Introduction

Now, with broadband multimedia services finally starting to roll out, the reality of what the broadband revolution means for service providers is rapidly becoming apparent. The impact of broadband multimedia services on the network will be enormous, with the greatest impact being felt by the metro optical transport network. The sheer volume of users and services, and huge increases in bandwidth, dictate a whole new approach to network planning. Support for emerging consumer broadband services, combined with high-speed business interconnection services, will require an incredibly flexible infrastructure, particularly since the rate of service penetration and market adoption is unpredictable.

Service providers will need an optical infrastructure that enables them to adapt to demand as it emerges, to add new services, and to increase bandwidth to existing services, all without impacting the ongoing operations of the network. They must be able to add nodes or modify services and technologies on existing nodes, so they can reach new customers and roll out new services quickly-again, all without impacting ongoing network services. Even the nature of the traffic will be changing over time. Initially, it is expected that the bulk of traffic will be generated by broadcast and multicast services (such as IPTV or pay per view). Increasingly, this will be overshadowed by interactive services, such as video on demand (VoD), gaming, and high-definition personal videoconferencing. At the same time, legacy services must be accommodated on the new infrastructure to maintain existing customers and revenues.

Service providers need to have in place an extremely flexible infrastructure-the solution being implementation of an infrastructure now that will continue to serve the broadband market needs over the next 10 to 15 years. This infrastructure shouldn't force the service provider to commit to a single technology or single topology. The market is far too dynamic for that. The ideal infrastructure is one that has been designed from day one for maximum flexibility, growth, and reliability, and for that you need an agile, service-transparent infrastructure that can be fully managed end to end. For that, you need wavelength networking.

As reported in Network World, Verizon is planning network upgrades that will support new services such as optical virtual private networks (VPNs) and high-speed home networking as well as reduce data replication among multiple services. On its national optical network, Verizon is installing reconfigurable optical add/drop multiplexers (ROADMs) and plans to migrate to wavelength switching to support automated operations and provisioning, according to Mark Wegleitner, Verizon senior vice president and chief technology officer.

The New Architecture: Planning for Uncertainty

The future is uncertain, but it is possible to plan for it. The new infrastructure must enable service providers to do the following:

• Flexibly add bandwidth to existing services as well as add new services, without impacting existing services
• Rapidly and flexibly add new service distribution elements without impacting existing services
• Scale the networks in all directions-the number of customers and services, as well as the bandwidth required per customer or service
• Deliver all services reliably and extremely quickly, day in and day out, so customers have no reason to look elsewhere
• Manage the network end to end to ensure that all resources are being used to maximum efficiency

To satisfy all these requirements, service providers need a wavelength transport infrastructure, such as the one shown in Figure 1.

Figure 1:
Optical Layer Evolution

Metro Access

The first thing to consider in terms of the metro access network is the customer end: the network must be "access agnostic." In other words, the network must be able to accept input from any source: digital subscriber line access multiplexers (DSLAMs); multi-service access nodes (MSANs); fiber to the user, node, or home (FTTx); passive optical networks (PONs); multi-service provisioning platforms (MSPPs); or any other type of access device. The customer end is also a key contributor to the scalability issues: The number of end points accessing the network and the bandwidth required to service those end points is going to grow enormously as a result of increasing demand for broadband multimedia services. For example, consider what is required to support broadcast video services. In the past, networks were planned around the assumption that each user experienced a certain amount of downtime within any block of time. With broadcast services, the entire customer population can be plugged in at the same time, expecting non-stop service. Attempting to deliver this level of service with a traditional network would be cost prohibitive-if it were possible at all. Instead, service providers must look for a solution that has been purpose-built for this environment.

The solution chosen must be open and flexible, supporting all technologies, not just Ethernet. While Ethernet is undoubtedly the main traffic type now, other technologies could easily evolve in response to new and currently unknown requirements. Service providers need to ensure that their new infrastructure has the flexibility to adapt to whatever the future has in store. The new network should also support legacy technologies such as ESCON, FICON, Fibre Channel, SONET, and SDH over a unified infrastructure.

Service providers must also have complete flexibility in terms of topology. Support for multiple topologies is essential for deep penetration of fiber into the access network, which in turn enables service delivery close to the subscriber. Not only must the network support all topology options now (mesh, ring, linear), it must be possible to change and adapt topologies, as need dictates.

