Path switched rings

Overview

This section describes the unidirectional path switched ring configuration available with Alcatel-Lucent 1665 DMX.

Purpose of path switched rings

The need to prevent service outage caused by network failure has created path switched ring applications. The path switched rings configuration provided by Alcatel-Lucent 1665 DMX is a self-healing network that automatically protects against service outages caused by cable cuts and equipment failures, which in turn protects customer traffic and increases revenue opportunity.

Alcatel-Lucent 1665 DMX path switched rings operate in an easily-managed, integrated, single-ended fashion. Restoration is fast and reliable. Complex network-level coordination is not necessary to restore traffic. Furthermore, bandwidth administration and network reconfigurations (for example, adding or deleting nodes) are simple because path switching does not require special time slot assignment rules.

Typical path switched ring application

A network that requires the majority of its traffic to be dropped at a single node is an ideal application for path switched rings. A typical access network, where most traffic is between the customer locations and a point-of-presence (POP) or end office, fits this mold. Such an application calls for reliable delivery between customers and POPs. In cases where a mixture of wideband and broadband services is required, an Alcatel-Lucent 1665 DMX path switched ring is ideal.

OC-3/12/48/192 path switched rings

The OC-3/12/48/192 path switched ring allows several remote sites to share the two-fiber ring facility back to the CO. Alcatel-Lucent 1665 DMX interfaces to the ring through the Main slots at the OC-3/12/48/192 rate and uses its programmable VT1.5/STS-1/STS-3c/STS-12c/STS-48c/STS-192c cross-connect capability. Path switching can be done on VT1.5, STS-1, STS-3c, STS-12c, STS-48c, , or STS-192c paths, or a mixture of these, and all can be added/dropped from the Alcatel-Lucent 1665 DMX path switched ring at any node. Using the ring's path protection scheme, time slots are reserved all the way around the ring. Cross-connections offer full flexibility in assigning signals between low-speed ports and the high-speed interface at each node. Alcatel-Lucent 1665 DMX can easily adapt to unpredictable growth at a ring node.

OC-3/12/48 UPSRs are supported on the low-speed (tributary) interfaces with the same characteristics as the high speed UPSRs described above. Alcatel-Lucent 1665 DMX supports path switching on STS-1, STS-3c, STS-12c, STS-48c, , or STS-192cand VT1.5 paths only.

Ring topology

The ring topology routes traffic between a CO site and a set of remote sites, or between multiple COs, while providing complete protection. In addition, only two OLIUs are needed per Alcatel-Lucent 1665 DMX, which provides a cost savings. Traffic can also be routed between remote nodes. The ring can start with as few as two nodes and grow to support many nodes through in-service node additions.

For protection against a CO failure, it may be desirable to include a second CO node in the ring. Alcatel-Lucent 1665 DMX's support for dual homing architectures allows all services to be routed to the alternate CO while the first CO is out of service.

Operation

The Alcatel-Lucent 1665 DMX OC-3/12/48/192 path switched ring operates as shown in Figure 3-23, Path switched rings. Traffic entering a path switched ring node is sent onto both rotations of the ring. At the receiving node, the signal having the highest integrity (based on SONET path information) is selected and dropped as outgoing traffic. At intermediate nodes, the traffic is "passed-through" without changing the SONET path information. The Alcatel-Lucent 1665 DMX VT1.5/STS-1/STS-3c/STS-12c/STS-48c/STS-192c cross-connect capabilities make the provisioning of add/drop and pass-through traffic quick and easy.

The self-healing nature of the path switched ring is shown in Figure 3-23, Path switched rings (b). In this case, the fiber failure between nodes C and D causes node C to switch from the counterclockwise ring to the clockwise ring, thus maintaining service between all nodes on the ring.

Figure 3-23: Path switched rings

Configuration advantage

Path switched rings are the industry standard for self-healing networks, providing reliable transport for access networks while accommodating almost any type of application.