Multiplex communications – Diagnostic testing – Fault detection
Reexamination Certificate
1998-05-29
2001-10-09
Vincent, David R. (Department: 2732)
Multiplex communications
Diagnostic testing
Fault detection
C370S537000
Reexamination Certificate
active
06301228
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to digital transmission networks and, more particularly, to embedded control of groups of individual signals transported through digital transmission networks.
BACKGROUND OF THE INVENTION
Digital transmission networks, such as those based on Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) standards, are used extensively for transporting broadband communications signals. In some applications, these broadband communications signals may include base rate signals, which are signals having a fundamental rate or structure. Base rate signals are typically combined with other similar base rate signals to create a higher rate and more complex signal. Using SONET as an example, a synchronous transport signal (STS-
1
) having a fundamental rate of 51.84 Mbps may be a base rate signal, and an STS-
12
signal may comprise twelve (12) individual STS-
1
signals to form a base rate signal group (BRSG) having a composite rate of 622.08 Mbps.
To achieve transmission efficiencies as well as other performance advantages, it is desirable in some applications to switch individual signals as a single, composite group rather than on an individual basis. For example, it may be advantageous to maintain equalized or uniform path delay for signals that are transported through a network. Moreover, it may also be desirable to perform group switching based on selected performance-related attributes, such as signal quality, which can be conveyed in the form of signal status for each of the signals. Building on the previous SONET example in a switching application, it may be desirable to switch the entire STS-
12
base rate signal group as a composite, higher rate signal through the network rather than individually switching each of the lower rate STS-
1
signals within that STS-
12
signal group. In the prior art, complex group switches are typically used for this purpose.
Complex group switches are known to have a complex switching structure comprising multiple, cascaded selection/switching stages with highly coupled and complex control structures. In order for the complex group switch to appropriately switch individual signals as a composite group, the signal status for each of the individual signals must be resolved to derive a group status at each particular selection/switching stage. This resolution of signal status adds excessive processing overhead which results in undesirable switching delays during signal transmission.
Out-of-band control techniques, which are typically used in prior art group switches to resolve group signal status, can also add further complexity to a group switch. For example, each selection stage in a prior art group switch will typically require its own complex control structure to provide group status information. The control structures for each selection/switching stage must also be closely coupled to preserve the group status as signals are transported through the stages. Additionally, an overall control structure may also be required to couple the control structures from each individual selection/switching stage along the transmission path. It is also known that the complexity of control increases significantly for configurations having distributed switching elements spanning multiple selection/switching stages.
SUMMARY OF THE INVENTION
Undesirable switching delays and other problems associated with complex control schemes used for group switching are substantially eliminated in accordance with the principles of the invention by computing a group signal status as a function of the signal status of individual signals in a group, embedding the group signal status in each of the individual signals in a group, and independently selecting each of the individual signals in a respective group as a function of the embedded group signal status using an elementary switch fabric. Although each individual signal in the group is independently selected, the individual signals are effectively switched as a composite group through the elementary switch fabric because the selection decisions are based on the same group signal status carried by each of the individual signals in a group. As such, all individual signals in the group are either selected or rejected together as a composite group.
In one illustrative embodiment, an independent signal monitor analyzes and reports the signal status of each individual base rate signal to a group status logic element which computes a group signal status for each respective base rate signal group. The group signal status is then embedded in the corresponding individual base rate signals by status encoding elements so that the group signal status propagates along with each of the individual base rate signals through the transmission path. At any point in the transmission path, the group signal status can be extracted from the individual base rate signals by status decoding elements. Control logic processes the decoded group signal status and provides the appropriate control signals to the elementary switch fabric to control the selection of the individual base rate signals. The elementary switch fabric is an m×n base rate signal selector switch comprising m individual base rate selectors capable of switching n base rate signal groups each having m channels. More specifically, each of the m individual base rate selectors corresponds to one of the m channels and selects a base rate signal for its channel from one of the n base rate signal groups. Because all individual base rate signals within a base rate signal group carry the same group signal status, the individual base rate selectors in the elementary switch fabric can perform the equivalent function of a group switch but without the complexity of prior art arrangements.
Although overhead is a factor in transmitting group signal status with each individual signal, improved switching efficiencies are achieved according to the principles of the invention by using a less complex control structure and a simpler elementary switch fabric as compared with prior art group switches. In particular, front-end processing logic is much simpler than in prior art complex group switches which have multiple selection stages and which require resolution of group status within each stage. Moreover, by encoding and propagating group signal status within each of the individual signals in a particular group, group signal status is locally available and directly extractable at each selection point in the transmission path. As a result, switching delays are avoided since derivation of signal status for each and every signal in the group is not required to formulate group signal status at each selection point.
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Bordogna Mark Aldo
Dietz Philip Sidney
Landry Joseph Elide
Towne Jeffrey Robert
Trested, Jr. Warren Clifton
Lucent Technologies - Inc.
Murgia Gregory J.
Vincent David R.
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