Hi to all.
My dears, following with the track of the XDSL technologies we are going to explain the VDSL and VDSL2 technology
xDSL: PRINCIPLES AND APPLICATIONS
Introduction to the VDSL/VDSL2 Technology
VDSL Overview
· Features of the VDSL technology
§ Very high bit-rate digital subscriber line
§ The transmission rate reaches 52Mbps
§ Symmetric and asymmetric
§ Transmission distance: 300 m to 1.5 km
§ Compatible with traditional voice and ISDN services
· The preceding two types of DSL technologies, ADSL and SHDSL, have a maximum transmission rate of 8 Mbps. VDSL which is short for a very high-speed digital subscriber line is a new generation of high-speed DSL technology.
· VDSL can reach a maximum transmission rate of 52 Mbps on common twisted pairs. It provides various transmission rates and multiple working modes, including symmetric and asymmetric transmission, to meet the requirements of different customers. Because the transmission rate of VDSL is high, the twisted pairs used in VDSL are shorter, usually from 300 m to 1 km. The length of the twisted pairs is inversely proportional to the transmission rate.
· Compared with ADSL, VDSL uses a higher frequency band than PSTN and ISDN frequencies on twisted pairs. Therefore, VDSL is compatible with existing traditional telephone services as well as ISDN services. VDSL also uses passive filters as signal splitters to support voice and ISDN transmission. The basic working principles of VDSL are similar to that of ADSL.
· VDSL is a video and data transmission technology over the voice frequency band. It provides multiple working modes and can transmit data at a high rate within a short distance. This technology enables telecom operators to use existing twisted pairs to transmit broadband services, such as VoDand high-speed Internet access.
· Currently, the internationally recognized VDSL system complies with the American standard formulated by T1E1.4 and the European standard formulated by ESTI TM6. Both standards adopt the G.998 standard and DMT/CAP modulation modes. The difference is that the American standard adopts the G.998 standard for baseband planning to provide the highest rate of 22 Mbps, while the European standard adopts the G.998 standard for baseband planning to provide the highest rate of 14 Mbps.
Relationship Between the VDSL Rates and Distances Defined by the ITU
· Although the transmission rate of VDSL is high, the transmission distance is far less that of ADSL
· Although the transmission rate of VDSL is high, the transmission distance is far less than that of ADSL. This is because high-speed transmission requires complex modulation modes, dense constellation encoding, and outstanding channel characteristics, but the length of transmission lines can pose negative impacts on channel performances.
· At the early stage of VDSL design, the ITU divides VDSL transmission capabilities into long-, medium-, and short-distance transmissions in asymmetric and symmetric transmission modes.
Relationship Between the VDSL Rates and Distances Defined by the ITU
· This is the reference model of the VDSL system. Basic modules include VDSL devices at the CO and subscriber sides. Devices at both sides are connected by twisted pairs through their own splitters. The other end of the CO device is connected to an ONU, and the other end of the subscriber device is connected to a network device or a small LAN.
· VTU-O is short for the VDSL transceiver unit at the ONU and has the same function as the CO-side modem ATU-C in ADSL. VTU-R is short for the VDSL transceiver unit at the remote and has the same function as the subscriber-side modem ATU-R in ADSL.
· Network interfaces defined by applications: Different data interfaces are used to aggregate data from upper-layer protocols to form unified data flows to be transmitted in fast and slow channels as required. Data flows are sent to the lower layer for framing. At the same time, application-independent data frames from the lower layer are split and used by different application interfaces and protocols.
· In VDSL, a splitter similar to that in ADSL is used to separate data signals from traditional voice/ISDN signals.
Development History of VDSL2
· The International Telecommunication Union (ITU) recently completed the formulation of a new technical specification that enables global telecom operators to provide the “super” triple services integrating video, internet, and voice services, with a rate 10 times faster than that of ordinary ADSL.
· ITU-T recommendations on VDSL2 enable telecom operators to provide high-definition television (HDTV), video-on-demand (VoD), videoconferencing, high-speed internet access, and advanced VoIP voice services through standard copper telephone lines, giving telecom operators the capability to compete with cable providers and satellite operators.
Advantages of VDSL2
· The rate can reach 10 times the average ADSL rate, and the maximum rate can reach 100 Mbps at 0 distance, effectively supporting the triple play of video, internet, and voice services.
· VDSL2 not only has the long-distance transmission capability of the ADSL2+ technology but also increases the data rate of VDSL from 70 Mbps (downstream)/30 Mbps (upstream) to 100 Mbps (upstream/downstream). To achieve such a high transmission rate within 350 meters, the working frequency of VDSL2 is increased from 12MHz to 30 MHz.
· To meet the access requirements of medium and long-distance loops, the transmit power of VDSL2 is increased to 20dBm, and the echo cancellation technology is also specified, so that the transmission performance is similar to that of DSL in long-distance transmission scenarios
Until here, the first post of the xDSL principles and applications
Thanks.
