1. A method comprising:
obtaining link quality to neighbor nodes for each node in a wireless multi-hop network;
iteratively removing a network element and determining alternative routes for each such removed network element; and
identifying critical network elements where inadequate alternative routes exist after network elements are removed.
2. The method of claim 1 wherein inadequate alternative routes are determined based on the ability of the network to provide service required by an application.
3. The method of claim 1 and further comprising creating an annotated graph of the nodes that identifies at least one critical network element.
4. The method of claim 1 and further comprising determining a quality of service for each alternative route.
5. The method of claim 4 wherein an alternative route is inadequate if the quality of service is below threshold required for at least one application being served by the network.
6. The method of claim 1 and further comprising building a list of nodes dependent on a removed network element to reach another node or gateway.
7. The method of claim 1 and further comprising assigning a criticality value to each node removed during the iteration as a function of the number of nodes left in the network that lack adequate alternative routes.
8. The method of claim 1 wherein a node is identified as critical if its failure adversely affects communications of at least one other node in the network below an acceptable quality of service level.
9. The method of claim 1 wherein a link between a pair of nodes is identified as critical if its failure adversely affects communications of at least one other node in the network below an acceptable quality of service level.
10. A computer system having computer executable code stored on a storage device to cause the computer system to execute a method, the method comprising:
evaluating for each network element in a wireless multi-hop network whether the network element is critical to adequate communications required by one or more nodes in the network; and
assigning a network element criticality value to each network element as a function of the number of nodes having inadequate communications should the network element fail.
11. The computer system of claim 10 wherein the computer system evaluates criticality of network elements by:
obtaining link quality to neighbors for each node in the wireless multi-hop network;
iteratively removing a network element and determining alternative routes for each such removed network element; and
identifying critical network elements where inadequate alternative routes exist after network elements are removed.
12. The computer system of claim 11 wherein inadequate alternative routes are determined based on the ability of the network to provide the service required by an application.
13. The computer system of claim 11, wherein the method further comprises:
determining a quality of service for each alternative route, wherein an alternative route is inadequate if the quality of service is below a threshold quality of service of an application being served by the network;
wherein a node is identified as critical if its failure adversely affects communications of at least one other node in the network below an acceptable quality of service level and wherein a link between a pair of nodes is identified as critical if its failure adversely affects communications of at least one other node in the network below an acceptable quality of service level.
14. A computer readable storage device having instructions stored thereon to cause a computer to execute a method, the method comprising:
obtaining link quality to neighbor nodes for each node in a wireless multi-hop network;
iteratively removing a network element and determining alternative routes for each such removed network element; and
identifying critical network elements where inadequate alternative routes exist after network elements are removed.
15. The computer readable storage device of claim 14 wherein inadequate alternative routes are determined based on the ability of the network to provide service required by an application.
16. The computer readable storage device of claim 14 wherein the method further comprises creating an annotated graph of the nodes that identifies at least one network element.
17. The computer readable storage device of claim 14 wherein the method further comprises determining a quality of service for each alternative route, wherein an alternative route is inadequate if the quality of service is below a threshold required for at least one application being served by the network.
18. The computer readable storage device of claim 14 wherein the method further comprises assigning a criticality value to each node removed during the iteration as a function of the number of nodes left in the network that lack adequate alternative routes.
19. The computer readable storage device of claim 14 wherein a node is identified as critical if its failure adversely affects communications of at least one other node in the network below an acceptable quality of service level and wherein a link between a pair of nodes is identified as critical if its failure adversely affects communications of at least one other node in the network below an acceptable quality of service level.
20. The computer readable storage device of claim 14 wherein at least one node is added to the wireless multi-hop network based on the identified critical network elements to reduce the number of identified critical elements.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An optical information reproducing apparatus comprising:
a laser source;
a first optical divider configured to divide a light beam emitted from the laser source;
a condensing optical system configured to focus on an optical information recording medium one of light beams divided at the first optical divider, the light beam being emitted from the laser source;
a variable focusing mechanism configured to cause a focus position of the light beam to be variable, the light beam being focused by the condensing optical system;
an interference optical system configured to cause signal light and reference light to optically interfere with each other, the signal light being focused on and reflected off the optical information recording medium, the reference light being obtained from the other of the divided light beams;
a splitting optical system configured to divide a coherent light beam at the interference optical system into a plurality of coherent light beams;
a plurality of detectors configured to individually detect the plurality of coherent light beams divided at the splitting optical system in a state in which phase relations are different from each other; and
a second optical divider configured to separate the plurality of coherent light beams into a first light bundle near an optical axis and a second light bundle in an edge portion and diverge the first and second light bundles so that the first and second light bundles are focused on the plurality of detectors,
wherein: a focus error signal is detected for the first light bundle; and
the focus error signal is used to control the variable focusing mechanism.
2. The optical information reproducing apparatus according to claim 1,
wherein: the second optical divider has a first light beam divider configured to further divide the first light bundle into at least two light bundles; and
a focus error signal is detected from at least one of the light bundles divided by the first light beam divider, and a readout signal is detected from the other of the light bundles.
3. The optical information reproducing apparatus according to claim 2,
wherein: the second optical divider has a second light beam divider configured to further divide the second light bundle into at least two light bundles; and
a tracking error signal is detected from at least one of the light bundles divided by the second light beam divider and at least one of the light bundles divided by the first light beam divider, and a readout signal is detected from the other of the light bundles divided by the second light beam divider.
4. The optical information reproducing apparatus according to claim 2,
wherein the light bundle divided by the first light beam divider satisfies R+1<R\u22121, where a light quantity of the light bundle used to detect a focus error signal or tracking error signal is R+1, and a light quantity of the light bundle used to detect a readout signal is R\u22121.
5. The optical information reproducing apparatus according to claim 3,
wherein the light bundle divided by the second light beam divider satisfies R+1<R\u22121, where a light quantity of the light beam used to detect a focus error signal or tracking error signal is R+1, and a light quantity of the light beam used to detect a readout signal is R\u22121.
6. The optical information reproducing apparatus according to claim 1, further comprising a third optical divider configured to divide the signal light,
wherein a focus error signal, a tracking error signal, or both are detected from one of the light bundles divided by the third optical divider.
7. An optical information reproducing apparatus comprising:
a laser source;
a first optical divider configured to divide a light beam emitted from the laser source;
a condensing optical system configured to focus on an optical information recording medium one of light beams divided at the first optical divider, the light beam being emitted from the laser source;
a variable focusing mechanism configured to cause a focus position of the light beam to be variable, the light beam being focused by the condensing optical system;
an interference optical system configured to cause signal light and reference light to optically interfere with each other, the signal light being focused on and reflected off the optical information recording medium, the reference light being obtained from the other of the divided light beams;
a splitting optical system configured to divide a coherent light beam at the interference optical system into a plurality of coherent light beams;
a plurality of detectors configured to individually detect the plurality of coherent light beams divided at the splitting optical system in a state in which phase relations are different from each other;
a second optical divider configured to separate the plurality of coherent light beams into a first light bundle near an optical axis and a second light bundle in an edge portion and diverge the first and second light bundles so that the first and second light bundles are focused on the plurality of detectors;
a third optical divider configured to divide the signal light; and
a selector configured to switch between a focus error signal acquired from the signal light divided by the third optical divider and a focus error signal acquired from the coherent light beam detected by the plurality of detectors,
wherein the variable focusing mechanism is controlled by switching between the focus error signals by the selector.