Keywords: broadband access network, broadband service, broadband network
1 Introduction
Broadband refers to the multi-channel (parallel) transmission of different channels on the same transmission medium using special technology or equipment, and the rate is above 256Kbps. As for how much rate is broadband, there is no international standard at present. Here we measure it as 256K according to the convention and the amount of network multimedia video data.
2 broadband backbone technology
2. 1 Gigabit Ethernet technology
The highest transmission rate is 1Gbps, which is backward compatible with Ethernet technology and fast Ethernet technology. On the transmission medium by? What happened? What's the matter with you? Collect calf yarn? 20 kilometers. In this way, the transmission distance is no longer limited by the transmission medium and can meet the needs of metropolitan area network. Moreover, because 80% of the network nodes in the world are in the form of Ethernet, optical Ethernet has the best compatibility with existing network forms. Ethernet has the characteristics of cheap equipment, low networking cost and easy operation and maintenance, which is very suitable for data services with large transmission bandwidth and low profit. It is especially suitable for metropolitan area network construction in small cities.
2.2 IP over ATM
Combining the technical characteristics of IP and ATM, the basic principle is that all IP packets are encapsulated into ATM cells at ATM layer and transmitted in the channel in the form of ATM cells. When a switch in the network receives an IP packet, it first processes the routing address according to the IP address of the IP packet through some mechanism and forwards it according to the route. Then, a virtual circuit (VC) is established on the ATM network according to the calculated route. Future IP packets will be transmitted through this virtual circuit. The cell transmission and switching technology is adopted to reduce the processing delay and ensure the quality of service, so that its ports can support from E 1(2Mbps) to STM- 1( 155Mbps), STM-4(622Mbps) and STM- 16(2.4Gbps). Advantages: 1, ATM technology itself can provide QoS guarantee, so this feature can be used to improve the service quality of IP services. 2. It has good flow control balance ability and fault recovery ability, and the network reliability is high. 3. It is suitable for all kinds of services and has good network scalability. 4. Support several other network protocols, such as IPX.
The disadvantage is that the network architecture is complex and repetitive. ATM and TCP/IP both have the functions of addressing, routing and flow control, and the overhead loss is large. They are mainly used for the collection of multi-services at the edge of the network and the general IP backbone network, and are not suitable for the application of very large IP backbone networks.
2.3 IP over SDH technology
It uses link and PPP protocol to encapsulate IP packet, and simply inserts IP packet into the information segment of PPP frame according to RFC 1662. Then, the encapsulated IP packet is mapped to the synchronous payload of SDH through the service adapter of SDH channel layer, then passes through SDH transport layer and network segment layer, and the payload is loaded into an SDH frame, and finally reaches the optical layer and is transmitted in optical fiber. High-speed optical fiber transmission is adopted to provide the transmission rate from STM 1 to STM64 or even higher in a point-to-point manner. Among them, IP over SDH technology is also called POS technology, that is, IP packets are directly encapsulated into SDH frames, which improves the transmission efficiency. Features: 1, strong support for IP routing and high IP transmission efficiency. 2, in line with the characteristics of Internet services, such as conducive to the implementation of multicast. 3. Using the loop of SDH technology itself can realize link error correction and improve the stability of the network. 4. The unnecessary ATM layer is omitted, which simplifies the network structure and reduces the operating cost. 5. It only provides good support for IP services and is not suitable for multi-service platforms. 6. It can't provide better service quality assurance like IP over ATM technology. 7. Limited support for IPX and other major network technologies.
The characteristic of this technology is to make full use of optical fiber bandwidth resources and greatly improve bandwidth and relative transmission rate. It is not only compatible with existing communication networks, but also supports future broadband service networks and network upgrades, and has the characteristics of universality and high survivability.
3 broadband access technology
3. 1 copper wire access
3. 1. 1 Asymmetric Digital Subscriber Loop (ADSL)
ADSL belongs to copper wire access technology, which is a point-to-point transmission technology with copper telephone line as transmission medium. It is an asymmetric digital subscriber loop, that is, the uplink rate and downlink rate of the subscriber line are different. According to the characteristics of users using various multimedia services, the uplink rate is low and the downlink rate is high, which is especially suitable for transmitting multimedia information services.
ADSL technology provides a standard method to increase bandwidth for families and small businesses. The downlink bandwidth of G.Lite or ADSL Lite published by the International Telecommunication Union is 1.5Mbs, and the uplink bandwidth is 384Kbps. The former is about 50 times of the existing dial-up analog modem. Therefore, in fact, two connections have been established with the network, one for telephone service and the other for data service, which can be opened and used continuously at the same time.
ADSL can not only provide telephone service, but also provide a variety of broadband services. In the next few years, ADSL access technology will be the most important broadband access method for end users.
The disadvantage is that the transmission distance is very limited, which requires high line quality. When the line quality is not high, it is difficult to popularize and use.
