Ansi/tia-921-b network Model for Evaluating Multimedia Transmission Performance Over the Internet Protocol
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- 6.4Advanced Uses of the Network Model
- 6.4.1.1.1.1(Normative) – Description of Discrete Event Simulator
6.3Hardware Emulator ConsiderationsFor a specified test case, the simulation produces delay and loss characteristics that can be used in a real-time emulator. The emulator accepts a packet stream under test, and plays out the same stream with packet delays and losses that match the corresponding simulation. The simulator creates .out files to represent the delay and loss experienced by each packet in a stream. These .out files can be used directly to control packet delay and loss in a real-time inline impairment emulator. In cases where the packet stream in the simulator is bursty, the delay and loss values in the .out file are non-uniform in time. Two methods to handle this situation are described in the following paragraphs. An impairment emulator shall provide Method 1 and may provide Method 2. Method 1: Resample the delay and loss values in the .out file so that they are uniformly sampled in time, and apply these in the inline impairment emulator using the resampled rate. For example, if the test stream is bursty with an average packet rate of 1000 packets per second, the .out file may be resampled using 1ms resample rate, and the resulting impairments could then be applied at 1ms update rate. This approach ensures that the resulting test always lasts the same amount of time, but some samples may apply to more than one packet, and other samples may not be applied to any packets, depending on the arrival time of packets at the inline impairment emulator. Method 2: Apply the delay and loss values from the .out files on a packet-by-packet basis. Each line in the .out file is applied to one packet without regard to the time value in the first column. This approach ensures that each delay and loss value is applied exactly once, but the test duration will vary inversely with the rate of packets applied to the inline impairment emulator. In other words, a higher packet rate applied to the emulator will consume the .out file samples more quickly, and thus the test finishes sooner. If a long duration test is required than the 10 minute length of the .out files the files should be looped. An impairment emulator shall shape the stream under test to account for the “self-interference” effect by traffic shaping using the token bucket method. The result of the token bucket shaping shall be equivalent to the result produced by the shaping code that is implemented in PacketGeneratorPCAP.cpp portion of the simulator source code. Packets that arrive too close together in time contend for the available bandwidth in the emulated network. The amount of shaping depends on the effective bandwidth available to the stream under test in the given test case. This available capacity is the rate of the access link (the lowest-rate link in the network) less the sum of the rates of the interfering streams at QoS priority the same or higher than the stream under test. The test cases described in this document cover primarily CORE-TO-LAN configurations, and this is well suited for emulation of IPTV service. Test cases for LAN-TO-LAN configurations shall be constructed by concatenating two CORE-TO-LAN test cases. For example, a LAN-TO-LAN test case could be constructed by running Dw1 in series with Gp3. Such a test case is called Dw1-Gp3. The delay and loss values for a LAN-TO-LAN test case are calculated by first performing Method 1 on the individual test cases so that they have a common sample rate and then summing the delay values and logically OR-ing the loss values for the resulting individual test cases. The bandwidth limitation is calculated as the minimum of the effective bandwidth (EB) for the individual test cases. DelayDw1-Gp2 = DelayDw1 + DelayGp2 Loss Dw1-Gp2 = Loss Dw1 “or” LossGp2 BW Dw1-Gp2 = Min[EBDw1, EBGp2]
