Ethernet DSL Access unlocks the broadband mass market
By Rohan Dias, Director of Broadband Access Marketing, Ericsson
A new low-cost, low-risk way to expand Digital Subscriber Line (DSL) based broadband service coverage and mass market take-up is being rolled out by a number of leading-edge operators around the world. Based on Ethernet technology, it prepares the network for emerging capacity-demanding services while offering dramatic reductions in deployment and operating costs.
There is a growing range of capacity-demanding services coming to market, and the number of residential and small business subscribers for broadband access, particularly Digital Subscriber Line (DSL) services, is taking off. Operators need to deploy a cost-efficient solution that offers the capacity, flexibility and scalability to meet both short-term expansion and longer-term needs.
DSL is the technology of choice for fixed network operators rolling out broadband services to residential, small office/home office (SOHO) and small to medium-sized enterprise (SME) customers. Fixed network operators are keen to make use of their large existing copper access networks to compete cost-effectively with cable and satellite providers.
However the roll-out of DSL services at a price–performance point that will attract these customers has been held back by the prohibitive costs associated with upgrading the ‘second mile’ of the network – between the DSL Access Multiplexer (DSLAM) and the nearest switching node – in order to provide the bandwidth needed to deliver DSL services to a mass market.
To date, this part of the network has been implemented using traditional TDM or ATM technology, which is unable to meet the new bandwidth demands cost-effectively or flexibly enough.
New DSL drivers
A number of developments are driving growth in demand for residential broadband access based on DSL. For example, home networking with wired (Ethernet) or wireless (WiFi) access is growing in popularity as a way of interconnecting a variety of domestic devices such as PCs, games consoles, Internet music and entertainment devices and IP-phones. DSL terminals with WiFi termination are also very attractive for building local hotspots, with DSL back-haul.
In addition, on-line gaming, digital content distribution and video-on-demand are growing in importance, and operators need to prepare their networks to cater for these new types of revenue streams, which predominantly have IP as the service delivery mechanism.
To meet these growing bandwidth requirements, the data rates available over DSL are improving all the time: Asymmetric DSL (ADSL) is being taken to new levels. One of the most important improvements is the capability of Annex J in the ADSL2 standard that will enable transmission of up to 3Mbit/s from the user.
For the DSL market to succeed fully, it is important that open interfaces continue to be provided over the copper loop. This is key to the availability of low-cost DSL terminals and the growth of a retail terminal market. ADSL2+ will build on the already approved standards by providing enhancements for shorter copper loops. Furthermore, adoption of the widely accepted global standards will avoid getting trapped in tight dependencies between access nodes and terminal products.
The Ethernet DSL access opportunity
There is a great opportunity for operators with existing copper access infrastructure to exploit this resource for broadband roll-out. Using Ethernet DSL access technology they can unlock the mass market ‘second wave’ for DSL services, following the first wave of early adopters. Ethernet technology dramatically changes the economics associated with enabling DSL services, providing very cost-effective high-bandwidth links in the ‘second mile’ – typically the bottleneck in today’s networks.
Ericsson has calculated that Ethernet DSL Access solutions enable the network operators to deploy the required second mile bandwidth for DSL services at less than half of the cost of an equivalent ATM-based alternative.
A key advantage of providing DSL services in this way is that existing standardized DSL interfaces are unchanged. The subscriber simply uses a standard DSL modem, which the Ethernet connection from the PC or LAN plugs into in the normal way.
The Ethernet-based solution offers the flexibility, scalability, and low equipment cost to meet the short-term need for new bandwidth in the second-mile network. It also provides operators with a technology platform that can be migrated into the first mile (between the subscriber and the first network node) as bandwidth requirements increase in the future – both over copper in existing PSTN networks and over fiber in greenfield deployments.
Updating the DSLAM concept
With Ethernet DSL Access, the original DSL Access Multiplexer (DSLAM) concept has been reinvented into a more IP/Ethernet-centric approach, in order to meet the DSL second wave challenges.
