CN108184175B

CN108184175B - MC node limitation-based elastic optical network multicast routing and spectrum allocation method

Info

Publication number: CN108184175B
Application number: CN201711482743.7A
Authority: CN
Inventors: 何阿成; 石鹏涛
Original assignee: Chongqing University of Post and Telecommunications
Current assignee: Chongqing University of Post and Telecommunications
Priority date: 2017-12-29
Filing date: 2017-12-29
Publication date: 2020-09-22
Anticipated expiration: 2037-12-29
Also published as: CN108184175A

Abstract

The invention relates to a MC node limitation-based elastic optical network multicast routing and spectrum allocation method, belonging to the field of optical fiber communication systems. The method comprehensively considers the factors of multicast modulation format, the number of Multicast Capability (MC) nodes in the network, multicast node selection and the like, provides an effective multicast routing and spectrum allocation algorithm (PSPT-DMRSA) for pre-calculating the shortest path tree, selects proper MC nodes in the network in advance before multicast routing, and then establishes a minimum spanning tree for the selected MC nodes so as to reduce the number of links occupied by the whole multicast request. The invention adopts the distance self-adaptive modulation mode when the frequency spectrum resources are distributed, selects the proper modulation mode for the multicast request, improves the utilization rate of the frequency spectrum resources and reduces the network blocking rate.

Description

MC node limitation-based elastic optical network multicast routing and spectrum allocation method

Technical Field

The invention belongs to the field of optical fiber communication systems, and relates to an MC node-limited elastic optical network multicast routing and spectrum allocation method.

Background

The rapid growth of global communications and the popularity of the internet have significantly changed our lifestyles, and this revolution has resulted in a tremendous increase in communication bandwidth each year. To meet the future internet needs, optical transmission technologies are developing towards the goals of high efficiency, flexibility and scalability. The concept of spectrum sliced Elastic Optical Networks (SLICE) was first proposed by NTT corporation of japan in 2008. The SLICE as a novel, high-spectrum-efficiency and expandable optical transmission network system architecture can provide a sub-wavelength service channel and a super-wavelength service channel, and meets the requirements of dynamic and efficient bandwidth service. The SLICE network breaks through the limit of a fixed grid in the traditional WDM network, and utilizes the O-OFDM signal modulation technology to carry out spectrum allocation and subcarrier multiplexing, so that the network utilization efficiency is greatly improved compared with the DWDM-based optical network. In addition, in resilient optical networks, certain transmission parameters fixed in the currently deployed network will become adjustable, such as signal rate, modulation format and channel spacing. In recent years, elastic optical networks have been determined by the industry as the direction of future optical communication network technology evolution, due to their potential to allocate spectrum in optical paths according to the bandwidth requirements of customers. In addition, with the advent of services such as cloud computing, interactive remote learning, video conferencing, stock trading and the like, an efficient multicast transmission technology is applied to a network, and is different from unicast point-to-point transmission, and a point-to-multipoint multicast transmission mode greatly improves transmission efficiency and saves network resources. As the demand of users for new multicast services continues to increase, more and more big data transmission services need the support of multicast transmission technology, and the proportion of multicast traffic in the network continues to increase, so that the research on multicast in the elastic optical network becomes very urgent.

To support multicast of optical networks, the concept of optical trees is introduced, which is a point-to-multipoint extension of the optical path (i.e. asynchronous channels). The main advantage of optical trees is that only one optical transmitter is required for transmission and multiple destinations can share an intermediate tree link. In order to support all-optical multicast efficiently, nodes in a resilient optical network must have optical splitting capabilities. Nodes with optical splitting capability can forward incoming messages over multiple outgoing channels and therefore have multicast transmission capability (MC), however, MC nodes are expensive. The literature first proposes a concept of sparse light splitting, which means that only part of nodes in a network are MC nodes, and the rest of nodes do not have light splitting capability (MI). Therefore, the cost of the network can be effectively reduced, however, how to place the MC nodes in the network to reduce the number of the MC nodes to the maximum extent is a problem to be solved. The document (Zhou F, air-ouhmed a, Cheref a. qot-aware Networking using column generation in mixed-line-rate optical networks C/Computing, Networking and Communications (ICNC),2016 international conference on ieee,2016:1-5.) studies the sparse light distribution problem in WDM optical networks, studies the routing and wavelength distribution (RWA) problem based on a modified modern heuristic algorithm, but is not applicable to routing and spectrum distribution (RSA) in elastic optical networks because the RSA problem in elastic optical networks needs to satisfy numerous constraints, such as spectrum continuity constraints, spectrum consistency constraints, and spectrum non-overlap constraints. Two different approaches have been investigated in the literature (Ruiz M, Veasco L.serving multicast on single-layer and multi-layer flexible networks [ J ]. Journal of optical Communications and Networking,2015,7(3): 146-. The authors propose a corresponding ILP model and heuristic algorithm, and in the scenario of this study, the problems of limitation and placement of multicast nodes are not considered. A multicast routing and spectrum Allocation algorithm (DMRSA) is introduced in the literature (moharam M, Fallahpour a, beiranv H, et al. resource Allocation and MulticastRouting in Elastic Optical Networks [ J ]. IEEE Transactions on Communications,2017.) to sequentially find the shortest path from the destination node to the source node during multicast routing, construct a multicast tree, and then adaptively select an appropriate modulation scheme for spectrum Allocation according to the constructed multicast tree. However, the DMRSA algorithm routes from the destination node to the source node every time, and cannot guarantee an optimal multicast tree structure. Therefore, the frequency spectrum utilization rate is not high, and the blocking rate of the network is high.

