Design And Implementation Of DTN Network Simulation System

Delay/Disruption Tolerant Network(DTN)has characteristics of long latency,frequent link interruptions,dynamical changes of network topology,low and asymmetric data capability and node resource constraints.Space communication network is a typical kind of DTN.Compared with land communication environment,it has rigour environment and cannot satisfy traditional Internet requirement of communication environment.Therefore,it is necessary to explore and develop a network system which is suitable for space communication.Moreover,China is the biggest developing country in the world and a space-faring nation.The exploration and development of DTN can make contributions to deep-space exploration and bring long-lasting significance to the development of space cause of our country.This thesis first analyses the network architecture of DTN and the protocols about DTN.The core of this network architecture is bundle layer which connects heterogeneous network through adding the bundle layer between the application layer and the transport layer.In order to avoid the data format mismatch between the application layer and the transport layer,it also adds a convergence layer as the interface between these two layers.Bundle protocol and Licklider Transmission Protocol(LTP)are two important protocols in DTN protocol stack.Bundle protocol takes the bundle as the basic data unit and utilizes store-and-forward to overcome frequent link interruptions.Custody transfer mechanism is optional service based on store-and-forward.It can increase the reliability of transmission.LTP protocol is a convergence layer protocol located between bundle layer and transport layer.It can provide reliable transmission and unreliable transmission based on the distinction between red-part data and green-part data.It can also suspend data transmission when link disconnect and retransmit undeliverable data when connection is restored.The design and implementation of bundle protocol and LTP protocol are carried out based on the analysis of DTN core protocol.Bundle protocol is divided into three parts:application agent part,bundle protocol agent part and convergence layer adapter parts tructurally.In Chapter 4,the function of the bundle protocol agent part of is divided into seven parts,and the implementation of each function module is introduced,and the corresponding program flow chart is drawn.The LTP protocol is divided into three parts:the storage part,the LTP protocol part and the management information base.This paper divides the function of the LTP protocol part,and draws the flow chart.Finally,the interface between the protocols is designed.A network experimental platform of the DTN network simulation system is build by using three computers.The transmission performance test is carried out by sending three pictures.The system can set the size of bundle and the LTP data segment,delay,connection period,connectivity time and other parameters.It can realize functions including data segmentation,encapsulation and reorganization about bundle and LTP segment,custody transfer,reliable transmission and so on.In addition,it is possible to simulate the delay time in the space communication by setting the delay parameter,and to simulate the periodic connection and disconnection between the two nodes in the space communication by set the connection period and the communication time.When the test is complete,the results of the different parameters are displayed.This system operates stably in the transmission test of different parameter which also verifies the feasibility of bundle protocol and LTP protocol.