ZXDSL 9210 (V3.1) Broadband Universal Access Equipment Technical Manual
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technologies solves the problem of accessed subscribers’ data security and
quality of service. Besides, this solution provides operators with convenient
methods of accounting, which solve the complicated problem existing in
previous Ethernet management and accounting.
1.2 Fundamental Principles of DSL
1.2.1 Fundamental Principles of VDSL
Generally, QAM is adopted by the IP-based VDSL, and connects both ends of the
existing twisted pair with its special modulation/demodulation hardware. It establishes
a 3-channel duct, as shown in Fig. 1.2-1.
Low-frequency channel
High-speed downlink channel
High-speed uplink channel
Fig. 1.2-1 VDSL Communication Duct
The duct has a high-speed uplink channel, a high-speed downlink channel (to the
subscriber premises), and a low-frequency channel (0 kHz to 900 kHz). The
low-frequency channel ensures that voice communication or ISDN runs normally even
if the VDSL connection fails. For the transmission rates of the high-speed
uplink/downlink channels, please refer to Table 1.2-1.
Table 1.2-1 Transmission Rates of High-Speed Uplink/Downlink Channels
Channel Average
Rate
Lowest Rate
Highest Rate
High-speed downlink channel
10 Mbps
4 Mbps
16.7 Mbps
High-speed uplink channel
9.1 Mbps
1.5 Mbps
16.7 Mbps
Note: This table is for reference only. Actual rate is subject to physical cable length, dimensions, and interference.
The IP-based VDSL needs no medium access control, so each subscriber can work in
the continuous full-speed environment. The VDSL rate depends entirely on line