Aiming at the multicast transmission RSA strategy in the elastic optical network, the performance of the network is improved under certain conditions, but the multicast tree structure cannot be fully utilized, so that the frequency spectrum utilization rate is not high, and the blocking rate is higher.

Disclosure of Invention

In view of this, the present invention provides a MC node-limited resilient optical network-based multicast routing and spectrum allocation method, which is configured to allocate multicast routing and spectrum to MC nodes, which are only part of nodes in a resilient optical network. By utilizing the characteristic that MC nodes can have a plurality of output links, a better multicast Tree structure is constructed, and Pre-calculation Shortest Path Tree multicast Routing and Spectrum Allocation, namely PSPT-DMRSA (Pre-calculating short Path Tree-discrete Routing and Spectrum Allocation), is provided for reducing the number of bandwidth slots consumed in the links and achieving the purpose of reducing the total cost of the optical Tree. According to the distribution of MC nodes in the network, the MC trees from the source node to all MC nodes are pre-established before multicast routing, and then the destination node is added into the multicast tree in sequence. The number of multicast nodes in the network and the selection of the positions of the multicast nodes are fully considered. MC nodes in the network are fully utilized in routing and spectrum allocation, and a proper modulation grade is selected according to the multicast tree structure, so that the utilization rate of spectrum resources is improved, and the network blocking rate is reduced.

In order to achieve the purpose, the invention provides the following technical scheme:

an MC node limitation-based elastic optical network multicast routing and spectrum allocation method comprises the following steps: before multicast routing, proper MC nodes are selected in advance in a network, then an MC tree taking a source node as a root is established for the selected MC nodes, and then a target node is sequentially routed to the source node or the MC node, so that the number of links occupied by the whole multicast request is reduced, and the bandwidth resources occupied by the request are reduced.

Further, the pre-selecting a proper MC node in the network specifically includes: when MC node selection is considered, excluding nodes with degree less than 3 in the network, then sorting all nodes in the network from high to low according to degree, then solving the shortest path between any two points in the network, counting the total times of the nodes appearing in the paths, and marking as count_iThen according to count_iAnd sequencing the nodes with the same degree from large to small, and finally determining the priority order of the nodes selected as MC nodes in the network by the sequencing.

Further, the establishing of the MC tree using the source node as the root specifically includes: firstly, determining the number N of MC nodes in a network, and then selecting the first N nodes as the MC nodes; inputting a multicast request, setting a multicast source node as a multicast node, and constructing a Steiner tree of the selected MC node and the multicast source node to minimize the total path cost of the whole MC tree, namely the MC tree with the shortest path.

Further, the multicast path adopts a KSP algorithm, specifically: and constructing a multicast tree structure from a source node to all destination nodes, sequentially calculating the distance from the destination node to an MC node in the obtained MC tree or the distance to an MI node with the degree of 1 in the current multicast tree, selecting the shortest circuit, the next shortest circuit or the Kth shortest circuit according to the current network state, and setting a reasonable K to reduce the blocking rate of the network until all the destination nodes are added into the current multicast tree.

The invention has the beneficial effects that: the invention mainly considers the problems of multicast routing and spectrum allocation of MC nodes which are only part of nodes in the elastic optical network, realizes higher spectrum resource utilization rate and adopts a pre-calculated shortest path tree strategy. In order to realize the pre-calculation shortest path tree strategy, proper MC nodes are selected in a network at first, and an MC tree including a source node is constructed, so that the multicast routing mode is changed, the route from a destination node to the source node is changed into the route from the destination node to all the current MC nodes, the local optimization is avoided, and the frequency spectrum utilization rate is improved. And when the KSP algorithm is used for selecting the route, a link which is congested can be effectively avoided, and the network congestion rate is reduced.

