Introduction of cable TV Cable (Cable) mode broadband access

Cable TV Cable (Cable) mode broadband access to the Internet is the standard docsis (Data over Cable Service Interface specification), Recently this standard has been upgraded to 2.0, and Imedia announced in April the DOCSIS2.0 chip IM6030 and a reference design that can be mass-produced immediately. This means that the new cable cat and head-end equipment will be on the market time greatly accelerated, the cost can guarantee a lower level, which is crucial to the development of cable broadband access markets.

Improved uplink transfer rate

The main improvement of the new docsis is to greatly improve the uplink channel rate, can reach 30Mbps, basic and downlink rate to achieve symmetry. The previous version of 1.0 and 1.1 was the uplink rate of 10Mbps and the downlink rate of 56Mbps (both peaks). The improvements are mainly in the physical layer, and the link layer above is still similar to Ethernet, for the IEEE802 LLC. DOCSIS2.0 introduces a new S-CDMA (Synchronous Code Division Multiple Access) modulation technique, compared with the old A-TDMA (sensitive time Division multiple Access) technology, the new technology is more conducive to the poor noise and interference and low bandwidth environment to effectively transfer data, and support more users, but also better support the quality of the business. The DOCSIS2.0 also contains two modulation modes for both S-CDMA and A-TDMA to ensure compatibility with old facilities.

S-CDMA allows multiple cable cats to transmit data at the same time, thus obtaining a high access rate. These cable cats must be synchronized at both the phase and the frequency to ensure that each data stream remains orthogonal and mutually exclusive, and the synchronized clock is provided by the header device. In order to maintain and TDMA equipment in the MAC layer compatibility, the original time frame is still retained, but from one-dimensional to two-dimensional, S-CDMA frame is a time frame matrix, One Direction of the matrix is time, the other direction is the code word. A channel can be allocated 128 orthogonal code words, each time frame using two code words, so that the simultaneous 64 cable cat transmission. S-CDMA also includes a forward error correction feature that avoids retransmission to some extent, which is useful in real-time operations such as video. In addition, S-CDMA also includes some tuning parameters for better transmission performance. ---http://bianceng.cn (computer science)

What are the advantages of the three access technologies?

Since it is broadband access, it should be access is broadband, that is, the downlink is broadband, and uplink is broadband. In this connection, ADSL is obviously a bit outdated, it is to adapt to the previous years of Internet browsing and video on demand, and other asymmetric business, and now the application has increased the proportion of uplink transmission, such as Peer-to-peer communications, interactive games, as well as groups of users. Therefore, technically speaking, DOCSIS2.0 and Ethernet should be the user's preferred access mode. In short, cable access has the following advantages:

The infrastructure is already widespread and has a fibre optic backbone;

has greater bandwidth than traditional telephone lines and wireless connections;

No need for dialing, no complex signaling protocol;

The media is a shared type without circuit switching, so the cost is low and the charges are not based on the connection time, which is in line with the spirit of the Internet.

For the new Smart community, Ethernet is definitely the ideal choice, not only low cost, high speed, more important is to meet the big technology trend, adapt to the future metropolitan Area Network Ethernet as the basis of the development direction. But for a particularly dispersed user, ADSL is the only option. For cable, the biggest advantage is that the cable network is quite popular, already has a huge infrastructure, no extra wiring works (but also need to do a one-way transformation of the two-way, that is, the end of the head to increase the cable cat system). Therefore, the cable access is the best choice for older community users as well as for the more dispersed Internet population. Another technical reason is that cable TV cable is a shared circuit, if the user is very centralized, each cable users will increase the noise, occupy the channel, reduce reliability and impact on the line of existing User Service quality, resulting in broadband is not wide situation. This is not the case with switched Ethernet and ADSL.

Technical observation of Dr. Chen Shaoqiang

From the pure technology point of view, cable access is not originally for the data two-way transmission business design, so there are inherent defects in the technology, such as narrow bandwidth, tree structure caused by the superposition of noise and single fault point failure, easy to interference and external damage and lead to security degradation, and so on. In order to overcome these obstacles, it is necessary to introduce complex technology. S-CDMA is quite complex, and in order to take advantage of limited bandwidth and to maintain back-compatibility, it is necessary to adopt complex coding and frame formats. This is compared with the simple baseband modulation of Ethernet, which, of course, means high cost and inefficiency. These technical limitations also limit the scope for further development of cable technology.

In view of the current application situation, some cities in China have already used cable access mode, and some cities have made it clear that they will give up the cable way, and the overall switch to Ethernet, this is certainly the reason for the cost, but the deeper reason lies in the bright future of Ethernet and technology development space. However, should see, cable technology also unceasingly develops and consummates, moreover cable way has the good fiber optic cable Foundation, in the future will not be able to make the contribution to the final optical fiber household.

Cable has the longest tentacles.

China currently has more than 100 million of the family has television, one-third of households have cable TV, and the annual growth rate of 5 million households. National Cable TV network line length has more than 2.5 million kilometers, cable trunk more than 300,000 kilometers, it can be said that China is the largest cable broadband access market. The key point is to establish a good business and profit model, which is the equipment manufacturers and operators should be united together to study the problem.

In North America, cable access is more market, basic and ADSL tied, on the one hand because the population distribution is not particularly intensive, on the other hand because the U.S. telecom operating policy is relatively loose. In China, the situation of cable access is much more serious, the key to its success is to use the existing HFC infrastructure as soon as possible, to seize market opportunities, to launch the business acceptable to the majority of users. It depends on three factors: one, institutional change. Currently responsible for the provision of data network services mainly in the telecommunications sector, the focus of telecommunications is of course on ADSL and LAN, the need to reverse this situation as soon as possible. Second, technically overcome the problem. Mainly is the standard localization, will adapt the DOCSIS standard to China's special situation to make the corresponding change. Third, reduce costs. This is the end user's hard demand, now the cost of cable cats has been low to 50 dollars, manufacturers are still trying to further reduce costs.