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The New Ethernet Aggregation Network Excerpts

The benefits of Ethernet are well understood: simplicity, compatibility with the enterprise networks and lower cost. The new, advanced Ethernet equipment can provide emerging sophisticated services, such as triple play, VPLS, L2 VPNs.

The emergence of triple play services has made the need for deployment of metro Ethernet aggregation networks prevalent. These networks must be able to deliver emerging multimedia applications. MPLS with Traffic Engineering is considered the best technology to complement Ethernet to deliver these applications.

Deployment challenges of Ethernet as a WAN aggregation technology are both technical and economical. Studies have shown that a single platform capable of operating as an Ethernet aggregator, BRAS, and a Provider’s Edge router can provide the optimal solution, technically and economically.

A sound strategy of supporting coexistence of legacy (ATM, Frame Relay, FTTx, cable, wireless, TDM) and the new Ethernet network is essential to protect service providers’ past investments and current cash flows.

The functional elements in construction of an Ethernet-based metro network capable of aggregation of multiple services are shown in Figure 1. Figure 1 depicts systems that require tight coupling with the Ethernet switch aggregators in a metro PoP:

• Broadband Remote Access Server (BRAS)
• Provider’s Edge Router (PE)

Figure 1. Functional Elements of a Broadband Services Network

Technical factors to consider in construction of such a network are traffic management, high availability, network topology, scalability, OAM, and security.

Traffic Management™ functions such as policing, shaping, scheduling, queuing, back pressure flow control are all necessary for expected delivery of services and efficient use of resources in the network.

A technically advanced Ethernet aggregator switch is capable of utilizing a hierarchical QoS scheme to apply to different applications that a single user has subscribed to. In this case, “Hierarchical Scheduling” of packets per point of interest, e.g., last mile link, DSLAM, packets stay in queues within the aggregator until transmitted via some pre-defined policy.

High availability for both hardware and software is critical. While each service provider may have a different view of what “carrier-class” equipment should support, the following requirements have been consistent according to a study by Infonetics Research

- Separation of Control and Data traffic
- Nonstop service - In service software upgrade
- Redundant hardware (power supplies, fan trays, port redundancy)
- Remote loop back testing and the ability to quickly pinpoint faults in the network
- Software reliability
- Network Reliability

For the choice of the network topology, the service provider must consider the required size of the network to accommodate the type of services to be offered to the expected user population. The choices can be broadly be categorized into one of: 1) Star (Hub and Spoke), 2) Ring, and 3) A “Hybrid” of the first two.

For delivery of emerging applications, e.g., IP-TV, scalability of MPLS-based services becomes important. MAC address scaling, support for a large number of users and groups in PIM-SM are examples of scalability requirements.

OAM functions can be summarized as one of configuration, fault-detection and statistics collection. Efficient OAM capabilities are gauged through fast provisioning time, quicker fault-detection and correction and availability of ample statistics information to make adjustments in the network and gauge its performance.

Network security requires that the Ethernet aggregation platform ensure defense against a malicious attacker to its control plane, sensitive internal tables, e.g., MAC address tables. Security categories to consider are:

1. Distributed) Denial of Service
2. Address spoofing
3. Frame Tagging
4. VLAN Hopping
5. Anti Replay

Economic and technical efficiencies can be gained if the Ethernet aggregator platform is integrated with the other network devices, specifically, the provider edge router (PE) and the Broadband Remote Access Server (BRAS). The industry refers to these platforms as Multi-Service Edge Routers (MSER). Figure 2 shows the architectural simplification that can result from a consolidated platform relative to the network in figure 1.

Figure 2. Multi-Service Edge Router — Consolidated Metro Aggregation and Service Edge

In addition to simplifying the network architecture, a consolidated platform can

1. Reduce latency and increase performance by eliminating the need for inter-system communication.
2. Use common security features in one consolidated platform to reduce network susceptibility to attacks and failures.
3. Integrate subscriber management functions such as authentication, application session establishment, and billing into this platform can provide further resource efficiencies.
4. Use a single consolidate platform to do network management.

In general, price expectations are low for Ethernet services; therefore, providers must look to two parameters to make a profitable business case: economies of scale and product differentiation.

An integrated platform (MSER) can provide the economies of scale as each incremental resource, e.g., a single port, needed to service an additional set of customers can provide functionality for all three sub-platforms. In other words, increasing geographical reach and therefore, the number of customers will not require an exponential increase in purchasing additional resources [O(n) in new resources as opposed to O(n²)].

Service provider’s product differentiation is to provide verifiable SLAs to its customers. The integrated platform must be able to provide differentiation with QoS per application.

In a major project for a European service provider, the Redback SE800 platform proved the advantages of a consolidated platform vs. a three platform solution. The SE800 is a highly scalable consolidated platform that offers the functionality of a BRAS plus an Ethernet Aggregator and a PE router. It is a carrier-class platform that uses a highly available modular operating system with In Service System Upgrade to minimize network downtime and service disruption. This platform is highly scalable as it offers tens of thousands of VLANs, PPP sessions, and DHCP sessions. It solved all of the deficiencies that were present in the incumbent’s product. Some of benefits realized by the service providers were:

1. With a single platform, services can be provisioned, established and monitored faster. The SE800 can provide per subscriber policies, per subscriber accounting, and subscriber profiles across any access method.
2. With hardware redundancy, modular operating system and extensive provisions for network resiliency, the service provider owns a carrier-class operation.
3. Application-aware H-QoS scheme and the traffic management in SE800 MSER provide a high performance network that uses bandwidth resources in efficiently.
4. The service provider can map and multiplex each S-VLAN to be used for VPLS or L3VPN (2547bis) simultaneously. This feature saves resource consumption of VLAN assignment by 50%.