ZyXEL Communications IES4005M, User Manual

Page: 165 / 236

IES4005M User’s Guide
165
C
H A P T E R
2 4
VDSL
Use these commands to configure VDSL settings on VDSL subscriber ports.
Very High Bit Rate DSL (VDSL) is an asymmetric version of DSL that is used as the final drop from
a fiber optic junction point to nearby customers. VDSL lets an apartment or office complex obtain
high-bandwidth services using existing copper wires without having to replace the infrastructure
with optical fiber. Like ADSL, VDSL can share the line with the telephone. VDSL2 (Very High Speed
Digital Subscriber Line 2) is the second generation of the VDSL standard (which is currently
denoted VDSL1). VDSL2 allows a frequency band of up to 30MHz and transmission rates of up to
100 Mbps in each direction. VDSL2 is defined in G.993.2.
Here is some background information about the key VDSL settings and features you can configure.
Power Spectrum Density
Power Spectrum Density (PSD) mask. PSD defines the distribution of a line’s power in the frequency
domain. A PSD mask is a template that specifies the maximum allowable PSD for a line.
Limit PSD Mask
To reduce the impact of interference and attenuation, ITU-T 993.2 specifies a PSD mask to limit the
VDSL2 transmitters PSD at both downstream and upstream.
Frequency Band Plan
Each VDSL mode operates in a different frequency band allocation, resulting in different upstream
and downstream speeds. Your system automatically changes the band plan based on the loop
condition and loop length.
A band plan example is shown next. Band plans include an optional band (between 25 kHz and 276
kHz) controlled by “limit PSD mask”.
The optional band is used for upstream transmission which is to be negotiated during line initiation.
The optional band frequency (for example, x and y) varies depending on the limit PSD mask you
use.
Figure 41
A Band Plan Example
US1 US2 US0 DS1 DS2
Frequency
12
(MHz)
x
y
3.75
5.2
8.5