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VDSL2: Next important broadband technology
Ericsson Review, no. 01, 2006
Written by: Per-Erik Eriksson and Björn Odenhammar
Download PDF file
ADSL2plus is currently being deployed worldwide as the new mainstream broadband technology for residential and business customers. But at the same time, the industry is gearing up for the next step of the DSL evolution: VDSL2, the second version of the very high-speed digital subscriber line (VDSL) standard from ITU-T, promises to deliver 100Mbps symmetrical traffic on short copper loops.
The greater bandwidth of VDSL2 gives telecommunications operators the ability to offer advanced services such as multiple streams of interactive standard and high-definition TV over IP over the existing copper plant. TV services are fast becoming strategically important to telecommunications operators who must now compete head-to-head with cable operators launching voice over IP (VoIP) and high-speed internet services.
The introduction of VDSL2 will have a major impact on the way access networks are engineered. To make the most of VDSL2, operators will have to move the DSL access multiplexers (DSLAM) out of the central office environment and build a distributed network with smaller nodes that sit typically less than 1500 meters away from end users. This puts more stringent requirements on outside plant building practices. In many cases, power and spacing might also be an issue because existing street-side cabinets lack space and often solely contain passive equipment.
Although fiber to every home is the ultimate answer, it is not yet an economically viable solution for overbuilding existing copper networks. This is because fiber takes a long to time to deploy and the cost of deployment runs between USD 1,000 and 1,800 per subscriber. However, in Greenfield building scenarios, fiber to the home (FTTH) is frequently seen as the best way forward.
DSL history
ADSL
While high-bit-rate DSL (HDSL) was still in prototype phase, Stanford University and
AT&T Bell Labs developed asymmetrical DSL (ADSL) technology from concept to prototype (1990-1992). Field technology trials began three years later and ANSI issued the first standard for ADSL in 1995 (T1 413 issue I); the second issue followed in 1998. The first ADSL recommendation from ITU-T (G.992.1), generally denoted ADSL1, was complete in 1999. This recommendation was based to a large extent on the ANSI standards.
ADSL was originally intended for delivering video on demand at a bit rate of 8Mbps downstream and 640kbps upstream. But it was the popularity of the internet that made ADSL a major commercial success. In fact, ADSL is today mainly used as a form of high-speed internet access. An option in the ADSL1 standard provides for a downstream data rate of up to 12Mbps. Moreover, plain old telephony service (POTS) or integrated services digital network (ISDN) technology can serve as the underlying service (by not using the frequencies occupied by their respective services: 0.3-25kHz for POTS or 1-120kHz for ISDN). A splitter filter can be used to separate the POTS band from the ADSL band. This means ADSL can share the line with either POTS or ISDN service. Figure 1shows how the frequency band is divided between POTS/ISDN upstream and downstream data.
ADSL2
The second-generation ADSL standards, ADSL2 (G.992.3) and ADSL2plus (G.992.5), were issued in 2002 and 2003.2 - 3 The most important new features of ADSL2 were
Download PDF file ADSL2plus is currently being deployed worldwide as the new mainstream broadband technology for residential and business customers. But at the same time, the industry is gearing up for the next step of the DSL evolution: VDSL2, the second version of the very high-speed digital subscriber line (VDSL) standard from ITU-T, promises to deliver 100Mbps symmetrical traffic on short copper loops.
The greater bandwidth of VDSL2 gives telecommunications operators the ability to offer advanced services such as multiple streams of interactive standard and high-definition TV over IP over the existing copper plant. TV services are fast becoming strategically important to telecommunications operators who must now compete head-to-head with cable operators launching voice over IP (VoIP) and high-speed internet services.
The introduction of VDSL2 will have a major impact on the way access networks are engineered. To make the most of VDSL2, operators will have to move the DSL access multiplexers (DSLAM) out of the central office environment and build a distributed network with smaller nodes that sit typically less than 1500 meters away from end users. This puts more stringent requirements on outside plant building practices. In many cases, power and spacing might also be an issue because existing street-side cabinets lack space and often solely contain passive equipment.
Although fiber to every home is the ultimate answer, it is not yet an economically viable solution for overbuilding existing copper networks. This is because fiber takes a long to time to deploy and the cost of deployment runs between USD 1,000 and 1,800 per subscriber. However, in Greenfield building scenarios, fiber to the home (FTTH) is frequently seen as the best way forward.
DSL history
ADSL
While high-bit-rate DSL (HDSL) was still in prototype phase, Stanford University and
AT&T Bell Labs developed asymmetrical DSL (ADSL) technology from concept to prototype (1990-1992). Field technology trials began three years later and ANSI issued the first standard for ADSL in 1995 (T1 413 issue I); the second issue followed in 1998. The first ADSL recommendation from ITU-T (G.992.1), generally denoted ADSL1, was complete in 1999. This recommendation was based to a large extent on the ANSI standards.
ADSL was originally intended for delivering video on demand at a bit rate of 8Mbps downstream and 640kbps upstream. But it was the popularity of the internet that made ADSL a major commercial success. In fact, ADSL is today mainly used as a form of high-speed internet access. An option in the ADSL1 standard provides for a downstream data rate of up to 12Mbps. Moreover, plain old telephony service (POTS) or integrated services digital network (ISDN) technology can serve as the underlying service (by not using the frequencies occupied by their respective services: 0.3-25kHz for POTS or 1-120kHz for ISDN). A splitter filter can be used to separate the POTS band from the ADSL band. This means ADSL can share the line with either POTS or ISDN service. Figure 1shows how the frequency band is divided between POTS/ISDN upstream and downstream data.
ADSL2
The second-generation ADSL standards, ADSL2 (G.992.3) and ADSL2plus (G.992.5), were issued in 2002 and 2003.2 - 3 The most important new features of ADSL2 were
-
an annex with extended upstream, which made it possible to have an upstream data rate of up to 3Mbps; and
-
an annex for extending the reach to more than 5km.
ADSL2plus
The ADSL2plus standard doubled the spectrum for downstream data (ADSL and ADSL2 have a spectrum of 1.1MHz; ADSL2plus has a spectrum of 2.2MHz), giving even greater data rates on short loops (Figure 1). ADSL2plus also defined a toolbox for sculpturing the downstream trans mission to meet different spectrum capability requirements, in particular when ADSL2plus is put in a cabinet. Figures 2-3 show the performance, during different noise conditions, of Ericsson's Ethernet DSL access (EDA) DSLAM for ADSL2 and ADSL2plus.
