Thoroughly modern networks

Next generation BRAS devices are the key to modernizing today's carrier networks

As today’s service providers begin to modernize and evolve their broadband access networks, they face some critical challenges. These challenges include the need to dramatically improve the scalability and the reach of their infrastructures, the need to enable higher-margin, premium services such as video-over-broadband and multi-player gaming and the need to transition to packet-based backbones—all while leveraging their existing infrastructures and driving down their CapEx and OpEx costs.

Fortunately, a new class of access product—the broadband remote access server (BRAS)—is now available that meets the specific demands carriers face. Designed to be deployed closer to the edge of the network rather than out at the carriers’ regional points of presence (POPs), the new devices allow carriers to do traffic grooming and deliver advanced services while supplying advanced subscriber management functionality, helping to ensure Quality of Service (QoS)/Class of Service (CoS), and reducing management complexity.

Three significant applications for these new, versatile BRAS platforms have emerged:

• DSL Forum TR-059

• Subscriber management system (SMS) upgrade/replacement

• Multipurpose IOC Platform, including remote terminal (RT) trunk aggregation

DSL Forum TR-059

The first key application for the new devices is as a solution for the DSL Forum’s TR-059, titled DSL Evolution–Architecture Requirements for the Support of QoS-Enabled IP Services. This important document is expected to strongly influence the evolution of broadband access networks, especially those of the world’s largest carriers. TR-059 proposes solutions to some of the key architectural challenges that exist in current broadband access networks, including those associated with scaling these networks to address significant expected subscriber growth and equipping these networks to cost-effectively provide a wide range of advanced services.

Legacy SMSs are quickly running out of capacity and carriers are being left with no rational upgrade options from a price/performance standpoint.

TR-059 proposes to address these challenges by IP-enabling the existing ATM broadband access network, a portion of the network that historically has contained only layer-two devices. Under TR-059, BRAS devices will be deployed in each CO, behind the DSLAMs, to subtend them. Expected benefits of this new architecture design include better scalability, improved and lower cost transport, simpler provisioning, on-demand differentiated services, increased access to service providers and standard subscriber connections.

The BRAS functionality incorporated into the new BRAS devices is highly differentiated from legacy ISP-oriented BRAS/edge router devices. These new devices are designed for the access network and feature a high performance, carrier-class integrated packet and cell architecture, programmable network processors, NEBS Level-3 certification and CO form factor–cost-optimized for widespread deployment in the access network. These devices also offer:

• Transparent virtual routing (TVR),  which enables distributed IP forwarding without appearing as a router hope or requiring modifications to or administration of subnets and IP addressing. This approach provides the benefits of IP forwarding and QoS much closer to subscribers, without the cost and complexity of dynamic routing protocol—and allows access providers to use IP without interfering with third-party ISPs’ IP administration.

• Comprehensive ATM switching, supporting native ATM virtual circuit (VC) and virtual path (VP) switching with full traffic management 4.1 (TM 4.1) support operating concurrently with point-to-point protocol (PPP) and IP-layer QoS/CoS functions.

Carrier Checklist As carriers evaluate the solutions available for modernizing their broadband access networks, BRAS devices should be high on their list. As they review their options, the following features should be kept in mind: Carrier-class reliability and redundancy Field-proven Native ATM switching functionality Standards-based IP Transparent Virtual Routing Easy-to-use Network Management with intuitive GUI A comprehensive, integrated range of Multilayer QoS features ATM switching capabilities with seamless ATM to Ethernet networking Advanced networking capabilities, including auto-configuration, dynamic bandwidth on demand and hierarchical virtual port scheduling

In addition to traditional BRAS functionality, such as PPP termination with IP aggregation, PPP over ATM and PPP over Ethernet into Layer 2 Transport Protocol (L2TP), and dynamic service selection, the new BRAS platforms offer enhanced multi-layer QoS capabilities, including session and bandwidth connection admission control and per-service scheduling in support of advanced services.

Placing a BRAS in each CO lowers carriers’ CapEx by requiring fewer costly ATM switches to be installed in the network. It also affords a high level of OpEx savings by requiring the deployment of fewer subscriber management systems (SMSs).

TR-059 states that the BRAS must support a DiffServ-aware hierarchical scheduler that allows it to manage the network so that any potential congestion in the access network between the BRAS and the CPE is avoided. Hierarchical virtual port scheduling (HVPS) was designed to overcome the inability of existing ATM devices to provide selective discard above the ATM layer (IP and PPP). Existing networks typically have one or two ATM hops back to a metro BRAS device. If there is congestion beyond the metro BRAS toward subscribers, there is no intelligent selective discard based on PPP or IP information. HVPS can provide IP and PPP-based QoS up to two ATM hops from the BRAS.

SMS Upgrade/Replacement

The second key application for this new category of platforms is as an SMS upgrade or replacement. Legacy SMSs are quickly running out of capacity and carriers are being left with no rational upgrade options from a price/performance standpoint. In some cases, manufacturers are simply discontinuing their SMS lines. In others, the upgrade paths vendors offer require service providers to overspend on expensive, edge router-based devices that are too large, complex and costly for the application at hand.

In contrast, the SMS functionality in the new BRAS devices offer service providers more than a ten-fold improvement in performance and active subscriber capacity compared to the most widely deployed subscriber management devices—along with improved reliability, advanced features and comprehensive network management—for a fraction of the cost of most edge routers.

Some of the key SMS features being offered by the new devices include:

• Significant performance improvement over most installed subscriber management devices

• Cost-effective upgrade path to increase active subscriber management capacity

• Carrier-class reliability and redundancy

• Comprehensive, easy-to-use graphical user interface (GUI)

• Advanced networking capabilities, including auto-configuration, dynamic bandwidth on demand (BoD), and HVPS

Despite the retrenchment in the telecommunications marketplace, broadband services continue to be a promising source of growth. To capture this revenue, carriers are expanding broadband capability beyond their existing COs into remote terminals, leveraging a host of new, feature-rich, next-generation DLC equipment.

Given this movement, the third key application for today’s new BRAS devices is that of a multi-purpose IOC platform, including cost-effective, scalable remote terminal trunk aggregation. With the large installed base of remote terminals, the significant introduction of more sophisticated RT solutions and the aggressive expansion plans of many carriers, there is a dramatic need for a simple, cost-effective way to aggregate and manage a variety of existing remote terminal devices—all while preparing for additional growth and the delivery of premium broadband services.

The RT trunk aggregation capabilities of today’s new multi-service access platforms protect carriers’ existing infrastructure equipment investments by enabling the redeployment of existing, lower-density DSLAMs to other COs or RTs and optimizing RT backhauling to reduce bandwidth requirements and costs. In addition, the following features enable these access devices to provide cost-effective, scalable remote terminal trunk aggregation: proven interoperability with commercial deployments subtending leading RT devices and a broad range of aggregation and wide area networking (WAN) interfaces, including T-1/E-1, DS-3/E-3, OC-3/STM-1, Ethernet and Gigabit Ethernet.

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Keith Higgins is Vice President of Marketing, Copper Mountain Networks, Inc., a provider of intelligent broadband access solutions based in Palo Alto, CA.

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