The Study Of Multicast Simulation Based On OPNET Modeler

Recently,multicast is used more and more widely,the requirement of network is more and more intense,and the huge superiority,of multicast compare with unicast or broadcast,people increasingly realize the merit and advantage of multicast.Multicast will be one of the indispensable network technology,it is more important to study multicast.However,during the study of multicast,facing to various difficult problem of network technology,people find that it is a difficult and unpractical thing to deploy and study multicast on existing Internet.However, before deploying the protocols and algorithms on the network,the practical validity of the protocols and algorithms must be evaluated,and we must get the external and reliable parameters of their performance.Therefore,the network simulation,as a new method on network programming and designing,becomes the importance step in multicast study absolutely necessarily.The network simulation technology is a simulation technology to get the data of network performance witch is needed for designing or optimizing the network,by building network device, link and protocol models and simulating the transmission of network traffic.With a particular method,it provides external,reliable parameters for network programming and designing.It shorten the network building cycle,provides scientific decision for network building,and reduces the invest risk on network building.OPNET is the famous software in network simulation,it has excellent user-interface,efficient 3-layer modeling mechanism and communication mechanism based on packets,provides a very good platform for researchers to design and analyze the network topology,devices and protocols.This paper uses OPNET to simulation and study on multicast problems,and proposes algorithms and schemes for them.PIM-SM is the most widely used multicast protocol.In PIM-SM,because of the use of shared tree,the "join" and "leave" of multicast member become simple,it has good extensibility.Because that only the routers on the tree have to maintain the information of multicast group members,it has good performance both on the quantity of state-information on routers and total cost of the routing tree.How to fix on the root node of the routing tree,is called the center(Rendezvous Point, RP)selection problem,it is first put forward by Wall.If the RP is not a good one,it will introduce high cost,high delay,and high congestion et al.network performance problems.However,the RP selection problem is a NPC problem,needs a heuristic algorithm.The main problem of existing algorithms is that they are easily run into local best solution and cannot reach the global best solution;it is because that they use the greedy algorithm.On the other hand,along with the dynamic "join" and "leave" of multicast group members,the multicast tree is changed gradually.It is impossible to maintain good performance by a preassigned RP.It needs relocate the RP and rebuild the multicast tree timely.This is called the center migration problem.This requirement is more exigent when the network scale and multicast group size are larger.Perfect RP migration algorithm should reduce the redundancy data and avoid losing data,besides reducing cost and delay,and should be as possible as transparent to the group members.This paper proposes a new RP dynamic relocating algorithm based on Tabu search;include a RP selection algorithm and a RP migration algorithm.Simulation result shows that the algorithm has good performance.Along with the network scale becoming larger,multicast expands to multi-layer inter-domain from single layer inner-domain.At present,the study on multicast in inter-domain is not sufficient, some schemes still in draft.PIM-SM expands from inner-domain to inter-domain,with the help of MSDP(Multicast Source Discovery Protocol)informing of the new source in other domain,and with the help of MBGP(Multi-protocol Extensions to BGP4)informing of the routing info inter-domain to build the multicast tree inter domain.PIM-SM/MSDP/MBGP is the scheme in the near future.This paper models this scheme on OPNET.On the other hand,along with the development of the network simulation technology,it is more and more exigent to building the transparent network model to users.During a simulation,we hope to join in the simulation,get correlative data,analyze,handle and implement some operations.Actually,network simulation software has little effect if it lack of interface to interact with uses.It has poor flexibility and poor versatility.Network simulation software with an interface to interact with uses can model a network which is very close to a true one;it could have changing topology and parameters set at will.This paper uses the HLA interface provided by OPNET,expands the inter-domain multicast model mentioned above to an interactive co-simulation inter-domain multicast model,and describes an example on the model.The example is used to check the validity of the model.This provides new reference for modeling larger scale and more flexible simulation system.In a dynamic network,because of the frequently transformation of the traffic in network,it is hard to measure,sometimes the nodes and links are disabled or recovered,the multicast routing is a very difficult problem.AntNet is an ant colony optimization algorithm used in electron communication network for routing problem,it can counterpoise the network traffic load efficiently,reduce the rate of blocking and packet loss rate.This paper models the AntNet on OPNET,and proposes a dynamic multicast routing optimization scheme based on AntNet.The simulation result shows that the scheme is effective.