Cable modem

A Modem cable (modulating demodulator) is a device connected to a television network by cable which offers numerical telecommunication services such as Internet. The modem-cable is bidirectional, it uses one Coaxial cable in the two directions, downstream for the data of the network towards the user and upstream for the data of the user towards the network.

The standard DOCSIS (Data Over Cable Service Interfaces Specification) uses carrying numerical in modulation QAM (Squaring Amplitude Modulation) 64 or 256 QAM able to offer a transmission speed from 30 to 40 Mbit/s towards the user (downstream). As regards the data of the user towards the network (upstream), the modem modulates carrying a QPSK (Squaring Phase Keying Shift) or 16 QAM for a transmission speed between 320 kbit/s to 10 Mbit/s. Several carrying can be inserted in the network of cable to serve a great number of users.

The speed of downstream and upstream can be controlled by the supplier according to the type of desired subscription.

External bonds

International Engineering Consortium
CableLabs

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