AT&T Turns to RPR for Metro MAN

A technology that gives Ethernet the capability to utilize metro ring topologies hits the spotlight as AT&T deploys its new Ultravailable Managed OptEring Service.

by Thor Olavsrud of internetnews.com [December 17, 2002]

Resilient Packet Ring (RPR), a small technology with broad implications, took the spotlight Monday when carrier AT&T said it would use it to push a cheaper and more scalable version of Ethernet for any-to-any Local Area Network/Metropolitan Area Network (LAN/MAN) interconnections.

The company also expects to eventually make it available for Wide Area Networks (WAN) as well.

AT&T's new Ultravailable Managed OptEring Service—currently undergoing a controlled introduction in New York City—utilizes RPR technology to offer efficient support for ring topology and fast data recovery.

Ring topology is often described as an expensive and difficult-to-install closed loop configuration of networked devices, so that each device is connected directly to two other devices, one on either side of it. They are useful for spreading high bandwidth near and far across a network.

RPR, well on its way to becoming an Institute of Electrical and Electronics Engineers (IEEE) standard (the IEEE advanced the IEEE 802.17 technical specification to working group ballot on Nov. 22, 2002), is a Layer 2 data link protocol which provides media access control (MAC) for packets transported over a ring topology.

AT&T said the new service would allow businesses with multiple locations in a metropolitan area or campus environment to interconnect the sites as a private or virtual local area networks, and would give customers highly available transport of data, packet video, and voice over ring topologies.

This, in turn, allows AT&T to provide applications such as storage, data mirroring and hosting in a virtual network environment. Businesses can also use the service for Internet access by connecting a business location to an AT&T POP.

AT&T's support may lend strength to the technology, which critics have predicted would never attract carrier attention.

The promise of RPR is to bring together legacy time-division multiplexing (TDM) and packet-data services, and to use metro fiber rings to transport voice, video, and data more efficiently than the two current approaches—Synchronous Optical Networks (SONET) and Ethernet—can handle alone.

A ring topology—which Ethernet was not designed to handle—uses sub 50 millisecond protection switching in case of a catastrophic event such as a fiber cut or link failure. With RPR as part of the protocol stack, Ethernet can handle ring topologies, allowing RPR to serve as a link that can combine the resilience and availability of SONET with Ethernet's simpler equipment stacks and lower costs.

In addition, RPR promises bandwidth multiplication through "spatial reuse." In other words, ring bandwidth can be reused for different traffic streams on separate parts of the ring. It also promises additional bandwidth-utilization efficiency through statistical multiplexing of traffic, while featuring LAN-like service provisioning.

AT&T plans to make that capability a selling point of the OptEring service, noting that spatial reuse of bandwidth within a fully meshed fiber infrastructure will allow businesses greater fiber utilization on fewer service channels. The company also noted that customers will be able to use Ethernet and TDM services on the same network infrastructure.

The Ultravailable Managed OptEring service features up to a 99.999 percent service-level agreement, and supports transport at speeds of 10 Mbps, 100 Mbps, and 1 Gbps over fiber rings.

"The suite of AT&T optical Ethernet services responds to the challenges facing businesses today, including increasing bandwidth demands, convergence to IP, reducing network complexity and protecting their existing network investments," said Eric Shepcara, AT&T vice president for application integration networking.

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