ADSL APPLICATIONS

ADSL technology offers high-speed access affordable to mass markets, taking us to new heights.  Its no wonder service providers are looking for new ways to introduce new profitable services which weren't available in the voiceband-modem era.
The following sections will describe two of the applicative services - multicast video and voice over DSL.

Delivering Multicast Video Over ADSL

Streaming video requires high downstream bandwidth, and relatively small upstream bandwidth. As a result, ADSL, being the most available DSL service in the market to date who offers great downstream bandwidth, is therefore most-suited to deliver multicast video services.

Video-over-ADSL Services Business Model
 
for service providers to offer any service it must be worthwhile for them, meaning they must see profit out of it.  We should look at the problem from two points of view - both service providers and users (a happy consumer means more profits). A few aspects must be taken into consideration in order to create a fine, stable, and profitable business model:

• Access control, management, and billing - to generate revenues, it is important to maintain an appropriate channel access model that allows providers to bill for premium content.  This can be done authentication, and by logging costumer's activities as accounting records in some billing system such as a RADIUS server.
  We will elaborate on the subject in the next section.
• Variable bandwidth rates - Most ADSL networks have heterogeneous bandwidths, which greatly affects video quality.  It is desirable for providers to offer contents at several speeds, rather than only broadcasting at the lowest-common-denominator rate.  This way, users with higher bandwidth can enjoy higher quality video.
• Variety of contents - service providers attract customers by providing variety of video contents, depending upon the source and audience type.  For example:  basic, premium, and commercial tv channels, special interest group video channels targeted at specific audience which might have the potential for rapid growth, E-learning, security webcams, and more. 
  Note that for some of those contents need the provider should offer a blocking mechanism to prevent access from not well suited audience such as children.

The architecture

A typical service architecture includes RADIUS servers (servers for remote user authentication and accounting), one or more Web servers, service selection gateways (SSG), and service selection dashboards (SSD). There may be optional servers for content processing (such as data mining) and advertisement insertion.

Users connect to the SSD server via a web browser (and perhaps an additional  plugin), which by using the RADIUS server retrieve the list of contents available for the user.   Because users can only log into subscribed packages, this limits user access to only those channels included in their subscribed packages, in addition to free channels.  After the user choose the desired channel, the user's PC issues an Internet Group Management Protocol (IGMP)-join request for the channel via interaction between plug-in and media player.  The SSG provides the subscription-based access to multicast video streams after interaction with the SSD (who informs it on the user's details & package), according to the channel chosen by the user.
The RADIUS server is in charge of  authentication, authorization, and accounting (AAA) by maintaining user and service profiles. The authentication is usually done with a username and password.  It also tracks the user's activities upon login into the system, and update the accounting records as needed.

As far as transport over the network is concerned, only one multicast video stream travels the transport network to a centerized access point (a router, a DSLAM, etc.), independently of the number of subscribers. The router nearest the subscriber dynamically (on demand from subscribers) replicates the multicast streams and forwards them to the subscribers using the IGMP protocol.  Note that the video channel bandwidth at this point cannot exceed the "last-mile bandwidth" to the CPE (since video quality will degrade and could appear broken).

Technology Enhancements

ADSL itself is still restricted in download, and is not enough for top-of-the-line high quality video.  Several technology enhacements can help service providers delivering some higher-quality multicast video services.  This enhancements include:

• Multicast Routing Protocols - Multicast routing is used to distribute data to multiple recipients.  Among some of the well known protocols are: Protocol Independent Multicast (PIM), Distance Vector Multicast Routing Protocol (DVMRP), Multicast Open Shortest Path First (MOSPF), and Core-Based Tree (CBT). 
• Encoding and Compression - helps reduce the capacity of video data for a more efficient transport.  Those include MPEG1, MPEG2, MPEG4 along with other de-facto standards (realmedia, apple's quicktime, etc.)
• Quality of Service (QoS) - Multicast video service is sensitive to packet loss and delay which affect the video quality.  Providers can minimize loss and delay by assigning higher QoS priority to video traffic.  It can also be used to reduce congestion.

Voice Over DSL (VoDSL)

Voice over DSL is a technology to convert voice calls into digital data packets and transmit them as multiple calls (lines) over a single copper line, thus enabling service providers to offer consumers several phone lines in additional to the standard POTS.  This can be done by using the extra DSL bandwidth that is not used for data to implement voice transmission. For greater efficiency, the bandwidth should be allocated dynamically, so that bandwidth is consumed only when a call is active.

There are two primary methods to implement VoDSL:

• Broadband Loop Emulation Service (BLES) - specially designed CPE  is installed at the home.  This equipment interfaces with the existing CPE, DSL network, and the local exchange (also called: class5 switch).  Basically it can be integrated in the modem, or come as a separate unit. 
  In the network, a voice or local exchange gateway at the CO sends the VoDSL voice traffic to the existing local exchange via a standard network interface.

Figure 1. BLES configuration

• Voice over Multiservice Broadband Network (VoMBN) - Similar to BLES, only does not rely on the local exchange.  At the home the equipment is the same as BLES. On the network however, a regional multiservice IP or ATM network, consisting of call signaling and processing servers and various gateway devices, replaces the voice-switching at the local exchange.

Figure 2. VoMBN configuration

The first option is best suited for service providers who already provide other voice-services, and the second option is for service-providers who wants to add voice-services to their repository .

Note that the technology is well suited for ADSL, but can work on any DSL line. 
In any way, VoDSL is very beneficial for consumers looking for an alternative to POTS, or just want to make the best out of their DSL connection, and also to service providers who easily make some profits with minimal cost.

Next: The next level - introducing ADSL2