Ansi/tia-921-b network Model for Evaluating Multimedia Transmission Performance Over the Internet Protocol
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- 4.7Packet Scheduling Algorithm
4.6Simulation OutputsOutput from the simulator is in the form of pcap files and “.out” files. The pcap files record the output packets along with their timestamps. Comparisons of input pcap and output pcap files can be performed to determine the effect of the impairment on, for example, video/audio quality or voice quality. Test stream pcap files with payloads can be input into the simulation and the test stream output pcaps can be analyzed for video/audio quality or voice quality under different network conditions. The “.out” output files contain delay and packet loss information (in ASCII CSV format) about the simulation result. This information is also implicitly contained in the pcap file, but because it is not possible directly to indicate packet delay or loss in a pcap file, the “.out” files are helpful for post analysis. For example, because the “.out” files are in CSV format, they can be read into a spreadsheet programs for analysis. The “.out” output files also can be replayed in a real-time emulator as described in section 6.2. The examples in Table , Figure , and Figure are from the same simulation. Table shows a few packets from the “.out” file. Table : Example Simulator Output for Case Dw4, Stream HD_cbr Downstream
Figure is a plot derived from the same csv file from which Table is a tiny excerpt. Note the first dropped packet around 21 seconds. 
Figure : Time Series Plot of Packet Delay and Loss The CSV file can be plotted and analyzed to show a time series of the delay patterns and loss bursts. Furthermore, Packet Delay Variation (PDV) histograms and Cumulative Distribution Functions (CDF) can be generated for these files to analyze network characteristics. Figure is the PDV histogram from the same Dw4 simulation.
Figure : PDV Histogram Complete simulation output of the standard test cases are found in 6.4.1.1.1.4. 4.7Packet Scheduling AlgorithmCapitalized nouns in the following description refer to objects in the C++ simulator source code. A Packet is driven into the simulation from a PacketGenerator, usually by reading Packets from a PCAP file, and sending them into a Port on a Switch. The Switch receives the Packet, determines where it should go next, and Schedules it for transmission out one of its egress Ports. The egress Port is connected by a Wire to another Switch and the Wire schedules the packet for ingress on the next Switch after the wire’s delay. This process repeats for the entire network topology being simulated and for all packets being simulated. When packets reach their final destination, they are stored in a file for post-analysis. 6.4.1.1.1.2, included as an electronic attachment, contains the C++ source code of the simulator. 6.4.1.1.1.1 is a detailed description of the simulator code. Directory: TR-30 -> TR-30.3 -> Public -> 1108%20Arlington Public -> Document submitted to TR-30 -> Document submitted to Download 1.57 Mb. Share with your friends:
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