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Breaking through the remote terminal bottleneck:
delivering voice, data and video over DSL

By Malcolm Loro, Director of Product Marketing, Catena Networks

Industry experts agree that remote terminals (RTs) have become a critical focal point for the immediate deployment of DSL broadband capabilities. RTs also lay the foundation to deliver new converged voice, data and video services over an efficient, mass-market oriented communications infrastructure. Remote terminals represent both a potential bottleneck, and a key opportunity area, for carriers looking to expand their DSL service footprints and to integrate enhanced broadband service offerings.

Traditional technology approaches available to carriers include co-locating DSL Access Multiplexers (DSLAMs) with remote Digital Loop Carriers (DLCs) and integrating DSLAM functionality into so-called Next Generation DLCs (NGDLCs) using combo cards. (Combo cards combine POTS, DSL and POTS splitter functionality.) However, both of these approaches have inherent limitations because they continue to treat DSL deployment as an add-on, niche overlay service to existing POTS infrastructures. The tight space constraints in RT deployments make it impractical to use DSLAM co-location approaches that were originally designed for CO environments. In addition, combo cards can impose extra operational costs because of the need to physically reconfigure remote systems to accommodate a changing mix of POTS and DSL line allocations.

In contrast, new Broadband Loop Carrier (BLC) architectures are designed, from the ground up, to fully integrate POTS and DSL on every line in an RT system – at costs approaching POTS-only solutions. This enables carriers to deliver advanced broadband services to all subscribers.

As described in the following sections, the realization of a true BLC architecture means much more than just merging POTS and DSL at the linecard level. To support universal provisioning of DSL, and full integration of enhanced services such as video-over-DSL, the BLC architecture must provide high capacity, system-level performance, superior network-level operational efficiency and the flexibility to deliver a comprehensive range of competitive services – for both today and tomorrow.

The Advantages of Integrating POTS and DSL at the Silicon Level
By integrating splitterless POTS and DSL at the silicon level, BLC architectures can deliver both traditional voice and new broadband data services on every line – at costs competitive with narrowband systems – without compromising line densities or requiring one type of service to be traded off against the other. Elimination of POTS splitters also significantly reduces system complexity and improves overall maintainability.

With POTS+DSL on every line, Broadband Loop Carriers ensure that there will be no loss of POTS capacity as DSL penetration grows. In contrast, NGDLC systems force carriers to contend with POTS capacity reduction as DSL is added to the system. This results from the need to swap cards as the service mix changes – and/or from inherent broadband capacity limitations.

POTS displacement necessitates the build-out of additional infrastructure and provisioning of additional linecards to maintain capacity, creating serious network planning challenges as DSL penetration rises. This problem is particularly acute when dealing with high DSL take-rates, such as with video deployments.

DSL take-rates often are unpredictable, influenced by factors such as local demographics, carrier marketing campaigns, and service pricing. In many cases, carriers deploy DSL “speculatively” in areas where higher demand is anticipated. These factors typically lead to a higher DSL linecard inventory and spares requirement than is usual with more predictable services. With BLCs, this problem is averted completely, as no separate DSL or combo linecards are required, and DSL service can be turned up through software, whenever and wherever it is needed. Consequently, carriers have the ability to exactly match their broadband deployments with subscriber demand.

BLC architectures also support line-by-line, voice-over-packet (VoP) conversion, to help carriers smoothly migrate services to cost-saving packet networks, according to their specific needs. Having POTS, DSL and VoP physically available and accessible on every line enables carriers to flexibly provision and manage all services, using a common Element Management System (EMS).

Ensuring Seamless, System-Level Integration & Performance
Beyond the linecard level, BLC architectures incorporate high-performance, system-level features that support seamless integration with legacy networks. These BLC architectures also provide a forward-migration path that supports converged services on next-generation, packet-based networks. Special emphasis on the switch fabric, backplane capacity and range of network interfaces ensure that BLC systems will scale with escalating traffic levels and new service requirements.

While convergence is already underway in the network core, most access networks continue to be based on traditional, circuit-switched infrastructures. Thus, BLCs provide standard backhaul interfaces to existing ATM and SONET networks, as well as emerging IP network interfaces such as packet-over-SONET (PoS) and Gigabit Ethernet (GigE). This ensures that carriers can meet both present and future requirements, without the expense of complete forklift upgrades along the way.