Network Load Generation: The output pcap files can be used as the basis of synthetic or dummy loads to inject onto networks to simulate different traffic mixes. 6.4.1.1.1.1(Normative) – Description of Discrete Event Simulator6.4.1.1.1.1.1Simulator Overview The TIA-921B impairment simulation is implemented as a general purpose discrete event simulator. This means that it contains discrete event models of generalized network elements, such as switches, routers and set top boxes, which are connected together by means of wires. Events in the simulation consist mainly of packet arrivals and departures from the different network elements, but other types of events are also possible. The simulator source code is implemented using object oriented design techniques in C++. 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. The inputs and outputs from the simulation are in the form of PCAP packet files. PCAP is a de-facto industry standard that can be read by a variety of commonly available tools such as wireshark and tcpreplay. 6.4.1.1.1.1.2Directory Structure ./ top level directory ./src subdirectory for simulator source code ./src/bin.debug subdirectory for simulator’s binary executable ./pcap subdirectory for input PCAP files ./tc subdirectory for test case parameter files ./tc/common.tcl shared TCL routines ./tc/Dw1.param input parameter file for test case Dw1 ./out subdirectory for outputs from test cases ./out/Dw1 sub-subdirectory for outputs from test case “Dw1” 6.4.1.1.1.1.3Building the simulator The source code for the simulation is written in the C++ language and has been tested under Cygwin 1.7 on Windows XP and Windows 7, Ubuntu Jaunty Jackalope (x86_64), openSUSE 11.1 (i386) and Fedora Core 8. It has been built using GNU Make 3.81 and GCC/G++ version 3.4.4 or GCC version 4.3.4. The simulator uses the TCL interpreter for reading simulation parameters, so the machine on which the code is built must have the tcl.h header file and associated library to link against. This has been tested with the ActiveState TCL distribution under Windows and with the native Linux TCL. In either case versions 8.4 and 8.5 have been seen to work. The path to the tcl.h and the library file is specified in the Makefile. You may need to modify the Makefile to adjust the path to these two files on your system. Once the paths for the TCL files has been set and verified, building the simulation requires running “make” If the simulator is built successfully, there will be an executable program called CORE2LAN.exe in the sim/src/bin.debug subdirectory. The following shows the result of a successful compilation. $ make Generating dependencies for CORE2LAN.cpp Generating dependencies for redblack.c Generating dependencies for Wire.cpp Generating dependencies for Switch.cpp Generating dependencies for SimParam.cpp Generating dependencies for Port.cpp Generating dependencies for PacketQueue.cpp Generating dependencies for PacketMonitorPCAP.cpp Generating dependencies for PacketMonitor.cpp Generating dependencies for PacketGeneratorPCAP.cpp Generating dependencies for PacketGenerator.cpp Generating dependencies for Packet.cpp Generating dependencies for Event.cpp Generating dependencies for Dispatcher.cpp Generating dependencies for Clock.cpp ------------------------ Compiling for debug - - - - - - - - - - - - g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/CORE2LAN.o CORE2LAN.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/Clock.o Clock.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/Dispatcher.o Dispatcher.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/Event.o Event.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/Packet.o Packet.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/PacketGenerator.o PacketGenerator.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/PacketGeneratorPCAP.o PacketGeneratorPCAP.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/PacketMonitor.o PacketMonitor.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/PacketMonitorPCAP.o PacketMonitorPCAP.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/PacketQueue.o PacketQueue.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/Port.o Port.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/SimParam.o SimParam.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/Switch.o Switch.cpp g++ -c -g -O2 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include -Wno-write-strings -o objs.debug/Wire.o Wire.cpp gcc -c -g -O4 -Wall -DDEBUG -I../lib -Isrc -I. -I/cygdrive/c/tcl/include – o objs.debug/redblack.o redblack.c
