Multiplex communications – Fault recovery
Reexamination Certificate
1998-06-22
2002-04-02
Olms, Douglas (Department: 2731)
Multiplex communications
Fault recovery
C370S235000, C370S252000, C370S395430, C370S437000, C370S465000, C370S907000
Reexamination Certificate
active
06366556
ABSTRACT:
SUMMARY OF THE INVENTION
This invention relates generally to high speed digital telecommunications systems, to the creation of virtual rings in a network from existing circuits to provide shared protection for network path segments, to expanding the addressing capability of the SONET path overhead to address more nodes in a virtual ring, to distinguishing between network maintenance alarms from external to a virtual ring versus generated within a virtual ring, and to the use of a multiframe structure to carry more information.
BACKGROUND OF THE INVENTION
The telecommunications network servicing the United States and much of the world is evolving from analog transmission to digital transmission with ever-increasing bandwidth requirements. Fiber optic cable has proved to be a valuable tool of such evolution, replacing copper cable in nearly every application from large trunks to subscriber distribution plant. Fiber-optic cable is capable of carrying much more information than copper wire, with lower attenuation due to the wide bandpass of fiber optic cable.
It has become increasingly important to maintain communications connectivity in the presence of transmission system failures. To this end, various schemes have been implemented to provide automatic protection for failed network segments by temporarily bypassing such failed network segments.
The disruption of telecommunications services in a telephone network is typically caused by an inoperable communications path (link) or terminal equipment within a service providing office (node). Any disruption of such services can be very costly to business users who rely on telecommunications services in the important operation of their businesses. The duration of a service disruption is typically based on a number of factors, such as, for example, (a) the amount of time required to identify the location of the service disruption; (b) the amount of time that is used to identify one or more routes that could be used to provide at alternate route for affected traffic around the service disruption; and (c) the amount of time that is actually needed to establish such alternate routes. In dealing with a service disruption by selecting an alternate route around an inoperable link or service providing node, one goal is to select the most efficient alternate route, one having least number of nodes and links.
In the prior art a number of service restoration arrangements have been implemented to enhance the reliability of telecommunication networks by providing alternate routes established “on the fly” to temporarily replace inoperable network links or service providing nodes. Other prior art provide an established backup alternate route to temporarily replace inoperable network links or service providing nodes. In all these service restoration arrangements failed network links or service providing nodes are temporarily bypassed until the failed equipment or cables are repaired.
In today's self-healing networks, of the types outlined above, four forms of restoration are primarily used: 1) centralized, controller-based, (2) linear protection, (3) path-switched rings (or sub-network connections), and (4) line-switched rings. Because of their speed of restoration, rings tend to be the vehicle of choice. However, rings are not universally deployed for various reasons.
Centralized, controller-based restoration, which takes on the order of thirty seconds to several minutes to restore a faulty circuit, has the advantages of fine granularity and deployment without regard to ring structures. However, these centralized systems are usually coupled to operations systems for failure information, and need to be told when to revert. As the network grows, the controllers become more complex and costly, and are a potential processing bottleneck.
A second type of network protection is a linear arrangement wherein for every primary fiber optic cable in the network that is used to provide service, there is a dedicated, secondary, backup fiber optic cable that provides service in the event there is a fault with the primary cable. A switch over occurs when the signal path in the primary cable, or its terminating equipment, is deemed defective. This is one-hundred percent redundancy which is very expensive. Also, the primary and secondary fibers are typically routed in the same conduit, so a fiber cut likely causes both primary and secondary cables to simultaneously fail. Accordingly, linear protection is not widely used as a network protection scheme for inter-office facilities because of the bandwidth inefficiency and the high probability that both primary and secondary fibers could simultaneously fail.
A third and more commonly used type of network protection utilizes network rings. There are a few types of ring service restoration arrangements. In a first arrangement, called Uni-directional Path Switched Rings (UPSR), telecommunication signals are carried from an originating node to a terminating node through a primary network path comprised of links and intermediate nodes and, at the same time, the signals are carried between the originating and terminating nodes over an alternate ring topology path also comprised of links and intermediate nodes. If there is a failure anywhere in the primary network path or the alternate ring path, there is no loss of signal. This approach is also very expensive and not widely used for inter-office facilities because there is 100 percent redundancy. The primary advantage with this arrangement is there is no need for communications and switching to set up the alternate ring path, because that path is already connected and in use. Therefore, the switch times are on the order of milliseconds. Also, another advantage is that the switching granularity is at the SONET path level, or circuit level. Thus, some of the individual paths within the line can be switched independently based on the health of each signal.
Another type of ring based service restoration, entitled Bi-directional Line Switched Ring (BLSR), utilizes alternate, shared secondary ring bandwidth that is utilized only as needed to provide alternate routes to temporarily replace primary ring traffic due to inoperable network links or service providing nodes. When a fault is detected all primary ring traffic carried on the cable where the fault is detected is switched to the shared secondary alternate ring bandwidth. For example, with reference to
FIG. 1
, if a failure occurs between nodes E and F, the primary signals within the cable are looped back to node A. The alternate shared secondary bandwidth from node A to node B to Node C to Node D to Node F is utilized to restore the primary ring traffic. The main advantage of BLSR network protection is the shared protection bandwidth. Various primary paths around the ring may utilize the shared protection bandwidth. Therefore, due to the shared protection concept, there are many traffic distribution patterns around the ring that allow much greater bandwidth utilization than path switched rings. The switch times are still on the order of milliseconds, even though the shared protection path needs to be allocated to the appropriate primary signals. A major disadvantage of BLSR is the granularity which is at the SONET line level not circuit level.
Signals carried through fiber-optic cable networks are in accordance with the Synchronous Transport Signal Level (SONET) standard. SONET defines a hierarchy of multiplexing levels and standard protocols which allow efficient use of the wide bandwidth of fiber optic cable, while providing a means to merge lower level DS0 and DS1 signals in a common medium. In essence, SONET establishes a uniform, standardized transmission and signaling scheme which provides a synchronous transmission format that is compatible with all current and anticipated signal hierarchies. The basic SONET signal (STS-1) has a base rate of 51.480 Mb/sec.
The optical equivalent of STS-1 is called Optical Carrier level 1 (OC-1) and is used for transmission across fiber optic cable. The basic STS-1 signal transmissi
Ballintine James E.
Bordogna Mark A.
Kremer Wilhelm
Funk Joseph E.
Hom Shick
Lucent Technologies - Inc.
Olms Douglas
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