Drawings

In order to make the object, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings for explanation:

FIG. 1 is an RSA in a resilient optical network;

FIG. 2 is a flow chart of multicast node selection in the present invention;

FIG. 3 is a flow chart of a routing and spectrum allocation algorithm of the present invention;

FIG. 4 is an overall flow chart of the strategy.

Detailed Description

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The method of the invention is mainly composed of two parts, namely MC node selection based on degree, routing based on multicast tree structure and spectrum allocation. The selection of the MC node is that a proper node is selected from a given network and set as the MC node, thereby realizing the greater light splitting capability and improving the use frequency. Routing and spectrum allocation, namely selecting a proper routing structure for the request and allocating proper bandwidth slots, so that high spectrum resource utilization rate is realized and network blocking rate is reduced.

Therefore, in order to implement the multicast routing and spectrum allocation strategy in the elastic optical network with the limited MC node number, the specific contents are as follows:

the selection of the MC nodes in the network is to select the MC nodes in a given network, so the priorities of all the nodes are to be sorted. The priority determination rule is degree-first, because a node with a larger degree can provide more light splitting capability, as shown in formula 1;

wherein

Representing the maximum split output, v, of the node_degreeRepresenting the degree of the node.

Because there are many nodes in the network with the same degree, the priority needs to be further determined, and the specific flow is shown in fig. 2.

The invention relates to routing and spectrum allocation of a multicast tree structure, which aims at the problem that only part of nodes in an elastic optical network are MC nodes and allocates the routing and spectrum of multicast. By utilizing the characteristic that MC nodes can have a plurality of output links, a better multicast Tree structure is constructed, a Pre-calculated Shortest Path Tree multicast Routing and spectrum allocation strategy is provided, namely PSPT-DMRSA (Pre-calculating short Path Tree-Distance adaptive Routing and Spectrum allocation) is used for reducing the number of bandwidth slots consumed in links, and the purpose of reducing the total cost of optical trees is achieved. According to the distribution of MC nodes in the network, the MC trees from the source node to all MC nodes are pre-established before multicast routing, and then the destination node is added into the multicast tree in sequence. As shown in fig. 1(a), in the figure, a node 1 is a source node, destination nodes are 4, 5 and 6, assuming that the

nodes

1 and 4 are MC nodes and the rest are MI nodes, a light path 1-2-4 from the node 1 to the node 4 is established in advance, then a shortest path or a next shortest path from the destination node to a current MC tree is sequentially solved by using a K-shortest path algorithm (according to a link resource usage state), and optical fiber links included in the whole multicast tree are 1-2-4-5 and 4-6. The total number of occupied bandwidth slots is 8. In addition, when the destination node is added to the current multicast tree, the MI node with the node degree of 1 in the current multicast tree may also be selected, as shown in fig. 1(b), the optical fiber link included in the whole multicast tree is 1-2-4-5-6.

(1) The physical topology of a resilient optical network is abstracted as a directed graph G ═ (V, E), where V and E are the set of nodes and directed links, respectively, of the network. With spectrum resources of BGHz for each link E. For a multicast scheme based on MC nodes, the resulting optical tree T consists of an MC tree and lightpaths connecting the MI nodes and the remaining destination nodes to the MC tree. The total cost of the optical tree is therefore equal to the sum of the cost of the MC tree and the bandwidth slots required for the links between the MI nodes connected to it.

Optimizing the target:

Minimize ∑_e∈E∑_f∈SSlot(f) (2)

where S represents a bandwidth slot available on the link; f denotes the bandwidth slot denoted by f; slot (f) is a Boolean variable, which is 1 when the bandwidth slot labeled f is occupied.

(2) Also, spectrum allocation in elastic optical networks also needs to satisfy spectrum continuity constraints, spectrum consistency constraints and spectrum non-overlapping constraints ξ are defined for multiple multicast requests_iAnd

are respectively multicast requests R_iAnd the occupation of the spectrum on link E ∈ E, then the three constraints are expressed as follows:

equation 3 represents the spectral continuity constraint, where f_i,eIndicates its real bandwidth slot number, n_iIndicating a multicast request R_iThe number of bandwidth slots occupied on link e is disclosed to ensure n_iThe bandwidth slot is continuous; formula 4 represents the spectrum consistency constraint to ensure the multicast request R_iAllocating the same bandwidth slot on all links; formula 5 is a spectrum non-overlapping constraint to ensure multicast requests

And

the bandwidth slots allocated on link e do not overlap (not so limited if at different times).

