Abstract

The effective design of a metropolitan area network (MAN) is a critical issue for tier-one carriers, especially considering current requirement to increase bandwidth for new subscriber services. Various MAN architectures supporting low-cost and high-reliable broadband connections, interoperability with legacy equipment and so on have been proposed so far for the purpose of minimizing both the capital expenditure (CAPEX) and the operational expenditure (OPEX). A next-generation MAN is expected to provide the high-capacity and multi-service functionalities to the carriers in a cost effective manner while maintaining the legacy SONET/SDH level of performance and resiliency. An Ethernet network based on existing layer 2 switches is not suitable for the large scale carrier’s MAN because of the unexpected emergence of loops and the long reconfiguration time of the spanning tree protocol. On the other hand, resilient packet ring (RPR) technology discussed and defined in IEEE 802.17 WG [1] is one of the most promising candidates to satisfy these requirements [2]. Although the 622-Mb/s RPR “cutouts” within 2.5-Gb/s SONET/SDH ring systems are widely deployed, the limitation of a wire rate transportation for a Gigabit Ethernet (GbE) as well as the granularity of bandwidth allocation based on the STS-1 unit exist in the system. The next-generation MAN based on the RPR should be a packet-centric network with a flexible bandwidth allocation. The future services, such as an IP-based video multicast and a video on demand, that will emerge in the MAN have to coexist with the legacy services, such as a voice telephony and a TDM-based private line, that are migrated over to the new network. However, it is not enough for construction of the next-generation MAN just to introduce the standardized RPR technology. When considering the increase of traffic transported over a MAN, the introduction of 10-Gb/s RPR is indispensable and straightforward. A 10-Gb/s RPR solution had never previously been commercially deployed due to the several technical issues, such as large optical losses and multiple reflection points caused by many connection points of dark fiber. As carriers construct the MAN using existing installed fibers including dark fiber, it is necessary to verify the feasibility of the optical link on installed fibers, before an introduction of a 10-Gb/s RPR in the MAN.

© 2005 Optical Society of America