Comparison of broadband access modes

The upsurge of education informationization has been pushing the pace of campus network construction, in the campus network construction, a very important question is to choose what kind of broadband access mode. The author has analyzed and compared the most common three kinds of broadband network access modes:

First, ADSL (asymmetric Digital subscriber line, asymmetric digital subscriber lines)

Advantage: ADSL can transmit wideband signal on the copper twisted-pair line of telephone network, and do not disturb the call on the same line. ADSL provides users with 1.5mbps~8mbps downlink rate and 640kbps~1.5mbps uplink rate, and the bandwidth is more stable. Each ADSL user has a separate line with the ADSL end of the link, its structure can be seen as a star structure, data transmission bandwidth is unique to each user, so that each user's bandwidth is fixed, not because of the increase in the number of users resulting in the decline in transmission efficiency. ADSL users to the local end of the use of point-to-point transmission, in terms of security than cable wired access to the HFC network better. Compared with other broadband access schemes, ADSL is the same as ISDN, DDN and other technologies, such as the telephone network based on the telephone twisted-pair for transmission media, can make full use of the existing installed telephone lines, without rewiring, building infrastructure, Only by adding a modem at both ends of the existing copper strand, the transmission rate can be increased by dozens of times times, so the transformation investment is small and the economy is comparatively economical. And ADSL has been internationally standardized by ANSI and ETSI, which means that ADSL network products based on these standards are more versatile.

Shortcomings: ADSL technology also has a shortage of places, it can provide 8Mbps of bandwidth, but it is difficult to expand further; ADSL pair of copper twisted pair wire transmission distance of up to 5 kilometers, but in fact, because the signal from the local to the client side of the way will quickly decay, by transmission distance, the signal quality will be reduced. Due to the aging of the telephone line or do not meet the standard of broadband data transmission, there may be some return noise, line crosstalk phenomenon, which will affect the data transmission.

Comments: The author of the region only some of the schools closer to the city is equipped with ADSL. This way the cost of investment is very low, but also more stable, just feel the speed of general.

Second, cable wired access

Advantages: Cable Wired access technology is based on high-quality two-way cable television network, HFC (Hybrid Fiber Coaxial) as the main transmission medium, is a hybrid network of fiber coaxial cable, is a new type of broadband network. Cable wired access can provide up to 10Mbps above the bandwidth, and has anti-jamming, fast data transmission characteristics, as a broadband network access has a more obvious advantage. The use of fiber and cable as the transmission medium, has a rich frequency band resources, and there is no due to the quality of telephone lines and crosstalk caused by problems. With the introduction of the new standard, the price of Cable modem is close to that of the ordinary modems, which makes the access cost lower and is very advantageous to the users. In addition, China's cable TV after more than 10 years of development, has been quite popular, the use of cable network resources to achieve broadband access has a great advantage, many relatively remote schools can access. Based on the HFC structure, the data Access service is realized by using cable modem, and interactive digital TV service and multimedia information Service can be provided.

Deficiencies: Cable Wired access technology network topology relatively backward, channel bandwidth is the overall user share, once the number of users increased, each user allocated bandwidth will be drastically reduced; In addition, because the transmission of radio and television signals to occupy part of the communication band, The remaining band resources cannot meet the requirement of high-speed data transmission in broadband network.

Comments: Cable Wired access is the most widely used in the author's area of broadband access, the overall feeling is that the speed is not stable, sometimes fast and sometimes slow, may be the number of users caused by changes.

Third, Ethernet access

Advantages: Ethernet access is a LAN technology, its bandwidth can reach the G-bit Ethernet or more high-speed. Ethernet frame format and IP are the same, especially suitable for the transmission of IP data. Generally can use FTTB broadband access, gigabit or hundred trillion to school, each node access rate of up to 10Mbps, if necessary can also be extended to 100Mbps. Using the FTTB network does not require dialing, and the user can connect to the Internet as soon as it is switched on.

Ethernet has excellent scalability, upgrade and expansion is very convenient; users enjoy a stable bandwidth, there is no ADSL maximum transmission rate is subject to transmission distance constraints, there is no cable wired access with the increase of users, each user divided the available bandwidth will greatly reduce the disadvantage.

Deficiencies: The early investment is large, it must be rewiring, laying lines have a certain degree of difficulty, IP Address resource requirements are too large, management level requirements higher.

Comments: This approach is mainly used in some larger schools, fast speed, but also more stable. But because the upfront cost is too high, at present is not suitable for the small primary and secondary schools use.