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Optical Ethernet redefines access

Posted: 01 May 2001 ?? ?Print Version ?Bookmark and Share

Keywords:ethernet? dhcp? lan? dns? vlan?

If the past is any indication, Ethernet will be a formidable competitor for access technology in a field currently dominated by a variety of point-to-point protocols.

Carriers and ISPs have been using Ethernet for years for building their internal networks. But recently, Ethernet has started to be the technology of choice for the distribution of network services to enterprises, individuals or other carriers and providers of various services.

In the latter role, the service is frequently referred to as optical Ethernet and is much more than just Ethernet in the fiber; it is an entire infrastructure.

Optical Ethernet can be defined as a switched optical LAN segment that can be used as the basis for many retail and wholesale services. Retail is defined here as enterprise access connectivity; wholesale is defined as interconnection within a service provider's own network or with other service providers' locations.

To the end user, optical Ethernet still looks like the familiar switched Ethernet LAN and certainly operates like one. But important differences appear on closer examination. The optical Ethernet LAN segment does not have physical distance limitations. It can span sites miles apart. It is more reliable than a typical LAN put together from standard switches and fiber. It has built-in, consistent traffic prioritization, bandwidth control and reporting models. It comes with a set of desirable network services, such as dynamic host configuration protocol (DHCP), domain name system (DNS) and traffic encryption. It does not need servicing or maintenance on the end-user side.

The simplicity on the end-user side and the flexibility on the service-provider side are possible thanks to a concept best described as an optical Ethernet virtual private network (OE VPN). Optical Ethernet VPNs are based, in part, on the concept called the virtual LAN (VLAN). The optical Ethernet VPN brings the notion of privacy to VLANs by separating, and optionally encrypting, traffic that belongs to different users.

A number of important improvements over VLAN make optical Ethernet VPNs suitable for carriers and service providers. The most notable are scaling, long reach and reporting.

Optical Ethernet VPNs are built using a collection of switched Ethernet segments designated for the service. Those segments are not offered directly to the end users but are used solely to create a uniform transport domain for the optical Ethernet service. The transport domain is fully redundant and features advanced mechanisms for quick failure recovery and no-hit maintenance and reconfiguration. For the end user, it simply appears as a very robust and trustworthy Ethernet segment.

The optical Ethernet VPN service is not limited to native Ethernet-over-fiber networks. Thanks to the resilient packet ring (RPR) technology, optical Ethernet can take advantage of the existing Sonet ring infrastructure, originally built for voice traffic.

RPR can convert a Sonet ring into a distributed Ethernet segment, where the ring becomes the logical backplane interconnecting distributed Ethernet ports. With these capabilities, RPR effectively allows a second level of traffic aggregation to increase the utilization of the fiber backbone network.

This is important for two reasons: It allows easy deployment in the existing metro networks while coexisting with voice; and it provides an on-ramp allowing long-haul optical backbones to increase their utilization with high volumes of revenue-generating Ethernet traffic. Suddenly, Ethernet has no geographical limits.

RPR can use all the bandwidth within a Sonet ring, or it can use only a fraction of it and leave the rest to traditional voice. RPR also makes the Sonet network dramatically more efficient in throughput through advanced aggregation techniques such as spatial reuse, which allows the destination to drain the Ethernet frames from the Sonet time slots. It allows for the normally unused protection path to be used.

Finally, RPR creates a fast-healing Ring Protection Protocol at Layer 2 to maintain the fast 50ms fail-over expected in ring networks. Through these techniques, RPR adds an order-of-magnitude more capacity than other techniques, which simply encapsulate Ethernet in Sonet time slots for transport over the ring.

To support scaling beyond tens of thousands of end-user devices connected to an optical Ethernet-based network, Layer 3 switches can be deployed to segment the network into routed domains. Unlike traditional Internet Protocol-based services with distributed-routing complexity, these switches can be at central offices or at data centers within a service provider's network. In an optical Ethernet service-provider infrastructure, these switches can be used as bandwidth exchanges or Ethernet cross-connects, interconnecting Ethernet circuits at wire speed through the service provider's core.

? Waldemar Augustyn

Nortel Neworks

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