Segmentation-based hierarchical graph multicast protection method applied to elastic optical network

Abstract

The invention discloses a segmentation-based hierarchical graph multicast protection method applied to an elastic optical network, which belongs to the technical field of the elastic optical network, and comprises the following steps: detecting and updating the current network spectrum resource use state, and waiting for the arrival of a multicast service request in the network; after a multicast service request arrives, establishing a hierarchical graph, and judging a link weight on a link until a destination node of a multicast request source is judged to be reachable; then distributing a working multicast tree segment for the multicast request of which the route is successfully selected; and selecting a protection path for the multicast work tree after the multicast work segments are successfully selected, and finally releasing residual spectrum resources of work and protection channels used by the multicast service request. Experimental results show that the LGMP has higher spectrum efficiency than the MLPA.

Description

Technical Field

[0001] The present invention belongs to the technical field of elastic optical networks, and in particular relates to a segmented layered graph multicast protection method applied to an elastic optical network. Background Art

[0002] Elastic optical networks provide an economical, large-capacity, highly survivable and flexible transmission infrastructure with attractive prospects. Many countries have invested a lot of research funds, especially in various aspects of optical transmission networks (from devices to network architecture, prototype manufacturing, field testing, etc.). At present, many research results have been commercialized and have generated huge economic benefits. Most of the research on elastic optical networks focuses on unicast or multicast service routing and spectrum allocation issues, ignoring the protection of multicast services and the rational use of spectrum fragments to protect multicast services.

[0003] Existing spectrum defragmentation algorithms and their advantages and disadvantages:

[0004] Greedy defragmentation algorithm and SP defragmentation algorithm. Both methods use a rerouting strategy to transmit services in the minimum available frequency band. The SP algorithm reroutes services to the shortest service path, reducing the complexity of processing, but the processing effect is average. SMFL is a spectrum defragmentation algorithm based on link fragmentation. It proposes a link fragmentation degree evaluation function and selects the link with the highest degree of fragmentation for defragmentation based on the function. The algorithm complexity is low, but only a part of the network services are defragmented.

[0005] The iterative frequency band partitioning algorithm based on the descending order of the initial spectrum of the service, namely the IDA algorithm, sorts the services in the network in descending order of the initial spectrum of the service, and then transfers the services to the lowest spectrum that can carry the service. Because the underlying services block the business activities of higher levels, but after a cleanup, those services that hinder the higher levels will be transferred. At this time, the services that were originally unable to move will be transferred to other places, and these services will also be reorganized to reduce the spectrum fragmentation in the network. The algorithm is highly complex.

[0006] The number of connection requests on a certain frequency spectrum of the periodic aggregate spectrum defragmentation algorithm PAD and the triggered aggregate spectrum defragmentation algorithm TAD is defined as the channel density. The larger the channel density, the more connection requests there are in the spectrum at this level. The minimum gap is the minimum frequency band of each link in its optical path and the adjacent communication volume, and this minimum gap is used to estimate the traffic congestion on each frequency band. The channel density, minimum interval PAD and TAD algorithms are used to evaluate the scattered services, and the TAD algorithm is used to cluster the scattered services. At the same time, the PAD and TAD algorithms also reallocate the services to the least hop routing, thereby reducing the communication overhead.

[0007] Due to the dynamic creation and removal of services on the elastic optical network, many small spectrum blocks are generated. These small spectrum blocks are neither aligned nor continuous in the link, so they are called spectrum fragments. Spectrum fragments will reduce the utilization rate of network bandwidth resources, cause a large number of service interruptions, and affect the overall performance of the network. In order to maximize the utilization of the network's spectrum resources, it must be divided into blocks to reduce its spectrum fragmentation and thus improve network performance. Summary of the invention

[0008] The technical problem solved by the present invention is to provide a segmentation-based layered graph multicast protection algorithm, a segmentation-based layered graph multicast protection method applied to elastic optical networks with low service blocking and improved spectrum utilization.