Linking bin.debug/CORE2LAN.exe - - - - - - - - - - - - g++ -lm -g -o bin.debug/CORE2LAN.exe objs.debug/CORE2LAN.o objs.debug/Clock.o objs.debug/Dispatcher.o objs.debug/Event.o objs.debug/Packet.o objs.debug/PacketGenerator.o objs.debug/PacketGeneratorPCAP.o objs.debug/PacketMonitor.o objs.debug/PacketMonitorPCAP.o objs.debug/PacketQueue.o objs.debug/Port.o objs.debug/SimParam.o objs.debug/Switch.o objs.debug/Wire.o objs.debug/redblack.o /cygdrive/c/tcl/bin/tcl84.dll 6.4.1.1.1.1.4Base CORE2LAN model The base simulator code contains the basic topology of a CORE-to-LAN configuration, with 15 nodes of a high speed core network, a high speed edge router, an access link (for example with a DSLAM and DSL modem), a residential firewall/gateway, a home LAN and 13 set top boxes and two PCs. 6.4.1.1.1.1.5Simulator Input Data Input to the simulator is in the form of PCAP files. These files are driven into the simulation as specified by the timestamps in PCAP files. The payload of the PCAP files, if present, is carried along with the packets in the simulation and placed in the output files. The simulation parameter settings can adjust the timing of the packets driven into the simulation, for example to speed up or slow down the playback, or to smooth out unintended burstiness. A full list of the adjustable parameters for the PCAP packet generator is given below. The parameters for running the simulation are given in a TCL file. The advantage of using TCL as a parameter file format is that it is a well-known file format, and it is extensible so that users can further customize the behavior of the simulation to suit their particular needs. An example of how this helps is that it gives a convenient way to comment out portions of code and to print messages to the screen for information or debugging. At the very top of a parameter file, the user must include the common support routines from the file tc/common.tcl. source "tc/common.tcl" The first section of the parameter file consists of variable settings using the TCL “set” command. It is no different from setting a normal variable in TCL, except that the names of the variables are specific to the simulator. The example below sets the simulation length to 10 minutes (600 seconds) # - - - - - - - - - - - - - - - - # Simulation length # - - - - - - - - - - - - - - - - set SimLengthSeconds [expr 10*60] In most test cases, the above line is commented out so that a default simulation length from common.tcl can control the duration of the simulation. Note also in this example that a TCL expression computes the number of seconds in ten minutes. While it is also possible to also specify 600 seconds, using an expression in this way helps to make clear what is intended (10 minutes) and also serves an example of how to use TCL expressions in the parameter file. Next, set the Access and Core network parameters (this example is from test case Dp4): # - - - - - - - - - - - - - - - - # - - - - - - - - - - - - - - - - Set_Access_Params dsl_p4_u4 Set_Core_Params p4_u4 The first line above sets parameters for the access network. The second line above sets parameters for the core network. The arguments to these two procedures is a text string that refers to a pre-defined combination of parameters that are given in common.tcl. Custom test cases can be created by setting the individual simulator control variables at this level. The table below shows the names of the predefined access parameters, and the corresponding access parameters: 
The table below shows the names of the predefined access parameters, and the corresponding access parameters: 
