Cable Modem access technology is developing rapidly in the world, especially in North America, with the number of users increasing at a rate of more than 100% each year. In China, Guangdong, Zhejiang, Sichuan, Guangxi, Shenzhen, Nanjing and other provinces and cities have opened Cable Modem access. It is the biggest competitor of the telecommunication company's xDSL technology. In the future, the xDSL access technology based on traditional telephone networks developed vigorously by the telecommunication company camp and the Cable Modem technology promoted by the broadcasting system and cable TV manufacturers will compete in the access network market (especially the high-speed Internet access market).
In China, the broadband access technology developed by the radio and television department on the cable television (CATV) network has matured and entered the market. The CATV network has a wide coverage area and a large number of users (according to statistics, the number of cable TV users nationwide has exceeded 100 million in January 1999); the network has a wide spectrum range and a high starting point. Most new CATV networks use optical fiber coaxial Hybrid network (HFC network), using adjacent frequency transmission system with bandwidth above 550MHZ, is very suitable for providing broadband functional services. Cable Modem (Cable Modem) technology is a network access technology based on CATV (HFC) network.
Cable Modem and the previous Modem are in principle that the data is modulated and then transmitted within a frequency range of the Cable (cable), and demodulated during reception. The transmission mechanism is the same as the ordinary Modem, the difference is that it is modulated and demodulated through a certain transmission frequency band of CATV. The transmission medium of the ordinary Modem is independent between the user and the switch, that is, the communication medium is exclusive to the user. Cable Modem is a shared medium system, and other idle frequency bands can still be used for the transmission of cable TV signals.
Cable Modem completely solves the congestion caused by the transmission of sound and image. Its rate has reached more than 10Mbps, and the downstream rate is even higher. Although the traditional modem has developed a product with a rate of 56Kbps, its theoretical transmission limit is 64Kbps, and it is impossible to increase it. Cable Modem is also a key equipment for building a metropolitan area network. Hybrid optical fiber coaxial network (HFC) backbone uses optical fiber, and tree-type bus coaxial cable network is used to connect users in optical node communities. The transmission frequency can be as high as 550/750MHz. It is necessary to use Cable Modem to transmit data in HFC network.
This is the necessary magic weapon for cable TV to enter the Internet access market. Since the successful two-way transmission experiment of analog and digital TV and data by Time Warner in Orlando, Florida in December 1993, Cable technology has become the most promising access technology. On the one hand, it can theoretically provide extremely fast access speeds and relatively low access fees. On the other hand, cable TV has a huge user base. Cable TV stations generally separate a 6MHZ channel from the TV channels between 42MHZ and 750MHZ for downlink transmission of data. Usually the downlink data adopts 64QAM (quadrature amplitude modulation) modulation mode, the highest rate can reach 27Mbps, if adopts 256QAM, the highest rate can reach 36Mbps. Uplink data is generally transmitted through a section of frequency spectrum between 5 and 42 MHz. In order to effectively suppress the accumulation of uplink noise, QPSK modulation is generally used. QPSK is more suitable for noise environments than 64QAM, but the rate is lower. Uplink speed can reach up to 10Mbps.
Cable Modem itself is not just a modem, it integrates the functions of MODEM, tuner, encryption/decryption device, bridge, network interface card, virtual VLAN proxy and Ethernet hub. It does not require dial-up Internet access, does not occupy a telephone line, and can provide a permanent connection online at any time. A VPN (virtual private network) connection is established between the service provider's equipment and the user's Modem. Cable Modem provides a standard 10BaseT Ethernet interface to connect to the user's PC device or local area network hub. In addition to the two-way Cable Modem access solution, COM21 also supports the one-way Cable Modem access solution. Its uplink channel adopts telephone MODEM backhaul, which saves the huge expenses required for two-way transformation of the current CATV network, saves operating costs, and can immediately launch high-speed Internet access services; however, it also loses the greatest advantages of Cable Modem technology: No telephone line, no dialing and permanent connection are required.