[0009] Technical solution: In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0010] A segmented hierarchical graph multicast protection method applied to an elastic optical network detects and updates the current network spectrum resource usage status and waits for the arrival of a multicast service request in the network; after the multicast service request arrives, a hierarchical graph is established and the link weights on the links are determined until it is determined that the source and destination nodes of the multicast request are reachable; then a working multicast tree segment is allocated for the successfully routed multicast request; after the multicast working segment is successfully selected, a protection path is selected for the multicast working tree, and finally the remaining spectrum resources of the working and protection channels used by the multicast service request are released.

[0011] Furthermore, if the multicast service connection request is to establish a new connection, the current network spectrum resource usage status is detected and updated, and the service request in the network is waited for to arrive; if the multicast service connection request is to release an old connection, the resources occupied by the service connection request are released.

[0012] Furthermore, the link weight b l [i] represents the state of link el in the i-th spectrum slot. If the i-th spectrum slice on the link is occupied, the link weight of the link is set to b l [i] = ∞; if the spectrum slots from i to i+C-1 of the link are occupied, the link weight is also b l [i] = ∞; if the spectrum slots from i to i+C-1 of the link are idle and i+C is occupied, then the link weight b l [i] = 1, if the spectrum slots from i to i+C-1 of the link are idle, and at least i+C is also idle, then the link weight b l [i] = μ + m (μ > 1), where the value of m depends on how many idle spectrum slots there are after i + C-1.

[0013] Furthermore, after the hierarchical graph G1 is established, check whether the source and destination nodes of the multicast service are reachable based on the link status on G1. If so, allocate a working multicast tree segment to the multicast request. Otherwise, set i=i+1 and continue to establish the hierarchical graph G2, and calculate the link weight of G2 until the source and destination nodes of the multicast request are reachable.

[0014] Furthermore, the MPH minimum spanning tree algorithm is used to select the working multicast tree.

[0015] Furthermore, the selection of the multicast tree does not consider the link weight, but the link with a link weight of ∞ is unavailable. If the selection of the multicast working segment fails, the output service is blocked. If the selection of the multicast working segment succeeds, a protection path is selected for the multicast working tree.

[0016] Furthermore, the method for selecting a protection path for the multicast working tree is as follows: first, the links with link weight ∞ are removed from the topology, and the working segments are also removed from the topology. Then, the improved Dijkstra shortest path algorithm is performed for the source and destination nodes of the first multicast segment. The resulting list is the sum of the number of links passed by the source-destination nodes arranged from small to large. The sum of the link weights of all arrangements is calculated and sorted from small to large.

[0017] Furthermore, a path with the smallest link weight is selected as a protection path for the multicast segment.

[0018] Furthermore, if the destination node of a segment serves as the source node of the next segment, the improved Dijkstra shortest path algorithm is run between this node and the destination node of the second segment to find a suitable protection path. The sum of all arranged link weights is calculated and sorted from small to large to find a suitable protection path. This protection path shares resources with the protection path of the first protection path and also minimizes spectrum fragmentation.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0020] (1) The present invention converts the number of spectrum slots of a link into several hierarchical graphs and calculates the weight of each link in the hierarchical graph. The size of the link weight represents the usage of the spectrum slot. The present invention makes use of spectrum resources that are just enough to be used as much as possible to avoid the generation of spectrum fragments and reduce the service connection failure caused by spectrum fragments in the network.

[0021] (2) The algorithm designed by the present invention is simulated and analyzed with the existing traditional algorithm in a network topology diagram based on realistic assumptions. The experimental indicators are blocking rate and spectrum resource utilization. The experimental data show that the spectrum utilization of the LGMP algorithm is higher than that of the MLPA algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1is a flow chart of a segmentation-based layered graph multicast protection method applied to elastic optical networks;

[0023] Figure 2 This is a schematic diagram of the node pair traversal method of the improved Dijkstra shortest path algorithm;

[0024] Figure 3 is the network topology of the present invention;

[0025] Figure 4 is the current network spectrum status of the present invention;

[0026] Figure 5 It is a network topology diagram in which all target nodes of the present invention are unreachable.

