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104 lines
4.0 KiB
Markdown
104 lines
4.0 KiB
Markdown
Simulation of a dumbbell topology using ns3 3.17
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dependencies (on Debian based distros):
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libns3-dev (= 3.17)
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compilation:
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make
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example execution:
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$ cat << END | ./dumbbell-sim > log
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UR TCP 536 0.0 1250
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UR TCP 536 250 500
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LR UDP 1000 750 1000 0.9Mbps
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END
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The file `log` then contains traces with the first column being the timestamp,
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the second column being the ns3 context and the third column being the traced
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value of this context. The traced values are TCP congestion window size
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changes, received packets and queue drops.
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The traffic description is done via standard input. Each line represents one
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flow and the dumbbell will be created such that it has as many clients on each
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side as there are flows. Each flow will originate from a unique node N on the
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left side of the dumbbell and reach node N on the right side of the dumbbell.
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This way, every node is involved in exactly one flow and the connection in the
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center of the dumbbell serves as the bottleneck.
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So above example would create the following topology:
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L1 R1
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\ /
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\+--+ +--+/
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L2---|LR|----|RR|---R2
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/+--+ +--|\
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/ \
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L3 R3
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The flow given in the first line would originate from `L1`, go through the
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bottleneck link between the left and right router (`LR` and `RR`, respectively)
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and end at `R1`. The flow given in the second line would go from `L2` to `R2`
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and the last one from `L3` to `R3`.
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Flow description format
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-----------------------
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Each line represents one flow between two unique nodes of the dumbbell, flowing
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from left to right. Each line is split by their white spaces. The first element
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represents the type of flow. There are three flow types.
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**LR**: this type stands for "limited rate" and allows to specify traffic which
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is limited by transmission rate. Start and stop times govern the duration of
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this traffic.
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**UR**: this type stands for "unlimited rate" and allows to specify traffic
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which is sent as fast as possible. Only TCP traffic is allowed. Start and stop
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times govern the duration of this traffic.
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**LT**: this type stands for "limited transfer" and allows to specify traffic
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which is sent as fast as possible. Only TCP traffic is allowed. The amount of
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data to transfer governs when this flow stops transmitting.
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The second element in each line is the transport type an can be either "TCP" or
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"UDP". Observe the restrictions of transport type with respect to the flow
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type.
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The third element is the package size to send. For TCP traffic this will also
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adapt the segment size of the underlying socket.
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The fourth element is the start time of the flow given in seconds.
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For `LR` and `UR` flow types, the fifth element is the stop time given in
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seconds. For the `LT` type, the fifth element is the maximum transfer size,
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given in bytes. For all types, the fifth element governs when the flow will
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stop.
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The `LR` type takes a sixth element, specifying the desired transmission rate.
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This value is given with a unit like "Mbps".
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Commandline Arguments
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---------------------
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While flow descriptions are read from standard input, commandline arguments
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allow to setup properties of the dumbbell topology. By default, the error rate
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of the involved links is 0.0, which means no packet is dropped by the physical
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links. The default TCP congestion-avoidance algorithm is NewReno and other
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options are Tahoe, Reno, Westwood and WestwoodPlus. The default bandwith and
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latency of the bottleneck link is 1Mbps and 50ms, respectively. The default
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bandwidth and latency of the access links of the nodes to the routers is 10Mbps
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and 1ms, respectively.
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When giving an error rate other than 0.0, a random element is introduced. It is
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possible to make this randomness deterministic by using the `--run` option
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which allows to make deterministic runs with the same outcome, given the same
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run number.
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Depending on the flow definitions you might want to start the simulation early.
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This is possible with the `--simstop` argument.
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You can enable pcap tracing of all links with the `--tracing` option.
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