The traditional chassis-based DSLAM was introduced in the mid 1990s, with a chassis supporting multiple xDSL board types and occasionally supporting integrated DSL/PSTN boards. The solution typically supports up to 1,000 lines per chassis and connects to the network over an ATM interface.
Ericsson’s Ethernet DSL Access solution provides a complete IP DSLAM on a board (see Figure 1), supporting both ADSL and ADSL2, and cost-effectively built to support installations ranging from a handful of subscribers to large site deployments.
To provide a complete service delivery solution, the IP DSLAM is combined with a standard Ethernet switch, a Power-over-LAN module and management system. Standard DSL devices are used on the customer premises.
This solution has already been deployed by operators around the world, including three Chinese Telecom operators, China Netcom, CTBC in Brazil, Eesti Telefon in Estonia and Emitel in Hungary. While these operators are using the solution to expand their DSL service coverage to subscribers or areas where previously the cost may have been prohibitive, they are also preparing their broadband networks for the traffic increases expected from capacity-demanding services such as for instance video broadcasting services.
Figure 1. Ericsson’s Ethernet DSL Access IP DSLAM is the world’s smallest, and serves from 10 ADSL subscribers, offering ‘pay-as-you-grow’ capacity with a very low starting point.
Opening up DSL revenue opportunities
One traditional barrier to rolling out mass-market DSL services is addressing sites with small numbers of users. The high fixed investment associated with addressing sites makes them less attractive or even unprofitable. Traditional DSLAM solutions typically offer poor downward scalability, as well as large size (footprint) and high aggregation and transport costs.
Ethernet-based DSL access solutions change the economics significantly, so that sites with as few as 10 lines can be implemented cost-effectively, and can be scaled in steps of 10. Capital investment is significantly reduced compared with traditional solutions. Moreover, the cost advantages are retained for large site deployments.
Ericsson’s Ethernet DSL Access solution can support both ADSL (over PSTN and ISDN) and ADSL2 from one universal ADSL line. Initially configured for ADSL, it enables lines to be upgraded to ADSL2 through the management system on a line-by-line basis. This makes it easier to serve the SOHO and SME markets, and is more flexible and cost-efficient than the dual line (ADSL/SDSL) alternative. A variety of customer needs can be met using the same equipment, and DSL plant is very well utilized.
Aggregation and transport costs are substantially reduced (up to ten-fold) compared with ATM-based alternatives. Concentration is provided within Ethernet aggregation nodes to reduce total capital expenditure (CAPEX).
Ethernet path to the future
After 30 years of widespread use in enterprise networks, the price-performance ratio of Ethernet is superior to any other broadband access technology. It is now a well-proven, mature and robust technology that follows an international standard and is used in the vast majority of Local Area Networks (LANs). All PCs manufactured today have Ethernet capabilities and almost all IP traffic originates and terminates as Ethernet.
The cost per Mbit/s of Ethernet has fallen dramatically over the past couple of years. In addition, standards directly targeting the public network, such as 10Gbit/s and EFM will further improve price–performance. Today, IP-over-Ethernet equipment is approximately one-tenth the cost of IP-over-ATM or IP-over-SDH/ SONET equipment in a typical regional network deployment. The operating costs associated with bandwidth management, provisioning, maintenance and upgrades for IP-over-Ethernet are also much lower: typically less than one-fifth those for IP-over-ATM or IP-over-SDH/SONET.
Ethernet DSL access provides a technology platform that can be migrated into the first mile as bandwidth requirements grow in the future – whether over copper in existing PSTN networks or over fiber in greenfield deployments. The first mile could be migrated to Ethernet when the EFM standard (IEEE 802.3ah) is introduced, and Ethernet will grow in importance as a back-haul technology when more advanced DSL technologies are introduced.
Ethernet-based DSL access solutions look set to revolutionize the way operators roll out DSL broadband services. Operators will be able to address smaller sites more effectively and reduce the cost of deploying bandwidth in the second mile of the network using future-proof Ethernet technology.
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