Packet rings aim at metro nets, part 1
By Robert D. Love, President, LAN Connect Consultants, RPR Alliance Chair, Raleigh, N.C.
EE Times <http://www.eetimes.com> (01/30/01, 11:55 a.m. EST)
Resilient Packet Ring is a new technology that has been optimized for the unique requirements of metropolitan-area networks. This market is expected to grow faster during the next five years than that for long-haul equipment; one estimate, from research firm RHK Inc. (San Francisco), has it reaching $13 billion by 2003.
Although Sonet/SDH equipment represents the largest share of the metro-area network (MAN) market today, its underlying technology was designed for voice traffic and does not scale to the demands of data networks. In response to customer demands for a network that addresses the unique requirements of the MAN, a number of vendors have developed proprietary offerings. However, they understand that a standards-based solution is required and have worked within the IEEE 802 LAN/MAN Standards Committee to form a new working group, IEEE 802.17. It will create the IEEE 802.17 standard, Resilient Packet Ring (RPR).
IEEE 802.17 will define a media access control (MAC) protocol for use in local-, metropolitan- and wide-area networks, employing existing physical-layer specifications such as Gigabit Ethernet and 10 Gigabit Ethernet, as well as OC-48/STM-16 (2.5 Mbits/second) and OC-192/STM-64 (10 Gbits/s), for transfer of data packets at rates scalable to many gigabits per second.
Using predefined, standards-based physical layers will both speed up the standardization process and allow for the straightforward and seamless attachment of IEEE 802.3- and Sonet-based LANs to the RPR-based MAN. Creation of the new MAC layer, optimized for MAN traffic and topologies, will enable RPR to deliver cost-effective, quickly provisioned, secure and reliable data links on a service provider's existing fiber infrastructure. End users will be able to "turn up" bandwidth on demand at rates from 1 Mbit/s to 1 Gbit/s and beyond.
To understand the motivation behind RPR, it is useful to examine the primary needs of the emerging packet MAN networks. The demands of packet-based MANs can be grouped into five categories: survivability, fairness, scalability, performance and efficiency.
Survivability or resiliency describes the ability of the access network to withstand equipment and facility failures, maintaining connectivity between the subscriber and the network. While redundancy at the equipment level can protect against faults local to a node, faults at the line or facility level can only be protected by the underlying networking technology. Communication technologies that offer varying degrees of survivability include Sonet, LAN bridges and routers. With its ability to protect circuit traffic service within 50 ms of an outage, Sonet has set the bar for network resilience, restoring service 100 times faster than bridges and routers.
Fairness, the ability of the access network to allocate bandwidth in a manner that is consistent with its defined service policies, cannot be satisfied by the contention-based and best-effort methods used in traditional routed and switched networks. Fair bandwidth management and allocation must apply independent of where a subscriber connects to the network relative to other subscribers. In particular, a subscriber that is closer to the traffic's destination than other subscribers must not receive any advantage in network access despite a favorable upstream location.
The architecture for the new access network must be able to scale to thousands of endpoints and must support thousands of applications. The applications themselves will require bandwidth services that can scale from tens of kilobits per second to gigabits per second. Scalability is a critical requirement for the metropolitan network. The access network must be capable of adapting quickly and accommodating rapid growth in the number of network users and applications.
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