VDSL enables capacities of about 52 Mbps, which are higher than the ADSL family. This is implemented by including more high frequency bandwidth in the copper cables and by deploying more efficient modulation. Furthermore, VDSL enables high speed symmetrical connections. The coverage of VDSL is on the contrary very short and is kept below 1.3 km. However, due to the aforementioned characteristics of copper lines, the capacity is very much dependent on the distance, and at the maximum distance the achievable capacity is about 13 Mbps. This implies that only in the very last part of the network (from street cabins to households) the current installed infrastructure is used, and a backbone network infrastructure must be established to supply these street cabins. This backbone network will mainly be based on optical fiber technology. Furthermore, this implies that compared to ADSL the cost of deployment is very high.
There are some limitations to VDSL, for example, the co-existence between VDSL and ADSL is a challenge due to interference. Interference from AM radio is also a source of problems for VDSL. Furthermore, there is a problem of supply of electricity to the street cabins, as in regular telephony it has not been necessary to have a power supply to these cabins. When it comes to interoperability, there are some advantages to using VDSL (at least in the short term), as it will be possible to offer symmetrical 10 Mbps Ethernet connections. VDSL2 is under standardization and the aim is to offer bit rates of up to 100 Mbps.
UDSL developed by Texas Instrument is the newest variant of DSL, which tries to utilize the un-utilized resources in the Copper network, and to give the PSTN operators the possibility to be competitive on the broadband market. UDSL promises aggregated bit rates of up to 200 Mbps, including 100 mbps symmetrical connections.
Uni-DSL comprises the whole DSL family: ADSL, ADSL2, ADSL2+, VDSL, the coming VDSL2 standard and UDSL. Hence the platform gives the operators a flexible possibility of offering a number of different connections to their customers. However, it is important to mention that offering high bit rate connections cannot be done using the current PSTN infrastructure and, as discussed in relation to VDSL, it requires the establishment of a new infrastructure and the use of the part of PSTN networks close to the households.