[0027] Figure 6 It is a network topology diagram in which the target node of the present invention is unreachable.

[0028] Figure 7 It is the network spectrum occupied by the working tree of the present invention.

[0029] Figure 8 It is a network topology diagram for selecting the working tree and protection path of the present invention.

[0030] Fig. 9 It is a state diagram of the defragmentation of the present invention.

[0031] Fig.10 This is a comparison of the average blocking rates of the LGMP algorithm and the MLPA algorithm in the NSFNET network under different network loads.

[0032] Fig.11 This is a comparison of spectrum utilization between LGMP algorithm and MLPA algorithm in USNET network under different network loads. DETAILED DESCRIPTION

[0033] The present invention is further illustrated below in conjunction with specific examples. The examples are implemented based on the technical solutions of the present invention. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0034] The invention discloses a segment-based layered graph multicast protection method applied to an elastic optical network, which is implemented based on a segment-based layered graph multicast protection algorithm (LGMP).

[0035] Input: network topology G of elastic optical network, multicast request r = (s, D, C).

[0036] Output: Routing and spectrum allocation for multicast path protection in elastic optical networks.

[0037] The method of the present invention is specifically implemented in the following steps:

[0038] Step 1: Detect and update the current network spectrum resource usage status.

[0039] Step 2: Wait for the service connection request to arrive in the network.

[0040] If the multicast service connection request is to establish a new connection, go to step 3. If the multicast service connection request is to release an old connection, go to step 8.

[0041] Step 3: If a multicast service request arrives, go to step 4.

[0042] Step 4: Calculate the layered graph.

[0043] In order to simplify the process of finding working trees and backup segments in elastic optical networks, the present invention adopts a layered graph method, and the link weight b l [i] represents the state of link el in the i-th spectrum slot. If the i-th spectrum slice on the link is occupied, the link weight of the link is set to b l [i] = ∞, if the spectrum slots from i to i+C-1 of the link are idle and i+C is occupied, then the link weight b l [i] = 1, if the spectrum slots from i to i+C-1 of the link are idle, and at least i+C is also idle, then the link weight b l [i] = μ + m (μ > 1), where the value of m is determined by the number of idle spectrum slices after the spectrum slot i + C-1. If there are m idle spectrum slots after the spectrum slot i + C-1, then the link weight b l [i] = μ + m.

[0044] For a network G and a multicast request r = (s, D, C), a hierarchical graph LG is a set consisting of graphs LG = {G i ,i=1,2,3,...n}.

[0045]

[0046] Where s represents the source node, D represents the target node, and C represents the number of required spectrum slots.

[0047] After the multicast service request r = (s, D, C) arrives, the layered graph G is first established i ,i=1,2,3,...n,layered graph G iThe establishment of is determined according to the status of the current network spectrum resources. First, let i = 0. If the i-th spectrum slice on the link is occupied, the link weight of the link is set to ∞; if the spectrum slots from i to i+C-1 on the link are occupied, the link weight is also b. l [i] = ∞; if the spectrum slots from i to i+C-1 of the link are idle and i+C is occupied, the link weight is set to 1; if the spectrum slots from i to i+C-1 of the link are idle and at least i+C is also idle, the link weight is set to μ+m (μ>1), where the value of m is determined by the number of idle spectrum slices after spectrum slot i+C-1. If there are m idle spectrum slots after spectrum slot i+C-1, the link weight is set to μ+m. After the link weight is updated, go to step 5.

[0048] Step 5: Based on the established hierarchical graph G i The link status and link weight on the multicast service are used to determine whether the source and destination nodes of the multicast service are reachable, and step 4 is repeated until the source and destination nodes of the multicast request are reachable.

[0049] After the layered graph G1 is established, check whether the source and destination nodes of the multicast service are reachable based on the link status on G1. If so, jump to step 6. Otherwise, set i=i+1 and continue to establish the layered graph G2. Calculate the link weight of G2 and repeat step 4 until the source and destination nodes of the multicast request are reachable.

