Optical communications – Diagnostic testing
Reexamination Certificate
1999-12-23
2003-09-09
Pascal, Leslie (Department: 2733)
Optical communications
Diagnostic testing
C398S059000, C398S045000, C370S222000, C370S223000
Reexamination Certificate
active
06616350
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of data transmission, such as data transmission that may occur in an optical network. More particularly, it pertains to a method and apparatus for providing a more efficient use of the total bandwidth capacity in a synchronous optical network.
BACKGROUND OF THE INVENTION
Within the ever-evolving telecommunications industry, the advent of numerous independent, localized networks has created a need for reliable inter-network communication. Unfortunately, this inter-network communication is difficult to accomplish in a cost-effective manner due to differences in the digital signal hierarchies, the encoding techniques and the multiplexing strategies. Transporting a signal to a different network requires a complicated multiplexing/demultiplexing, coding/decoding process to convert the signal from one scheme to another scheme. A solution to this problem is SONET, an acronym for Synchronous Optical NETwork. It is an optical transmission interface, specifically a set of standards defining the rates and formats for optical networks. Proposed by Bellcore during the early 80s and standardized by ANSI, SONET is compatible with Synchronous Digital Hierarchy (SDH), a similar standard established in Europe by ITU-T. SONET offers a new system hierarchy for multiplexing over modern high-capacity fiber optic networks and a new approach to Time Division Multiplexing (TDM) for small traffic payloads. SONET has several advantages, including:
meeting the demands for increased network Operation and Maintenance (OAM) for vendors and users by integrating the OAM into the network, thus reducing the cost of transmission;
standardizing the interconnection between different service providers (Mid-Span Meet);
allowing the adding and/or dropping of signals with a single multiplexing process, as a result of SONET's synchronous characteristic.
The Synchronous Transport Signal (STS) frame is the basic building block of SONET optical interfaces, where STS-1 (level 1) is the basic signal rate of SONET. Multiple STS-1 frames may be concatenated to form STS-N frames, where the individual STS-1 signals are byte interleaved. The STS frame comprises two parts, the STS payload and the STS overhead. The STS payload carries the information portion of the signal, while the STS overhead carries the signaling and protocol information. This allows communication between intelligent nodes within the network, permitting administration, surveillance, provisioning and control of the network from a central location. At the ends of a communication system, signals with various rates and different formats must be dealt with. A SONET end-to-end connection includes terminating equipment at both ends, responsible for converting a signal from the user format to the STS format prior to transmission through the various SONET networks, and for converting the signal from STS format back to the user format once transmission is complete.
The optical form of an STS signal is called an Optical Carrier (OC). The STS-1 signal and the OC-1 signal have the same rate. The SONET line rate is a synchronous hierarchy that is flexible enough to support many different capacity signals. The STS-1/OC-1 line rate was chosen to be 51.84 Mbps to accommodate 28 DS1 signals and 1 DS3 signal. The higher level signals are obtained by synchronous multiplexing of the lower level signals. This higher level signal can be represented by STS-N or OC-N, where N is an integer. Currently the values of N are 1, 3, 12, 48 and 192. For example, OC-48 has a rate of 2488.320 Mbps, 48 times the rate of OC-1.
Existing optical networks can be formed by several inter-connected rings, each ring formed itself by several nodes connected to one another. In a Bi-directional Line Switched Ring (BLSR), there exists between every two nodes of the ring both working and protection bandwidth. In the situation where the working bandwidth fails, the protection bandwidth is used to perform data transmission. In the situation where both working and protection bandwidth fail, the data transmission is re-routed around the ring using the protection bandwidth available between the other pairs of nodes within the ring.
In a four-fiber BLSR, two lines connect neighboring nodes, a working line and a protection line. The working line provides the working bandwidth and the protection line provides the protection bandwidth. Each line is formed of two fibers, one for each direction of traffic flow. Thus, the working line includes a send working fiber and a receive working fiber, while the protection line includes a send protection fiber and a receive protection fiber. The term “bi-directional” of BLSR refers to the fact that if one fiber of the working line fails, or if a piece of equipment to which one fiber of the working line is connected fails, traffic for both directions is re-routed. Specifically, if a working line suffers a data transmission impairment, either a fiber failure or an equipment failure, a span switch allows the protection line to be used as an alternate route of transmission. If both the working line and the protection line fail (link failure), or should there be a node failure, a ring switch allows for the data transmission to be re-routed around the ring via the other nodes in the ring network, specifically over the different protection lines. Both the span switch and the ring switch are different forms of protection switching.
Optical networks such as the BLSR are no longer used simply to transmit voice data, but rather are now carrying more and more pure data such as Internet traffic in addition to voice data. Network users are demanding greater bandwidth capacity and are requiring less and less protection of the data transmissions, due to the very nature of the Internet, within which routers take care of re-routing traffic when failures occur.
One solution to provide greater bandwidth capacity currently in implementation is the use of stacked overlaid BLSRs. For each node within a BLSR, a second (sister) node is installed at the same site. The two nodes at each site are inter-connected using new fibers and exchange complicated signaling control information. In addition, the new nodes are all inter-connected by a second ring using new fibers, thus forming a second, stacked ring. Unfortunately, this solution is very expensive to implement and is still limited with respect to the amount of working bandwidth available to customers, due to the reservation of one protection fiber for each working fiber.
Another solution is the implementation of a mesh network, in which any one node may be connected to any other node of the network. Although this solution is theoretically proven to be less expensive to implement than a BLSR and to provide greater bandwidth capacity to network users, it becomes very complicated to provide an adequate level of protection within the mesh network.
The background information provided above clearly indicates that there exists a need in the industry to provide a method and apparatus for increasing the degree of utilization of the total available bandwidth in optical networks such as to either transmit more data or reduce the infrastructure necessary to transmit the same amount of data.
SUMMARY OF THE INVENTION
The present invention provides in one aspect a local node for use in a synchronous optical network ring. The local node includes a group of working transmission lines for exchanging data with a remote node in the network, and a single protection line associated with the group of working transmission lines for exchanging data with the remote node in the event of a data transmission impairment on any one of the working transmission lines. The node is operative to monitor the working transmission lines and, upon detection of a transmission impairment over any one of the working transmission lines, invoke a protection switch event whereby the traffic normally sent over the working transmission line that suffers the impairment is re-routed over the protection line. This protection switch e
de Boer Evert
Olajubu Joseph
Paré Louis R.
Phelps Peter W.
Ryan Darryl C.
Nortel Networks Limited
Pascal Leslie
Payne David C.
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