G.now is a MARVELL brand for a broadband access platform based on the G.hn technology. G.hn is a family of ITU-T Recommendations (G.996x) defining home networking over phone lines, power lines and coaxial cables. G.now systems use standard G.hn chips and apply system-level software enhancements to deliver an access solution over phone lines of length of 200 meters (700 feet) or less. G.now can also operate over coaxial cabling.
G.hn and consequently G.now share many of the features of older DSL, but include many enhancements and adaptations. Just like ADSL and VDSL, G.now makes use of advanced Discrete Multi-Tone (DMT) modulation. However, G.now operates up to frequencies of 100 MHz, well beyond VDSL maximum frequencies of 17.7 or 30 MHz. G.now also uses Time Division Duplexing (TDD) for separation of downstream and upstream transmissions, which enables a programmable downstream to upstream asymmetry ratio. As for G.fast, G.now transceivers operating in the same bundle must use the same TDD ratio and TDD frames must be synchronized to a common clock to eliminate Near-End Crosstalk (NEXT).
Additional G.now Features
G.now also has a number of advanced features such as automatic retransmission, and forward error correction based on LDPC codes with programmable FEC rates (1/2, 2/3, 5/6, 16/18, 20/21). Bit loading is dynamically recomputed based on real-time signal-to-noise ratio (SNR), channel frequency response and statistics from errors and LDPC decoder iterations. This means that bit-loading and the rates of each line can change in less than a second without having to wait for a long initialization cycle to complete.
G.now does not use a vectoring engine, which means that crosstalk cancellation is not performed. Marvell reports that the effects of crosstalk for 0.4mm phone lines and 0.4mm UTP-5e appear to be weak. Marvell also reports that for a single line, the aggregate upstream and downstream PHY rate is 850 Mbps over 100 meters (300 feet) of phone-line. In deployment scenarios with strong crosstalk – for example for multi-port systems with high-density copper cabling – a cloud-based crosstalk management solution can help mitigating crosstalk and enables higher speeds.
G.now Deployment Scenarios
There are several possible deployment scenarios for G.now; these include a single-port G.now system suitable for a single-family home or apartment; and multi-port G.now systems for small or large multiple-dwelling units. G.now systems are fed by GPON, EPON or active Ethernet; G.now can use either phone lines (up to 200 meters or 700 feet) or coaxial cabling.
Finally, G.now switches can operate with reverse-power configurations like those for G.fast.