Hello everyone!
Welcome to the Access Network HCIA Learning Class.
Today, we will learn xDSL.
DSL has become the most popular fixed broadband access technology since the birth of this technology in the 1990s. In addition, the DSL technology was continuously seeking for technical breakthroughs and optimization, owing to which the services supported by DSL have been enriched from the original data service only to multi-play services, such as high-speed Internet (HSI), IPTV, VolP, private line access, and mobile service bearing.
xDSL Development
Development and Characteristics of DSL
DSL Performance Summary
DSL Technologies Evolution-Speed
DSL Rate Restriction Factors
2. Vectoring Principle and Application
Why Vectoring
Crosstalk: The Killer of VDSL2 Speed
Crosstalk is the dominant source of noise in VDSL2 which leads to significant performance loss
In electronics, crosstalk (XT) is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or channel, to another.
VDSL2 performance is determined by the cable attenuation and the noise in the cable, while Crosstalk is the dominant source of noise in VDSL2 which leads to significant performance loss.
There are two types of crosstalk:
NEXT: Near-End Crosstalk
Interference between two pairs in a cable is measured at the same end of the cable as the interfering transmitter. It means the interference between upstream and downstream.
FEXT: Far-End Crosstalk
Interference between two pairs of a cable measured at the other end of the cable with respect to the interfering transmitter. It means the interference between upstreams or the interference between downstream.
Incidence of Crosstalk
Crosstalk mainly exists in the basic unit and sub bundle.
How to Cancel the Crosstalk?
NEXT: This can be eliminated by filter since that VDSL2 use different frequency for downstream and upstream.
FEXT: This cannot be eliminated by filter since the interference and useful signal are both upstream or downstream signals that use the same frequency.
What can Vectoring do?
Bandwidth improved more than 50%
100Mbps@300m, 80Mbps@500m
Crosstalk is the dominant source of noise in VDSL2 and the number of crosstalk increases with signal frequency. It is especially a problem in the extended VDSL2 bands 12-30 MHz. It is typically 20-30 dB stronger than other noise sources in a VDSL2 system. Crosstalk leads to significant performance losses.
It decreases data rates, service penetration rates and can cause frequent re-initialization of the CPE. One solution to protect against crosstalk is to use more transmit power, but this leads to higher power consumption and can break national frequency management plans, and cause interference with other systems.
Access Network HCIA Course Series will be continuously updated.
Thank you for your participation and we'll learn together!
