Metro edge networking with photonic layer systems

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By Robin Andrew

Demand for high-bandwidth Ethernet, video, and storage applications is accelerating, and a new market is developing for technologies that enable service providers (SPs) to efficiently connect these new services at the metro edge. An architectural approach based on an open photonic layer fits the unique needs of metro edge applications, enabling profitable connectivity of video on demand (VoD), FTTH, Gigabit Ethernet (GbE) and 10-GbE, and wireless services.

The fiber build-out in the late 1990s resulted in overbuilt capacity on long-haul and select regional networks. More recently, competition in the metro resulted in metro core builds, particularly core fiber rings connecting the same top tier one customers in tall shiny buildings. Now the long-forecasted growth in ultra-broadband services is really happening. Numerous new technologies and services are being deployed or planned for access networks that will deliver VoD, FTTH, GbE, 10-GbE, DSL, and other services.

But to address this growth and connect these services to existing fiber networks in the core, SPs must solve the connectivity gap at the metro edge (see Figure). This solution will connect new services over fiber from tier two customers within the metro and from customers located in new regional markets in distant vicinities.

The requirements of the metro edge are unique in the network. Whether it is a multiple systems operator (MSO) backhauling new VoD services from a distant hub to a private site or an ILEC requiring new capacity for increased DSL traffic, metro edge transport is driven by the need for simple cost-effective service connectivity. Specific requirements include:

• A traffic profile of straight backhaul to the metro core.

• Thin route connectivity; four to eight channels typically addresses existing services and future service growth needs.

• Optical reach of 100 km and beyond to reach outlying vicinities.

Management within the existing operational umbrella of core transport systems.

• Simple deployment; installation is typically by union labor with minimal training working at remote sites.

• Multivendor operability to seamlessly interwork with a wide range of core and access service platforms.

Until recently, systems providers typically chose among three options for metro edge transport: traditional SONET/WDM systems, direct optical ports on WAN and CPE (customer premises equipment) service nodes, and standalone optical solutions such as amplifiers and passives. None of these solutions is optimized to address the needs of the metro edge, however.Th 177816

While significant attention has been paid in the past to long-haul and metro core communications as well as the access network today, approaches to cost-effective communications at the metro edge have been slow in coming.

For example, traditional WDM and SONET transport systems include electrical aggregation features, transponders, high scalability, and wide-ranging topology support not typically required for the metro edge. This unnecessary complexity translates into higher footprint/power and cost, with a corresponding reduction in service margins.

Direct optical ports on WAN and CPE service nodes (Ethernet switches, routers, DSLAMs, etc.) offer direct connection but typically don’t reach the distance required. This approach also lacks the scale and flexibility required to optimize fiber usage for thin routes. Long-reach and WDM optical ports also can be expensive-and depending on the systems vendor selected, optical link engineering assistance may not be available.

The third current alternative, standalone subsystems such as media converters, amplifiers, or passive solutions, typically lack carrier grade management capability and do not scale well to meet the needs of the metro edge.

Conversely, a photonic layer approach is optimized for the needs of the metro edge. This system architecture is based on the philosophy of an open photonic layer that translates into space/power and cost savings for increased service margins. The characteristics of a photonic layer approach include:

No packet/protocol specific processing. Eliminates additional costs of electrical grooming, expensive transponders, or a centralized grooming matrix for optimal cost/service channel for straight optical backhaul.

Open ITU interfaces. With the rapid adoption of pluggable optics on CPE and WDM service nodes (Ethernet switches, routers, etc.), connectivity can now be done directly at ITU CWDM and DWDM wavelengths. That eliminates the cost of transponders on both the service node and transport solution. Why convert twice?

Architecture cost optimized for four to eight channels. Addresses optimal cost point for metro edge with additional scalability to 32 channels.

Integration of complete photonic functionality in a single platform. Includes amplification, signal conditioning, management, multiplexing, and wavelength conversion. This feature avoids the need for expensive external solutions such as standalone amplifiers.

To offer “deployability” and proper network fit in a carrier’s environment, the photonic layer approach meets several stringent criteria. For example, it provides carrier grade functionality, including environmental, safety, and operational requirements. It also offers service-platform node-independence. Open ITU interfaces enable connectivity with all service types and platforms: edge routers and switches, SONET multiservice provisioning platforms (MSPPs), wireless edge devices, etc. For legacy devices where ITU interfaces are not available, wavelength conversion enables connectivity at any optical interface.

A properly implemented photonic layer strategy also includes equipment with TL-1 and SNMP interfaces for seamless integration into third-party element and network management systems as well as remote operations through an optical supervisory channel. Finally, the photonic layer approach offers ease of deployment. Simple installation and commissioning means no complex training is required. The photonic layer architecture meets the “truck and turnaround” needs of the metro edge.

As SPs and MSOs roll out new data services to grow their revenues and maintain margins in a very competitive market, a photonic layer strategy can deliver the required capacity at a price point that guarantees a strong return on investment while leveraging their installed assets. Examples of how carriers have capitalized on the attributes of a photonic layer approach include:

SONET/SDH reach extension. Existing carriers often need to expand existing SONET/SDH core networks to deliver new private-line services to customers at the metro edge. Typical distances are 70 km and beyond. Interoffice or tributary interfaces facing the metro edge on metro core SONET/SDH platforms often are only available at 1310-nm wavelengths; if 1550 is available, the cost is often so prohibitive that direct fiber connectivity is not an option. A photonic layer system deployed with amplifiers and WDM multiplexers at the customer site and metro core site can extend the reach of multiple SONET/SDH links for typically 50% less cost than traditional transport equipment, resulting in an improvement in the carrier’s ROI of up to 100%.

VoD metro connectivity. MSOs are widely deploying VoD services to compete against the ILECs. Service connectivity requires backhauling VoD streams contained in GbE links from metro hub sites to a router at the headend. To deliver VoD profitably, MSOs are targeting a cost point of about $10 per video stream or $2,400 per GbE. Existing transport equipment based on traditional metro WDM results in a cost point of about $25 per stream. Deploying photonic layer equipment with WDM multiplexing at each end of the network for GbE transport results in a cost point of less than $5 per video stream.

Private-network Ethernet connectivity. Private enterprises, government organizations, and municipalities are widely deploying Ethernet WANs for high-bandwidth data connectivity and Internet access. Deployment of these networks results in Ethernet switches dispersed across the metro. Metro edge service connectivity requires connecting these sites and backhauling GbE and 10-GbE pipes to a central point of presence for Internet handoff. A photonic layer metro edge system provides a simple solution for Ethernet backhaul, with a system located at each site connected in an eight-channel ring. Ethernet connections are duplicated in each direction around the ring for resilient cost-effective backhaul. Traditional transport architectures based on NET/SDH and/or metro DWDM systems can be four times as expensive.

With widespread deployment of high-bandwidth new generation services in the access becoming a reality, service providers are facing the practical challenge of connectivity at the metro edge while maintaining service margins. Photonic layer systems optimized for the metro edge address this need, reducing capital and operational expenses to unlock the revenue potential of new voice, video, data, and storage services.

Robin Andrew is a strategic marketing consultant at BTI Photonic Systems (Ottawa, Ontario). She can be reached at randrew@btiphotonics.com.

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