Packet transport network tech offers high reliability

NEC Corp. has developed packet transport network technologies for next-generation networks (NGNs), which enable construction of 10Gbps-class broadband MAN that deliver carrier-grade reliability, fast recovery and flexible network expandability.

Partly supported by Japan's Ministry of Internal Affairs and Communications (MIC), the new technologies consist of a resilient packet ring (RPR) card redundancy technology that enables swift fault recovery and highly reliable network systems, and an inter-link redundancy technology that enables expansion of highly reliable networks by connecting two ring-topology networks with multiple links.

Fault recovery features
RPR card redundancy technology and optimization of the packet forwarding mechanism between cards allow two cards to operate simultaneously, so that when one card fails, the other card takes over RPR card control, achieving network service continuity. In addition to guaranteeing highly reliable network equipment, the RPR card redundancy technology realizes a maximum client add/drop rate of up to 20Gbps during normal operation.

The inter-link redundancy technology, which allows multiple links between two ring-topology networks, provides rapid fault recovery in less than 50ms, protecting networks from fatal service interruption caused by trouble on inter-link connections. This new technology ensures highly reliable expansion of multi-ring networks.

Network carriers have started to introduce multiservice transport systems employing RPR technology for packet ring networks. The RPR technology realizes a high level of reliability in single-ring-topology applications by employing a failure recovery procedure. The procedure consists of packets being switched to either one of the two rings for transmission, where they are directed clockwise or anticlockwise to prevent failure. Such a system achieves fault recovery performance superior to Ethernet technology. However, as the protocols for reliable inter-link connection are not defined in the RPR, or other packet layer standards, it has been difficult to realize carrier-class reliability on networks consisting of multiple-packet RPR rings.

Next-gen networks
Although MANs are constructed with fault-tolerant multiple-ring topology, they have been designed for legacy telephone services. NEC's new technologies, which enable highly reliable network systems and the construction of flexible and scalable regional packet-optimized ring network infrastructure, are a significant step toward the realization of NGNs that provide various IP-based services including broadband video on demand, HDTV and fixed-mobile convergence. Once installed, the technologies facilitate easy expansion of networks by operators, in accordance with their needs, thereby enabling optimization of hardware and operational resource allocation and a reduction in initial network construction costs.

The two new technologies developed by NEC respond to strong market demand to enable network expansion that offers reliability equivalent to that of single ring-topology networks, and to enhance reliability of redundant duplicated cards for increased service capacity. In the future, the technologies are expected to achieve highly reliable packet transport networks, and strengthen NEC's existing product portfolio of multiservice transport platforms (transport systems).