Overview of VDSL Interfaces
ADSL provides limited bandwidth for image services at high costs, which hinders ADSL development. VDSL is the most advanced digital subscriber line technology that provides high bandwidth for broadband services such as image services.
Advantages of VDSL
Compared with ADSL, VDSL has the following advantages:
Data transmission rate.
ADSL provides the upstream transmission rate of 640 kbit/s to 2 Mbit/s and the downstream transmission rate of 1 Mbit/s to 8 Mbit/s. VDSL provides the upstream transmission rate of 0.8 Mbit/s to 6.4 Mbit/s and the downstream transmission rate of 6.5 Mbit/s to 52 Mbit/s. VDSL transmits services faster than ADSL.
Line activation rate.
ADSL provides high transmit power, so lines interfere with each other. ADSL provides the line activation rate of only 10% to 30%. VDSL provides low transmit power, so there is less crosstalk. VDSL provides the line activation rate of over 90%.
Transmission mode.
ADSL provides only asymmetrical transmission, but VDSL provides both asymmetrical and symmetrical transmission.
Frequency band.
ADSL transmits digital signals at the frequency bands of 25 kHz to 1.1 MHz, but VDSL uses higher frequency bands of 0.138 MHz to 12 MHz.
Transmission quality.
VDSL provides good transmission quality and supports HD video conference, VoD, and BTV, whereas ADSL cannot provide these services.
Deployment cost.
VDSL transmits signals over a copper twisted pair without layout of new lines or reconstructing the existing network.
Service compatibility.
Compared with ADSL, VDSL supports both traditional voice services and ISDN services. VDSL can use the same phone line with the existing phone line and ISDN.
Both VDSL and ADSL can provide Internet browsing, email receiving and sending, file upload and download, working at home, remote education, and remote shopping. VDSL meets requirements of users for high-speed access, makes full use of existing twisted-pair telephone lines, protects carrier investments, and solves the bottleneck of the last mile.
VDSL System
- A DSLAM is an aggregation device that terminates VDSL packets on the central office.
- A CPE provides interfaces for users, modulates and demodulates data signals, and uploads user data to a DSLAM.
The router functions as a CPE.
In the VDSL system, downstream transmission refers to data transmission from a DSLAM to a CPE, and upstream transmission refers to data transmission from a CPE to a DSLAM. VDSL interfaces on the device are upstream interfaces.
Service Supported by a VDSL Interface
This section provides only the physical attribute configuration of VDSL interfaces. For details about the configuration of the VDSL interface working in ATM mode including the PVC configuration, see ATM Configuration in the Configuration Guide - WAN. For details about the configuration of the VDSL interface working in PTM mode including the PVC configuration, see PPPoE Configuration in the Configuration Guide - WAN.