The LMDS operates in the millimeter wave band and has a usable frequency band of at least 1 GHz. A typical LMDS consists of multiple conveyors in a similar cellular configuration with a single cell coverage of 2 to 5 km. LMDS not only provides Internet access, but can also be used to interconnect regional networks. LMDS can provide almost any kind of business, such as voice, data, images, etc. It also supports standards such as TCP/IP and MPEG2. In general, broadband fixed wireless access technology represents a new and non-negligible development trend of broadband access technology. It is fast to open, simple to maintain, and low in cost when users are dense. It can be used as an important part of wired access for telecom companies. supplement. Broadband transmission network is accompanied by the development of optical fiber communication technology. The main physical medium for broadband network transmission is necessarily optical fiber. The advantages of using fiber to build a broadband transmission network are threefold: it can provide high frequency bandwidth. The bandwidth of the optical fiber allows high-speed data transmission, and can fully adapt to the transmission speed requirements of multimedia communication through multiplexing technology and data compression technology. Very low attenuation. The optical signal transmitted through the optical fiber has a low attenuation characteristic, which means that long-distance transmission can be performed without a repeater, which not only reduces the cost but also reduces the breakpoint formed by the intermediate link. Strong confidentiality. The transmitted optical signal is non-electronic and immune to electromagnetic influences. SDH transmission system is a new type of complete and strict transmission network technology system. It has a unified network node interface in the world, which simplifies signal intercommunication and signal transmission, multiplexing and cross-connection process; it has a lot of overhead. The bit is used for network management and maintenance; it has a unified standard optical interface, which can achieve horizontal compatibility on the basic cable segment; SDH networking technology can also form a highly reliable self-healing ring structure to ensure business realization. Transparency, which is important for certain aspects of business application. Optical fiber communication continues to develop in large capacity and high speed, providing the most solid foundation for broadband networks. At present, the high-speed transmission system using dense wavelength division multiplexing technology can reach 400Gbps, and the research level of the laboratory has exceeded 3Tbps. This also provides a reliable guarantee for the QoS of the IP network. In the case of bandwidth redundancy, guaranteed QoS can be provided when network utilization is below 70%. The current traditional voice network and data network are moving toward unity. The TCP/IP protocol will dominate the entire network. IP can carry all services, including interactive multimedia services such as data services, real-time voice, and video. The future network is a large-scale broadband IP network that integrates voice, data and video with IP technology as the core. However, the IP network can only be built on various basic transmission networks. Currently, the IP transmission mode is as follows. IP over ATM ATM with dynamic bandwidth allocation and high QoS is an exchange, transmission, and multiplexing device. It is also an ideal platform for carrying all IP services. IP over ATM is a unified connection between wired ATM and unconnected IP. It is also an optimized combination of routing and switching. It can take advantage of ATM's fast speed, large capacity, multi-service support capability, and IP simplicity and flexibility. Easy to expand and unite, to achieve the purpose of complementary advantages. For telecommunications networks, ATM is ideal as a multi-service platform for quite some time. Even in the future, at the edge of the Internet, ATM is still indispensable as a business gathering point. The combination of IP over SDHIP and SDH attempts to map IP packets directly to SDH frames through PPP protocols or SDL protocols, thereby eliminating the intermediate ATM layer, preserving the Internet connectionless features, simplifying the network architecture, and improving transmission efficiency. Reduce operating costs, easily adapt to different technical systems and achieve inter-network interconnection, and channel high-speed data streams on the backbone network based on IP services. From the theoretical point of view, IP over Optical adds ATM and SDH between the IP and the transmission link layer. Therefore, IP over Optical is an ideal architecture: fewer layers, avoiding overlapping functions; low complexity of equipment and network management; low overhead, high transmission efficiency; simple networking and network configuration; and direct use of DWDM technology. Broadband switching network When the transmission technology is gradually moving toward broadband, the switching equipment that makes full use of transmission resources for various services has also developed accordingly. The packet forwarding and switching technology represented by IP and ATM is the current network. Hot spots in construction. The flexible nature of IP and the fast switching capabilities of ATMs are invaluable and will play a key role in future network technologies. ATM asynchronous transmission mode - ATM is currently a solution to the broadband service exchange. In order to meet the requirements of multimedia communication, users must support different networks: data network, voice network and video network. The network structure must also adapt to different applications. Ethernet, Token Ring and FDDI are used for regional networks, and PPP, SLIP and Modem are used for wide area networks. Such complex requirements are beyond the reach of previous exchange levels. The emergence of ATM technology solves these problems by providing a common, unified network switching framework that supports users' comprehensive needs for data, voice and video. The basic carrier for transmitting information in ATM technology is ATM cells. ATM cells are very similar to packets in packet switching, but they have their own characteristics. It uses a fixed length of 53 bytes of cell length, the entire cell byte includes 5 bytes of the header and 48 bytes of information fields, the header is used to carry the cell control information The subsequent information field is generally carrying user information. In the header information, the VPI represents the virtual path identifier, and the VCI represents the virtual channel identifier, and the two parts together form the routing information of the cell. The ATM switch selects the routing line based on these two pieces of information. The broadband switching network based on ATM technology is oriented for connection. When the transmitting end wants to communicate with the receiving end and exchange information data through the network, a virtual circuit will be established. After that, the information to be transmitted is divided into ATM cells, and transmitted to the receiving end through the established path. When all the information is transmitted, the virtual circuit will be cancelled. The goal of the ATM broadband switching network is also its biggest feature, which is to achieve the best resource utilization for any form of data transmission. In this way, the broadband transmission network can transmit multimedia information at high speed, and the transmission destination network can be quickly and flexibly selected through the switching network without delay. The routing switch routing switch combines the performance of Layer 2 switching with the traditional software routing based function. It uses hardware dedicated circuits for route identification, calculation and forwarding. Because it implements non-blocking switching, it is fast and can handle full line information on the line. Also known as wire-speed routing switches. Because it is based on Layer 3 IP routing switching, it is also known as Layer 3 routing switches. At present, gigabit routers can reach linear rates, and higher-rate terabit routers are also available, enough to compete with ATM exchanges. With the advent of the information society, the demand for multimedia communication is becoming more and more urgent. Although the narrowband telecommunications network has vitality for a long time, we should see that the trend of broadband is coming to us. We must pay enough attention to prepare for the planning and construction of the network. An easy-to-use, secure, multi-functional, information-rich, open-source broadband telecommunications network will be built as soon as possible to lay the foundation for the construction of the information superhighway.

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