3. 1.2 high bit rate digital subscriber line (VDSL)
VDSL is an upgrade of ADSL, and DSL technology is developed according to the requirements of HDTV, video conference and symmetric/asymmetric services. This technology was put forward in the second half of 1994, aiming at achieving higher transmission rate than ADSL on twisted pair. VDSL provides higher bandwidth and meets more business requirements. It not only supports the same application as ADSL, but also supports high-fidelity music, high-definition TV, multi-channel video service, MPEG-2 images and so on. This is a real full service access (FSAN) method. It is characterized by fast transmission rate, short effective distance, variable and adaptive rate, and can be configured into symmetric and asymmetric transmission modes as required.
3.2 Fiber Coaxial (HFC) Access Technology
Cabel Modem is a technology based on hybrid fiber coaxial network (HFC), which can access and access Internet information in the frequency band without affecting cable TV broadcasting. Its downlink transmission rate can reach10 Mbps to 30 Mbps, and its uplink rate can reach above 5 12kbps. Another outstanding advantage of this technology is that it only occupies a small part of the available spectrum of cable TV system, so users can watch TV and use mobile phones while surfing the Internet.
Disadvantages are the need for two-way transformation, limited capacity for further bandwidth expansion, and inability to build an independent community intranet platform.
3.3 Ethernet access technology
Ethernet technology, which was originally mainly used in computer networks, has greatly expanded the transmission distance of Ethernet due to the development of technology, and can fully meet the data communication requirements of access networks and metropolitan area networks. This technology is becoming the main means to provide high-speed access for enterprises and institutions because of its good cost performance, scalability and easy installation. At present, more than 80% enterprises and institutions in the world use Ethernet access.
The disadvantage is that the existing community needs to be re-wired.
3.4 Wireless Access Technology
Wireless access technology is divided into three series: fixed wireless access, mobile wireless access and cellular mobile.
fixed wireless access
(1) Local Multipoint Distribution Service (LMDS)
Its biggest feature is broadband, and the available spectrum is often above 1GHz. In different countries or regions, the specific working frequency band and bandwidth allocated to LMDS by telecom management departments are different, and most of them set 27.5 GHz ~ 29.5 GHz as LMDS frequency band. China uses 26GHz and 38GHz.
Because this technology uses large-capacity points to transmit multi-point millimeter waves, it can provide almost any kind of services such as voice, data, video and images, and can realize the user access rate from 64Kbps to 2Mbps, even as high as 155Mbps. It has high reliability and is considered as a "wireless optical fiber" technology.
LMDS system usually consists of four parts: basic backbone network, base station, user equipment and network management system. Because LMDS directly supports wireless ATM protocol, it can improve link efficiency.
The disadvantage is that the coverage is small, covering 30 square miles.
(2) Multipoint and Multichannel Distributed System (MMDS)
MMDS can provide services to every user through the antenna installed on the roof without the intervention of local telecom or cable broadcasting company.
MMDS was originally used for one-way transmission of video broadcasting services, including wireless network systems between cities. Now, bidirectional data service transmission can be adopted, allowing more flexible use of MMDS spectrum. On the other hand, LMDS technology belongs to regional wireless technology and can be applied to small-scale communication networks in cities and suburbs.
(3) Free Space Optical Communication (FSO)
Compared with the previous wireless communication using electromagnetic waves, laser wireless communication has the advantages of large capacity, small transmitting devices and power, no need for government permission and no impact on human body. However, it is easily affected by weather and obstacles, and is generally used for indoor short-distance communication, such as the transmission of various remote control signals and data communication between microcomputer and mobile phone. Now it is used in outdoor communication, but it needs to use adaptive technology to combat weather deterioration. Free-space optical communication (FSO) uses optical pulses to modulate signals. According to the regulations of FSO alliance, two infrared wavelengths can be used: long wave 1550nm and short wave 800nm. Provide data rates of 100, 155 and 622Mbps.
Mobile wireless access
(1) broadband wireless local area network
Wireless local area network is the product of portable mobile communication, and the terminals are mostly portable microcomputers. It consists of wireless network card, wireless access point (AP) and wireless router. At present, the most popular standard is IEEE802. 1 1 series, which is mainly used to solve the wireless access of user terminals in offices, campuses, airports, stations and shopping centers.
On the basis of 802. 1 1, IEEE has successively introduced two standards: 802.1b and 802.1/a. The main technical differences between them are MAC sublayer and physical layer. 802. 1 1b adopts dynamic rate drift, which can be switched between 1 1 Mbps, 5.5 Mbps, 2Mbps, 1 Mbps due to environmental changes, and between 2 Mbps and 802. 1 Mbps. 802. 1 1a works in 5GHz band, with a physical layer rate of 54Mbps and a transport layer of 25Mbps. It can provide 25Mbps wireless ATM interface, 10Mbps Ethernet wireless frame structure interface and TDD/TDMA air interface.
⑵ Bluetooth technology
Bluetooth is a short-distance wireless connection technology, which is used to provide a low-cost short-distance wireless connection solution. Because of the short distance, the home information network can use Bluetooth technology.
Bluetooth uses 2.4GHz ISM (Industrial, Scientific and Medical) frequency band, which is not affected by uneven frequency distribution in various countries.