VDSL

The VDSL is the hybrid technology which combines the fibber and the cooper media. The fibbers are used in the operator network and so-called the last mile (i.e. the connection between the nearest provider’s device and the customer) is covered by the cooper line. The VDSL solution is described in ITU-T G.993.1 standards and it uses up to 12 MHz spectrum. This technology provides both symmetric and asymmetric links.

The VDSL was developed as the last mile access solution, because it enables much higher throughputs than the ADSL. Therefore, this is the perfect solution for Triple Play services, i.e. the telephony (analogue or VoIP – Voice over IP), the television and the Internet access. This is the great example of FTTB/C (Fibber to The Building/Curb) technique. Thanks to this approach, the VDSL should gain great popularity, because operator’s investment costs are limited. The provider has to moderate only its infrastructure and does not have to replace cables which are already installed in the buildings.

The fastest asymmetric mode offers up to 52 Mbps speed in the downlink direction and up to 16 Mbps for the uplink at the distance of 300 meters. The symmetric implementation provides up to 34 Mbps throughput at the same distance, i.e. 300 meters. In case of the long distance (i.e. 1 500 meters) it is possible to achieve 13 Mbps speed for downlink and 1.6 Mbps for uplink. The symmetric link offers the comparable capacity at the same distance, so it provides up to 6.5 Mbps in both directions at the distance of 1 500 meters.

The newest version of VDSL2 described in ITU-T G.993.2 standard predicts the usage of up 35 MHz bandwidth and up to 250 Mbps capacity, i.e. the sum of throughput in both directions. The original version of this standard predicts 30 MHz bandwidth usage with the summary 200 Mbps throughput. The frequency band plans allow the provider to serve the symmetric or asymmetric links. The G.993.2 standard supports several VDSL2 profiles. For an example, 12a and 12b profiles offer similar performance to the VDSL, i.e. the 34 Mbps symmetrical link. The 17a profile uses wider bandwidth, i.e. up to 17 MHz, whereby the symmetrical link provides 50 MHz throughput. The 100 Mbps data rate in both direction is possible to achieve using 30a profile.