A wavelength-based infrastructure can meet all the access requirements. It provides the optical layer resiliency necessary to deliver non-stop services, which is essential for any service provider that wants to compete in the multimedia market. By supporting Gigabit Ethernet directly on wavelengths, the service provider can avoid unnecessary complexity and overhead. The wavelength infrastructure can handle the scalability requirements, even as growth goes from 1 to 2.5 Gbps per access point to 10 Gbps. A carrier-grade wavelength infrastructure enables the service provider to monitor the network end to end, to quickly deploy new service end points, and to optically switch and optically replicate wavelengths from a central management point. Ideally, network-planning tools will be available to help the service provider keep one step ahead as new services roll out and new markets develop.

Metro Core

Initially, due to the uncertainty of where services will be needed and which services will be in demand, service providers will likely opt for a centralized service delivery model in which the metro core acts as the sole service delivery point. This will enable service providers to control costs by limiting capital expenditures while service demand is building. However, the infrastructure must be adaptable and allow service providers to expand from the centralized model into a distributed network of service-delivery points as demand grows. Any adaptation of the network-including topology changes, additions and deletions of nodes, services, technologies, etc.-must be possible without disrupting ongoing services.

The bulk of the traffic handled in the core network will likely be Ethernet. However, like the access network, the core must be able to handle traffic from legacy systems. To enable the service provider to operate a single, unified infrastructure, the metro core network should also support the interconnection of large data centers and SANs. The ideal metro core network is based on flexible wavelength distribution and supports:

• 10 Gbps-based wavelength services today, with a planned migration to 40 Gbps
• N x 10 Gbps wavelengths today
• Multiplexing of 1 x GigE channels onto a single 10 Gbps wavelength
• Deployment of new service points, as well as reconfiguration and addition to existing end points in line with service demand
• Optical resilience, including the ability to manage the entire service-delivery architecture end to end, with features such as auto power balancing

Metro Switching

The only cost-effective way to get huge amounts of traffic from the access to the core is through switching. A new node, called the metro services switching point, provides switching and grooming of broadband multimedia services. Optical wavelength switching ensures service resiliency: a must for video (and voice) services. The switching point implements switching on an "as required" basis; service processing is only undertaken when it provides value. Otherwise, the traffic simply passes through the switch. The switch also offers course wavelength division multiplexing (CWDM) and dense wavelength division multiplexing (DWDM) termination. Optical media replication supports cost-effective distribution of broadcast multimedia content to multiple simultaneous end points, all with optical resiliency and speed.

To support broadband multimedia service delivery, multiservice switching is required for:

• Wavelengths, to provide:
  • Networking of wavelength services,
  • Frequency translation (CWDM/DWDM) and 3R, and
  • SONET/SDH to groom legacy traffic for local service delivery platforms.
• GigE, to provide:
  • Grooming for delivery to local service-delivery platforms,
  • Switching for Ethernet services, and
  • Short-haul data services, to provide managed networking for legacy services and eliminate the need for an overlay network.

With a unified service-delivery infrastructure, service providers can transport services from the access point through the core of the network, aggregating as appropriate to ensure maximum utilization of fiber. They can also plan and manage the network from end to end. Now, with the metro services switching point, they can switch traffic, which enables service providers to put optical services deeper into the network (i.e., closer to the customer).

Centralized Service Delivery

Centralized service delivery allows services providers to use the optical network to deliver services through to the customer service delivery point without requiring it to pass through multiple service-layer processing hops. This reduction in processing preserves the customer experience and increases the efficiency of the network.

Distributed Service Delivery

A distributed service-delivery model enables service providers to replicate multimedia streams at the optical layer. Doing replication as close to the service-delivery point as possible provides significant cost benefits. This distributed service-delivery model can be implemented reliably and cost-effectively over an optical wavelength infrastructure.

With models that support broadband multimedia services, the provider can be ready for anything the broadband revolution has in store. It's clear: Maintaining status quo is not an option. Service providers need an infrastructure than enables them to leverage optical scalability, resilience, and service assurance. They need to deploy optical wavelength networking deep into the access network and only undertake service-layer processing when it adds value. Above all, they need to be able to manage the network from end to end.

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