[0050] Step 6: Allocate working multicast tree segments for successfully routed multicast requests

[0051] Layered graph G i If the multicast service can be successfully routed, a working multicast tree segment is allocated for the multicast request. The working multicast tree is selected using the MPH minimum spanning tree algorithm. In order to reduce the algorithm complexity and service blocking rate, the multicast tree is selected without considering the link weight. However, links with a link weight of ∞ are not available. If the multicast working segment selection fails, the output service is blocked. If the multicast working segment selection is successful, go to step 7.

[0052] Step 7: After the multicast working segment is successfully selected, a protection path is selected for the multicast working tree.

[0053] The multicast working segment is successfully selected. Next, the protection path is selected for the multicast working tree. First, the links with link weights of ∞ are removed from the topology, and the working segment is also removed from the topology. Then, the improved Dijkstra shortest path algorithm is run for the source-destination node pair of the first multicast segment. The resulting list is arranged from the sum of the number of links passed by the source-destination nodes from small to large. The sum of the link weights of all arrangements is calculated and sorted from small to large. The path with the smallest link weight is selected as the protection path of the multicast segment. In order to achieve the sharing of protection resources, if the destination node of a segment is used as the source node of the next segment, the improved Dijkstra shortest path algorithm is run between the node and the destination node of the second segment. The sum of the link weights of all arrangements is calculated and sorted from small to large to find a suitable protection path. This protection path and the protection path of the first protection path achieve resource sharing and minimize spectrum fragmentation.

[0054] The present invention adopts an improved Dijkstra shortest path algorithm, which essentially finds all link-disjoint paths for each pair of nodes according to link weights, thereby providing multiple options for sub-band routing and balancing network loads.

[0055] Define the link weight w, the link distance is h (km), [x] is the smallest integer not less than x, then the link weight is defined as:

[0056] W = [h% 10]

[0057] The network node is defined as n i , i=1,2,3...., the link between two nodes is defined as The link distance between two nodes is The weight is Define two node sets P and Q.

[0058] The improved Dijkstra shortest path algorithm is as follows:

[0059] Step 7.1: First, let set P = {n1}, set Q = {n2, n3, n4...}.

[0060] Step 7.2: If Figure 2 The figure shows the traversal method of node pairs. First, let i=1, j=2.

[0061] Step 7.3: n i and n j As a node pair (i, j), link weights are calculated for all links according to the formula W=[h%10], and a path with the smallest sum of link weights between the node pair (i, j) is found.

[0062] Step 7.4: Delete the path found in step 3 from the topology map, update the topology map, and add the path to the path list of node pair (i, j). Continue to find the link with the smallest weight sum from the updated topology map, delete it from the topology map, and add the path to the path list of node (i, j). Repeat the above steps until all link-disjoint paths between node pair (i, j) are added to the path list of node pair (i, j).

[0063] Step 7.5: Restore the initial topology, set j = j + 1 and repeat steps 7.3 to 7.5 for node pairs n1 and n3, n1 and n k Update the path list of nodes (1,3)...(1,k).

[0064] Step 7.6: If Figure 2 Delete n1 from set P and move n2 from set Q to set P, that is, P = {n2}, Q = {n3, n4...}, then let i = i+1, j = j+2 and repeat steps 7.3 to 7.5 until all paths for all node pairs are found.

[0065] Step 8: Finally, release the remaining spectrum resources of the working and protection channels used by the multicast service request.

[0066] When a connection release request arrives, the resources occupied by the service connection request are released, the remaining spectrum resources of the working and protection channels used by the request are released, and the process goes to step 2.

[0067] In order to describe the algorithm of the present invention in detail, an example is given. The network topology diagram is as follows Figure 3 As shown in Figure 2, the current spectrum status of the topology is as follows: Figure 4 As shown in the figure, assume that there are 7 spectrum slots on each link, where the gray shaded part indicates the occupied state, and the green diagonal part indicates the spectrum occupation state currently used as protection resources. Before each request arrives, check the spectrum resource status of each link. The current spectrum resource occupation status of the network topology is as follows: Figure 4 shown.