(3) The network resources requested to be occupied in the elastic optical network are calculated by bandwidth slots, the number of the bandwidth slots requested to be occupied can be changed by selecting different modulation schemes, and meanwhile, the maximum transmission distance can be influenced, and the corresponding relation is shown in table 1. For multicast traffic with bandwidth request b, the appropriate modulation class m is selected according to table 1. The number of required bandwidth slots can be determined as follows:

wherein C is_BPSKIs the capacity of a bandwidth slot using BPSK, we have C_BPSKAnd Δ g is the guard bandwidth at 12.5 Gb/s. Because different modulation formats are used, a guard bandwidth needs to be added between adjacent requests in order to avoid the influence of cross-phase modulation.

The specific steps of the construction and the spectrum allocation of the multicast tree are as follows: 1) initializing a network, setting the number N of MC nodes, and inputting a multicast request r ═ s, D, b }; 2) assuming that the source node is an MC node, constructing a Steiner tree from the source node to all MC nodes, and recording a set of MC nodes as V_k(ii) a 3) Sequentially constructing a multicast tree by using the shortest path from a target node to an MC node; 4) and determining a modulation level according to the farthest distance from the multicast tree source to the destination node, and allocating a bandwidth slot. The algorithm flow chart is shown in fig. 3.

The overall flow of the multicast routing and spectrum allocation strategy for realizing resource saving of the present invention will be described with reference to fig. 4:

step 1: prioritizing all nodes in a network on a degree-first basis

Step 2: initializing a network, setting the number N of MC nodes, and inputting a multicast request r ═ s, D, b };

step 3: calculating the shortest path among MC nodes, constructing a Steiner tree by taking s as a root node, and recording the MC node set in the current MC tree as V_k；

Step 4: obtaining the number n of the required bandwidth slots by a formula 6 if m is 4;

step 5: solving for d according to network state_iTo v_kiK shortest path of (d)_ikWherein v is_ki∈V_k. If d is_ikIf not, the Step is carried out to Step 7;

Step6：V_k＝V_k∪d_iand Step5, 6 is executed circularly until all the multicast destination nodes are added into the multicast tree,

step 7: and m is m-1, m is greater than 0, and the process goes to Step 5.

Declaring that: all multicast request source nodes are assumed to be MC nodes. There are multiple requests within a multicast and if a request is not reachable, i.e. the link cannot provide enough bandwidth slots, this multicast traffic congestion is defined. Steps 4-7 comprise a spectrum allocation process, a classic First-First (FF) algorithm is adopted, the value of m ensures that the current multicast request selects the optimal modulation mode, and the shortest path d_ikThe relationship between the modulation class and the maximum transmission distance shown in table 1 needs to be satisfied.

TABLE 1 modulation system, modulation class and transmission distance relationship

Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, although the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. The MC node limitation-based elastic optical network multicast routing and spectrum allocation method is characterized in that: the method comprises the following steps: before multicast routing, selecting proper MC nodes in a network in advance, then establishing an MC tree taking a source node as a root for the selected MC nodes, and then sequentially routing a target node to the source node or the MC node, so that the number of links occupied by the whole multicast request is reduced, and bandwidth resources occupied by the request are reduced;

the pre-selecting of the appropriate MC node in the network specifically includes: when MC node selection is considered, excluding nodes with degree less than 3 in the network, then sorting all nodes in the network from high to low according to degree, then solving the shortest path between any two points in the network, counting the total times of the nodes appearing in the paths, and marking as count_iThen according to count_iSequencing the nodes with the same degree from large to small, and finally determining the priority order of the nodes selected as MC nodes in the network by the sequencing;

the establishment of the MC tree with the source node as the root specifically includes: firstly, determining the number N of MC nodes in a network, and then selecting the first N nodes as the MC nodes; inputting a multicast request, setting a multicast source node as a multicast node, and constructing a Steiner tree of the selected MC node and the multicast source node to minimize the total path cost of the whole MC tree, namely the MC tree with the shortest path;

the multicast path adopts a KSP algorithm, and specifically comprises the following steps: and constructing a multicast tree structure from a source node to all destination nodes, sequentially calculating the distance from the destination node to an MC node in the obtained MC tree or the distance to an MI node with the degree of 1 in the current multicast tree, selecting the shortest circuit, the next shortest circuit or the Kth shortest circuit according to the current network state, and setting a reasonable K to reduce the blocking rate of the network until all the destination nodes are added into the current multicast tree.