4.4.1 Analogue access
Nearly all users currently have analogue access. There are currently 24.5m residential exchange lines in UK and 10m business exchange lines. Modem technology has developed rapidly and V.90 modems can support speeds of up to 56 kbit/s on a dial-up connection. This is quite sufficient for voice and data, as some Internet voice codecs use less than 10 kbit/s.
4.4.2 ISDN
Some users have ISDN access which offers speeds of up to 128kbit/s using both channels. The main advantage of ISDN over modems is the very greatly reduced time between initiating the access and being able to send or receive useful data. For ISDN this time can be reduced to less than 1 second compared to 5-15 seconds for a modem. However, the basic access ISDN market for residential users has not grown much and is not likely to grow in view of the development of xDSL and the introduction of flat rate modem access (FRIACO).
4.4.3 xDSL
A range of new Digital Subscriber Line (DSL) technologies are becoming available for making greater use of Copper access lines. The technologies are summarised in figure 24.
| Data rates | Pairs used | | Range | Main application | ADSL (Asymmetric DSL) | < 512 kbit/s
from the home | 1 | Yes | < 4 km | High speed Internet access and delivery of video-on-demand | HDSL (High speed DSL) | 2 Mbit/s
symmetric | 1-3 | No | < 4 km | Services to small businesses | VDSL (Very high speed DSL) | >> 2Mbit/s | 1 | No | < 500m | |
4.4.4 ADSL
ADSL is the best developed technology and the one most relevant to residential customers. It enables high speed internet access to be provided in parallel with continued use of an exchange line by an analogue telephone. The Internet access can also be used for the various forms of VoIP.
Figure 25 shows an ADSL service to a residential customer provided by the provider of the copper loop (eg BT). With ADSL the format of the network termination point for the Internet access would be either a LAN connection or a USB interface. IP packets are normally carried on ATM across a network owned by the access provider with each customer having a permanent virtual circuit (PVC) to their Internet service provider.
Figure 25: ADSL by the provider of the copper loop 
Figure 26 shows ADSL on an unbundled loop where the other operator provides both the ADSL access and the telephony service.
Figure 26: ADSL on unbundled loop 
Figure 27 shows the plans for line sharing option where the ADSL access is provided on an unbundled loop but the loop owner continues to provide the telephony service. The ADSL provider manages the loop and passes the analogue telephony access circuit back to BT.
BT introduced ADSL during 2000 and its service seems to be growing well. Following substantial intervention by Oftel, local loop unbundling to enable others to offer ADSL will be rolled out during 2001 with the aim of making it available in most areas by July 2001. Although strong demand for unbundling was expected, the initial order level was very low because operators were not satisfied with the commercial and operational arrangements. We have been informed that experience with Bell Atlantic in the US suggests that operational difficulties are likely with unbundled loops and that it will be may be 1-2 years before all the issues are resolved adequately.
4.4.5 VoDSL
Voice over DSL (VoDSL) is a generic name for techniques for providing multiple voice accesses over a single physical access line. The technology is not yet standardised and some vendors use ATM rather than IP for the voice access whilst providing separate IP access for data.
Verizon (Bell Atlantic) announced in July 2000 that it was running a VoDSL trial with 16 telephony circuits on one copper pair.
VoDSL is likely to grow rapidly as a delivery technology for small businesses offering a combination of analogue ports for conventional telephones and IP over Internet accesses for PCs or IP telephones from a local area network served by one or more copper pairs. We think that the possibility of using VoDSL technology on unbundled lops will create significant incentives for incumbents to introduce next generation technology at the local level.
The cable industry is planning to use cable modems for broadband access. Communications are provided by fibre of coaxial cable between a cable modem on the customer’s premises and Cable Modem Termination System (CMTS) at the head end. The CMTS is connected to a managed IP network that supports:
Figure 28 shows the arrangement
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