With the rapid development of science and technology, especially Internet technology, and the opening of the telecommunications market, a situation where the three major networks of telecommunications network, cable television network and computer network coexist and merge with each other has gradually formed. China Telecom has realized the transmission and switching of the backbone network and the digitization of the relay and switching of the local network, but the user access network still uses analog copper wire as the main transmission medium, which has become the bottleneck of the modern telecommunications network. The explosive development of Internet technology has caused more and more multimedia data such as video, audio and high-definition images to be transmitted on the network. This information is swallowing limited channel bandwidth resources at a terrible speed. The traditional access network must develop towards high bandwidth. Using the existing HFC network, local cable TV stations can quickly transform into TV program providers and broadband Internet data service providers, thereby winning new money-making opportunities and sharing the promising broadband data service market.
According to the forecast in 1999, the population of the U.S. using Cable Modem to access the Internet via cable television broadband data networks will soon exceed 3 million, and it is predicted that the population using Cable Modem will grow rapidly. Many well-known technology and entertainment multinational companies such as Cisio, 3com, Nortel, General Telecommunications, AT & T, Time Warner have invested in the industry of cable TV broadband Internet access, which is equivalent to setting the highest level of cable TV broadband Internet services. Good guarantee. In our country, the number of people going online through the cable TV broadband data network is increasing exponentially. There are dozens of domestic listed companies, dozens of cable TV stations or cable TV network companies, including well-known domestic high-tech listed companies and provincial cable TV stations. : ZTE, Shanghai Bell, SVA, Oriental Pearl TV, Guangdong Cable TV, etc. have all invested in the cable TV broadband network industry. If the cable TV broadband network does not have broad development prospects, these companies will invest heavily in this industry. Is it? Why can cable broadband Internet services grow to such an astonishing number? Let's make a simple comparison between broadband Internet access and telephone Internet access: Dial-up Internet access is generally 33.6Kbps/56.6 Kbps, while the ISDN dedicated line Internet service generally provided by local telephone companies, the connection speed is 128Kbps, if you use ADSL The data dedicated line is used to access the Internet, and the connection speed is about 1.8Mbps, but the transmission distance cannot exceed 5 kilometers, and the equipment is very expensive. Internet access through cable TV broadband, using Cable Modem, the data transmission speed can reach between 10M-36Mbps, through the optical fiber backbone network transmission, the distance can "cross continents and provinces", through the HFC network to transmit data, can cover the entire large and medium-sized cities; If the cable television broadband network is transformed to the level of fiber to the building in the future, a full data network is realized, and the transmission speed can reach more than 1000Mbps. This is the real information highway. In addition to high-speed Internet access, it can also achieve High-speed data transmission services such as video telephony, video conferencing, multimedia distance learning, telemedicine, online games, IP telephony, high-speed digital broadcasting, VPN, and video-on-demand.
Many people worry that the bandwidth of the Cable Modem is shared. If there are more people going online, the speed will decrease. Here we explain from different perspectives such as technology and trend to help you understand the bandwidth of Cable Modem. It has been mentioned earlier that Cable Modem can generate 27 M / 36 Mbps bandwidth on a single cable TV channel with different modulation techniques, which is equivalent to the bandwidth of 16-22 ADSL dedicated lines. Based on the bandwidth of each Cable channel and the number of users who are online at the same time on this channel, we can calculate the average bandwidth per person. The "feeling" is used here because the bandwidth of Cable Modem is the same as Ethernet0, which is shared by all users. Regarding the estimation method of the bandwidth available to each person on a shared media (Shared Media), it is estimated using a model called "statistical multiplexing". When other users are not carrying out a large number of transmissions, users Almost all bandwidths can be enjoyed exclusively. This is why cable modem users can often enjoy super-high speeds. According to estimates, each broadband Internet user can enjoy an average speed of 200-500 Kbps, the fastest 1500 Kbps (equivalent to The transmission speed of an ADSL dedicated line). In the future network development, when the transmission speed reaches 1Gbps or more, the average speed that each user can enjoy will be more than 2Mpbs.
The areas where the Shanghai Cable Link did not open:
Shanghai City: Baoshan District, Beicai, Chuansha, Cao Road, Gong Road, Waigaoqiao, Zhangjiang, Pudong District, Tang Town and Sanlin Town.
Shanghai suburbs and counties: Songjiang District, Nanhui District, Fengxian District, Jinshan District, Chongming District, Jiading District, Qingpu District
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