From a performance standpoint, BLC systems provide non-blocking aggregation of both voice and data traffic for backhaul transport across the carrier’s network. Moving beyond conventional TDM-based architectures that dedicate a fixed portion of the bandwidth to every connection, BLCs use advanced switch fabrics to carry much higher aggregate traffic levels. As carriers continue to deploy DSL, and begin rolling out new services such as video-over-DSL, BLCs can help them scale to handle peak loads from all linecards. Additionally, BLCs can support high-bandwidth optical backhaul connections such as OC-3, OC-12 and OC-48.

Achieving Network-Level Operational Efficiencies
While BLCs provide high line-density POTS and DSL to immediately optimize carriers’ capital investments, by far the more important issue for most carriers is controlling ongoing operational costs. This has been a major issue with NGDLCs, because carriers still must roll trucks to remote sites to change the physical configuration whenever a service activation or change is needed. Not only does the truck roll (and technician time) add significant cost, it also delays provisioning of the circuit. This further costs the carrier in lost revenue and lower customer satisfaction.

Carriers need a way to deploy broadband services as cheaply and as quickly as narrowband services are deployed today. CLASS services, for example, can be deployed through a set of simple keystrokes, and DSL deployment should be just as simple. With today’s DSLAMs and NGDLCs that require dispatches to the RT to activate service, valuable service revenue is lost the longer it takes to complete the service order. BLCs enable carriers to accelerate time-to-revenue through software-based, remote service activation.

Because both DSL and POTS are already resident on every line in a BLC system, there is no need for physical intervention or reconfiguration at the remote site. Instead of having to juggle the allocation of system resources to get the right mix of POTS and DSL, carriers can simply turn on the required services in a BLC system through remote software commands, without requiring a truck-roll to the remote location. In effect, the initial investment in each BLC system acts like an ongoing annuity that repays dividends in the form of hard cost savings ? every time a new service is provisioned or changed.

Providing Comprehensive Service-Level Flexibility
One of the most important advantages of transitioning to a true BLC architecture is the ability to seamlessly integrate advanced broadband service offerings. Because BLCs are designed to handle both voice and broadband data in a high-performance packetized environment, they can inherently deliver new services such as voice-over-packet and video-over-DSL.

Video-over-DSL offers a particularly appealing new service option for many rural carriers because they can leverage their BLC remote terminal deployments to compete strongly against rural cable providers. In some cases, rural carriers can use the greater reach of BLC-based RT networks to leapfrog ahead of cable suppliers and become the primary provider of video throughout their customer serving areas.

To enable deployment of competitive video-over-DSL service offerings, advanced BLC architectures include built-in support for multicasting standards such as Internet Group Management Protocol (IGMP). Multicasting allows efficient distribution of content, such as streaming video, from a single source to all computers on the network that have identified themselves as interested in receiving the content.

Seamless Service Delivery to All Customers
For carriers, the bottom line is the ability to cost-effectively deliver a complete range of competitive services over a seamless footprint that reaches out to all users – whether served by central offices or by remote terminals. The rollout of new services such as DSL and video-over-DSL can be stalled when a large number of interested subscribers must be turned away because they are connected to RTs that can't handle broadband service delivery. Unresolved gaps in either the carrier’s service offerings or in the service footprint can lead to customer dissatisfaction and subscriber churn, as end users shop around for other alternatives.

Broadband Loop Carriers resolve this dilemma by fundamentally integrating POTS and DSL, from the ground up, within the remote terminal environment – at costs approaching POTS-only solutions. Network management is greatly simplified because all services can be provisioned and managed under a common software environment. Operational costs are significantly reduced through elimination of unnecessary truck rolls to remote terminal locations, and customer satisfaction is enhanced by more rapid response to new service requests.

BLC architectures are designed to fit into existing circuit-switched networks and to provide line-by-line, software-managed migration to packet-based networks. These architectures provide the bridge for immediate, mass-market delivery of broadband and the foundation for migrating to converged public networks. BLC deployments not only solve today’s RT bottleneck; they also help carriers cost-effectively evolve their networks to support new, value-added services and maintain their competitive edge.

For more information, please contact:
Malcolm Loro:   mloro@catena.com

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