VDSL provides operators the ability to offer a multitude of digital video service that increases their phone deals and existing Internet services. VDSL has the capacity to support Digital Television Broadcast, Video on Demand, and HDTV over standard twisted-pair copper.
In addition to digital video and Internet services, VDSL also supports interactive video services, Web TV, e-commerce, video conferencing, and video games, which is a set of services currently not available from cable operators or DBS.
Providing access to high speed Internet is an essential value for home users, small businesses, hotels, institutions and other multi-site buildings. The Internet is growing at a phenomenal rate and this growth is the expansion of new and varied applications to take advantage of the increased availability of equipment, software, access, and users. These new applications require more resources than can be provided with the existing infrastructure, which limits the profit potential in providing these applications.
While other DSL technologies such as ADSL and G.lite, can meet the limited requirements of Internet applications today. These systems will soon run out of bandwidth. However, VDSL has the capacity to support today’s applications with dining support emerging applications of tomorrow, creating new revenue growth opportunities, while preserving investment in DSL technology.
As the Internet grows increasingly architecture backbone is replaced by ATM. ATM technology is the preferred Internet backbone FSAN to manage the growing burden to support daily operations and mission critical applications. The ATM architecture was chosen because it allows a single ATM network to be used to support all data transport, voice and video instead of delivering them to separate and incompatible networks. The combination of VDSL and ATM technology provides Internet services today in an architecture that supports the applications of tomorrow.
A key service for every telco is the delivery of lifeline telephony services. One thing that has become universally expected is that no matter what, the phone will work. VDSL, like other DSL technologies, supports a lifeline POTS connection. This is a basic requirement that must be met by a telephony service provider. VDSL offers this feature and gives the telco opportunity to provide additional voice channels derivatives on the same pair of existing copper.
The Voice over IP (VoIP) and Voice over ATM (VToA) technologies are providing standard quality telephony services over a digital network. Because ATM can also transport communications based on IP, ATM over VDSL will support both digital telephony standards. Although Voice over DSL (VoDSL) initiatives seek to develop a standard for carriage on flavors of DSL, bandwidth is always the question. Higher bandwidth VDSL provides more derived voice channels.
Cable operators are starting to enter the market of voice using these technologies, but they face a major obstacle in providing Lifeline Services. The capacity of the new class of telecom operators offering comprehensive services to provide lifeline POTS along the derivative telephony, Internet access, and digital video services is a key advantage over cable and DBS operators.
The deployment of the full service access network is progressing with the deployment of fiber-based networks. The final architecture is fiber-to-the-home and business, but it will take a number of years and significant resources to implement.
Deployment scenarios for today are the fiber-to-the-trade (FTTEx), fiber-to-theneighborhood (FTTN), FTTCab and FTTB. VDSL is only suitable for FTTEx, where customers are served within reach of the central exchange (CO). FTTN and FTTCab are suitable for standalone deployments, VDSL switch or as part of a New Digital Loop Carrier Generation (NGDLC).
FTTB would bring fiber directly into a building like a multi-site unit (MDU) or business of the company and end the VDSL.
Major VDSL2 Activity
Following are the countries, which are using VDSL2.
- Presently, 5-band 100/50Mbps and 30MHz 100/100M VDSL deployments occurring in high volume at NTT, UCOM, and KDDI. Softbank field-testing of FTTN VDSL systems is also happening currently.
- CHT 5-band 100/50Mbps 480k port VDSL are deploying currently.
- Has been aggressively rolling out QAM VDSL for over three years. More than 75% coverage of the country with ADSL and VDSL. Will begin VDSL2 evaluating 30MHz − 100/100 systems in September.
- SBC Project Lightspeed to bring IPTV via FTTN VDSL systems to over 4M households in the next three years.
- Verizon deploying Fiber to the Premise (FTTP) and Fiber to the Cabinet (FTTCab) now. VDSL to Multi-Dwelling Units will have some volume in 2006.
- BellSouth field-testing VDSL systems. Bell South & AT&T are now expected to merge and therefore have a common VDSL BBA strategy around VDSL2.
- Presently, Swisscom and Belgacom VDSL deployments are occurring in small volumes now.
- Deutsche Telecom 17MHz deployments on hold pending system issues.
- KPN and Telefonica deployed VDSL in 2007.
- Telecom Italia is in lab evaluation with VDSL DSLAMs at present.
- PCCW in Hong-Kong Awarded Tender for ATM VDSL Deployments.
- China has done their second VDSL lab testing session.
- Singapore Telecom lab testing VDSL2 systems are being deployed.
VDSL Access Deployment Models
The following illustration describes the VDSL access deployment models.
VDSL2 Key Features
Following are the key features of VDSL2.
- Same as ADSL
- Bandwidth increased from 30 MHz ( 14x ADSL2+)
- Up to 4096 tones (8x ADSL+!)
Worldwide Versatile Standard
- 8 Profiles defined for different services
- Different band plans for different regions
- Variety of PSDs to optimize spectral compatibility
Support for a variety of Services
- Integrated Quality of Service features
- ATM as well as Ethernet payload
- Channel bonding for extended reach or rate
VDSL2 − DMT (Discrete Multi-Tone)
The concept of discrete multi-tone is − The frequency band is split into sub-channels equally spaced. Each sub-channel has data modulated on it using QAM. The number of bits allocated to a sub-channel depends on the SNR measured on this sub-channel.
ADSL2/2+/ VDSL2 8a,8b,8c,12a,12b,17a = 4.3125 kHz
VDSL2 30a = 8.625 kHz
Bin number × Tone spacing = Bin frequency
For example − Bin 64 × 4.3125k = 276 kHz
The advantage of this is that, it adapts to the characteristics of the channel / loop.
Vocabulary − sub-channel = sub-carrier = tone = bin.
The individual bands of a frequency band plan is filled with the spectrum generated from either technology. Here, we will show a case-using plan 998 for both QAM and DMT.
Downstream Transmit Power −
- Tx power in VDSL1 is limited to 14.5 dBm for CO deployment and 11.5 dBm for cabinet.
- Why do we need high power?
- Improve the reach of high rate.
- Reduce the impact of FEXT from ADSL.
- PSD level raise only in DS1.
High TX power is only with the 8M profiles, as defined in the following table −
|Profiles||Tx power (dBm)|