Technical description of broadband cable modem access

Cable Modem is developed in recent years, mainly for CATV network data transmission. Most new cable networks now use fiber-optic coaxial hybrid (HFC) networks, and their huge bandwidth and relative economics make them attractive to cable companies and newly established telecoms companies. Because cable modem is a kind of equipment that provides data service on HFC network, it is usually equated with HFC broadband access technology.

Using 64QAM technology, Cable Modem can provide 30mbit/s downlink data rate on a single TV channel, and can also use 256QAM to elevate the rate to 40mbit/s. The upstream channel from the client can use QPSK or 16QAM modulation technology to provide the rate of 320kbit/s to 10mbit/s. Uplink and downlink bandwidth is shared by the consumer connected to the cable network section, typically a cable network segment connects 500~5000 families.

Cable modem and previous modems in principle are the data modulation into analog signals in a frequency range of cable transmission  receiver Demodulation, the analog signal into digital signal, input computer, the transmission mechanism and the same as ordinary modem. But the cable modem itself is not simply a modem, it generally has two interfaces, one to connect the cable TV port, the other is connected with the computer, it sets the modem, tuner, encryption and decryption devices, bridges, network interface cards, Simple Network Management Protocol (SNMP) agent and Ethernet hub function in one, and through the HFC network of a transmission band for modulation and demodulation. The normal modem transmission media is independent of the user and the switch, that is, the user has exclusive communication media. Cable Modem is a shared media system, and other free frequencies can still be used for the transmission of cable TV signals.