The next section of the parameter file specifies the input and output packet streams. PacketGenerators read input PCAP files and drive them into the simulation. PacketMonitors receive packets from elements within the simulation and saves them into PCAP format, and also saves delay and packet loss information. An example of this for test case Dp4 shown in the box on the following page: # ===================================================================================================================== # Managed Bandwidth PCAP Stream Generators and Monitors # # Name File Start BW PPM Rand Prio Repeat PIR PBS # --------------------------------------------------------------------------------------------------------------------- PCAP_Generator PktGenPCAPFwdI1 voip_g729_fwd 2.0 1.0 0.0 0.0 1 -1 PCAP_Monitor PktMonPCAPFwdI1 VoIP1_Fwd PCAP_Generator PktGenPCAPRevI1 voip_g729_rev 2.0 1.0 0.0 0.0 1 -1 PCAP_Monitor PktMonPCAPRevI1 VoIP1_Rev # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - PCAP_Generator PktGenPCAPFwdI4 SD_cbr 5.0 0.260 0.0 0.0 2 -1 ;# 2.0Mb/s PCAP_Monitor PktMonPCAPFwdI4 SDTV1_Down # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - PCAP_Generator PktGenPCAPFwdI5 SD_vbr 5.0 0.361 0.0 0.0 2 -1 ;# 2.0Mb/s PCAP_Monitor PktMonPCAPFwdI5 SDTV2_Down
# Residual Bandwidth PCAP Stream Generators and Monitors # # Name File Start BW PPM Rand Prio Repeat PIR PBS # --------------------------------------------------------------------------------------------------------------------- PCAP_Generator PktGenPCAPFwdI7 HTTP_Down 0.0 0.40 0.0 0.0 7 -1 PCAP_Monitor PktMonPCAPFwdI7 HTTP_Down # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - PCAP_Generator PktGenPCAPRevI7 HTTP_Up 0.0 0.50 0.0 0.0 7 -1 PCAP_Monitor PktMonPCAPRevI7 HTTP_Up_out # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - PCAP_Generator PktGenPCAPFwdI9 P2P_Down 2.0 0.25 0.0 0.0 7 -1 ;# 0.473 Mb/s PCAP_Monitor PktMonPCAPFwdI9 P2P_Down # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - PCAP_Generator PktGenPCAPRevI9 P2P_Up 2.0 1.35 0.0 0.0 7 -1 ;# 0.384 Mb/s PCAP_Monitor PktMonPCAPRevI9 P2P_Up # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - PCAP_Generator PktGenPCAPFwdI8 ipfax_v34_t38_fwd 0.0 1.0 0.0 0.0 7 -1 PCAP_Monitor PktMonPCAPFwdI8 Fax_v34_t38_Fwd PCAP_Generator PktGenPCAPRevI8 ipfax_v34_t38_rev 0.0 1.0 0.0 0.0 7 -1 PCAP_Monitor PktMonPCAPRevI8 Fax_v34_t38_Rev The parameters for the input PCAP generators are specified in columns as shown above. The meanings of the columns is described briefly below
The Packet Monitors that write output PCAP files and “.out” files. There are only two parameters for the PCAP monitor command
Note that if a PCAP_Monitor line is commented out or not present, the output files will not be written. This is helpful in situations where only a subset of the output files is needed so that disk space can be saved. The simulation predefines two global variables for use by the TCL code in the parameter file
6.4.1.1.1.1.6Running the simulation with convenience scripts Two convenience scripts are provided to help automate the process of running a simulation and plotting results. The first is a shell script to run one test case from the command line. To use this script, type the command: ./runone.ss Dw1 Similarly, there is a convenience shell script to run all test cases that match a given shell filename pattern. To use this script, type the command: ./runall.ss [GD]w[1-3] (this runs GPON and DSL well managed cases number 1 through 3). When the simulation is run, it prints a variety of messages to help the user understand what is happening. At the beginning of the simulation, it prints out information regarding the input PCAP files, and the output PCAP files. Then during the simulation, it prints some special characters to give an indication of simulation progress, specifically:
An example simulation output is shown below $ ./runone.ss Du1 + cd src
+ make + src/bin.debug/CORE2LAN tc/Dw1.param INFO: PacketMonitorPCAP saving CSV stats to out/Dw1/VoIP1_Fwd.out INFO: PacketMonitorPCAP saving PCAP output to out/Dw1/VoIP1_Fwd.pcap INFO: PacketMonitorPCAP saving CSV stats to out/Dw1/HDTV1_Down.out INFO: PacketMonitorPCAP saving PCAP output to out/Dw1/HDTV1_Down.pcap INFO: PacketMonitorPCAP saving CSV stats to out/Dw1/Fax_v34_t38_Fwd.out INFO: PacketMonitorPCAP saving PCAP output to out/Dw1/Fax_v34_t38_Fwd.pcap INFO: PacketMonitorPCAP saving CSV stats to out/Dw1/VoIP1_Rev.out INFO: PacketMonitorPCAP saving PCAP output to out/Dw1/VoIP1_Rev.pcap INFO: PacketMonitorPCAP saving CSV stats to out/Dw1/Fax_v34_t38_Rev.out INFO: PacketMonitorPCAP saving PCAP output to out/Dw1/Fax_v34_t38_Rev.pcap ..E...E.. ^..EE...
^.EE..E..EE. ^....E..E. ^E...EEE. ^......E..E. ^. ^
^..E....E ^.E..E..
^... ^....
^.E.EE..E.E.E.... ^. ^.E...E.E..EE.E.. ^ ^.E.
^.EE.E ^E..EE.E.EE.E.. ^...... ^.E.E.
^.. ^....E.E.E.E. ^
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