[0068] When a multicast request r = (A, {B, D}, 2) arrives, the hierarchical graph G1 is first established. Figure 4 The occupancy of spectrum slice No. 1 in the layered graph G1 is used to update the weights of each link. The topology graph after link weights are updated is as follows: Figure 5 , the source node is node A, and the weights of the links adjacent to node A are all ∞. At this time, all destination nodes are unreachable, so it is impossible to successfully select the working path and the corresponding protection path for the multicast request.

[0069] Next, the layered graph G2 is established, and the weights of each link in the layered graph G2 are updated according to the spectrum occupancy status. Figure 6 As shown by Figure 6 It can be seen that the weights of the links adjacent to the destination node D are all ∞. Since the links with weight ∞ are unreachable, there is no path to reach node D.

[0070] Then, the layered graph G3 is established, and the weights of each link in the layered graph G3 are updated according to the spectrum occupancy status. Figure 7 As shown, the black bar shadow is the spectrum resource occupied by the working path. First, the links with infinite weight are removed from the topology, and the multicast working path of the multicast request is found according to the MPH algorithm. As shown in the figure, the working segments are AB and AFD.

[0071] After the working segments are determined, protection paths are sought for each segment. Figure 8 First, find protection resources for the working segment AB, run the improved Dijkstra shortest path algorithm between AB, select the first three segments (the value of k in this section is 3) of reachable paths from the list, calculate the link weights and of these three paths respectively, and select the path AGB with the smallest sum as the protection path for segment AB.

[0072] Next, we search for protection resources for the working segment AFD. The algorithm uses the SRLG algorithm (one implementation method can be found in the third issue of "Journal of Photonics", 2007, "Research on SRLG-based Unrelated Shared Protection Algorithm", Zhang Pei et al., 2007-07-09), and shares protection resources with the protection path AGB of AB. Therefore, we only need to select the path with the smallest link weight between nodes BD as BICD, so the protection path of the segment AFD is AGBICD. If the path selection between nodes BD fails, the improved Dijkstra shortest path algorithm is run between AD, and the first three reachable paths are selected from the list. The link weights of these three paths are calculated respectively, and the path with the smallest sum is selected. Fig. 9 The algorithm selects working paths and protection paths for multicast services while sorting out spectrum fragments in the network.

[0073] The spectrum allocation technology used in elastic optical networks strictly follows the following bandwidth constraints: (1) Spectrum continuity constraint: the spectrum positions assigned to the service request must be aligned on all links in the routing path where the service request is located; (2) Spectrum adjacency constraint: when assigning spectrum resources to a service request, the gaps in each link must be adjacent and identical; (3) Spectrum non-overlapping limit state: when the service has not left the network, the spectrum resources assigned to the service request cannot be assigned to a new service.

[0074] The present invention converts the number of spectrum slots of a link into several hierarchical graphs, calculates the weight of each link in the hierarchical graph, and the size of the link weight represents the usage of the spectrum slot. The present invention makes use of spectrum resources that are just enough to be used as much as possible, avoids the generation of spectrum fragments, and reduces service connection failures caused by spectrum fragments in the network.

[0075] The segmented layered graph multicast protection method applied to elastic optical networks of the present invention conducts simulation experiments and analyses on the designed algorithm in a network topology graph based on realistic assumptions and with existing traditional algorithms, and the experimental indicators are blocking rate and spectrum resource utilization.

[0076] like Fig.10 The figure shows the comparison of the average blocking rate between the LGMP algorithm and the traditional multicast light-tree protection algorithm (MLPA algorithm) in the NSFNET network under different network loads. Fig.11 The figure shows the comparison of spectrum utilization between LGMP algorithm and MLPA algorithm in USNET network under different network loads. Fig.10 As shown in Figure 2, the LGMP algorithm and the MLPA algorithm have similar effects in terms of service blocking rate. Fig.11 As shown, when the multicast service request D=2.3.4 is compared respectively, the spectrum utilization rate of the LGMP algorithm is higher than that of the MLPA algorithm. Therefore, the above data results show that the method of the present invention is equivalent to the conventional algorithm used in the prior art in terms of service blocking rate, but has a higher spectrum utilization rate, and the spectrum utilization rate is higher than that of the traditional multicast light tree protection algorithm.

