Broadband access encompasses various technological platforms and businesses that improve network capacity and current services, be it through broadband fixed-line networks, higher capacity mobile networks, or other platforms that allow the general public to access useful services and content.

Technology Alternatives
Till date, digital subscriber line (DSL) deployment has been driven primarily by the need to provide basic high-speed Internet (HSI) service to the largest possible number of people. This has included applications such as Web browsing, chat, e-mail, data downloading, and in recent years a surge in peer-to-peer applications with MP3 and video-file exchanges. These applications have been easily accommodated using current asymmetric digital subscriber line (ADSL) technology. Operators have succeeded in doing this by focusing deployment of the DSL infrastructure in their central offices (CO) to achieve mass coverage at the lowest cost.

Various DSL variants can be considered for future evolution of the access network. They differ primarily in their spectrum masks and the number of tones used for transmission in each direction. The different reach, bandwidth, and spectral compatibility characteristics can be leveraged for different deployment approaches

n ADSL: ADSL, recently updated with the ADSL2 standard, is deployed primarily in the COs today. With a reach of 5 km at 1 Mbps, it is excellent for mass deployment.

n Reach Extended ADSL2 (READSL2): It aims to extend service to 5.5 km (on 26 gauge loops) with a minimum downstream/upstream bitrate of 192/96 kbit/s in addition to the standard telephone service. The extra reach is achieved by boosting the power spectral density in the lower ends of the spectrum (both upstream and downstream) and using a narrower frequency band while maintaining the same total power as ADSL2. Deployed in the CO, it is possible to slightly increase the reach using this variant of ADSL2 technology.

n ADSL2plus: This important variation on the ADSL2 standard substantially increases the bandwidth by doubling the spectrum to 2.2 MHz, resulting in a throughput of 5.5–15 Mbps in the range 1.5 to 3.2 km. The performance over longer distances is equivalent to ADSL2.

n Very High Bit-rate DSL (VDSL): The VDSL standard has been under consideration for several years. It provides an asymmetric downstream bandwidth of 5–25 Mbps over 1–1.5 km (or a symmetric bandwidth of 2–10 Mbps). Because of its shorter reach, nodes must be deployed closer to the customer, thereby increasing deployment costs.

Two variants of VDSL have been standardized based on single carrier—quadrature amplitude modulation (QAM) and the multi-carrier discrete multi tone (DMT) modulation. DMT offers advantages over QAM in terms of performance, robustness to noise and spectral flexibility. It also allows interoperability with ADSL, thus making it possible to use multi–DSL line cards on which each individual line can be configured at run time in ADSL (or ADSL2), ADSL2plus, or VDSL mode depending upon the user profile and the connected customer’s premises equipment. Consequently, DMT is the preferred line code for VDSL.

n Passive Optical Networks (PON): Passive optical network technologies provide a cost-effective means of deploying fiber directly from the CO to the customer’s premises. Various standards are being defined (Broadband-PON, Ethernet-PON, and Gigabit-PON), all of which allow for completely passive fiber aggregation. This eliminates ongoing operations costs and optimizes the lifecycle cost for fiber to the home (FTTH).

Service Evolution
We are seeing new services emerge, as users demand richer content, as electronics vendors introduce new multimedia consumer devices, and as operators seek to generate additional revenue. Some services will be in the areas of gaming and video services, including traditional broadcast video, video on demand and enhanced video streaming. In turn, these will drive up the bandwidth requirement.

In its brief history, broadband access has given an extensive range of innovative Internet applications, clearly illustrating the creativity of the developers. These have been made possible by the open, application-agnostic nature of the Internet, which allows new services to be rapidly introduced.

Different types of content-delivery mechanisms vis-à-vis the type of content

However, translating this technological success into financial success has proved more difficult. Most Internet applications are free; consequently, the network providers who offer broadband access for a flat fee are not compensated for the higher traffic that such applications generate. Today, lots of Internet application and content providers are trying to move to subscription-based models. However, it is not easy to persuade users to pay for something that used to be free. For this reason, revenue-generating broadband Internet services are currently in their infancy and have a limited audience.

In the consumer world, the end-to-end approach should guarantee freedom of choice, ease of use, and user mobility. Thus, users of the new multimedia systems must get the following.

n Applications for business purposes and personal information (e.g., tele-working and e-learning)

n Applications for social use (e.g., tele-healthcare and community TV)

n Applications for entertainment and daily uses (e.g., tele-shopping, networked games, and interactive digital TV).

Four mechanisms can be identified for the delivery of digital multimedia content to subscribers over a telecommunication network, based on two criteria.

On the one hand, content can be either streamed to the user or downloaded. With streaming, the content is consumed in real time by subscribers. A streaming server sends a content stream that can be used immediately (i.e., viewed or listened to) by the receiver before the full content has been delivered. This delivery method requires a certain quality of service assurance from the communication network in order to work properly. Lost packets are typically not retransmitted. The higher-layer protocols can deal with a certain amount of packet loss but the network manager has to make sure that the actual packet loss does not exceed the acceptable limits. In the case of downloading, the complete content needs to be delivered before the consumer can enjoy it. Downloading is typically done using a protocol such as the transmission control protocol (TCP), which can retransmit segments in the event of packet loss.

On the other hand, content can be either delivered in unicast or in multicast modes. With unicast, content is delivered at a specific moment in time from a specific server to a specific subscriber (point-to-point delivery). In contrast, multicast delivers the content simultaneously to a group of subscribers (tree-structured delivery).

Network Provider’s Challenge
It is difficult to accurately predict the evolution of the basket of services to be offered via future broadband access systems. Still, three things are certain.

n Services will have strong regional flavors

n Successful business models will always be based on an ecosystem of broadband content delivery partners consisting of content owners, content aggregators, service providers, network service providers, and network access providers to serve the broadband consumer

A network provider’s success depends on deploying platforms with open interfaces

n Network providers (operators) will play a central ‘service delivery role’ in the value chain

In such a situation, the key imperative for success, for a network provider, is to deploy a future-proof broadband services delivery and management platform. Such a deployment can only be facilitated by open interfaces between the major business roles—content aggregator, third-party application provider, network access provider, and user.

Typically, a four-layered approach to the delivery of new broadband services solution (which is sufficiently generic to encompass most services, such as media-on-demand and conversational services) should be considered.

n Network Layer: Supports a predictable network QoS among other functions

n N-services Layer: Provides a common set of enabling services that can be used by various service providers. Some of these services can only be implemented by network providers, while others could be offered by either the network operator or service provider, depending on the chosen business model

n Application Layer: Implements the functions as defined in the service provider’s role. The idea is that this layer can interact with the enabling n-services layer in an open-standard way

n Content Layer: Implements the functions defined in the content role. Again, in an open architecture, it is preferable that the content providers can interact with the service provider layer in a standard way

While there are a few issues while choosing the technology for deploying a network that will offer broadband services to the customers, choosing the right mix of services that can be offered to the consumers has to be thought about very carefully.

The issues have remained primarily because the learning curve for effective management and services delivery mechanism has not yet established.

However, a delivery mechanism that uses the optimal mix of services that are more personalized in nature would help service providers hook customers to services. This kind of an approach would eventually provide them with different avenues for revenue generation out of broadband services.

Subhash Bana director, software centre, Alcatel India