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VDSL2 Interface Overview


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.

Table 1: VDSL2 Interface Details

Interface Details


Interface name


Supported on

For information about platforms support, see hardware compatibility tool (HCT).

Interface type

  • 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.

For information on VDSL2 hardware specifications, see 1-Port VDSL2 Annex A Mini-Physical Interface Module (SRX-MP-1VDSL2-R).

Features Supported on the VDSL2 Interface

Table 2 describes the key features supported on VDSL2 interface.

Table 2: Key Features Supported on VDSL2



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.


  • 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.

For more information on supported features and profiles on VDSL2 interfaces, see1-Port VDSL2 Annex A Mini-Physical Interface Module (SRX-MP-1VDSL2-R).

VDSL2 Network Deployment Topology

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
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.

Figure 2: Backward-Compatible ADSL Topology (ATM DSLAM)