[0077] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A segment-based layered graph multicast protection method for elastic optical networks, characterized in that: Detect and update the current network spectrum resource usage status, and wait for the arrival of multicast service requests in the network; after the multicast service request arrives, establish a hierarchical graph and determine the link weights on the links until it is determined that the source and destination nodes of the multicast request are reachable; Then the successfully routed multicast requests are assigned working multicast tree segments; After the multicast working segment selection is successful, a protection path is selected for the multicast working tree, and finally the remaining spectrum resources of the working and protection channels used by the multicast service request are released.

2. The segment-based layered graph multicast protection method for elastic optical network according to claim 1, characterized in that: If the multicast service connection request is to establish a new connection, the current network spectrum resource usage status is detected and updated, and the service request in the network is waited for to arrive; if the multicast service connection request is to release an old connection, the resources occupied by the service connection request are released.

3. The segment-based layered graph multicast protection method for elastic optical network according to claim 1, characterized in that: Link weight b l [i] represents the state of link el in the i-th spectrum slot. If the i-th spectrum slice on the link is occupied, the link weight of the link is set to b l [i] = ∞; if the spectrum slots from i to i+C-1 of the link are occupied, the link weight is also b l [i] = ∞; if the spectrum slots from i to i+C-1 of the link are idle and i+C is occupied, then the link weight b l [i] = 1, where C represents the number of spectrum slots required. If the spectrum slots from i to i+C-1 of the link are idle, and at least i+C are also idle, then the link weight b l [i] = μ + m (μ > 1), where the value of m depends on how many idle spectrum slots there are after i + C-1.

4. The segment-based layered graph multicast protection method for elastic optical network according to claim 1, characterized in that: When the hierarchical graph G1 is established, check whether the source and destination nodes of the multicast service are reachable based on the link status on G1. If so, assign a working multicast tree segment to the multicast request. Otherwise, set i=i+1 and continue to establish the hierarchical graph G2, and calculate the link weight of G2 until the source and destination nodes of the multicast request are reachable.

5. The segment-based layered graph multicast protection method for elastic optical network according to claim 1, characterized in that: Use the MPH minimum spanning tree algorithm to select a working multicast tree.

6. The segment-based layered graph multicast protection method for elastic optical network according to claim 5, characterized in that: The selection of the multicast tree does not consider the link weight, but the link with a link weight of ∞ is unavailable. If the selection of the multicast working segment fails, the output service is blocked. If the selection of the multicast working segment succeeds, a protection path is selected for the multicast working tree.

7. The segment-based layered graph multicast protection method for elastic optical network according to claim 1, characterized in that: The method for selecting a protection path for a multicast working tree is as follows: first, remove the links with a link weight of ∞ from the topology, remove the working segments from the topology, and then run the improved Dijkstra shortest path algorithm for the source and destination nodes of the first multicast segment. The resulting list is the sum of the number of links passed by the source-destination nodes arranged from small to large, and calculate the sum of the link weights of all arrangements and sort them from small to large.

8. The segment-based layered graph multicast protection method for elastic optical network according to claim 7, characterized in that: The path with the smallest link weight is selected as the protection path for the multicast segment.

9. The segment-based layered graph multicast protection method for elastic optical network according to claim 8, characterized in that: If the destination node of a segment serves as the source node of the next segment, the improved Dijkstra shortest path algorithm is run between this node and the destination node of the second segment. The sum of all arranged link weights is calculated and sorted from small to large to find a suitable protection path. This protection path shares resources with the protection path of the first protection path and also minimizes spectrum fragmentation.

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