| New protocol exploitation and network performance test is very important for the network development,popularization,management and maintenance. Network simulation,network emulation and real-world tests are the most extensively used technology for network protocol test and system performance evaluation. However, since simulators are composed of logical models, it is not possible to accurately assess how the network under test would behave in a real environment. For the restriction of environment and resource, real-world tests cannot be widely used. Thus, network emulation as a bridge between simulation and real-world tests, makes up their disadvantages, has very important value. In this paper, using tactical communication network as an application instance, a wireless network emulation platform on the LAN was designed and realized. The impact from the run mechanism of LAN was eliminated by the central control and distributive operation system structure,the poll channel access method and the theory of low speed network emulated by high speed network, the network emulation based on network in the near-true environment was achieved.The main work completed in this paper is as follows:1,Two kinds of wireless network communication system of emulation platform were given, one is on the basic of the Windows Sockets and the either is on WinPcap, the characteristic of them was compared and analyzed. For avoiding the interference from collision and retransmission made by the protocol running mechanism, the polling channel access means was used. The theory of low speed network emulated by high speed network was advanced to achieve the judgment and emulation of physical layer event. The three wireless channel models, which were Free space model,Two-ray ground reflection model and Shadowing model, were used for the emulation of the wireless channel. The capture effects in wireless communication was considered, the noise resisting performance of the system was emulated by the transfer from code error ratio to frame error ratio.2,The structure of the emulation platform was designed, which consists of one control center and several terminal nodes, contains polling control,topology management,operation control,filter,emulation modify,wireless channel model and data track collection module, etc. Aimed at the emulation of MIL-STD-188-220C on LAN, the theory of low speed network emulated by high speed network was analyzed and used. On the basic of the analysis on the miscarriage of justice on collision and time delay error of the system, the method to eliminate the error by NAD to zero frame transmission and serial number record was given.3,The tactical communication system was achieved on Ethernet in the VC++ 6.0 environment, on the basic of this, the network emulation platform on LAN (NEPN) was realized. The realization of virtual network topology,emulation scene,node assignment and data track collection module were expatiated. At last, the system performance was tested, the effect of host performance for the emulation was analyzed, and the validity of the emulation platform was approved, by the comparison with NS. 4,The rules of transmitting frame,network timing and network medium access of MIL-STD-188-220C data link layer are analyzed in the first part of the article. The five Net Access Delay (NAD) algorithms were simulated on NEPN and the performance of the algorithms were compared and analyzed. Then the scene apply to them was given respectively. The DAP-NAD algorithm has improved, the theoretical analysis and simulation results indicated that the performance of the improved DAPER-NAD algorithm is all right. The end to end delay was greatly reduced, while the high throughput of the DAP-NAD algorithm was held. |
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