Very-high-bit-rate digital subscriber line (VDSL) technology
is part of the xDSL family of modem technologies, which provide faster
data transmission over a single flat untwisted or twisted pair of
copper wires. Table 1 specifies
the key details of the VDSL2 interface.
pt- represents VDSL2 interface when you configure
pt- to function as VDSL2.
Interface pt-1/0/0 comes up by default.
Use cases
Connects you and the service provider networks over a
single connection to provide high bandwidth applications (triple-play
services) like high-speed Internet access, Telephone services (VoIP
(Voice over IP protocol), High-Definition TV (HDTV)), and Interactive
gaming services.
VDSL2 carries the data and multimedia on the copper wire
without interrupting the line's ability to carry voice signals. VDSL2
provides an ADSL interface in an ATM DSLAM topology and a VDSL2 interface
in an IP or VDSL DSLM topology.
Table 2 describes the
key features supported on VDSL2 interface.
Table 2: Key Features Supported
on VDSL2
Feature
Description
Packet Transfer Mode (PTM)
Uses the named interface pt-1/0/0 and transports
packets (IP, PPP, Ethernet, MPLS, and so on) over DSL links as an
alternative to using Asynchronous Transfer Mode (ATM).
Based on the Ethernet in the First Mile (EFM) IEEE802.3ah
standard.
Discrete multitone (DMT) modulation
Separates a digital subscriber line signal to a usable
frequency range of 256 frequency bands (or channels) with 4.3125 KHz
each.
Uses the Fast Fourier Transform (FFT) algorithm for demodulation
or modulation for increased speed.
Backward compatibility
Backward compatible with most ADSL interface standards.
In ADSL fallback mode, VDSL2 operates on the ATM encapsulation
interface in the first mile and uses the interface at-1/0/0.
Takes about 60 seconds to switch from VDSL2 to ADSL or
from ADSL to VDSL2 operating modes.
Vectoring
Employs coordination of line signals to reduce crosstalk
levels to provide improved performance.
The ITU-T G.993.5 standard also known as G.vector, describes vectoring
for VDSL2.
IPv6 Support
Supports IPv6 on the DSL encapsulations like ATM physical
interface encapsulations, atm-pvc, ethernet-over-atm, ethernet-over-atm,
and ATM logical interface encapsulations except for atm-vc-mux and
ppp-over-ether-over-atm-llc.
To configure IPv6 addresses on DSL interfaces in ATM or
PTM mode, include the family protocol type as inet6.
The VDSL2 interface uses either Gigabit Ethernet or fiber as
second mile to connect to the Broadband Remote Access Server (B-RAS). Figure 1 shows a typical
VDSL2 network topology.
Figure 1: Typical
VDSL2 End-to-End Connectivity and Topology Diagram
The ADSL interface uses either Gigabit Ethernet or OC3/DS3 ATM
as the second mile to connect to the B-RAS. Figure 2 shows a
backward-compatible ADSL topology using ATM DSLAM.
