This report provides a detailed, independent, introduction to broadband access technologies, for regulators, investors and for the management and technical staff of carriers and other corporations. We explain the key technical principles behind the major broadband technologies: Fibre to the Premises or the Home (FttP/FttH), VDSL (Very High Rate Digital Subscriber Line, also known as Fibre to the Node or Curb - FttN/FttC), ADSL (Asymmetrical DSL), Hybrid Fibre Coax (HFC) Cable and Broadband over Powerlines (BPL, also known as Powerline Communications).
This report also contains explanations and analyses of:-
- Historical background
- Principles of operation
- Technical standards
- Critical analysis of strengths and weaknesses
- Competition with other technologies
- Opportunities for new services
- Combining technologies
- Links to industry consortia, standards bodies, regulators and key vendors
- Explaining established technologies in detail
We begin our discussion of DSL technologies with a description of twisted pair copper telephone cables and the traditional POTS (Plain Old Telephone Service) and ISDN (Integrated Systems Digital Network) services they carry.
Fibre has long been recognised as the highest performance broadband access technology. Recent developments with Passive Optical Networks (PONs) have lead to fibre deployment to millions of homes and offices. PONs use a single fibre for communication in both directions, with two wavelengths of infra-red light and often a third wavelength to carry a hundred or so channels of analogue and digital broadcast and subscription video. Each fibre is split, typically to serve 32 customers, enabling high performance and low fibre counts for most of the network, with distances of 20km or more achievable without any need for equipment in street cabinets. Our discussion focuses on the two major Gigabit PON standards: ITU G.984 GPON and IEEE 802.3ah Ethernet PON.
ADSL, including ADSL2 is currently the most widely deployed broadband access technology, due to there being no need to install new cables or infrastructure between homes and existing telephone exchange buildings. We explore the history of ADSL, the characteristics of ADSL2 and ADSL2+ and the barriers to its widespread adoption, including already installed pair-gain systems.
With the advent of VDSL2 and reductions in equipment costs, VDSL is finally able to fulfil its promise of delivering tens of Megabits per second over several hundred metres of already-installed twisted pair telephone cable. We explain the major advances leading to the VDSL2 standard, its compatibility with ADSL and its relationship with Ethernet in the First Mile. We examine the challenges of converting an existing telephone network to VDSL2 FttN/FttC operation, including the impact on traditional telephone exchanges and backbone networks.
Hybrid Fibre Coax Cable (HFC) networks are the other main broadband last mile technology. We discuss the history of HFC, its forthcoming DOCSIS 3.0 standard and HFC’s emerging Switched Digital Video architecture.
Finally, we discuss Broadband over Powerline technology. After many years of development, BPL/PLC is being implemented by a number of manufacturers, most of whom use a common chipset. The European OPERA initiative has developed a technical standard intended to ensure interoperability between equipment from different manufacturers and so to foster widespread deployment. We examine BPL/PLC in great technical detail, critically evaluating the claimed high data rates in the context of the many barriers the system faces on ordinary street and home power cables.
The correct choice of broadband technologies involves many technical and practical issues – with huge social and economic costs and benefits at stake. This report assumes only basic familiarity with telecommunications technology. It enables readers to understand the key principles and practical aspects of the major broadband technologies and to foresee their applicability in particular settings.