Three Technology Choices For Deploying Broadband
6 November 2015 |
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What are xDSL, DOCSIS and G.fast?
In this blog, we explore three basic technology choices for deploying broadband services to the end user.
Digital subscriber line (xDSL) – how much longer can we use it?
Digital subscriber line (xDSL) is the most mature of the broadband technologies in terms of its early acceptance, standardization and use. This family of technologies (including ADSL2+, VDSL, VDSL2) provides Internet access by transmitting digital data over a local telephone network. Basic DSL requires fiber build-out to a node, or terminal, which is close to the customer. From the node, a twisted pair copper connection is made to the existing copper within the customer premises.
- Cost per subscriber typically low compared to most competing technologies,
- Leverages copper in existing homes
- Approximately 80% of brownfield builds in the world have twisted-pair copper in them
- Ability to provide broadband service over the existing copper infrastructure – and not spend additional money
- To provide greater bandwidth, nodes must be moved further into the field and even closer to the customer
- Reduction in coverage area since distances are shortened as bandwidth increases
- Requires power in the outside plant where electronic equipment resides
- Electronic equipment in the OSP makes the network potentially vulnerable to natural disasters, such as floods
Ultimately, DSL will reach the point where it can no longer provide enough bandwidth to enough customers – thus, a major technology upgrade will be required.
DOCSIS – positioned to compete
DOCSIS (“data over cable service interface specification”) is an international telecommunications standard used by many cable television operators to provide high-speed data or Internet services over existing hybrid fiber-coaxial (HFC) infrastructures. Similar to the DSL, fiber is run to a node where the signal is transferred from the fiber to coaxial cable and extended to the customer in a direct line to the home.
- Coaxial cable better shielded than twisted-pair copper, making it a much better medium for data transmission
- With release of a Gigabit standard for DOCSIS, this technology meets present-day bandwidth requirements
- In some parts of the world, it is less susceptible to damage from natural disasters, as nodes are located above ground on power poles
- Power source required within the outside plant
- Remains a copper-based technology, with ultimate bandwidth limitations that implies
With the popularity of premium cable television and bundled video, data and phone services,
DOCSIS should continue to enable cable television providers to remain competitive for as long as it can meet rising bandwidth requirements.
G.fast – the new kid on the copper block
G.fast is a new access technology being developed to extend the life of copper beyond a Gigabit. This technology targets brownfield deployments as a fiber alternative that reuses existing copper infrastructure in homes and other buildings.
- An alternative to the higher cost and slower rollout of fiber in brownfield scenarios
- Reuse of existing copper infrastructure
- Relatively quick rollout
- Rapid return on investment
- Distances are limited; G.fast equipment must reside close to the end user to produce a Gigabit of bandwidth.
- Reliance on reverse power feeding requires power from end user’s terminal to G.fast interface
- Crosstalk affects performance; without vectoring noise cancellation, G.fast rates are severely degraded
- Does not use frequency division duplex (FDD), but rather time division duplex (TDD) utilizing different time slots for upstream and downstream transmission. Transmission speed of 1 Gbps typically refers to the sum of both upstream and downstream bandwidths
Still, if G.fast can achieve Gigabit speed, it can meet bandwidth requirements in homes for the next four or five years and provide an upgrade path to FTTH. This makes G.fast a viable technology for service providers seeking higher bandwidth delivery in brownfield situations.